I have no idea at this time how to fix the following backlash problem and would appreciate suggestions. The only thing left to me as I see it is to add a 0.001" shim back onto the right side.

After assembling the pinion gear and the ring gear/carrier unit, my backlash was way too low at under 3 thou (0.003"). I have 2-cut gears (hobbed) and the backlash spec is 0.003" - 0.006".

To get more backlash, I added 0.004" worth of shims to the right side of the carrier bearing race to move the carrier toward the ring gear side. I only subtracted 0.003" from left side to tighten the carrier preload a tad.

Result: My backlash increased to over 6 thou and the ring gear felt clunky as I turned it against the pinion.

Here's a photo of the gear marking (attachment #1). Note the pink and blue paint marks on the edge of the ring gear. Look only at the three teeth either side of those marks since the rest is back-wash from the pinion gear.

To reduce the backlash, I removed a 0.002" shim from the right side and added a 0.001 shim to the left side. The reduction the day before had made it nearly impossible to insert a 0.010" shim. It warped.

The results can be seen in attachments #2 and #3, The gear markings are both on the heel side of the teeth and nearly off the end of the tooth.

For some reason, Yukon claims this is an acceptable marking, although I don't understand why.

 

Looks to me like the pinion is too shallow.

What shim is in it? With the new sleeve, what did the preload end up at?

 

The guy in the shop who pulled the old rear pinion bearing and installed the new one claimed it had a 0.030" shim in there.

If the pinion was too shallow, don't you think the markings would be toward the face or the flank? Even before I shimmed the carrier, the marks were fairly well centred although closer to the flank, and either heel or toe. After shimming the marks seem to be closer to the face but now both coast and drive are on the heel side.

Are you aware that with 2-cut gears the marks are diagonal rather than straight across?

Re sleeve. Have not changed it yet as explained...have to be off the driveway I am using in a week. If I have a few days left, I will replace the sleeve but for now I need to see if the vehicle will run as is so I can move it.

The pinion preload is still at 25 INCH-pounds.

If push comes to shove, do you think it will drive OK with the marks as in attachments 2 and 3 without jamming or breaking teeth? The ring gear turns very smoothly by hand and the current backlash is 4.7 thou.

I am not looking at that as a full time fix, just to be able to move it for now.

 

Taking your modus operandi, here is some math.

-With my stock carrier shims in place, the backlash was below 3 thou, which is too low.
-Adding 4 thou to the right moves the ring gear away from the carrier till the backlash is greater than 6 thou.
-Subtracting 2 thou from the 4 thou drops my backlash to 4.7 thou, therefore a shim change of 2 thou gives a backlash change of 6 thou - 4.7 thou = 1.3 thou.
-a 1 thou change should decrease the backlash by half of that or about 0.65 thou, leaving me around 4 thou, which is perfect for my type of gears.

With 4 thou of shims, my coast side is centred not badly but the backlash is too high.. Yukon says to ignore the drive side on used gears and to focus on the coast side, which will likely have less wear.

With only 2 thou of shims on the right side, the backlash is in bounds but the marking on the coast has moved a fair amount off the heel end of the teeth.

Does it make sense that dropping the right side shim to 0.001" (1 thou) would drop the backlash to about 4 thou, which is perfect and move the coast pattern back onto the teeth further?

If so, any tips for getting a 1 thou shim in there without bending it?

 

New or used gears? If they are used then you can forget about reading the pattern on the drive side. Your only hope is to set it by the coast side pattern.


Your Yukon shim set is designed to be used like a sandwich. You put the thin shims between the thick outer shells and drive them in like that.


I see that you have the Governor Lock. Hope you don't plan on abusing it much.

 

Used.

I am slowly cluing in to what needs to be done. I over-estimated the size of the shims required by a good amount. I had read that 10 thou added to the right side (looking into the diff cover opening) would increase backlash about about 7 thou.

I only needed to increase it by about 1 thou to get it in range for 2-cut gears. I have 2 thou in there now and the backlash is 4.7 thou, which is on the high end of the Yukon recommended setting of 4 thou. If I replace the 2 thou shim with a 1 thou shim, I should be well within the range and that should move my coast side back onto the teeth appreciably.


Thanks. I called Yukon and that's what they told me as well. The trick for me is getting enough shims overall to get the carrier preload in range and not mangle the shim when inserting it. Even though the lighter shims can be protected by a 10 thou shim with a collar, the 10 thou will distort if tapped in with a brass punch.

