Questions about differential

OZgreen69

OZgreen69

Well-known member
Joined
Apr 24, 2016
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220
Location
Perth Australia
In the parts that I have to built my racer, I have an apparently rebuilt 4.10 diff (told by the P.O) that I am having a closer look at.
The free lateral play in the stub axles was quite alarming enough to make me removing the cover.

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As it has been stored with no oil in it, you start to understand my concerns.
At first the inside wasn't looking too bad until I started to clean the goo left by the yellow marking compound, and checked the bearing drag with my new CDI wrench.
Readings all over the place. Then, crown wheel's out and I noticed the rusty bearings!! Pinion to follow and same same ! Do I really need a shim on a crush sleeve ??

thum_3934591ebd18da6bb.jpg

Now, I am thinking about re gearing to 3.73 with gears that I bought from Tom's. And I need your help.


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On the picture, I have the original ( craked ! )posi housing with a 3.08 gear and the actual 4.10 . I understand that the height of the flange are not the same depending on your ratio. But if I want to use my 3.73 gear, do I need to use the thick one or the thin flange ?

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Another question is about posi housing model

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Would you know if I can use the housing with the square opening , or this is a older model ?

Thanks in advance.
 
If you are lucky Gary will answer your questions. But, definitely read his diff rebuild threads. Also, a young guy wrote a long thread on rebuilding a diff, he was being coached by an expert. Stinger was his screen name.

Buy or borrow a good case spreader, I made one, but a pro tool would have been better.
 
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Thanks RTJ, I have been following all Gary's threads for some time now here and on other forums and yes the thread from the young guy is really good.
About the speader, mine is for Dana diff, too big , thinking about modifying it.
 
Well after a nice breakfast and a good cup of coffee, I found some old posts from Gary's ( must have been blind last night ) who answer all my questions
To resume : I need a 3 serie carrier to go 3.73, the thin flange one. And the carrier with a square window is to be avoided. Old design prone to cracking.

Thanks RTJ for that good start of the day.
 
Hi
I just stopped by and saw this.

First off there is no 410 ratio for a vette, there is a 411 really not much of a difference. Just as GM never had a 373 for vette it was a 370. The 373 has more teeth and it stronger in my opinion.

The difference between the 3 series and 4 series is the flange thickness. The old way of converting from a 3 to 4 series gear was to use a thin spacer ring between the flange and ring gear. That often led to the RG bolts loosening up and the gear breaking. Tom has has 4 series gears made for 3 series cases for many years now. Tom's gears are the BEST made for 63-79 vettes. They are the only usa made gear set left for a 63-79. The others are imported, if a vette vendor claims their gears are USA made keep in mind they do not make them they just rebox Tom's gears - if they are USA made.

The square window posi's were used from 65-68, some early 69s too and are NOT that good. They were better then the 63-64 Dana but not by much. I have reused them but not until I checked them in several places for cracks and FULLY polished them. I have not seen one posi polished like I do them, possibly the owners like yourself will do it but not one vette rebuilder out there has one fully polished. Some claim to or that their case is just as good but they are typically self serving BS artist's. Personally I would not use a square window case for a HP build. I purchased a skid load of the GM posi cases when they were obsoleted years ago and these are the best cases to use. The new loaded cases are ok but not as good as a NOS made for GM Eaton posi case.

Building a posi for HP use depends on application, HP, Trans, Traction, and Driving style. Answer those questions and rest can be determined. For instance a 400hp automatic car with street tires doesn't need a Super 10-( a Real one not the current knock off on the market) or a 12 bolt -unless the owner doesn't care about the cost or the builder is dishonest.

Tom sold his business but is still helping out so I would figure on what type of build you are going to get and buy the parts now.

If you have the patience, tools, work area and access to machines you can build one as good as mine and one that is better then the rest.
 
Looking back over the 2nd picture- Check the pinion OD for a groove where the seal rides. If your finger nail catches in it then you need a speedy sleeve or new yoke.

There is also a small shim shown, I am assuming it is for the crush sleeve. You don't shim those, they should be crushed for 15-20 in/lb of drag. I go 17-20.

The new master kit should have a new sleeve. Measure the old one and crush the new on in a press on an pinion with slip fit bearings to about 030" over the old length then test it in the diff. The press will start the press for you and once you get it going it will compress fast so be careful
 
Still gathering parts for the posi. I have a really nice set of 18 teeth gear who came with the diff, but I found a second hand set of 17. One gear, the 17 side is slightly marked,you can feel it a bit with your nail.
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this is the driving side, the opposite is smooth.
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The other 17 gear has no marks at all.

Can I use it ? I may swap them for side, the marked one fitted on the right side of the LSD ?
Any thoughts ? Gary maybe?

Thanks in advance.
 
IF you can feel a step with your finger nail I wouldn't use them. If not then you might be able to.
Depending on your application you can use the 18's. I have tuned posi's with them for guys who didn't want to upgrade to 17's and didn't plan on aggressive driving. So if the 18's look better, you're under 400hp and are not going to drag race use them.
Tom ran out of the spiders he has made for him about 4 years ago but now has good spiders. I have stock on the old ones in both 17 & 30 spline since I stocked up when they were still avail. I will use them for future builds.
 
GTR1999 said:
IF you can feel a step with your finger nail I wouldn't use them. If not then you might be able to.
Depending on your application you can use the 18's. I have tuned posi's with them for guys who didn't want to upgrade to 17's and didn't plan on aggressive driving. So if the 18's look better, you're under 400hp and are not going to drag race use them.
Tom ran out of the spiders he has made for him about 4 years ago but now has good spiders. I have stock on the old ones in both 17 & 30 spline since I stocked up when they were still avail. I will use them for future builds.
Click to expand...

Someone on another forum said the spiders Tom's stocks now are actually better than the old ones. Must have read that on CF.
 
I thought that tuning the posi was a big thing, well not at all. Except the 50 turns that you need to do for any changes !! A machine would be nice, as I found that you can load or unload the side gears using the lever in a horizontal plane, and giving you a false indication how tight is the posi .
Anyway, learning !!
 
I like the work area you have.

Some observations if I may. I like to mill the cross shaft bolt pad down 100"-.120" to give more support to weak side on the bolt. I have seen the bolts break there and break out the side of the posi case.

I like to really polish the OD and ID of the case along with the windows. I realize that the so called rebuilders out there doing diff's everyday are not going to do this because of the time required but it does make a difference.

When you completed the tuning, does the cross shaft slide out freely with the posi in any position? If it drags on one side but not the other it is not balanced and will not function correctly. There should be no lash at all in the spiders and the posi should be smooth or slightly knotchy.

I have done a lot by hand as well but once I build a machine it really does make a difference in the dial-in. I run them in about 200 times per set up and about 800 overall.

Good job
 
Thanks Gary,

For the bolt, I had one in all my bits and pieces, longer than the other six ! How it can be, I don't know but bargain !! It was like 0.5 of a mm longer if I remember correctly.

About the polishing side of it, I did the inside all the way but could have been more courageous for the outside. I have been careful about "radiusing" the windows properly to eliminate the risk of cracks. But you are right about doing it more. Oh ! Did I said that I had the casing X ray before starting on it ? Maybe not.

For the cross shafts to slide properly took me some time, as I was confusing myself with shims thickness by not writing down the changes ! But yeah, really happy about how they do slide now. Not falling, but a nice greasy slide, smooth and consistent in any positions.
I do have the spiders slightly notchy.

800 turns overall !!!:crap: I did 200 each side and still feel the pain !!

Thanks for your input, much appreciated.
 
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