I see on the site it says that the Berlinetta's came with 3.08 gears. I still have the original rear in my car and it is Semi-posi. I'm wondering how I would have to go about changing it from being Semi-posi to Posi.

 

Oh, not sure what the spline count is but I know it's a 10 bolt main also.

 

Im not sure what you mean by semi posi. Theres three types of diffs. open diff, limited slip, and one type that never comes from the factory, a spool.

If it is a open diff you can easily put in a spool for about 80 bucks. Then you always have posi even when you dont want it. They are hard to drive in the rain with spools.

 

Only my passenger rear tire spins when i accelerate, but if i reverse several feet i can have it lock up the other tire. I want it so i have both tires spin.

 

The 10-Bolt FAQ sticky at the top of the page may provide some useful info.

JamesC

 

You have a standard differential (no such thing as semi posi). The '84 will have 26 spline axles. The 3.08 gear in the 7.5 uses a 2 series differential, which is going to limit your choices for a good posi. The Eaton Posi is very good, but not available in a 2 series. You might look into one of the Power Trax lockers. They are easy to install and you don't have to reset the backlash. If you have been doing a lot of one wheel burnouts you may have damaged the differential case, which will cause the Power Trax to not work right. One wheel burnouts are destructive to the differential.

 

I'm no mechanic just learning as much as I can as I go reading and asking questions to make sure what I read is accurate or I understand correctly.

Now the differential controls how the axles turn, being standard, or posi?
Does the ratio come from the ring and pinion? like 3.08, 3.73.
But the differentials (series II, series III) only work properly with their given ratios, unless modified?

"What Carrier Do I Have?
There are two: Series II is 3.08 down, series III, 3.23 up. Steeper gears, say 3.73’s, can be swapped into a series II with gears designed for such a swap, or by purchasing a series III carrier. (This would be an appropriate time to upgrade to limited slip and 28-spline axles.)"
From JamesC 10-Bolt FAQ post.

I'm trying to figure out which way I'd like to go with my rear. I want it posi, but debating on changing the ratio maybe to 3.73. I know someone selling a 3.08 posi rear for ~$150 says it's in excellent condition but if I can alter mine cheaper than that for a temporary change then i'd rather do that. Now if the price to change my standard 3.08 to posi is quiet a bit (~$200+) I'd rather spend it on a setup to go to 3.73 gears. Just don't know how a rear-end works and which part controls what.

 

There are special after market gears that are designed to work with your 2 series differential without using a spacer. Changing gears is not cheap. You will need a $120 installation kit along with the gears. Labor is going to run about $250 to $500 depending on where you take it. If you have found a cheap posi rear end that is ready to use then that would be a better way to go if you are trying to save money.

 

If i can get that 3.08 posi for that $150, could i rebuild my old one and get 3.73? Me and my father can do the work he is a mechanic but mainly a dodge guy. My above post is that correct on my assumptions?

I see a eaton 26 spline 7.5 10 bolt main for a chevy on ebay for ~400 then i would need the ring and pinion right for the 3.73 ratio?

http://www.ebay.com/itm/GM-7-5-CHEVY...r#ht_714wt_486

 

Yes, if you get the Eaton Posi you can get the standard 3.73 gear set and the installation kit to do it yourself. Do you know how to set the pinion depth, bearing preload and backlash to get the correct contact pattern? Do you know how to read the contact pattern so that you will know what adjustments need to be made to the pinion depth and backlash?

 

"Yes, if you get the Eaton Posi you can get the standard 3.73 gear set and the installation kit to do it yourself."

Meaning the differential, ring and pinion, bearing kit? ~$500-$800 I'm guessing

As for how to do it I'm not 100% sure if my father does. Don't know if it differs from Chrysler/Mopar.

 

So he will be upgrading to 28 spline axles and carrier to 3 series with 28 spline so he can use the standard 3.73 gears.Is that right?

 

Ya if the rear is to be upgraded to 3.73 the spline is gonna be changed to 28's. what do you mean by standard 3.73 though?

 

The standard 3.73 fits the 3 series differential. The thick 3.73 fits the 2 series differential.

 

Ah ok.
http://www.youtube.com/watch?v=gIGvh...eature=related
just watched that and brung up a question.

are there 2 posi units? limited slip and locking?

 

Limited slip is what most people call posi. There are clutches attached to the axle gears (clutch plates or cones) that cause friction when power is applied. This causes both axle gears to mostly lock up with the differential case and make both wheels turn. The Governor Lock is what Eaton calls a locking differential. They were used mostly in GM trucks, but a few of them found their way into the 3rd gen Camaros. These allow one wheel to spin a little before a governor locks in the clutches and makes both wheels spin. These are not good for performance use. There are other lockers that work much different from this, but these are the 2 that were offered in the 3rd gen Camaro.