When I took the stock shims out during disassembly, they were in there tight yet the carrier preload read zero. Same for the pinion preload. When I reassembled for the first time, the stock shims were really hard to get in but the preload was still negligible. The stock shims are 23 thou.

I added 2 thou to the left side to bring the preload up and it increased about 10 INCH-pounds, but 10 thou shims wont take the force the 23 thou shims take.


Nope. I wont be treating it harshly. I wanted to get a better Positrak but they were $500 or more. I spoke to a guy who does rear ends only and he had a used/rebuilt Eaton for about $350. He told me to inspect the small gov-lock gears, like on the governor, and if they were not stripped, just to leave it, based on the kind of driving I would be doing.

 

I'm not understanding what you are saying about the shims. The Yukon shim set has a thick outer washer with a lip around the inside diameter that is designed to hold the thin shims and the other thick washer in place. I haven't measured the thickness of the outer washers, but they are at least .075 inch thick or more. I've hammered in hundreds of them without damaging any shims.

 

When I registered for the forum I had not noticed that the forum is specifically for third-generation cars like Camaros. Whereas I am a Camaro fan, and have been since the early days of the 396 Z28, my 7.5 diff is in a GM 2001 Safari cargo van.

Sorry about that, I should have read the intro better before registering. In fact, I skimmed it and saw nothing specifically about Camaros. My Safari is a second generation Safari and I guess I confused the generation with the axle.

In my Yukon bearing kit, which is for the 7.5 axle (YK GM7.5-C), the shim you talk about is 10 thou and the collar is 10 thou for a total of 0.020".

Even the stock carrier shims are only 0.023" but they can be pounded in easily and finished with a brass punch. Last time I drove one in with a 0.002" shim in place. I torqued the carrier body over a hair with a crowbar to get the shim started and had a very light coating of grease on the 0.002" and the 0.023" so they would not grab and distort.

I am hoping the same technique will allow me to squeeze the 0.023" past a 0.001" shim. On the other side I have a sandwich using 2 x 0.010" with a 0.001" on the collar. I did not subtract the same thickness of shims from the left side to tighten up the carrier preload.

 

Stock shims in this model of rear are in the neighborhood of .250" thick, NOT .025".

The aftermarket shims are 2 .100" thick ones, that you then stack up a few .008", .010", etc. to get the thickness you need. .230" (NOT .023") sounds pretty typical for a stock shim, so your replacement ones should be about the same.

Having a .032" shim on the pinion is probably the cause of your pattern problem. When I said "too shallow", that means, the pinion isn't deep enough into the housing, so the contact pattern is toward the outer circumference of the ring gear teeth... exactly what you have.

I have never taken apart a 7.5" rear in any vehicle of any year or any vehicle model and found ANYTHING BUT a .035" shim. Not saying your shop guy is wrong; only, if it was me I'd have asked him to take it apart for me, and I'd have measured it myself and so forth. But, a pinion shim that's too thin moves the pinion toward the outer edge of the ring, which is pretty much consistent with the pattern you're getting. See my signature for a mental hint at interpreting observations. Like Big says, you're not going to get a "clean" pattern on used gears, no matter what; it'll be WAY big and spread-out and nebulous. But is should be better centered on the teeth than what you've got.

The way the carrier shims work is, you've got a carrier made with high precision to some size, and a housing with the 2 ends of the space for it cut to some random distance apart, between about .450" and .500" greater than that. Gears and carriers are made with VERY high precision, but housings are NOT. Therefore what you are REALLY doing, is not "shimming the gears"; you are shimming the HOUSING. (even though some of the shims are installed on the gears... never forget, the variable part that you're trying to adjust for, is the HOUSING). So, in the case of the carrier, you're going to need a total shim thickness somewhere between .450" and .500", that needs to be about .010" - .015" larger than the space in the housing to preload the carrier bearings, with the total thickness split between the 2 sides correctly to locate the ring gear the right distance from the center of the pinion. Therefore to change the backlash you MUST subtract a certain amount from one side and add back THE SAME AMOUNT to the other side, so that the total width of the carrier + shims = the space in the housing + .010" to .015". You CANNOT take shim out of one side and not put back an equal amount in the other: they MUST be varied together.

On the scale of what you're doing, .001" - .002" is NEGLIGIBLE. .005" is the size of a SMALL increment.

