92RS_Ttop

iTrader: (3)

I've been thinking about converting my open rear to posi and I do eventually want to change my 3.42's to 3.73's. I found a low-mileage 7.5" 10 bolt rear in the local U-Pull with posi 3.42's. If I were to try and swap just the posi carrier into my rear, would I need to mess around with setting pinion depth and all that, or can I just pull my current ring gear, swap my open carrier for the posi carrier and then put it all back together with the same spacers and everything from my rear?

If I can do this, I figure I can wait and swap the gears out later when I find some 3.73's. If I have to mess around with setting the pinion depth changing spacers, etc. then I will probably just wait till I can find a posi 3.73 rear and do it all at once.

ryan91rs

iTrader: (1)

best to swap the whole rear. I have done it both ways and even if for fun you took what you have out and put it right back in you would have to go back and setup the whole thing.

I have done a 7.5" open to auburn. took me a long time.

then did a 7 5/8 open to posi. pain the butt.

Lastly i just found a fourth gen rear and swapped in for my old rear. It was the easiest. There is a lot of bad info out there on how to do it right. Its a long process and a 7.5" is not worth the effort IMHO.


You figure you have to put on new bearings on all around (timken) than get an install kit. Your looking at around 150 bucks min. just to start off. Than the posi, fluid and gasket. Then renting or buying tools to do it and the instruments to see if your close. Than you have to read the tread pattern.

If you got time (week or two) and do your research than its a possibility. If you have a tendency to get anxious like me or miss one step or do one step wrong your posi is toast and your gears.


I suggest finding a limited slip complete rear out of a 93-02 camaro. Put new fluid in, gasket and replace your whole rear end with it. Most simple and most economical. Expect to pay 300-350 if you find a good one. You might get lucky and find a disc rear and kill two birds with one stone. I did it and got a 3.42 from a V6. Runs great!!!!

92RS_Ttop

iTrader: (3)

I've got the time and the tools. Or at least I can buy the tools. Time is not a factor as the car gets garaged over the winter for working on. I will eventually do the swap, as I want to do it for the learning experience as well as the increased performance. I just don't want to spend the money for the bearings and seals and everything twice. I'm on a very tight budget for any mods or upgrades to the car, but even if I had unlimited funds why pay for something twice?? I've been researching this for the last 2 weeks, and couldn't find a definitive answer about just swapping the carrier over. I also don't want a 4th gen rear because I want like the stock 15" rims (I'm crazy, I know) and I'm afraid they would stick out too far to look good and there aren't any 4th gens in the JYs near me. At least in ones that will give me a reasonable price on the rear. The JY I found this carrier at would only charge me $30 for it. That's the main reason I was considering doing it in 2 steps. I could still buy the carrier and then find a set of 3.73's from another car and put them together to do the swap right? A 3.42 carrier should bolt right up to a 3.73 carrier if my research is right.

big gear head

If you just want to swap in the posi you will have to set the backlash. You don't have to mess with the pinion at all. Read this.
http://www.nastyz28.com/forum/showth...t=install+posi
This is for the 8.5 rear end, but it is the same for the 7.5 too.

92RS_Ttop

iTrader: (3)

Great link, thanx!! That's exactly the info I was looking for. One last question though. Can you get just the bearings and shim, or do you have to buy the whole install kit?

Make that 2 questions. The bearings and shims are the same for all 10 bolts? If I pull the posi out of say, an S10 it will take the same ones as the Camaro would have it it originally had posi, right?

big gear head

Yes and yes. You can get just the bearings and shims without getting the complete installation kit. I think they are $45 for the set. All of the 7.5 rear ends use the same differential bearings, but not all use the same pinion bearings.

92RS_Ttop

iTrader: (3)

I see. So if I replace the pinion bearing at all, like if I happen to find a set of 3.73's from an S10 in the JY, I need to use the pinion bearing for the Camaro, right? Or is the bearing specific to the pinion gear being used, not the housing I'm putting it in?

big gear head

The gears are all the same. It's the housing that is different. Use the Camaro bearings. As far as I can remember all of the S10 trucks and Camaros use the same bearings. It is the earlier 7.5 that was used in the G body cars that had the smaller pinion bearing.

92RS_Ttop

iTrader: (3)

Bringing this back from the dead as I finally have all the parts I need to do the swap and I 'have a few questions.

