Filling transmission bushings w/urethane: all upside, no apparent downside

irish44j · 06-06-2018, 01:37 PM

I know I'm far from the first to do this, but recently my 924S has been getting a mild "clunk" from the rear on upshifts to 2nd (and the occasional gear grind). I didn't feel like a transmission issue, and the CV axles are in good shape, bolted in tight, etc. Figured it must be the mounts. Note that on the 924S and early 944s, there are mounts on each side of the transmission, which makes it really easy to remove them as opposed to the later cars with the center-mounted bushings and require the subframe to be pulled.

Anyhow, this is a street driver, so after a bit of looking at what others had done I decided to go with 60A rather than the 80A that some people do. The goal here wasn't to get ultimate response, but to just improve the stock bushings (worn or otherwise) and get rid of the clunking.

Like many others, I got the stuff through McMaster for about 30 bucks.

After consulting with a visiting neighbor....

.....I pulled the old, nasty greasy/oily ones. Cleaned them up good and then scuffed up the rubber parts. They didn't seem all that worn or damaged at all, actually, I could make them deflect a bit by hand but I've seen many far worse bushings this style,

Then masked off with some tape and cardboard and mixed the stuff, filled it up and let it dry.....

Voila..

After a couple days I took it for a drive a little while ago and wow...significant improvement. Clunk gone, shifts in all gears are much more positive (note I already have all the linkage stuff from Only944.com), and no grinding gears on speed-upshifts or downshifts. Zero additional NVH that I could feel/hear.

All in all, a highly-recommended and easy upgrade for way less than the cost of a new OEM (or aftermarket) bushing.

v2rocket_aka944 · 06-06-2018, 02:10 PM

nice, been meaning to try this on my own '85 for almost a decade, have never gotten around to it (but have done plenty of late cars like this).

irish44j · 06-06-2018, 02:56 PM

Quote:

Originally Posted by v2rocket_aka944

nice, been meaning to try this on my own '85 for almost a decade, have never gotten around to it (but have done plenty of late cars like this).

And it's so much easier on the early cars. I literally didn't have to remove any other part on the car to do this. Just put a jack under the trans and unbolted the mounts, period. None of that "unbolt the right shock and unbolt the fuel filter and unbolt the subframe and slide it out" stuff haha..

RedCarGuy · 06-07-2018, 12:52 PM

I did it with the 80A on my car, as you say: no downside. I didn't notice any detectable increase in NVH

irish44j · 06-07-2018, 01:34 PM

Quote:

Originally Posted by RedCarGuy

I did it with the 80A on my car, as you say: no downside. I didn't notice any detectable increase in NVH

yeah, I wavered back and forth, but since I have little intent to use this car for motorsports (I have other cars for that), I leaned to the softer side to just be sure to minimize any possibility of NVH. I figured the 80A would be ok as well, but not much point in it for my purposes.

flash968 · 06-11-2018, 12:41 AM

other than the design issue of no longer having as much "give" to absorb vibration, though i have to wonder just how much is really needed, the only thing i would be watching is the temperature. polyurethane melts at a pretty low temp. you may find that your bushing turns into goo. it will really depend on how hot it gets down there. my 968 transaxle got pretty hot. so did the area around the muffler, to the point that they added a heat shield there. i would just keep an eye on it for a while.

curtisr · curtisr's Garage

+1 and filed for future reference!

irish44j · 06-16-2018, 06:20 PM

Quote:

Originally Posted by flash968

other than the design issue of no longer having as much "give" to absorb vibration, though i have to wonder just how much is really needed, the only thing i would be watching is the temperature. polyurethane melts at a pretty low temp. you may find that your bushing turns into goo. it will really depend on how hot it gets down there. my 968 transaxle got pretty hot. so did the area around the muffler, to the point that they added a heat shield there. i would just keep an eye on it for a while.

IDK, i run 60A poly motor and trans mounts on my e30 stage rally car, and one is located 2 inches from the header, so it gets HOT running at high rpms for long stretches. And the exhaust passes directly beneath the trans mounts on that car as well 3 years on those mounts now with no issues....and nothing is harder on mount bushings than stage rally

In any case, this is a street car that won't likely see much/any track duty, so even if somehow the urethane fails on these, the stock rubber is still there too. Not sure if these are as close to the exhaust as the 968, necessarily.Will definitely hit it on my annual checklist though!

flash968 · 06-16-2018, 11:47 PM

yeah - just something to take a peek at from time to time. may be just fine.

i'm not sure why they designed in so much slop in that bushing. i always thought it was odd to not have that trans locked in a lot more, especially since it is a torque tube design connection. maybe they need it to save the motor mounts from falling apart, if they were handling all of the isolation. the motor mounts are prone to failure as it is, and perhaps they needed some free play in the rear as well.