My current differential, a 1979, 3:55, is showing a significant amount of play with the side yokes, on both sides. I can't give you a measurement because I don't have a dial indicator. By sight only, I am guessing 3/16 inch which works out to 18 to 20 thousands.
The pictures above are of a differential I acquired 5+ years ago from a shop in Ohio wherein the owner passed and the wife was selling off the inventory. Supposedly, it has new bearings and seals. The original ring and pinion were retained. Seeing the ring gear as GM original, I believe the story to be true. I can see little marks on the ring and spider gears that indicate they are used. It turns free, but is just a tad tight. Definitely not freely like a used differential usually does. It is a 3:36, as seen on the ring gear (11-37) and the ring gear indicates a 5 -79 stamp. The housing cast date, I think is "L288" which would be December 28, 1978. The "L" being December, the "28" being the day of the month and the "8" being the year cast. The stamping is "2AT 2 19 69 W". I am not sure what that indicates or decodes to. So, I am looking for confirmations on my thoughts and I am looking for recommendations where to get side yokes. The car is a hobby and doesn't get more than 1500 miles a year. The engine is a 496 CI backed by a Tremec 5 speed. I do not race the car or punish it with loads of burn outs etc. I do run it thru the gears often, never from a dead stop start. I always have a rolling start. It does spin the tires thru first and second gear. I am not considering going to 30 spline yokes. Just looking to replace the 17 spline side yokes with good quality. I am sure I will not put enough miles on it to wear through the ends of another set. Please give me your opinions and critiques. You can not hurt my feelings,

 

The side yokes typically have some amount of slop with the springs in the posi carrier.
Do you have a feeler gauge?
If you do you can measure between the diff posi pin and the side yoke. Both sides.
Then post the measurements and a close-up pic of the ends of the side yokes here.
Measure the ends with a digital caliper, the side yokes should measure about 0.189" from the end of the side yoke to the top of the c-clip groove, when they are almost like new.
.020" + wear would be a lot. But your .020" slop you mentioned may not be wear, it may just be in the posi fit.
If the 45 degree bevel is worn off the end, or they are worn down to the c-clip groove, they are doorstop candidates.

Pic of a worn set from another thread:
https://www.corvetteforum.com/forums...ide-yokes.html
These measured .170 & .180". Taper gone on the left one.

 

Nice looking vette, really, looks ready for a nice Sunday cruise, as I sit here in 30* weather.

The diff in the picture is not a 1979 differential It is a vendor's rebuilt 1969 diff assembled on Feb 19,1969 AT code = 308 BB diff. It has 1979 gears in it, also cheap axle bearings and mostly nothing more than a bearing kit installed. If built by a good vendor it should be dialed in for lash and pattern, if built by some of the hacks out there anything is possible. Regardless, it isn't one I would use as is behind a 496 than might be in the 450-500 hp range.

You mentioned 30 spline axles so you must have done some homework. There are the original 30 spline axles and the knockoff 30 spline axles, which ones did you look at?.

If the posi case is the original 69 it will have a 1" square window, that doesn't appear to be a 69 case but actually a better case but it needs to be checked for cracks and you cannot trust a slap together rebuilder not to use a cracked posi- seen it too many times.

For replacing the axles you can buy new or rebuilt. They both are not good options and for good reason. However, if I was to go into detail on why here I would probably just get some people to upset. So, I would do some more research. Axle endplay should be between 005-007" maybe up to 010"- beyond that you either have worn parts or a lousy rebuilt diff and sometimes both.

The pinion yoke is a 1330 most Tremec come with a 1310.

Sorry for being blunt but you said it was ok and I see junk sold every day now so be careful.

 

As Gary (GTR1999) points out, the differential is from a 69. The stampings decode as follows:
The 2 indicates it was assembled on the 2nd shift, the W indicates the Warren (MI) assembly plant.

The pinion yoke is most likely from an automatic car as manual transmission cars got the smaller 1310. The yokes are interchangeable so no big deals there.

The axle tips wear, typically, from the fact that GM’s QC went south in the early 70s and the axles were not properly hardened. They should be in the low to mid 50s on the RC scale. Finding good used ones is very difficult. If you have access to a competent machine shop that will work with you, you can fabricate a pair of tip “buttons” that press into the axle tips. Search the forum as there have been recent threats on the topic. Unfortunately, no one has stepped up to manufacture a run of these for sale. Van Steel sells both rebuilt axles and new. Mark Williams sells 300M 30 spline axles but they are VERY expensive ($2100/pr).