IMO .004" of backlash is too little. Reason as follows: as you are assembling this thing, it's cold. When it runs for awhile, it gets hot. Running temp should be somewhat comparable to the engine or trans, maybe not quite as warm but somewhat close. I'd say 150° would be expected. When parts heat up, they GROW; meaning, when the gears get warmed up, the backlash decreases.

Now: I doubt there's any such thing as the "perfect" backlash for any given set of gears; keeping in mind that "perfect", whatever it is, would be a VERY NARROW range (say, .00001" from "too much" to "too little"), and would CHANGE as the gear temp changes. So, no matter what, there will ALWAYS be error. The question then is, in which direction would the error be more, or less, harmful? Well, let's think about what would happen in each case... if you have too little backlash, the gears grow more than the backlash, and you then have 2 moving metal parts trying to occupy the same volume. What are the consequences of that? Pretty scary, no?? OTOH, if the backlash is too great, it will actually close up some as the rear warms up, and in the end you'll just have the same situation as will exist anyway after the rear has run for a few tens of thousands of miles and the bearings wear a bit. So between those 2 choices, which would you rather install in your car? Not hard to choose, really.

Plus, think about what happens to all that stuff as it wears and goes through 200,000 miles of changes. Bearings wear; whatever preload you put in there now, will go away over time. Backlash only grows as the gears wear, which is VERY slight MAYBE .002" over their life; or, increases catastrophically when the carrier bearings fail. Consider how you should set it up NOW, so that it stays the way you want it LONG-TERM as it undergoes its natural evolution both from wear and temp changes; IOW, such that as the error from "perfect" alignment moves around during temp cycling and long-term wear, it passes THOUGH "perfect", and ideally when it stabilizes during normal use, it's right close to "perfect". "Perfect" sitting on the bench is not as good as "perfect" RUNNING.

I tend to set up these rears (rears in general really) with preload on the high end of the range on both pinion and carrier, and backlash toward the high side of the spec. For the simple reason that as the parts are used and as they wear, preload and backlash both automatically go away, at least until the bearings reach the end of their life at which time the backlash increases dramatically. Another thing is, the pinion seal has drag on the pinion; it adds around 3 to 5 in-lb or so in most cases. Therefore if you set the preload to the low end of the spec with the seal present, you're going to automatically START OUT LIFE with too little to begin with. For that reason I prefer to set up pinion preload with a solid spacer and shims NOT a crush sleeve, WITH THE SEAL OUT, and once I get the shim stack right, install the seal and final-assemble the pinion to the housing with the shims I just picked.

I recommend you buy a solid spacer such as the one I linked you to in your other thread, a new seal, and a new head bearing and tail bearing; take the pinion back out and throw away the crush sleeve; hone out the tail bearing you have now with a brake cyl hone, until it slides freely on the pinion; replace the head bearing and put a .035" shim under it; set up the pinion preload with the solid spacer and no seal installed; once you get that shim stack established, put the seal in and assemble the pinion into the housing with the new tail bearing, and tighten the nut as tight as you can possibly get it (listen for it to scream for mercy); and start over on setting up the carrier. I'd recommend around .008" of backlash and around .010" - .015" of preload. Expect the shim pack on each side to be in the .225" - .250" range. I prefer to use 2 C-clamps to press the bearings together GENTLY to fit into the housing rather than pounding on the shims. I don't have a case spreader and I doubt you do either, but if you do, you don't have to pound anything.

 

I don't know what you are using to measure these shims, but I think either it is way off or you are reading it wrong. I have rebuilt more 7.5 rear ends than I can count, including Astro and Safari van rear ends and I have never seen one with shims that thin. They are always somewhere between .220 and .255, and I have never seen a Yukon kit with shims thinner than .006.

 

I appreciate the detailed explanation. You are absolutely right. I messed up in a big way.

Just went out and measured them again and the stock shims are 0.230", not 0.023". Also, the shims I have added are 0.020" and 0.010".

I started with adding 0.040", which pushed my backlash too high. I cut it back to 0.020" and that brought the backlash into range but pushed the gear markings off the heel end of the gear teeth.

I am thinking that if I change the 0.002" to a 0.010" it will leave my backlash in range and move the markings back onto the teeth properly. With the new pinion rear bearing and the stock 0.230 shims, my backlash was too low for 2-cut gears. It was reading under 0.003" and Yukon recommends about 0.004" for 2-cuts.

