Trans mount and tunnel clearance

[Timothy B.]

I just replaced my transmission mount on my 67 MT conv and the new mount is slightly thicker than the one I was replacing. I called Paragon and their mounts also are the same thickness as the one I installed. Difference is about 1/4", and this makes the transmission sit higher on the car and the clearance to the tunnel insulation is very tight. Have any of you experienced this and can share your comments? My old mount wasn't really worn out, but I was replacing various potential causes of a clutch chatter I am experiencing.

When you have replaced a rear engine mount (or the trans mount I call it), did your clearance with the tunnel go to about nothing??

[Mike M.]

Re: Trans mount and tunnel clearance

good rule of thumb: 3/8" is minimal clearance for any drivetrain compoments that can move.if your clearance is that or more, you'll be ok. mike

[Joe L.]

Re: Trans mount and tunnel clearance

Tim-----

I've never found the aftermarket mounts to be the same, dimensionally, as the original GM rear mount. However, the GM mount is now discontinued, so aftermarket is "the only game in town". Not many folks purchased this mount when it was last available from GM. Several years before it was finally discontinued, the part number changed (although the mount did not) and the GM list price went up to about $200.

[Timothy B.]

Re: Trans mount and tunnel clearance

Interesting Joe, do you or anyone else know what the "correct" GM part thickness was? I am referring to the distance between the two mounting planes of the mount, from where it mounts to the transmission to where it mounts to the frame support bracket? The replacement I have measures 2", as do the parts available from Paragon. The one I replaced measured 1 3/4" and didn't appear to be significantly compressed. I am not sure where I bought the one that has been installed since the early 80's, but it MAY have come from GM but more likely a local auto parts house.

Joe, do you have one of the real GM parts that you can take a measurement off of? Paragon sells two almost identical mounts, one for MT cars and one for Powerglide. The mounting height is the same however with only a difference in elongated holes on the AT mount being the only difference that the guy on the phone at Paragon could see. Thanks for your help.

[Joe L.]

Re: Trans mount and tunnel clearance

Tim-----

I have LOTS of these GM mounts [none for sale, of course]. The problem is that they're a Group 0 (and Group 4) item. I have LOTS of tote bins of Group 0 and Group 4 parts and they are all very heavy and some hard to get at. If I can find one in one of the easier-to-get-at tote bins, I'll measure it.

The GM mounts have several GM part numbers embossed on the rubber portion of the mount. So, if the old one you have has these numbers, then it's an original GM. Otherwise, it's likely not. These mounts DO compress a bit after long installation on the car. They absolutely WILL NOT come off and be the same "thickness" as a brand new mount, even if the brand new mount is a GM mount.

[Joe L.]

Re: Trans mount and tunnel clearance

Tim------

Well, this turned out to be easier than I thought. I used a little "creative thinking" and remembered that I had set aside one of these NOS GM mounts in one of the boxes of stuff for the "ZL-1" installation. So, I only had to go through those boxes and they were a lot easier to get at.

The thickness of the GM mount, from the face of the trans mount bolt plate to the rear of the steel frame of the mount is 1.875".

[Timothy B.]

Re: Trans mount and tunnel clearance

Thanks Joe for finding that. Well it seems that the new mount I have is slightly thicker, but only by an 1/8" or so. Mine measures 2". The older one I have that was installed for years measures 1.75".

It seems that changing mounts didn't fix my problem anyway. I called LUK technical support to discuss my situation with chatter during low speed initial engagement, and the bottom line is that I probably need to pull the trans again and reinspect. Oh joy, I am thrilled about that....I just did that in November. I had my flywheel turned by a reputable shop, but I didn't actually check runout on the car like I should have. So, if it seems that trans clearance is still an issue when I put it back in again, I may reinstall the old mount since it gives more clearance.

Thanks,

Tim

[Dale S.]

Re: Trans mount and tunnel clearance

Tim , Did they grind your flywheel with a with a flywheel grinder like a Winona or machine it? We were having trouble when we machined flywheels. After we bought the Winona wet grinder we got rid of most of our problems.I think Van Norman makes one also. Dale