I picked up a 4thgen posi disc rear at the local U-Pull this past summer from a 95 Trans Am. Last summer I managed to find a good 3.73 ring & pinion in a late 80's S10 at the same yard. I've cleaned and painted the axle and installed new pinion bearing races, axle bearings, and seals. I have a basic install kit with the shims, only thing I am missing are the carrier bearings. I have a shop press to get the pinion bearings on and off to change the shims, and a dial indicator with magnetic base to measure the backlash.

Thanks to Big Gear Head's link above, I have a good basic understanding of the process of installing and setting up the gears, but need a few questions answered:

I'm not sure where to start with the pinion shims, I just kept the original one that was on the pinion gear I'm using. Is that a good starting point or should I use the one from the pinion gear that came in the axle?

Should the outer pinion bearing be a near press-fit? The one that goes in from the front of the housing. I thought it should slip onto the pinion shaft fairly easily?

I still have the original carrier shims from the axle, should I measure those to get a starting point for shim thickness? I know I can't reuse them since they are the factory shims.

When does the crush sleeve go in? If I understand the process correctly, it is used to get the final preload on the pinion, right?

I guess my main problem is that while the link above gives a great how-to for installing the carrier(which is what the thread was originally about), I'm not sure of the process to install the pinion. I'd appreciate any info you guys can give me on this. I think once I have my starting point set, and the pinion part of things down, I'll be fine since I understand the part about reading the pattern and installing the shims to correct it.

big gear head

Start with the original pinion shim for the housing that you will be using. This will get you close, especially when using GM gears.

The outer pinion bearing should be a tight fit. Somethines they are tight enough that you have to use a hammer to lightly drive the pinion out and sometimes it is a snug slip fit. It just depends on how the gear was ground.

I don't know what shim set you have, so I'm going to suggest that you put the differential in the housing with the bearing races and add shim to the left side until the ring gear has just a little backlash. Use a screwdriver or something to push the right bearing race tight against the bearing while you rock the ring gear back and forth to check backlash as you add to the left side. Then put shim in the right side until it's tight. Then you can check backlash with the dial indicator and make adjustments from there.

The crush spacer goes in at the final assembly. Don't use it until then. Be sure that you set the bearing preload the same for each trial assembly as it will be on the final assembly.

Setting the pinion depth depends on your ability to read the contact pattern. This will tell you what pinion shim you need to use. Used gears are usually much harder to read than new gears, so if you are using used gears this might be tough.

supr_fly03

iTrader: (2)

When setting up used gears, the drive side tends to have a strange pattern so look at the coast side because it has less wear and should produce a good pattern.

Also, make sure you are loading the carrier. I usually use a rag and a pry bar wedged between the housing and the ring gear with a little bit of force. Rotate the pinion 2 or 3 times in both directions. This will ensure you have a clear pattern on the gears.

I will be making a thread about setting up gears in a 10 bolt either tonight or tomorrow. It will include pictures of patterns and it took me several attempts to find the correct pinion depth so you will be able to see how changing shims affects the pattern.

As a side note you can alter the pattern on the gears by changing back lash, so it is imparative that back lash is correct everytime you make a change to ensure you will have a correct pattern during final assy.

When hammering the pinion out, use a large dead blow hammer or a brass hammer. This will ensure you dont damage your pinion nut threads.

big gear head

I have much better results reading the pattern if I use an axle to turn the differential. When I turn the pinion I get blured or irregular shaped patterns. If I'm setting up a rear end with a standard differential I use a wrench on a ring gear bolt to turn the differential. Try it and you will see that the pattern is much easier to read if you turn the differential instead of the pinion.

supr_fly03

iTrader: (2)

Never tried it that way, but I will give it a shot. I still need to make a pinion shim change tonight because I have a good pattern, but it is a little low on the flank (pinion too close) and I would rather have a more centered on the tooth pattern. The Ratech kit i got does not have a good selection of pinion shims and I can only make even number changes so I am going to have to bump the pinion back .002 which might be too much. (In my book, close to perfection in gears is not good enough)

92RS_Ttop

iTrader: (3)

That will work with a posi carrier? Not sure what you mean by "a standard differential"?

supr_fly03

iTrader: (2)

Standard differential just means that it is open, or "one wheel peel". When you look inside all you will see is the spider gears. Posi of course has visible springs and clutch packs in it.