Right again. I have two pairs each of 0.100" and one has a 0.100" collar for stacking them.

However, the smaller sized shims are 0.005", 0.010" and 0.020". I need to get a better digital caliper because mine wont read under 0.010". I have to stack two 0.005" shims together so I can read 0.010".

If he was using calipers like mine, or being sloppy using a mechanical type, he could quite easily be 0.005" out.

I was taking a chance using the stock shim, I know that, and it may come back to haunt me. I don't have the facilities to pull it again and if I do it will likely destroy the bearing.

If I had a lot more time, I'd buy a new bearing and make up a bearing with a honed inner collar so I could remove it easily. I have learned a lot from doing this but i am running out of time.

Thanks. I was aware of that. I added 0.020" to the right side to move the carrier toward the ring gear and that increased my backlash. I took roughly the same amount off the left, but I had no preload reading with the stock shims and I added 0.010 to the left side to tighten up the preload.

It seems low to me as well but from 2001 onward, Safari changed to 2-cut, hobbed gears. The different between them and the older 5-cut faced gears is that the 2-cut teeth are the same height from heel to toe whereas the 5-cut slant from heel to toe. Also, the 2-cut are cut with a bias so the gear marking shows up as an diagonal pattern across the teeth.

In the manual with their bearing kit, Yukon specifies 0.003" - 0.006" backlash for 2-cuts and 0.006" - 0.010" for 5-cuts. As a rule of thumb they recommend 0.004" for 2-cuts.

I have it set at 4.7 thou at the moment and the play feels decent. You can see it move back and forth on the ring gear as you tune into the clunking sound of the gears as they start to mesh.

I agree totally that the prognosis is pretty scary if there is not enough backlash. Being a noob at this it's particularly scary. However, if they recommend a range, and I exceed it, I could have another problem with gear noise and clunking.

Another thing that is scary is the position of the gear markings on the teeth. Yukon claims having the marks on both the coast and drive faces is acceptable if both are at the heel end or the toe end. I would prefer to have the marks in the mid-tooth and centered from flank to face.

I have written to Yukon about that and they have failed to respond.

You have supplied solid advice and i really appreciate it.

This all good stuff and I wish I had the space to work on this over the long term. I understand now that setting up a pinion and a carrier requires a lot of patience, and time. I need to find a space where I can do that but for now, I need to get this beast running and out of the way so the people who own the driveway can get onto it.

I hope you or Big Gear Head don't take offense at me not following your advice re the pinion preload. It's all good advice you have offered but I am really up against it for time. I just hope the rain holds off till I get this finished.

 

You're right, I'm a dummy, I have been reading the calipers wrong.

The shim kits in my Yukon kit are 0.100", one with a 0.100" collar and one without. The other shims are 0.020". 0.010" and 0.005". My calipers wont read under 0.010" so I have to stack 2 x 0.005" to get a reading.

Thanks for pointing that out anyway. I have worked with such measurements for a long time and I have no idea what I was thinking.

 

Ok, so you should be able to put the thin shims in between the thicker ones and get them in without damage.

 

"Safari", "2001 onward", DOESN"T MATTER. Doesn't matter what sheet metal your rear is wrapped in. You have a 7½" GM 10-bolt. Your gears are .... 7½" 10-bolt. THat's all there is to that.

"Hob" is the most widely used method there is for cutting gears. Has been for over a century. https://en.wikipedia.org/wiki/Hobbing Nobody "changed" to or from it; not in minivans, not in 2001, not GM, not 7½" rears, didn't happen. Your rear, and its gears, are the same as everybody else's 7½" 10-bolt. Blee dat. We call this "mass production".

So when you got a new head bearing and put the .035" shim under it when YOU installed it, and then set the pinion preload as I described, and then set the backlash more sensibly, what did the pattern look like?

Are you going to DO THIS, or are you just going to keep posting on the Internet?

 

The longer you keep posting on the Internet instead of getting out there and DOING IT, the less time you have to get it done. Get your parts, quick before the week evaporates into the weekend, USE what you've learned, straighten it out.

DO

IT.

Whip it. Into shape. Shape it up. Get straight. Go forward. Move ahead. It's not too late.... to whip it. Whip it good.

At some point, ya gotta crawl outta yer shell, and DO IT. I know it's all scary; but, the longer you cower in dread of actually FOLLOWING WHERE YOUR MIND AND REASON take you, .... the longer it will be before your car works again.

