DeenHylton

I just pulled my center section out yesterday and want to swap out my 3.90's back to my original 3.55's. After looking in my Motors Manual and then in my Haynes Corvette repair book I find there is only a couple of sentences on pulling the third member but no specific details on rebuilding it. I also have about 1/8th inch slop on the side yokes (in/out) but the c-clip grooves look tight and the end of the axles look good (no mushrooming or wear on carrier pin)
Does anyone have details/pictures on rebuilding the third member?

I also wanted to drop the rear end support cross member (the one that holds the rear end cover in place) , after loosening the bolts it does not drop ...even after prying a little with a small pry bar. What's the trick? Thanks guys/gals... :confused:

gearheadz

If you're going to swap gears you need to have the specific tools, instruments & expertise to set the proper bearing preload, pinion/ring pattern & backlash. There is a gear vendor that makes a "how-to" video that covers all the common rearends but you're still missing the proper tools.

Unless you have these prerequisites, my advice is take it to a professional.

Mark

Stingy74

How long has your crossmember been attached to the frame? If it's been awhile it may take some persuasion with a big pry bar. I put a mixture of white grease and dielectric grease in the pockets of the crossmember where it bolts to the frame so things don't get seized over time. It makes pulling the diff apart down the road a breeze.


[Modified by Stingy74, 11:38 AM 12/16/2001]

tzavaleta

I just went through all of this. One yoke had about 1/8th of an inch play and the other significantly more. We opened up the rear and noticed BAD mushrooming on one and not the other. My thoughts are that one may not be original (there are other indications as to this fact). So we removed them both.

Does anyone have the measurements of how long the shaft/yoke should be? I figure just a measurement of the splines would be good enough. This way i can tell if the "good" one has any wear.

The process for removing them is very simple. Drain the oil, remove the cover bolts. Then inside, one the pumpkin, there is a small bolt (small head size, but very long). This comes right out and then the big center rod (sorry for the lack of technical terms) slides out. Real easy. I also had a little trouble with shims from the spider gears sliding out, so i'd watch for that.

After the rod was out removing the yoke was as simple as pushing it in and then removing the c-clamp. Although on mine (I haven't seen others so i don't have a basis for comparison) the clamp didn't just slide out. I had to use a special tool (I can’t remember what it’s called) but it’s basically reverse pliers with little pins that stick out at a 90 degree angle from the pliers’ head ($8 at local parts store). With the tool I separated the c-clamp and then pulled it out off the tip of the yoke’s splines. With the clip out the yokes slid right out.

As far as the cross member I didn’t have much trouble with mine. I started a couple weeks early spraying penetrating oil all around the attaching points. Then when it came time to remove it I put a BIG screw driver in between the cross member and the frame and pulled down. It slid right off.

Hope this helps!!

-thomas

69ttop502

Actually I learned agreat trick for pulling the crossmember down on this forum. Loosen the bolt just a little and then take a 2 armed gear puller wrapping it around the crossmember and running the puller bolt onto the crossmemeber bolt and slowly tighten. It will pull right off. Do the same on the other side and make sure you have a jack under the rear cover to catch it. This worked like a charm for me, both sides in less than 10 minutes.

redvetracr

DeenHylton,
If your going from a 3.9 to a 3.5 you need a posi for a 3-series gear as the GM 3.9 fits a 4-series posi. ...redvetracr

DeenHylton

Thanks for all the answers so far! You guys are great.
Richmond 3.90 gears do fit a 3-series carrier...they are built thicker and do not need a spacer to fit.

I will try using wd-40 and a puller to pry the cross member down...I can't believe that GM only uses two 7/16 bolts to hold the crossmember in, I guess they weren't thinking of all us hotrodders that would be transplanting 450 HP and up engines into their GM chassis.

Anyone have the specs on allowable in/out play on the axles?

I have the dial indicator to set backlash and my torque wrenches are all you need to set bearing preload...the problem I have is that the original GM gears have no markings on them to set pinion depth (I do not have a pinion depth gage but I usually purchase tools as I need them...depending on price that is!) Does anyone have a shop manual or any other literature that goes into DETAIL?

PatsLs1vette

whats wrong with the 3.90 gears?just wanted a lower gear.

DeenHylton

Nothing is wrong with the gears but a blown street engine works best with a 3.40-3.55 gear ratio...with the 3.90 gearing I'm spinning the blower over 14,000+ RPM at 6000 engine RPM (this heats the air charge too much at the top end and you actually lose HP). If your asking if the gears are for sale they probably will be, but I'm not bothering with selling them until I get my car back on he road. Deen

GTR1999

Keep me posted on what you find. I think I'm going to try to do this in a while.I not changing gears only bearings and seals. The unit only has 55k miles on it so the posi is probably still pretty good.
Gary