What that means for differential rotation and pattern reading on a posi, you can just turn one axle shaft or the other since they will both turn at the same time in the same direction (this means the differential is turning) causing the pinion to spin creating a readable pattern.

On an open differential you cannot do this because the oppisite axle will spin in the oppisite direction and not turn the differential (make sure the pin is in the diff, or you will just toss your spider gears out of the housing). So to counteract this, use a wrench on a ring gear bolt to turn the differential which will make the pinion turn to obtain a readable pattern.

92RS_Ttop

iTrader: (3)

Gotcha. I thought that's what he meant.

Thanks guys, hopefully I can get it set up Tuesday night and everything goes smoothly.

big gear head

Thank you, that's exactly what I meant.

supr_fly03

iTrader: (2)

I will try and get my step-by-step gear install thread up tonight. The biggest thing is to not accept an ok job here. Take the time to do it right, the process is monotonous and time consuming when you have to make a bunch of adjustments to get things right (sometimes you get lucky and it is perfect the 1st try), but do it right once and you wont have to do it again.

If you dont have a case spreader (my pins were too big) the hard part is getting the correct carrier pre-load using shim packs. They are easy to damage trying to force the case and shims into the housing. I recommend you use the factory cast iron shims in the factory spots to start. I used factory shims as I have a few laying around in varying thicknesses so I could adjust my backlash.

If you have to use shim packs, measure the factory shims (just like the pinion) and use that measurement (i.e.: .240 on the left side and .230 on the right) to make your new shim packs from. Use two thick shims with all of your thinner shims in the middle. To make setup easier, you can subtract .007ish from each shim pack during setup to make it easier to get the diff in and out of the housing. (I usually spread the case .015 and make it so the diff will go in and out of the case snugly by hand) Then add the required carrier preload upon final assy (whatever amount you took out, add back to each side). Just make sure you check back lash one last time (.006 - .010) after torquing the carrier bolts (55-60ftlbs).

Edit: Dont forget to mark your caps before removal, I stamp mine with letters L and R on the caps and the case. That makes sure I install them correctly. You can also use a center punch and do one side with one dimple and the other with two dimples.

92RS_Ttop

iTrader: (3)

Using the factory shims is just for a starting point, right? I was under the impression I couldn't actually run them in the axle with different gears?

I did mark the caps when I pulled it all apart. Long ago I got into the habit of marking parts as I removed them and making sure I put them back in the right spot. Seems to make reassembly easier(or maybe its just me)

supr_fly03

iTrader: (2)

You can use them as a starting point and see where you are. If backlash is within the specs, use them. Those shims are tough and as long as the carrier bearing hadnt spun, the shims will still be good. Just make sure you can still see the machining hash marks on both sides, if so you are golden. (If the shim is bad you will be able to easily tell) They also take the abuse of being jerked in and out of the housing where shim packs generally do not unless you have a case spreader.

Pinion shims however, I do not reuse. Measure the old one and put together the same shim pack (or as close as possible) for a starting point. Use the shim that was under the original pinion bearing that came out of the axle you are building. If you dont have it, a good starting point on these 10 bolts is .030 under the pinion bearing.

NOTE: When I do gears on other axles like dana 30's, 44's, and dana 60's, I do not reuse those shims because they go under the carrier bearing on the diff. Any shim that goes under a bearing is a one time use item to me.

big gear head

If you try the original differential shims first then you need to be sure that you put the thin shim on the left side when you try it. If you start out with a shim that is too thick on the left side you can damage the gears because the ring gear will be jambed up against the pinion. You want to start with too much backlash and work your way over until the backlash is right.

92RS_Ttop

iTrader: (3)

Do either of you guys know if GM switched to an oddball threading on the 4thgen LT1 pinions? I have been having a hell of a till getting the nut on there. I finally took the pinion back out of the housing and used the impact wrench on it. It just barely was able to get the nut on, and when I backed it off it looked like it had new threads cut into it or the threads were cut deeper. I can't see any defects in the threads on the pinion itself, and I was using a factory GM nut. I've had the same problem with the nut in the rebuild kit I got as well.