Irrespective of the axle issue, would pull the posi carrier out and measure the running torque on the pinion and see what you get. You need an in-lb dial indicator torque wrench to do this correctly. Pulling the carrier will allow you to inspect the side bearings.

Rebuilding these differentials properly takes a lot of knowledge. Gary is the expert on these and I read many of his posts on this forum and Digitalcorvettes before I rebuilt mine. Gary is very generous with his time and willingness to help us DIYers.

This is my 69 just before assembly.

 

Thanks for the replies and opinions, all of them. I think I am going to backup and unbolt the half shafts and take some measurements before proceeding with a direction. I like the idea of the pressed in buttons.

 

This is the driver's side differential yoke end play with a dial indicator (13.75 thousandths). Passenger side end play with dial indicator (27 thousandths). Not what I wanted to see. It's gonna have to come out.
Opinions, comments and advice welcome

 

Might be worth an inquiry to see if these are much better quality than the ones that run $150-$180 at the corvette vendors. They look very similar to ones I bought 7 or 8 years ago after the overseas ones failed. Heat treated on the ends to harden the tip preventing wear. USA made as well.


https://www.zip-corvette.com/63-79-d...s-us-made.html

 

At .013" and .027" are they out of spec?
I know that affects rear alignment, but is it worth pulling a rear apart for .022"?
Is there any risk of failure at the looseness you have?

I worked at a large industrial facility and if this was our component, I am pretty sure the welder would have put a stellite tip in it, the metallurgist would have told us if and how to heat treat it, and the machinist would have put it within .0005" of what I wanted. I can't believe nobody is repairing these.

 

.013" & .027" is not terrible but does indicate some wear. Gary said his spec is .005-.010" I see that you did have it out at one time. How I would proceed would depend if it is back together now or not.

If it is together, and a low yearly mileage driver, you could just live with it for quite a few years and check it occasionally. It may or may not cause some tire wear on the one side. I seriously doubt you could feel it in the handling. Check carefully where the yoke gets close to the case and see if it is in danger of contact near the oil seals. If it hits it could kill the case. Or you could pull the diff again.

If the diff is still out, I would definately take the back cover off, pull the yokes, and measure from the tip of the axles to the-clip groove. .190" is a near-new measurement. Then I would pull the posi section and tune the posi using Tom's Diff method / videos. That should remove most of the slack you measured, and your yoke slop/clearance may be pretty good without any further work or axle replacement. Tuning it will also remove the slack from the spider gears as well and make them more likely to withstand that 496 LOL.

If the tips of the yokes are still useable at that point you could send them out and have them hardened. GM yokes are stronger than most of the offshore replacements, so I would try to save them. If they need to be rebuilt, I would try to have those yokes repaired rather than replaced. At that point I would just send the whole diff to Gary as new hardened yoke tips need to be carefully fitted. It is possible to get .005-.010" clearance, but not without that level of effort.

While you have the posi unit out, clean it, spray some brake-clean on it, and as it evaporates, check very carefully for cracks in every opening of the posi case, especially the window corners. Ask me how I know what a BB can do to 3 of them. Almost no rebuilder except for Gary checks closely for these cracks, and they are very common.

Good luck and keep us posted.

And I am only 2 hours away, and I have no desire to ever rebuild a diff again, but I could help you look it over if you need a second opinion as to which way to proceed.

 

I think I may have confused some. I have 2 differentials. The one in the car is a 3:55 from a 1979 car. It has the side yoke end play issue. I have had a 3:36 on the bench that I thought was from a 1979 car and rebuilt. The casting date on the case is *L288*. which I thought was December 28, 1978. The ring gear is clearly 11:37 (3:36) and 5-79 indicating from a May 1979 car. However the stampings on the bottom of the case are 2AT 2 19 69 W, I am told this indicates it was a 1969 3:08 BB car when it left the factory. So when I got it as a rebuild 5+ years ago, it apparently is a late 1968 case with a 1979 ring and pinion. It did not come with side yokes. Taking a close look at the spyder gears and carrier, they are all used parts; but, to me look to be in good shape. However, I admit I am a novice to the internals of a differential. The in-car 3:55 works really well with the 5 speed Tremec, especially the first three gears which produce a hard acceleration, then of course 4th is 1:1 and 5th is overdrive .064 which gives me a 2200 rpm at 75mph. Hopes this provides some clarity.

 

What's your first gear ratio.

 

3:27
I believe Muncy's first gear are either 2:20 or 2:57

 

 

TREMEC RS 500
Input / Output Gear Ratios
1st 2nd 3rd 4th 5th Rev GM, 3.27,1.98, 1.34, 1.00, .68 Rev 3.00