68raggtop

I have a extra complete (used) differential that I want to swap into my 68bb. The current one is a 3.70 and has to much slop in the side yokes, as well as the clutches are wore out in the posi. Before I put the 3.55 differential in I checked the end play of the yokes and found .022 and .03 between pin and yoke ends, however, the yoke ends have almost no wear (I can still see the tool marks on the end of one). My question is, as the posi clutches wear, wont that also make the side yoke clearance larger? If so, would brand new yokes even close up the clearance, or should I replace the clutch packs first?
Thanks,
Dave

JBR

No expert here. But yes the clutch packs will wear. They offer shims to take up the slop, I beleive under .008 is ok. Gary Watson @ www.corvetteperfection.com sells them.

GTR1999

New clutches are about .068"-.069" thick and they should have a nice diamond pattern to them. As they wear down they will allow more yoke end play. Since you have it apart why not go through it so you know it's in good shape when you install it. New clutches run about $80, rebuild kit about $100. Depending on how you rebuild the posi will also affect the clutch to yoke gap. My part cost to rebuild them is about $650-700 but that's with new gears,HD rear cover,and new yokes.
Let me know if you need any help
Gary

68raggtop

Gary, Thanks for the input, I was wondering about if I should replace the clutches as you replied. I was also trying to find the paper you wrote a shgort while back on rebuilding the differential, but since the forum change, search only goes back to June. I did run across this though, and would like your opinion as to it's accuracy on our posi's. http://www.fullsizechevy.com/fscu/eatontech/
I think the rest is in good shape, and from the link, it looks like I should be able to replace the clutches without pulling the whole posi carrier out, or am I ?
Thanks,
Dave
Also, Anyone tried shims behind the clutches like JBR suggested?

GTR1999

Dave,
You can find my paper on www.corvettefaq.com search for differential rebuild.
If the clutches are the solid type and still within .001" of .068", have no burn or shiny spots you can reuse them. If you have the snow flakes then buy new solid steel clutches. The article you referenced uses the newer fiber clutches- I've never used them. I've heard of some problems with them but haven't worked on any yet. There are shims behind the clutches now,that's how the backlash is set. The paper will cover the setup of this,but I don't use the 4 springs anymore. You have to remove the carrier to replace the clutches,it's much easier to do it on the bench then in the housing.
Let me know if you need some help.
Gary

68raggtop

Gary, I tried to get the paper from corvettefaq.com but it just redirects to the old forum link, which doesn't work anymore. I sure hope they fix that soon.
Dave

turtlevette

i don't understand how the clutches have anything at all to do with horizontal yoke play.

68raggtop

turtlevette, I am only guessing as I haven't taken it apart yet, but I was told by the alignment guy that as the clutches wear, the distance from the spider gear to the retainer snap ring increases. That lets the yoke move farther away from the pin than end wear on the yoke alone. Hopefully Gary or others will correct me if I'm wrong.
Dave

GTR1999

Correct, the reference was for the "gap" between the yoke snap ring and clutch. It will limit movement outward but not inward. If the yoke end is worn then you will have a gap between the end and the posi shaft also called a pin. As the clutches wear, and this isn't a fast process, they will compress and there will be a wider gap between the snap ring and the clutch. Depending on how well they were shimmed up in the first place determines more onthe play then the clutch wear. When I install new steel clutches and set them up with out the 4 springs the gap between the snap ring and clutch is just a few thousands. Add to that rebuilt yokes and the gap between the yoke end and pin is tight to a few thousands. Does this clear things up?
Gary