3.08 to 3.42 posi- questions
 

Hey all,
Just dropped my 12 bolt 3.08 open differential. Put in a 3.42 posi from an 87 suburban. Drums and shoes fit, leafs and shocks fit, the u joint on the pinion basket (yoke) is larger than the u joint from the drive shaft side.

The 3.08 uses a 1 1/8th u joint cup. The 3.42 uses a larger and wider one. Anyone know what that is?
Also, can I just change the u joint on the drive shaft rather than change the basket on the pinion shaft? Or, do I need to change the drive shaft? The pinion shaft on both differentials is 27/32 and the 3.08 takes a 29mm socket while the 3.42 takes a 32 mm socket (or imperial equivalent) so the baskets should interchange. *** Edit- Found out that the yokes can't be swapped- has to do with tolerances.***
See picture below of 3.08 basket (yoke). and 3.42 under the truck.

Re: 3.08 to 3.42 posi- questions
 

I think you can buy a conversion joint to fix the problem. It has one size crorr and rollers to fit your orig drive shaft and a larger cross and rollers to fit the new axle.
Ask your parts man and he should be able to give you more info on it.

I noticed you are running an XE262 cam . Ccan you hear it at idle or is it pretty tame?
Frank

Re: 3.08 to 3.42 posi- questions
 

Thank you sir. Appreciate the suggestion.
Been sunny down there? Miss Austin.

I have some head issues (valve guides worn and seals leaking) but when its cold to about 160 degrees I get a nice snap and a little lope which is just right. When its hot and at operating temp the guides get sloppy and the snap disappears and the lope is less noticeable.

Re: 3.08 to 3.42 posi- questions
 

here's an update;
When moving to a 10 bolt rear from a 12 bolt, the differential yoke holding the drive shaft uses a larger u-joint.
There is a universal joint (cross joint) made by Napa for this, the cups in the drive shaft stay at 1.125" (1/8") with a 2.563 spread while the yoke on the 10 bolt takes cups with 1.188" cups and a 3.620 spread.

Thought comes to mind- is there a drive shaft off one of these trucks that eliminates the 'cross-joint'?

Re: 3.08 to 3.42 posi- questions
 

I run a 12 bolt with a 10 bolt drive shaft. No problems. My truck did destroy two cheap joints. I installed a Spicer conversion joint. It's holding strong to pedal abuse. You have to swap the rear ujoint cradle to elminate the adapting joint. You can also use the 12 bolt driveshaft if it's the same length.

Re: 3.08 to 3.42 posi- questions
 

Do you know anyone who has swapped the cradles? I was told it couldn't be done but the pinion shaft is the same size on both, just the nuts are different.

Re: 3.08 to 3.42 posi- questions
 

damn sounds like the problem i have on mine

Re: 3.08 to 3.42 posi- questions
 

Sorry to hear that.
If I believe what the speed shop told me up here, its definitely the heads you'll be needing to replace to fix that. I also get ash deposits on the #5 and #6 plugs every 2 months and I add a quart of oil about every 800 miles.
If I do a 1-2 hour trip on the hwy at 60 mph- it will need 2 quarts after 2 hours. I' not burning any blue, just grey when I let off the gas and the engine vaccum sucks oil past the seals.

Re: 3.08 to 3.42 posi- questions
 

No, I don't anyone that has swapped the cradles. I meant the rear cradle on the shaft. A good driveshaft shop can do it for you. I wouldn't worry about it. Pleny of us drive 12 bolts with 10 bolt driveshafts.

Re: 3.08 to 3.42 posi- questions
 

not to hijack.. but yeah.. you can notice it a bit.. http://s103.photobucket.com/albums/m...nt=Movie-3.mp4

Re: 3.08 to 3.42 posi- questions
 

Oh, that would be better in the long run- u-joints are cheaper too then. thx.

Yep, that's what it sounds like. Just enough lope.