Still having problems getting the outer pinion bearing on as well. I measure the pinion bearing and pinion shaft with my digital caliper and the shaft is about .008" bigger than the inner diameter of the bearing. Is this normal? I was thinking of taking some 800 grit sandpaper and trying to open up the bearing's inner diameter a bit so it goes on easier?

supr_fly03

iTrader: (2)

Go read this thread.
https://www.thirdgen.org/forums/tran...axle-gear.html

It outlines the whole process. I would have to guess that you, or who ever removed the pinion did so with a steel hammer and not a brass hammer or deadblow hammer. This causes the first few threads to be mushroomed slightly and I am surprised you can even get a nut on it. I am not sure the best way to fix it other than a thread file and lots of patience. As far as the pinion bearing, it is supposed to be a tight fit. That is so the bearing does not spin on the pinion. You should be pressing it on in a press, or as Drew in my thread suggested you can heat the pinion (in your oven if you can) and it would probably help to put the pinion in the freezer over night. Should allow the pinion to go on pretty easy. What ever you do, dont sand the inside of the pinion unless it is your setup bearing.

92RS_Ttop

iTrader: (3)

Already read that thread twice, and took notes

I have used a steel hammer to get it out of the housing, but the threads show no signs of damage. They all appear to be straight, and come to a clearly defined point. Only 1 revolution of the thread is any different. It has the end flat on it instead of coming to a point, and its the 4th turn from the end. The threads on the end are fine.

I was thinking of carefully knocking that thread down a bit. Just wanted to make sure that was the fix before I go making things worse.

I think we're talking about 2 different bearings. The bearing that goes on the pinion shaft closest to the gears I installed using my press. I knew that one would be a tight fit. I'm talking about the other, smaller bearing. The one that you install from the front of the housing and rides right behind the yoke. I don't think that one should be a press fit should it? Wouldn't that make it impossible to set the bearing preload if you had to put the whole axle in a shop press to get that bearing in?

supr_fly03

iTrader: (2)

Oh, yes the small pinion bearing is also a tight fit and must be knocked off of the pinion everytime you make a change. As long as you can get one or two threads on it it should walk the yoke up on the pinion driving the bearing on as well. It sucks but that is the only way. If you dont have a brass hammer, you can use a block of wood to cushin it when hitting the pinion.

As far as the threads, you most likley wont be able to see the mushroom effect. It is probably only the first thread or two. What will change is not the sharpness of the thread, but the pitch. It will make the threads closer together. It dont take much to mess up a good thing.

92RS_Ttop

iTrader: (3)

That's what I was trying to do. Use the pinion nut to push it back on. Problem is, I get it about 3/8"-1/2" from where the pinion seats into the race and then I can't turn the nut anymore. I'm using a 20" breaker bar and putting all my 250 pounds into it and it just won't turn. I've even tried the impact wrench on it and no luck there either. I'm not hitting the end of the threads, in fact the nose of the pinion isn't even poking through the end of the nut when it stops. That's why I was wondering about how tight that bearing is supposed to fit to the pinion.

supr_fly03

iTrader: (2)

I have had a few stubborn ones like that, I have used a dead blow hammer to help seat the yoke enough to get the nut started. If you can only go so far with the nut, you may need to get a new nut. In the past I have gotten large nuts at a local hardware store like an ACE hardware (Just take the pinion with you). Your new nut should thread on by hand without assistance, if you cant, the threads on the pinion are messed up and you will need to chase them with a rethreader, tap, or a thread file. Use that to do all of your setup work since they dont have any locking threads on them. Just make sure you lube the threads a little and use the hardened washer.

big gear head

I agree that you have probably done some slight damage to the threads that you can't see, but I don't think this is what is keeping you from getting the yoke on enough to set the bearing preload. Just to be sure, you don't have the crush spacer installed do you? I have used a brake cylinder hone to loosen up a bearing slightly, but not enough to make it slide on and off easily.

92RS_Ttop

iTrader: (3)

No, I haven't put the crush spacer on yet.

That's what I wanted to do with the bearing, open it up a bit in the middle, but not to the point where it is too easy to get on. If I take the pinion out and put the nut on, I can get it on the whole way. It's tight, but I can get it there. When I put it in the housing with the bearing, that's when I absolutely cannot get it on far enough. It always stops at the same point. That is why I am leaning towards the bearing being too tight.

