stingraymax

Mike, I have a question...

I just installed new side yokes and when I check the backlash on the side yokes I get on one side 0.12 and on the other side 0.18 between side yoke and cross shaft.

The posi has all new clutches in it and the side yokes are brand new.

What did I do wrong that I have such a big gap between the yokes and cross shaft when I pull them out ?
Should I open the Posi again and re-pack the clutches ?

Thanks,

tracdogg2

Where did you get the stub axles?

stingraymax

they are from lonestar caliper co.

tracdogg2

That looks like a mid 70's 297 carrier. You clutch shims should be around .045-.050 on each clutchpack. I'll go set up the same carrier and confirm what I come up with.

stingraymax

Indeed it's a '75 differential.

stingraymax

Just realized that I made a mistake with the numbers

It is 0.018 and 0.012 between the yokes and cross shaft.

Is this ok or do I open the posi and re-do the clutches ?

Thanks

tracdogg2

.018 and .012 is just too much. You need to redo your shims.

stingraymax

Ok, I'll get back to you with what was in it.

stingraymax

Got the posi out and broke it open again, I have 0.045 shims on each side.

What is my next step ?
Increase the shim size ? go to 0.050 on each side ?

Also if I put a thicker shim on the side that had 0.018 backlash will that affect the other side too ?
If I want the 0.018 side to come down to 0.008 will I have to add a 0.010 shim on that side ?

76strokervette

Tom has stated .005 to .008 backlash for a tuned unit. That makes me believe you'll probably have to shim one side more than the other.
So it looks like .01 on one side and .005 on the other which would put you at .008 and .007. I would verify with Tracdogg2 ( Mike Dyer) he is the expert on these differentials.

stingraymax

OK, I'm about ready to throw the darn thing...

I added 0.005 on one side and 0.010 on the other side, put it back together and it was impossible to turn by hand.

I took the 0.005 one out and left the 0.010 on, so 0.045 on one side and 0.055 on the other side.
Still impossible to turn by hand and extremely hard with lever.

Went to 0.045 on one side and 0.050 on the other side and then the posi was turnable by hand.

I checked the backlash on the side I increased the shim with 0.005 and no difference, still 0.018 between crosshaft and yoke.

I am at a complete loss now..

Any help is welcome on this

zwede

Measure from the snap ring groove to the end of the yoke. Tracdogg can give you the number, I think it's supposed to be 0.187". Cross shaft new or used?

stingraymax

The cross shaft is new. I measured and I believe it was indeed 0.187.

zwede

No chance you messed up the install of the spider gears on the cross shaft? Double washer, wrong washer? Just grasping at straws. I'm out of ideas.

stingraymax

I have no idea what I could have done wrong with the spider gears ...

The cross shaft moves freely and I used only one washer behind them.

I'm clueless too....

76strokervette

This may be a long shot, but on Tom's tuning video he mentioned the clutches having a dimple on one side. He then said to have them face a specific direction and that the dimple would flatten out during the tuning process. The video is on youtube so you watch yourself. If that isn't it I would try to get a hold of Tracdogg.

stingraymax

OK, found the problem.

I measured the side yokes again and to my surprise found out that the "new" yokes were even worse than my "old" ones.

So much for new yokes , one measured .168 and the other one .166

tracdogg2

If this is the case I would Ken at LoneStar. Who did you buy them from?
I still need to know how you are determining the shim thickness in each clutchpack. What is the spider gear backlash?
Mike

stingraymax

I shim the posi as tom discribes in his video. I started with .040 on each side and tried until the cross shaft was moving freely in either way I positioned the post, then I added shims in .005 increments until it had a good resistance but not binding or impossible to turn by hand.

I haven't measured the backlash yet on the spider gears.

tracdogg2

You need to set up each shim pack individually. There is no set number, each on is different.
Set up one clutchpack, install the small spiders, thrust washers and shaft. Then preload it and measure your backlash. You are shooting for less than .001.
Then set it aside and do the other one.

If it goes together easy, you're way too loose.