Differential cushion replacement

[srthom13]

Any suggestions/tips on changing the differential to frame cushion on a 66? I noticed that the rubber cushion on my is a little deformed and probably should be changed. So I purchased a poly kit from Echlers. The kit included the two cushions, bolt, washers, sleeve and a nut. On the original cushion the nut is facing down with the bolt obviously inserted from the top ( body side ). The nut came off with no problem but the bolt can not be removed because it hits the body/drive shaft when you go to push it out. Has anybody attempted this replacement with the entire rear and suspension in place? Steve

 

[magicv8]

Many have done it

The hard part is overcoming the weight of the rear suspension that is pivoting the diff into the cushion when the car is in the air.

RTFM (Read The Factory Manual) - the 1966 Chassis Service manual (that is).

This is not a simple job, and can be dangerous. Be careful. :eek

 

[JohnZ]

The factory manual has a good procedure for this, especially the part about using a piece of wood to hold the nose of the diff down. Check the poly parts carefully - many of the poly diff cushion kits I've seen have a lower cushion that's much thinner than the factory cushion, which raises the nose of the diff somewhat. This puts the rotating rear U-joint VERY close to the tunnel, and alters the operating angle of the rear U-joint, which can cause a driveline vibration. The OEM factory parts work just fine, and are made correctly.

 

[srthom13]

JohnZ, Thanks for the heads up. Me thinks I will return the poly kit and go with the original. I thought poly would be better but did not consider size problems. I guess size does matter. Thanks again. Steve

 

[srthom13]

JohnZ, I read the CSM and I am still a little lost as to where to place the 1/2" piece of wood or steel. Doesn't the nose of the carrier attach to rear cross member -- it doesn't seem to be near the floor pan. Have you done this procedure and did you drill 3/4" holes in your floor wells to get out the carrier bolts out ? Do you think it would be a little easy if the vehicle was on ramps instead of being jacked up ? Maybe this would take the load off of the suspension. By the way, I called Echlers, where I purchased the poly kit, and they assured me their parts are the same as factory. I am going to measure them today to see if that is true -- in either case I am going to replace with factory parts. What is your opinion on poly replacement parts ? Thanks, Steve

 

[WayneC]

The nose of the differential does attach (via a bracket and two small cushions) to the crossmember forward of the differential. The block would be wedged between the top of the nose of the differential and the floor, to keep the nose from swinging up while you change the cushions.

But, based on your most recent reply, I am confused now as to what you are trying to replace. Why would you need to drill any holes, unless you are trying to remove the entire differential from the car?

Responders have assumed you are replacing the two small cushions (#65 in this illustration: http://www.licorvette.com/pdfcatalogfiles/cat22/51.pdf ). Blocking/wedging the nose of the differential to prevent it from swinging up will hold it in position as you loosen the bolt and replace those small cushions.

If, rather, you are trying to replace the large #3 cushions in the illustration, that's a whole new ballgame and requires that the nose cushions, driveshaft, struts, swing axles, and spring be removed first to free the differential, then the crossmember (#1 in the illustration) is removed (by unbolting the end cushions on the crossmember) with the differential still attached to it.

 

[JohnZ]

Have you done this procedure and did you drill 3/4" holes in your floor wells to get out the carrier bolts out ? Thanks, Steve

No need to remove the horizontal carrier bolts at all - only the single vertical bolt that goes through the carrier bracket, cushions and frame bracket; that's why you use the piece of 2x4 wedged between the top of the nose of the diff and the floor.

 

[srthom13]

JohnZ, Wayne C, When I first attempted to remove the cushions ( 65 ) and bolt, washers and nut ( 64 ) I had the vehicle on jack stands with both wheels off the ground. I then removed the nut from the vertical bolt that holds the cushions together. At this point I did not have a block of wood wedged between the nose of the carrier and the floor. However, nothing moved, not even the carrier. With the nut completely off I tried to remove the bolt but I was unable to get the bolt completely out ( upwards ) because it hit the drive shaft. Even with the nut off and the bolt almost out the cushions were not loose enough to move nor did the carrier move. At that point I put the nut back on and called it a day. I figured I was doing something wrong so I left it alone. By the way John, I compared the new poly cushion to the old original rubber one ( on the vehicle at this point ) and the old original is thicker. Thanks again for the heads up. Thanks for the input Guys, Steve

 

[Gerry]

srthom13,
I did the same on my car last year and used polygraphite from PST for entire suspension rebuild, the parts fit perfectly. I have been extremely happy with my suspension but I like it stiff. You use the wood to push down the nosepiece enough to clear the bolt removal. I also removed the horizontal bolts to facilitate everything. It is tight but it will come out.

Best regards,
Gerry

 

[WayneC]

It's been a long time since I did one, but here are my thoughts...

1. You do need to block the differential nose; if it hasn't moved yet, it will, and you'll need to use a crowbar to get it back down!

