I finally got my Race Ramps (awesome by the way), and backed my car onto them today.
The rear end clunk I was hearing has now become apparent as a "rear differential front mounting bushing" (aka snubber). The original is absolutely toast. Split, shredded, just nasty.
From what I've read, the job is very straight forward. I have a replacement kit, so I was tempted to start wrenching immediately, but I used better judgement and applied some penetrating oil and came back to the forum for guidance.
My main concern is, do I have to drop the driveshaft to install the snubber bolt from the top? Is there clearance enough to allow me to do so without dropping the driveshaft?
Any advice is appreciated, as I am anxious to install this and see if it is indeed the source of my "CLUNK" when shifting.
Thanks as always.

 

you dont have to drop the driveshaft but it sure would be easy if you did

 

There are two videos on YouTube that will boost your confidence. One of them is good (dialogue and camera angle). Also, Willcox published a very helpful set of instructions at their website. It does appear very straightforward on the earlier C3s, and neither dropped the driveshaft. Just be sure to install the replacement in its correct male-female/washer configuration as shown on the package. (I got mine from Willcox). Put the trans in neutral when lifted onto jacks (not the break-in job for your new race ramps) because you'll manually need to rotate the u-joints a bit to line up your access to remove/install the old & new components, saving time. And, only use a rubber (vs. poly) replacement snubber. The polys are too harsh and can break stuff in use as snubbers.

While it does not affect you, it is NOT as straightforward to replace the snubber bushing on a late model C3 because the aluminum axle housing is larger than its steel cousin, eating up most access & maneuvering space compared to a steel housing. This significantly inhibits reaching in and removing the old one and inserting the new one. It is the only job that I ever started (on jack stands in my driveway) and decided to put back together and take to a professional out of frustration. You know what to do but can’t maneuver in such restricted space. You definitely need a hoist and it GREATLY helped to have a second pair of hands. My C3 Mechanic (Bob at Bobby's Corvette Shop, Ypsilanti, MI) appreciated my help and it still took us an hour (to his frustration). And, yes - the old one - while it really didn't look that bad from my undercarriage view - turned out was just plain nasty as you describe. As an aside, my Mechanic chose to clean up and reuse the thick washer that was originally on the car because it was noticeably more robust/supportive than the one that came in the replacement kit. Also, I noticed that it reduced the clunk noise & feel by about 50-60%. It does not appear to entirely eliminate it. But, it needs to be done.

The good news is that you will never need to do it again!

Dave

 

Sometimes the dif. will want to twist upward may want to chock it with a piece of wood.

 

I don't envy the job you have in front of you, I have looked over snubber and luckily it is in fine shape. I did have reason to check and see if that bolt was tight and getting in there to do what was a bee ouch

 

I've never done one before, but with my car up on ramps, it looked very accessible. I was tempted to start spinning that bottom nut off and attempting to remove the bolt and worn bushings. I opted instead to touch base with my friends here and approach it with a game plan. The response has been encouraging, so I'm sure if I take my time, I'll knock this out.

 

yeah its a **** easy job, 20 mins if you go slow

 

I more or less, agree. I replaced this bushing on my wife's former '79, about 25 years ago. I don't recall having any issues whatsoever.

 

"****. Easy".
Where the mysterious "pee-sey" part of "Easy Peesey" derives?
:leaving

 

Just as easy as replacing the power brake booster? Well, no, but the snubber is pretty easy. I disconnected the driveshaft straps and nudged it over a bit to get better access to the snubber. Yeah, pretty easy on a '76 but I don't rush repairs in my retirement. And by all means, use poly if you so desire. It won't break anything no more than poly engine and tranny mounts would break anything.

 

I agree with Res... Pretty easy job, and actually you can drop just the rear of the driveshaft and that will help with access - push it off to the side as far as you can. I reach over the top with a box end to hold the bolt/nut and then use a ratchet from the bottom. You may have an issue getting a wrench on the top if it has not been changed before, as that pocket can collect grime. Once you clean it up it's a one-bolt job. If I remember correctly - pull the rear of the driveshaft but leave it in the trans, and remove the front bolt out of the rear housing that holds onto the snubber bracket, and loosen the rear bolt. That will allow some up/down movement. Those bolts in the rear end housing probably have a pin holding the nut/bolt in.

 

I agree.... but I would replace it with a solid aluminum disk rather than the rubber...

 

Your most difficult job will be getting the wrench in the limited space to loosen the bolt. If the bolt and nut are not rusted fast you should be done in about 30 minutes. I would suggest getting the polyurethane bushings and the "kit" that includes new bolt, washer and nut.

 

As noted in my earlier feedback, I would respectfully veto the use of a poly snubber, if they still even make them based on Willcox's (former Chevrolet/C3 Corvette Dealership) insight per below. Why take the chance on busting the crossmember based on extensive experience from a respected SME, as well as why tolerate the unnecessary harshness? The rubber snubber bushings should last 25-30 years..

Quote from Willcox's snubber Installation Instructions: "A word of caution: Never install poly bushings in this location. We’ve had to repair the bracket on the crossmember in many cases. This bushing was designed to have "give" in it and not be solid. The force of the poly can tear the bracket from the member."

C3 Snubber Replacement Instructions: http://repairs.willcoxcorvette.com/1...-instructions/

Something to consider. Have fun.

D

 

Finally got the snubber done today. OMG! (as the kids say), what a difference! Smooth positive shifts, no clunk on acceleration, awesome! Thanks to everyone here for their guidance. This C3 experience would be much different without you.

Now for a road trip!

 

 

No extra vibrations from a solid piece?

 

hmmmm.... Let me tell you my experience here... I started out with rubber... then poly... then solid.

I seem to have purchased everything for this car 2-3 times as I work to the next step. So I have been down several roads here. Balance is VERY important. Drive shaft and half shaft proper alignment is also VERY important. IF everything you have is perfectly balanced and aligned... from the water pump to the trans to the rear end to the wheels and every thing in-between.. Then no, not really. Rubber dissipates vibration, it is a band aid to a problem or to cover less well balanced parts.
The only vibration I really have is a direct link to the tone of my exhaust. Up to 7500 rpm. If i feel vibration something is wrong in the driveline somewhere. And I am pushing 650+hp through a super 10 and deflection is serious at that power level. The solid reduces this deflection in alignment.

 

Interesting info.
I was aware of the poly vs rubber discussion but don't remember hearing about an aluminum disk.
I have the solids for clamping down the diff cross member.
I guess I need to research that one.
Got a link to the disk or a recommendation on who to get it from....???
Thanks
Bman

 

If you bolt the snubber up solidly there's still torque at the differential crossmember rubber cushions moving the crossmember a little bit, even with the solids and maybe even in the member itself. Which means you are trying to stress the front crossmember welds, right? Why is that a good thing? What's the advantage here, I don't see it? Do I have this wrong?