 

Here's a page showing the differential choices available. = http://www.eaton.com/Eaton/ProductsS...ials/index.htm
I chosethe Eaton Posi Differential (LSD) because of the positive comments made in my search for the one that fit my application best. (Daily driver , street/strip ) This choice was also picked by the installer of the unit. I'm going to post a link to my build so it will give you a idea as to what some of the process looks like and what it cost me. = https://www.thirdgen.org/forums/tran...de-photos.html

 

So if i was to change the stock rear in my 84 to posi 3.73 28 spline i would need:

Posi unit, bearing kit, ring and pinion, and axles?
how would I go about looking up axles? 7.5 28 spline? or are there other measurements?

Found a decent price for the other stuff minus the axles.
http://www.ebay.com/itm/GM-10-Bolt-C...e74011&vxp=mtr

 

From the auction listing:

"BRAND NEW GM 7.5" / 7.625" Eaton-Style Posi Unit..."

NOWHERE does it say it's an Eaton.

NOWHERE do I see the Eaton logo on it.

NOWHERE does it say what it ACTUALLY IS.

Given that the Eaton posi costs over $500 all by itself at Summit, http://www.summitracing.com/parts/ETN-19599-010/ the gears are close to $200 http://www.drivetrainspecialists.com...duct-1799.html and the kit is about $100 http://www.summitracing.com/parts/RAT-308TK/ (total $800 worth of stuff from some of the lowest price reputable outlets), I'd be REAL SUSPICIOUS of something being sold for THAT MUCH cheeeeeeeeper.

I'd also be REAL SUSPICIOUS of the "GM" wording; does that mean "GM brand"? "from the same supplier that GM buys from"? (which would be AA&M/Motive) "fits GM"? Is it just part of "GM 7.5" like the posi description? Weasel-wording? Again, GM charges AHELLUVALOT to buy those gears at their stores. It's probably not ANY of it, actually "GM" parts.

If something seems too good to be true, it probably is.

"Trust, but verify". BEFORE giving em your money.

For axles, I'd recommend these. http://www.summitracing.com/parts/SAG-EV10-4/

 

Be sure your master bearing kit contains axle bearings and seals. If not just buy them separately.

 

Thanks for all the help, appreciate it very much. So just in parts i'd be looking at $800-$1,000+, ignoring the phony, cheap, non-brand sales on ebay. Was just looking around for prices but you made very good points @sofakingdom.

Now "IF" i wanted to just change my current stock Berlinetta rear to posi, I'd have to change just the differential? or add something to it? and would it cost less than $150 because I can possibly get another rear same ratio ~70k miles on it for ~$175. And use that til i build my current one up to the 3.73.

Seen what big gear head said earlier "You might look into one of the Power Trax lockers. They are easy to install and you don't have to reset the backlash."
and see they're about $300+ not looking to spend that much to keep this rear setup.

 

The differential in that ebay auction is a Yukon Dura Grip, which is a good differential. MUCH better than the Auburn. I have installed many of them and they are an exact reproduction of the Eaton Posi. The Eaton parts will interchange with the Dura Grip parts. The main difference between them is the clutch material. Eaton uses carbon fiber and Yukon uses a Raybestos material like Ford uses in the Traction Lock.

Yes, your list of parts is what you need to do the job that you want to do.

I can recommend a dealer who can get you a good price on all of the parts that you need. I don't recommend buying rear end parts from Summit or Jeg's. They are like Wal Mart, they sell the cheapest parts that they can make the most money on. There are much better places to get rear end parts.

 

That's a little bit extreme...

So you're saying that all the name brands they carry - Eaton, Superior axles and gears, Richmond, Moser, AA&M/Motive, Ratech, etc. are all to be lumped into this category?

 

No, I should have put that a different way. You can get a better deal on those parts in other places. The installation kits that they sell are junk. Ratech, Richmond, Summit, Jeg's and the other installation kits that they sell are not worth the box that they are packed in. If you go to a business that builds rear end and sells parts they will have the best parts because they use the parts that they sell.

 

I keep reading complaints about Eaton switching to C-F, so the DG suddenly seems more interesting. I gotta disagree on the Auburn, even though BGH explained what's wrong with it many months ago: It contaminates the gear lube. But I say it's so good to daily-drive year-round in Northern Utah's occasional snow that it is worth frequent lube changes. I gotta disagree about Ratech's shims also, they're so much better than the cheap alternatives that even a non-pro like me can tell it, just with vernier calipers and how scratch-resistant and bending-resistant they are. I can say my last Ratech install kit included bearings that weren't American made, but I believe they now offer genuine Timkens as an extra-cost option. I believe Timkens are worth the cost.