Be glad we're not kicking you off because this isn't a 3rd gen Camaro/Firebird, and get off yer butt, and DO IT.

Did I mention, DO IT???? (yes I have been accused of being the R. Lee Ermey http://rateyourmusic.com/artist/r__lee_ermey of thirdgen.org about get off yer lazy a$$ and take yer fate into yer own hands )

 

I have done that. On the left side I built a sandwich using a collared 0.100" shim and a non-collared 0.100 shim. I put a smaller shim on the collar of the collared 0.100" shim. However, that one can be sat in there next to the axle housing before the carrier is put in.

My problem is on the right side. Initially, I built a sandwich and tried to tap a non-collared 0.100" shim in there. It was very tight and actually distorted the shim by forcing it out of round.

I replaced that with a 0.230" stock shim and a 0.020" shim. I placed the 0.020" shim into the shim space by the axle tube with a very thin coat of bearing grease on it. I applied a very thin layer of grease to the 0.230" shim as well. It tapped it in without distorting the smaller shim.

I meant to measure the carrier preload but I stuck the axles in to see if there would be any problems. As I said, I have less than a week to go in my current work space and I did not want any surprises at the last minute.

 

If the 2 outer parts of the shim set are .100 each and you couldn't get them in place, but a .230 with a .020 shim went in then something isn't right.


You can't measure the preload on the differential shims. Get it tight enough that you can't pull it out by hand and it's tight enough.

 

Got your point but I have two in rebuttal.

1)I figure it's better sitting back to think things through, even if it costs me a couple of days. Monkeying around under the vehicle, working in the dark, does not strike me as being productive. Having said that, sometimes that is the best way.

2)I'm retired and I have been hurting pretty bad the past few days. I did something to my ribs and my lower back and I felt pooped. Experience has taught me that when I feel like that to back off and rest.

The way I felt two days ago, I was ready to put the rear cover back on, filler er up, and take my chances. Today, after a couple of days rest, I am seeing things differently. I'm ready to give it for another couple of days to see if i can get it right.

Of course, you know how that can go, it can get worse, but lets not go there.

As Groucho might have said, I'd never hang around a forum who would allow a guy like me to post.

 

I like the Groucho quote.

I'm trying to urge you on toward the goal... assuming of course, that the goal is, a completed job with the end result as good over the long-term as the factory made it. Just trying to hack it back together with whatever is already done wrong, left as-is, is a recipe for CERTAIN disaster. There is little to no chance of success, unless all you want to do is to jam it back together enough to move it somewhere else and immediately start over. Otherwise you will simply find yourself right back where you are again soon if you don't start over from scratch and get it right, except that you have a pretty good chance of destroying stuff that's still good meaning it will cost you ALOT more to clean up the mess than to straighten it out now.

You now have a great deal more knowledge about it than you did, and knowledge is power. It should be much faster and less trouble the next time around.

Frankly, there isn't much that I hate worse than working UP UNDER a car, laying on my back. I go to great lengths to avoid it. In fact I won't usually try to build a rear that way; usually I'll take it out, just because that makes it SO much faster and easier. Sure, seems like it would create more work; but that impression would often be wrong.

In any case, sometimes there's nothing left but to just suck it up and face it head-on.

 

If I had a press it would have been done by now. The shop I took it to had a press and they ended up cutting the rear gear collar off the pinion shaft.

As you know, the outer roller bearing race cannot take the stress required to pull the inner collar if it gets jammed on. The outer race will just break, like mine did, and I had to cut it off. I even had a heck of a time getting the front and rear pinion races out of the housing. Upon further inspection, there was serious corrosion welding the race into place in a small area on the top of the race cavity.

I could not push the new races in till that corrosion was removed. I am theorizing the corrosion is partly due to electrolysis since it had build up a small **** of corrosion that had welded itself to the old rear race. It was not till I had ground that out that the race would go in.

The rear bearing collar was on there good. I have a puller suited to pulling that gear off the pinion and it would not budge the gear. Cutting the outer roller bearing race off to access the inner collar did nothing. There is a ridge on the inner collar that will take a gear separator and hooking onto that ridge is an accepted method by many to get the inner collar off using a press or a puller. With my puller, all it did was break chunks of the collar.

In the future, I am looking forward to doing this right. At this time, there is no way I am messing with that rear bearing, given my recent experience, with the amount of time I have left.