2. Chances are the bottom cushion is in compression, ie, the differential nose is pushing upward. That's the purpose of the block, to keep it from pushing upward. Once blocked, you can remove one bracket bolt (#68) and loosen the rear-most one to allow you to swing the bracket downward to gain some working room... actually I think the illustration may be incorrect, as I seem to remember the bolt that goes through is the rear one and that the front holes on the bracket actually use short bolts that thread into the carrier nose, but I could be wrong and it may be the reverse; at any rate I think one mounting point is too close to the body to be able to remove a long through-bolt, so the short bolts are used there.

3. If the driveshaft is in the way of removing the cushion bolt, you'll have to unbolt it from the carrier (remove the "U" bolts) and get it out of the way.

4. Even then, the cushions may be "welded" to the brackets and will take some wrestling to break loose.

 

[srthom13]

Thanks guys, I will look at it again and use the tips you suggest. Although I can not see the top cushion the bottom large one seems to be in fair shape -- not bad for originals. As I mentioned before I am going to return the poly kit ( to Echlers ) and put in original rubber. Echlers said they were factory spec but they are thinner that the original rubber ones that are on there now. ( even after 38 years ) Gerry, were your poly cushions the same thickness and did you replace the bolt, nut and sleeve? Thanks again for your time and tips, Steve

 

[66427-450]

I’ve also heard that the poly front bushings are thin, and tilt the nose of the differential up to high.

I’m tore down right now, and want to use poly up front when I bolt things back together, I figured I’d just shim the poly bushing with large washers to get the proper thickness (to match a compressed rubber mount), unfortunately I didn’t measure before I tore things down………. Does anyone know the proper distance from the top of the carrier bracket mounting surface to the bottom of the bracket on the frame?

 

[Gerry]

I inquired about the slight difference and was told that because the polygraphite ones don't compress like the rubber originals the end result would be the same. Yes, I used all new bolts,etc. I have had excellent results and as I have said before I drive this car hard,fast and for many miles ( I use it to commute when weather permits, 63 miles one way). To be certain about your kit I would measure/mark/level the location of the diff nose, just remember it ain't the same as it was 36+ years ago so check for levelness and then proceed to return the system to the ideal position. Good luck and remember this should be the only time you have to do this so get it right now.

Best regards,
Gerry

 

[srthom13]

Gerry, Thanks for the info. And you are absolutely right, I would like to do things only once -- that is why all the questions. 66 427-450, My bottom cushion, which is the original and still on the vehicle ( compressed ), measures a tad over 3/4". The top one I can not see. The new bottom ( large one ) poly cushion measures 1/2" and the new top ( small ) poly cushion measures 5/8" with a small inner collar of about 1/8". Steve

 

[66427-450]

.........My bottom cushion, which is the original and still on the vehicle ( compressed ), measures a tad over 3/4". The top one I can not see. The new bottom ( large one ) poly cushion measures 1/2" ............

ok, so the poly is ~ 1/4" thinner than a compressed rubber bushing (the poly won't compress). get some washers ready and shim it to the same installed thickness as the rubber.

but i'd consider staying with rubber, unless you're up around ~500 ft/# of torque and plan on high powered launches.

 

[allcoupedup]

I went through this recently too. I didn't use a block of wood but wish I did. The old cushion was split and came out easily. The only way for me to get the new one in was to basically hang on the tip of the carrier.

Here's a tip I learned after I had to redo everyting after the addition of washers--- the cushion isn't under as much pressure with weight on the wheels as I now have a 4 post lift. You may want to try ramps.

The bolt will come out the top w/o removing the propeller shaft - you will have to dislodge the upper cushion to do so. The upper cushion has a coller that will stop you from pulling the bolt out sideways - unless you raise the collar up out of the frame hole first.

Check out the setup on the right - it's what was on my car. Ignore the one one the left - that was a body mount cushion the parts guy gave me as a replacement - it didn't work!

 

[srthom13]

allcoupedup, I thought the same, using ramps ( not having the wheels hang ) would probably relieve some of the upward travel of the carrier. Great photo, what did you finally install, poly or rubber ? Steve

 

[allcoupedup]

Steve,
I went with rubber replacements from GM. Had to increase the gap with washers as the end of the shaft was thunmping the underside of the body under hard acceleration.

upper: 3788637
lower: 3795333

My car had a rough past. It's a '65 but has a '63 rear end and the fiberglass above the U-joints in the back has a substantial repair. The '63 carrier was notiorious for having elongated mounting holes - notice in the picture above that someone welded washers to the openings. So either my carrier is bad, the body repairs are bad, or the whole body pan is sagging which is bad.

Here's the cushion and washers

Brian

 

[srthom13]

Brian, Thanks for the GM part numbers. I bought the poly parts but I have decided to use the GM rubber parts. Even with the fat GM rubber cushion you still needed all those washers? How does your trans mount cushion look? Maybe that has collasped and is giving the drive shaft an unusual angle. By the way, what is the proper torque on the carrier cushion nut? Steve

 

[allcoupedup]

Srthom13 - My trans mount was nasty, but did not appear to be collapsed. I think my problem is due to a frankenstein situation. The The only parts I've found to be original are the intake, carb, and distributor...oh yeah and the bellhousing (I think) and I just found out that is trashed too.

The 1965 AIM lists the torque spec. at 55-75 ft. lbs. I never really understand why they give such a large range. I try to split it down the middle.

Good luck.