I was thinking about trying to press the bearing on with my shop press, just to see if it is possible for it to go the whole way on. The only reason I haven't done it yet is because I am not sure I can get it turned in the press to press the bearing off.

92RS_Ttop

iTrader: (3)

Ok, so just to update things I managed to fix the threads last night. I spent the day at work online searching all the local hardware stores for a thread file, but nobody around here carries one. I guess that's the downside of living in a small town. Anyhow, I had bought a cheap set of small files at Harbor Freight a few years back and I grabbed one of them and was able to fix the threads with some careful filing. The nut still drags a bit, but I can get it all the way on now without resorting to excessive force or the impact gun.

I still could not get the pinion installed however. The nut still becomes impossible to turn about 1/4" before the bearing seats into the race. So I pulled it all apart and stuck it in the press. The bearing pressed on really easy. Easier than the rear pinion bearing(the larger one) in fact. Unfortunately, I forgot to slip something on the pinion shaft before pressing the bearing on so I could press it off without damaging the cage and I bent the cage while pressing it off. So I need to pick up a new bearing. Not much of a setback as I'm still waiting on my in/lb torque wrench to arrive.

I also found out that the install kit I have is the Ratech kit. I had purchased it from another member here and wasn't sure what brand it was, but I found "Ratech" stamped on one of the pinion shims I hadn't used.

When I pressed the rear pinion bearing off, I measured the original shim that came under the rear pinion bearing and it is .026". Is that a normal thickness for a factory pinion shim?

big gear head

The kit that you have may not be Ratech. Many kits have Ratech pinion shims in them, but that's it. The Yukon kits that I use have Ratech pinion shims too, but nothing else is Ratech.

I wish I could see what is going on with your pinion. I can't think of a good reason for it to be doing this. When you put the yoke on does it slide on easy? Will it go all the way to the bottom of the splines?

supr_fly03

iTrader: (2)

I am agreeing with Big Gear Head, you must have a spline engagement problem with your yoke or something. Do you have any factory sealant in the yoke splines? Look at the yoke splines and pinion splines for burrs or something that could be catching. You are using a washer when trying to install the pinion right?

92RS_Ttop

iTrader: (3)

I just saw the Ratech stamp, and assumed it was a Ratech kit. Makes sense though, and it's entirely possible the member I bought the parts from bought the bearings and shims separately.

I cleaned all the sealant and other gunk from the splines with a small wire brush on both the pinion and the yoke before I ever attempted to put them together. I can push the yoke on all the way down to the bottom of the splines by hand when its not installed in the housing. And yes, I am using the washer.

I think my next step is to try clamping the pinion in my bench vise and then trying to put the bearing and yoke on and see if I can determine what is stopping it from going on the whole way.

I doubt this is the problem, but just a thought: The rear is from a 4th gen Trans Am and the ring & pinion are from a mid-late 80's S10. Is it possible that the pinion shafts are different lengths between the 2 axles?

supr_fly03

iTrader: (2)

Do you have the original pinion from the camaro axle to compare it with?

I am not sure about the S-10's. I heard that some of the 4x4's might have came with 8.5's but take that as a rumor because I dont really know. Maybe Big Gear Head knows.

I would do as you said, put the yoke in a vise and assemble like normal and see if the pinion bearing can be drawn all the way down. If so maybe you have the wrong bearings for the pinion?

big gear head

The gears that you have might be the smaller 7.5 gears. The later 7 5/8 gears are better, but they will interchange. As long as both are the 7.5 and 7 5/8 then everything should go together. The 8.5 wasn't used in the S trucks until the mid 90s and the ring gear would not have fit the differential if that was the case.

92RS_Ttop

iTrader: (3)

I compared the 2 pinions, and they look the same. Spline and thread length are the same, as is the overall length.

I clamped it in the vice and everything went on without a problem. I ran the nut all the way down to the end of the threads and there was no binding or other problems. I took the yoke off and pressed the bearing off. Then I put everything back in the axle and tried again. This time it went on the way it should. I can't explain it. The only thing I can think of is maybe I was getting the bearing cage caught on the edge of the race and it was binding. I don't see any markings on either one though to indicate this. But its the only thing I can think of.

Once my in/lb torque wrench arrives, I can set the preload and start the fun part.

supr_fly03

iTrader: (2)

Glad thing finally went together for you. Let us know how the assy goes.