 

If you ever used a good installation kit from DTS, Tom's Differentials, Dewco or Yukon you would never use another Ratech kit again. The shims in these kits are far better than Ratech kits. These kits also have better ring gear bolts, pinion nuts and Timken bearings are standard.

 

This is going to look more like argument than debate, but I see no point in worrying about the strength of the ring gear bolts and pinion nut when they are NOT the weak links in the 7.625" axle. Have you checked the cost of those kits? There's doing the job right, then there's wasting money. And for a weak 7.625", those kits are wasting money. When was the last time you checked the Ratech shims? I know they used to be junk a couple of years ago, but what I just used 2 weeks ago was not the same old same old. I don't do this all day every day like you do, but me not being a pro may mean my experiences are easier for everyone else here to relate to? You may have lost that perspective? Most of us care what'll work adequately for minimal skills combined with tight budgets. Using the best bolts means nothing when the gear teeth are the primary failure. A load bolt might help, but not better ring gear bolts.

 

What type of problems is the Eaton Posi. having ? Can you be a little more specific.

 

Tom of Tom's Differential reportedly said that "when you start getting into some serious power (around 500-550hp) the carbon-fiber clutches will warp" BGH himself once posted this: "The original Eaton used the 18 disc steel set. I'm not a big fan of the carbon-fiber cluthces. There are only 14 discs in that set. More discs means better lock up." And this: "The carbon-fiber plates seem to work well on the street. The only problem is that if you ever slip them real bad and get them hot they seem to glaze over and stop being as effective." And this: "The original Eaton Posi that was used in the '60s and early '70s Chevy muscle cars had 18 disc steel clutches and 200 pound springs. These are still working well in many of these cars 30 + years later. The new Eaton is designed to be smoother and last longer." ( More bite, less life, more life, less bite. The bite is the whole entire point. That's why the silly thing is rebuildable ) Here are other findings: "If you want the 800 lb/springs ( and that's kind of the whole entire point of buying a HP diff ) you can't combine them with the carbon-fiber clutches." "Additional traction out of a corner that you will get with the 800 lb springs." " Ijust rebuilt mine. Those carbon-fiber clutches were falling apart on it as well. They actually use 1 LESS pair of clutches compared to the more common all steel set. That's less surface area available and when that carbon-fiber falls off you lose a bunch of pre-load too. " "Carbon-fiber is great for road racing BUT drag racing stick with the steel clutches and they can handle more abuse. I have seen many carbon-fiber clutches actually peel from the plates they are glued to." "The natural lubrication (graphite) of the carbon-fiber clutch discs allows smooth low speed operation." Things that are lubricated don't have much friction, and those discs are there to create friction for traction, which is why posi's get friction-modifier additive to the gear lube ) "The new Eatons use carbon-fiber clutches. They don't last as long as the old steel ones did. Just about every one we put in the customer calls back in about 1000 miles complaining they only spin one tire. If I was going to buy an new Eaton i would take the carbon-fiber out and replace them with the old steel ones. We install about 10 a week and they still have that problem." "It does chatter, even thought the end user doesn't hear it. " "Use a Parifin based lubricant....... and since friction modifier, not the synthetic type like RedLine, is Parifin based..... it homogenizes much better and negates the chatter and inherent heat build up in the clutches." ( When you tear down engines every day, you begin to notice the problems are mostly in the ones that ran Parafin-based motor oils, like Pennzoil and Quaker-State. since it's not good for engines, why would I want it in my axle? To save the C-F clutches that still have every other problem listed above? Absurd ) "We try to push the Auburns. They don't have the clutch issue that the Eaton has. I have always used Auburns in my personal car and have never had any issues." "I used to have an Auburn Gear high performance series limited slip. It was a great unit. I was really impressed. The street driveability was pretty flawless, and it always seemed to lock up when I needed it to." ( I agree ) I'll let that suffice though there is more. To be fair, IF BGH spends 40 hours EVERY week playing with Eatons, then he SHOULD be able to get results that satisfy him. BUT, IF so, then he's NOT putting ANY effort into giving the Auburn a fair test.

 

Interesting,I don't rebuild engines or differentials so I rely on what I read and information picked up talking and working with mechanics,etc.. I have spent the greater part of this evening searching and searching, and let me tell you I am thorough. Nothing even coming close to a bad review or opinion so I'm going to rely on your information. I bought a Eaton Posi. when I upgraded my 10 bolt 3 years ago.
After doing my research and getting the recommendation from the installer I went with that. I feel that the Eaton Posi unit I have is perfect for my application .I'm not going to be pushing it to its breaking point any time soon and those that do I believe have picked the wrong unit. As you have mentioned ,there are some lockers and others that are designed to take the 500 hp and up hard launches over and over. Guys that spend any time at the track should know that.
The only thing that I might do if mine ever wears out is have the steel clutch plates you mentioned installed.

