downtownj

How long do the clutches generally last on a 74 Vette?

I've never worked on a Diff before.
Where do I start? Can I buy just the clutches or a rebuild kit.
I've got 3.55's so I am happy with them.

Larry B.

What is the problem? Why are you wanting to replace the clutches? You can buy posi kits. I think GM still sells them. If you are experiencing chatter then all you need is new oil and most import the GM posi-traction additive. If you are fixing another problem like side yokes, don't mess with the clutches. :nonod:

mrvette

Silver, I somewhat disagree with you on your statement the way it reads....

I think if yoke wear is excessive, that metal particles went somewhere, and caused premature wear, in the one's I've seen anyway...and so one of the primary wear points is the posi clutches, if the tips of the steel are worn smooth enough it will cause excessive end play, as it in the thickness of the clutch pack that limits the outward end play of the yokes...there are shims or extra clutch discs that can be inserted into the pack to make that end play nearly zero....

if the yokes are shot .....I have found the small pinion bearing and the carrier side bearings to be worn/distressed....most often....now why the large pinion bearing pressed on next to the pinion head survives sometimes, is a question I can't answer....

other than that yoke arrangement there is nothing about the vette differential that's much differant from a 10-12 bolt in a A body.....

I check the posi clutches by judgement on color, mostly silver and smooth is badly worn, mostly black with silver tips in the checkering is fine....
I know there is someone with better knowledge and a micrometer that can give a better opinion on that......

GENE

GTR1999

To add a couple of thoughts on the posi clutches.I'm not an expert or differential rebuilder, I just like doing my own work. I have 2 differentials apart now, a 72 and 78. They both have under 60k miles on them. The 78 clutches look good still, I "mike" them on the tabs and compare that to the thickness of the center areas and these were the same so I would reuse them.
I haven't removed the 72 clutches yet. The yoke play in the 72 was .045" each side and the right carrier bearing was badly pitted, the pinion bearigns were ok.
While discussing the differential one thing I still have to figure out the procedure to is pattern checking under load. The book calls for checking under drag or load of 40#? How do you guys do this?I'm thinking baout creating a drag brake on one of the yokes.
Also does anyone check the peload on the posi? I can lock up one side yoke and apply force with a torque wrench and the other yoke will spin at 15-20 ft/lb's I think the factory setting is 30? I'll post these questions on another post for more exposure if knows.
Thanks,
Gary

Larry B.

Gene... I have changed side yokes on a couple of cars. My 69 is apart right now for this. I do agree that the oil gets metal in it. I know that it is not good but I do not know if it really hurts anything. I have never had a bad bearing or posi clutches so I guess I am lucky? I think it is a "do what fits you budget thing" If you are rebuilding the whole unit just for the sake of having everthing new I would replace the clutches. I had 104K on a 71 when I changed the yokes. They were worn almost to the snap rings. When I put the new yokes in there was only about .005" play and the clutches lookd fine. I drove the car for a few years with no Chatter or noises and the posi worked fine. :cheers:

Dusky

Thread revival , I know. But does anyone know if this is true? No info in my service manual.

GTR1999

First off what do you want to know is true? My response 15 years ago was kind of a "feeler" set of questions for someone else at that time. I never got a response from that party which answered my non differential inquiry at that time.

Now if you want to know the answers to those questions posed above I can certainly answer them for you.

First off there were/are 3 types of posi clutches used in these posi's, 2 were factory supplied, the other is presently aftermarket.
1- solid steels 63-71= although the 63-64 were DANA not Eaton, avail in the after market today
2- slotted or a term I coined before the above response-"snowflakes" =mid 71-79 and service parts into the 90's
3- Fiber coated over solid steels- available for about the past 10 years in the after market.

Yes it is possible to measure and reuse solid steels, I have done so in my own vette years ago without issue but with proper setup. If I was rebuilding a diff I would use new solid steels. The solid steels are the best to use, the snowflakes break with abuse and the fiber coated constantly are wearing away from friction.

All the bearings should be replaced if you are rebuilding a diff, while the manual will instruct replacing a bad bearing as part of a repair, the amount of work to remove a diff makes it worth the time and money to replace them all.

045" axle endplay is about average for a stock setup posi with about 50k miles on it, most of the endplay is with the posi setup but endplay also can be from worn axle faces, (72-79's typically), or even oblong cross shaft holes in the posi case. I set axle endplay in the 005-007 range but that is dependent on if original axles, rebuilt axles or Tom's HD 30 spline axles are being used and if the posi is tuned or stock built with springs and plates. 045" is sloppy but usable if all items check out and the diff is in the car, certainly not even close to being good if the diff was rebuilt.

Pattern checking should be done with a load applied for proper patterning, now with 5 cut gear becoming a thing of the past the setup procedures will change as will the pattern appearance. I would rather use 5 cut gears over the 2 cuts but once the last set of Tom's gears are sold out, and that may be by now, they are gone for good it looks like.

Posi break away torque, applying force to one axle while the other is secured, should be 40 ft/lbs or more- With a stock spring setup posi- this doesn't apply to properly tuned posi.

Posi tuning will not be found in any book and not something a common rebuilder will apply. If you are not familiar with that term the late Tom Watt has a tutorial on you tube showing the process. Posi polishing is not addressed and the term is loosely used by some rebuilders since some think a simple radius is good enough while others never do a thing to the case.

The original posters question can not truly be answered since production built posi's were all over the place and the spring pack did a nice job as a band aid. In this case a 74 posi had the snowflakes so a weak motor automatic may be just fine but a hp motor, stick and abuse and those same clutches are turned into junk. The only way to know is to take it all apart, know what to look for and how to set them up.

So I am not sure what your specific question(s) were but did this help?

lvmyvt76

it answers my questions, and I did not have any question to start with!!!!