transmission support bushing- need advice

[mhunger]

I am thinking of replacing the rear transmission support bushing on my 2l gtv. The gearbox seems bouncy when driving over bumps, etc. the stock "thong" type bushing does not seem stiff enough to me. Two choices I have been considering are using the earlier model bushing, which is less cut away (centerline lists this as a performance upgrade for the 2l) or using paul spruell's aftermarket kit.

Can someone weigh in on the pros and cons? Does anyone have experience with the spruell set up?

thanks

[torcia]

I installed Paul Spruell's rear tranny mount and also the motor mount reinforcements. I like the way they have made the engine and tranny seem more a part of the car. My car is a 75 Spider with IAP performance springs, Koni shocks (almost full stiff on the front and 2/3s on the rear), and poly sway bar bushings. So the car is pretty stiff to begin with. The Spruell set up will allow a lot more of the engine/tranny vibrations and torque to pass on to the body but I like the feel. If it was a daily driver/tourer then I might change my mind.

Install was a no brainer.

Here are some pics.

[mhunger]

Thanks for the feedback. when I talked to my mechanic, he was opposed saying "you need that flexibility or other things will start to break". are you aware of anything that would be overstressed by stiffening these mounts up? Have you had anything crack (frame, mounts, driveline) or break?

thanks again.

[torcia]

No cracks yet anywhere......... I only have about 1500 miles on the car since the new engine with the upgrades went in. I guess the rear tranny mount crossbar may be getting more stress with the new stiff mount but up front on the motor mounts I would not think there would be much of a problem.

[VELOCEMAG]

Torcia is right. It does transfer alot of vibrations through the car. IAP also sells a poly insert that does the same thing but it's much easier to remove if you don't like it.

[Alex]

Plenty of people advise against seriously stiff gearbox mounts - do a search in here and take a look at http://www.ebspares.co.uk/new20.htm as well.

Alex.

[BigSwede]

on a race car, sure
on a streetcar, never.

Plenty of NVH problems by stiffening the mounts, gear whine being the biggest problem I'm guessing.

[Bertonemorten]

When ordering the transmission rubber bushing for my 66 GT junior, 2 types were available, 1 for hydraulic clutch and 1 for mechanical clutch. I took the last one because my car has mechanical clutch, but I think it was the wrong choise. I noticed the old bushing was all softened up by oil due to a leaky transmission (shifting tower). Now I have much more vibrations, probably because the bushing is very stiff. I have tried to take out the two plastic pins but without succes. Next winter I'll change to a hydraulic type bushing, it has much less rubber and must therefore absorb vibrations better.

[Alfajay]

Maybe I'm picking nits here, but isn't Spruell or anyone else troubled by the difference in geometry between the stock mount and the stiffer alternative? I have re-posted the photo that Torica posted on 6/28. Seems that the transmission would sit lower with a mount that has its mounting bolt hole centered relative to the OD (as the Spruell mount appears to), since the stock mount has this hole biased toward the bottom.

Dropping the trans relative to the bearing that supports the front driveshaft would a) put an angular flex into the giubo joint (which will shorten its life), and b) present a different angle between the rear of the front driveshaft, and the front of the differential (U joint pairs don't deliver a constant velocity with a difference in angle).

A solution might be to add washers between the front driveshaft bearing's two mounting "ears" and the body to drop it by the same amount (assuming the studs are long enough). You want to have single, straight axis through the front driveshaft, transmission mainshaft, and engine crankshaft.

[bryan]

Quote:

Originally Posted by Alfajay Maybe I'm picking nits here, but isn't Spruell or anyone else troubled by the difference in geometry between the stock mount and the stiffer alternative? I have re-posted the photo that Torica posted on 6/28. Seems that the transmission would sit lower with a mount that has its mounting bolt hole centered relative to the OD (as the Spruell mount appears to), since the stock mount has this hole biased toward the bottom. Dropping the trans relative to the bearing that supports the front driveshaft would a) put an angular flex into the giubo joint (which will shorten its life), and b) present a different angle between the rear of the front driveshaft, and the front of the differential (U joint pairs don't deliver a constant velocity with a difference in angle). A solution might be to add washers between the front driveshaft bearing's two mounting "ears" and the body to drop it by the same amount (assuming the studs are long enough). You want to have single, straight axis through the front driveshaft, transmission mainshaft, and engine crankshaft.

[Joe Glass]

Mhunger, have you done the aft mount job yet? I`m going to do mine and am wondering how you got the old one out and new one in?

[mhunger]

No, I haven't done it yet. there is a special puller a local mechanic lets me use. He also says you can heat the surround with a propane torch and then push it out, but I like the first method better.

[Sniady]

air hammer!!! just be careful.

[60sRacer]

I made a removal tool out of a few pieces of pipe and a threaded rod. Find a pipe that just fits inside the housing (just smaller than the bushing but bears on the metal edge), and another that fits outside. Both about 4-6 inches long. A thick flat washer larger than either or a square bit of steel with a 3/8 hole on both sides, and a threaded rod. Just crank the nut on the small side and push the bushing into the pocket created by the larger one.

I have a shop press from harbor freight so its even easier; you only need the smaller pipe bit, and use the standard bearing plates that come with the press (of course this only works if the tx is out of the car, otherwise use the threaded rod)....

Robert

[George Willet]

The height of the rear mount and the crossmember is different between the mechanical clutch and hydralic clutch. Substituting the rear mounts can cause a missalignment of the "donut" and of the u-joints, resulting in a vibration that is hard to solve, let alone increasing wear on the components.

Stick to the correct parts unless you are familiar with gauging driveline angles.