92RS_Ttop

iTrader: (3)

So now that the major holiday stuff is out of the way, I have finally been able to get some setup work done. I have included a (fuzzy) pic of my first attempt. If I am understanding things right, I need to add some shim to the right(passenger) side of the carrier, and take some shim out of the left(driver) side? Pinion depth looks pretty good to me. Backlash is right at .006-.007".

I'm having trouble getting a good visible pattern on the gears though. It took me about 6-7 tries to get even that good of a mark. Any suggestions there? On the drive side of the gears, its impossible to see anything there is no grease left on the teeth after spinning the gears. All I can see is the original wear pattern on them. I have tried spinning the gears by hand using the yoke, by hand using and axle, and using a wrench as BGH suggested.

big gear head

If this is a used gear you need to look at the coast side more than the drive side. Did you change gears or just the differential? If you did not change gears then just set the backlash and don't worry much about the pattern.

92RS_Ttop

iTrader: (3)

Sorry for the confusion there. Everything is used - gears, carrier, axle, etc. The carrier and axle are a matched set(both came from the same 94 Trans Am). The ring and pinion are a matched set as well, but from an 80's S10.

So you're saying I can ignore the drive side completely? That would be a good thing cause I could swear I was getting a completely different reading from it than I got from the coast side.

big gear head

The drive side will have much more wear on it than the coast side. You will have a very hard time getting anything to look right on the dirve side. Look closely at the coast side and make your adjustments based on what you see there.

supr_fly03

iTrader: (2)

As big gear head said, look at the coast side and make adjustments off of that. If your back lash is good at .006 - .007 your adjustment will need to be a pinion depth adjustment based on your coast side pattern.

If your pattern is low on the tooth, that means you need to remove shim from the pinion gear. If it is high on the tooth, then you would need to add shim to the pinion gear.

If the pattern is really close, make small adjustments of .001 or .002. If it is not so close (half moon shaped and no fading) make large adjustments of .005 or .006

Left and right carrier shim changes move your back lash around. This does has a slight impact on pattern, which is why you always want your back lash in spec before trying to make and read patterns.

92RS_Ttop

iTrader: (3)

Ok, I think I got it now. I was trying to move the carrier shims around to change the pattern when I should have been changing the pinion shim.

My latest setup I decreased the pinion shim by .006" to .023" to get a better pattern. I then had to change my carrier shims to get backlash back to .007".

I know the pic is a bit fuzzy, but how's the pattern look now?

big gear head

I couldn't see the pattern in the pictures. I think you need a little more compound on the gear. I also didn't see a picture of the coast side, which is what you need to be looking at.

supr_fly03

iTrader: (2)

Yeah it is hard to see. Cant tell if it is low or centered. Dont be afraid to put a thick coat on about three teeth then run the pattern.

92RS_Ttop

iTrader: (3)

Ok, I'll try and grab some better pics tonight. Whenever I slather a lot of grease on the teeth, it hasn't been giving me a good clear pattern.

BGH - I thought the pics I posted were of the coast side? Maybe I've got my sides backwards in my head? When I look at the other side of the teeth, I can't make out anything.

big gear head

The drive side is the side that is almost straight up and down. The coast side is slanted more.

92RS_Ttop

iTrader: (3)

Ok then, I was definitely looking at it backwards. Took me a minute to figure out what you meant, but I got it now. I think I just have everything backwards in my head.

So "low" on the gear refers to the pattern being too close the base of the teeth(where they attach to the ring gear), not that its too close to the axle shafts(or center of the ring gear's diameter)?

92RS_Ttop

iTrader: (3)

Ok, so I tried it again and used the "good" camera to take the pics this time. I seem to be getting a better pattern on the drive side, but still not getting much of a pattern. Maybe its the cheap stuff I'm using.

Anyhow, here are the best pics of the bunch on the coast side.

92RS_Ttop

iTrader: (3)

And the best pics of the drive side. I put more stuff on this time, but it just seems to take more revolutions till I can get any kind of visible pattern.

Each of the pics of the coast and drive sides is after a full revolution of the gears. The first time around, not much stuff comes off and it just seems to push it around instead of squishing it properly so I can see any kind of pattern. The second and third revolutions give better results, but not much as you can see.