 

All I can do is pass on the things that I have learned over the years and the experience that I have had with good and bad parts. Suppliers change the parts that they put in their installation kits from time to time.

The installation kits that I listed above come with the super shims for the differential. These shims have a thick inner and outer shell that hold thin shims in between. The outer shells interlock so that they act as one piece as you drive them in. The thin shims are protected inside the shell so that they don't get damaged and they can't work their way out. The thin shims can be added or removed so that the over all thickness can be adjusted. These are the best and easiest shims that I have found, and they are easier to use than the Ratech shims. The Ratech shims are all flat and they don't lock together. This can allow the shims to seperate after time and some of them can partially work their way out. I've seen this happen.

Ratech uses ring gear bolts with small 5/8 heads on them. These are actually Chrysler bolts, but they are cheaper than the GM bolts, which have a 3/4 inch head. The small 5/8 head can make an imperession in the differential case, which will remove the preload from the bolt and allow it to become loose. I know this for a fact because it happened to me more than once, even though the bolts were torqued to 65 foot pounds and red Locktite was used on them. I've had to redo a few rear ends because the ring gear was loose on the differential because of the small head on the bolts. After examining the differential you could see where the bolts had sunk into the case. Now if I ever do a rear end with these bolts I install a Ford hardened washer under the head to prevent this from happening again. Most people don't have these washers, so they can't do anything to prevent this.

The Ratech kits use some kind of hardware store pinion nut. It's not an OEM style nut, and it's not hardened. These rear ends have a reputation for the pinion nut backing off. I always use red Locktite on the pinion nut and I use new GM nuts, but I have still had 2 or 3 that backed off. Using a lower quality nut is not a good idea in my opinion.

You are correct, I haven't used a Ratech kit in several years. If they have started using better quality parts in their kits then that's great, but even a guy who is doing his first rear end needs to use quality parts. It can be very frustrating when you put a lot of work into something only to have everything go bad because of a $5 part. I have also seen the parts in the kits that I listed change. I've seen them go to the small head ring gear bolts and back again, and I've seen some of the cheap pinion nuts in those kits. I can't controll the quality of the kits, but I can report on what I have seen and used. Some of those kits might be using the cheaper stuff right now. I have closed my business so I can have more time to do other things, so I'm not using any of them now. In the past they have been high quality kits, and I would expect them to be that way now.

As for the Auburn, the poblems that I have had with them is their short life, no way to rebuild them and the metal that they put into the oil. I know that people have had better success with them, but all of my experiences with them have been bad. I stopped installing them many years ago because I got tired of having to replace them in less that a year, and having to clean all of the metal out of the housing when they wore out.

These are all my opinions and experiences. I know that many are not going to agree with me, and I'm not trying to start an argument. If my experiences can help someone else then it's worth it, but my opinions and experiences will not always be the same as others.

 

Ok so the discussion went a little more to track and high hp, Im mainly looking to upgrade it for street driving but have the kick if i need it. Currently at about 350ish hp, and if down the road i decide to upgrade the engine i'd bump it up to about 400-450 no higher.

So which brand should i go with that will cover what i'm planning to do? Is that ebay deal not bad? or should i go eaton?

 

Why is it that my posts all end up as one mega-paragraph, when I have them broken into several shorter paragraphs when I click on "submit"? The Eaton wouldn't still be on the market if it wasn't somewhat good for some applications. It is very strong, and it has a good name. Auburn gets bashed, but so does the GM Gov-Lock. Why? They get abused. There are different styles for different uses. Eaton: drag racing on the street. Auburn: canyon carving and winter driving. Gov-Lock: winter driving by grandpa. Truetrac: canyon carving. Lockers: dragstrip and mud. ARB: everything except canyon carving and winter driving.

 

Ok on my way this afternoon to pick up a 3.08 posi with only 70k miles on it from a z28 for $150. Can start tearing down my old rear and clean the houseing and get it ready to build the 3.73 over the next for years. Forgot to ask what my dad was asking me to make sure of. On his 74 charger the u-joint part of the driveshaft has a different fitting for a posi vs open dif. Do i have to worry about this if the posi rear was from another third gen camaro?

 

No, they all use the same 3R u joint and yoke.

 

ok, so picked up the posi rear today for $150. A little while ago I put it on some stands so I can clean it up tomorrow, come to find out that the shock mount on the driver side was twisted. So now I'm in a bind.

I could take the posi diff out of it and put it in my rear correct? If I do should/could I use the same ring and pinion in my car which is also a 3.08? Making the job easier than having to reset the pinion baring? Also how would I go about changing the diff? Measurements, steps, precautions?

Thanks again for all the help, Learning A LOT!

 

http://www.nastyz28.com/forum/showthread.php?t=19773
Read this.