I have a chance of getting a rebuilt eaton posi not sure of the ratio yet i haven't asked!!! and wondered if they are a good unit or not very durable, i am putting out about 400 tq and 400 bhp with a th200r4 by bto 2400 stall and stock tires but looking to go to bigger sticky rubber What sort of price could i getone for in the states.
Peter

 

Eaton is the OEM supplier to GM for posi units. The clutch packs detremine the strength of the posi, early solid packs are good for high HP applications, later "daisy type" units (after about 1971) are more fragile and the current carbon fibre units are not too good at all in my humble opinion. Your Vette should already have a Eaton unit in it that can be rebuilt for around $200 in parts, check with Tom's Differentials for hardware. New units (with the carbon fibre clutches) sell for around $400 last time I checked. The good news is they can be retro-fitted with earlier solid clutch packs. If you rebuild your existing unit, ring/pinon set-up is OK if you change posi unit, you will have to re-setup the gears, another cost add-on.

 

Are you talkin about a complete rebuilt differential or posi?

The eaton posi was used on the 65-79 corvette, in 3 and 4 series. The difference being the flange thickness for 273-456 gears.
In addition to the series there were 2 designs, the earlier being ID'd by a small sq window and used from 65-68.These are not too good and often crack.
The later 69-79 are better casting but still crack. The spider gears also changed as did the clutch design.
Both designs can be improved on with some machine and hand work to eliminate the problems and potential cracking.
Properly polished and setup they should be good for street use up to 450-500 hp depending on use(abuse) and traction.
You need to see what is for sale. If it's a 4 series they're practically useless and hold little value unless you have a GM or Richmond set of 411,456 gears. Then you have to check it for cracking and wear in the cross shaft hole. Any cracks and it junk. The holes can be machined for a 12 bolt shaft or bushed.
Value, a good used bare case can bring up to $200 but I wouldn't spend that much for one. I'd say $100 or less. A new Eaton loaded with lousy clutches,spiders,and springs cost about $500.

A rebuilt differential can go for $500-$4,000 all depending on what it is and how it was rebuilt. In general used diff's are $250-$400 over that and they're generally not worth it since just about all of them need attention unless you like to gamble on using one out of another car without inspection.

 

I'm talking about a complete unit.

 

I have a Eton carrier with carbon fiber clutches with a Richmond ring and pinion (350 something). running 400+ hp and tq at the rear wheels and have not popped it yet... I run it hard and love to push it.... but it does have less than 5K miles on it .... Then again the entire drive train, suspension and braking all have less than 5K miles...

Popped the old carrier and had it rebuilt with new carrier, clutch pack, and R&P for less than $1K. from a gentleman up in the north east... did a great job.. was all tight and the backlash was perfect!

 

Spoke to the guy and he is not sure which gear is in it and will have to check!
He thinks it will definately be a later casing as he was not sure that there was any different series made (Me neither) not that up on differentials it has no side yokes fitted and no front yoke or a carrier and he wants £400 for it, it is new and has not been used, is it worth it ? and how easy is it to fit new yokes? and the rear carrier anything i need to know first.
Thanks for your advice guys keep it coming

 

 

How much is that in USD?
Without a pinion yoke there is no preload on the bearings so how do you know it was setup correct? New parts are good but what was installed?
Side yokes slide in and the endplay should be in the 005-010 range but if the posi is setup stock you may find 020-030" which is sloppy. I grind to fit all my yokes.

The carrier is the housing, is that what you mean or rear cover?

 

I think the pound is around $1.50 USD so that would make it $600

 

For $600 USD I doubt it's worth it- unless you can varify it is rebuilt and correct. Even then it's pushing it.

 

Thanks for your comments he said it cost him £1000 to build and he will except £400 for it.
got to go running late

 

Sorry gary it is my inept diff knowledge, it is the rear cover that is missing, the one job i would struggle to cope with is work to do on a diff as my knowledge on them is very limited and i'm a bit lost when you talk about preload,! didn't realise that you could grind down side yokes? would you also have to cut a new groove to reposition the inner circlip? I have tackled almost every job i have ever done on the vette but i'm not sure about the diff if it is out of the realm of my skill, (not really sure how hard it is to set up properly) Are there any comprehensive guides to rebuilding a diff or setting up the preload etc so it is in words that the layman can understand?


Peter

 

Peter
I should clearify the end yoke grinding so you and others don't start grinding on new yokes until you understand what I mean. If the posi is stock setup, with springs, then a lot of them are sloppy. Not all for sure but there's enough hacks out there that slap these together with backlash all over the place. The way I set them up is not using the springs but setting the lash much tighter then most. As a result of this "tuning" the new yokes will have little if no endplay. I don't like them too tight, so I end up setting them up in a surface grinder to face them and then set the endplay to the 005-010 range I like. There is no spec I know of that is published with this in mind. The though probably was to set the lash to between 001-008 and use those springs. This worked but it also was the cause of clutch hammering. Properly setup there in no hammering,less clutch wear, and posi action.
I used to have a lot of pictorials here, you may still find them? If not you can look elsewhere and find all of them. They will show you how to do the job.
I'm doing one tonight in fact, I have to grind 002 off a set of shims to dial in the lash I want.
Good luck.
If you need a diff and they're hard to find over there then maybe that one is a good deal for you considering shipping cost. I still think it's too high for the US market but that is your choice.
The pinion preload is set by setting the rotational drag on the bearings and using a sleeve in between the races or loctiting them in place.

 

Cheers gary thanks for your help, i'll try a search for your pictorials as i find they normally make it easier to understand the principle of working on very technical items.
Gary i think you'll have to do a video with your expert knowledge, i for 1 would buy a copy

Peter

 

Gary, I have decided to go for that diff. The chap said it has been set up correctly by a specialist shop, and has done 100miles on his own car and then decided to use his other diff instead,he said all i need to do is fit my side yokes on and torque front yoke up. is it as simple as that or do the side yokes need shimming at all?? it was completely rebuilt before it was fitted to his car!!!!

Peter

 

Side yokes should not be shimmed. Depending on how well the posi was setup will determine if the yokes need to be fit. Measure the yokes to be used, they should be .180-.187 from the face to snap ring.
The yoke is not setup to torque load unless a solid sleeve was fit. Crush sleeves are set to to drag, with a used bearing that would be about 5 in/lbs. With new non run bearings 15-20.
Replace the seal while you have it out and check the yoke OD where it rides on the seal for a groove.
Good luck

 

Thanks for your reply, he told me that the every thing was set up before i.e. crush sleeves! so all i have to do is torque it up to 155ft lbs when i fit my yoke, it does sound too simple to me, and you make it sound like an exact science, dont get me wrong i know from what you have explained to me it is very time consuming to set up but once it is done as this one has been , so i'm told it should be straight forward to change thew yokes over?? would you still change the seals even though it has only done 100 miles


Peter

 

Do not torque to 155 ft/lbs that is incorrrect and may over-crush the sleeve putting too much load on the bearings. You need a dial 0-30 in/lb torque wrench like I show in my rebuilding threads.