The Stovebolt Site Forums The Shop Area General Truck Talk Transmission mount pad

Drug my transmission mount ('51 3-speed) out to do a little clean up on it. The rubber between the two riveted plates is still there, but in pretty sad shape. I also discovered that one of the mount ears had been welded back in place, which might account for why part of the rubber is missing.

Has anyone tried using pourable polyurethane to restore the pad? I looked at some of the material available and have some questions about it.
Anyone know what hardness the pad should be if I attempt it? I'm thinking about 65 Shore. I think it would be easy enough to clean out the old stuff (basically burn it out) and make a form to keep the parts in position till it cures. I know that replacements are available, but ~$75 for a repop or ~120 for revulcanization is a bit steep. Besides, I like to try fixing things myself.

Kevin,

I get snowplow neoprene grader blade mat’l for such jobs, comes in rolls 1” thick by 4” wide, of course cannot vulcanize it, but has lots of uses, relatively cheap. Ought to be some where you live.

Ed

I would humbly suggest to consider the operating environment for a bit before choosing a material
I’m not sure where exactly this mount is
But if it’s like my trucks that whole area is messy and hot with trace amounts of everything found in the engine bay


If the part will be exposed to motor oil or traces of gasoline then perhaps neoprene is not considered a suitable material as it score at the bottom of chemical compatibility charts for both of those items (unacceptable for use in contact with/)

Heat and incompatible chemicals is going to lead to premature failure
Sure it might last a while but it won’t be anything like using a compatible material while going though the effort of rebuilding it.

What I do in cases like this,
Look up chemical compatibility charts online
Make a list of the best few materials for your application
hunt sources for those materials while considering how you would mold or machine them for your application
-s

The transmission mount is right under the u-joint ball of the torque tube. Can be oily (especially when a bolt is left out - which was the case on mine), but not hot. I think Polyurethane would stand up to oil pretty well. It will have to be a pourable substance that sets up, because there are two plates riveted together and a center plate with larger holes in it so the mount "floats" without metal-to-metal contact.

I purchased one of the reproduction mount many of the vendors sell. The metal parts are okay but the rubber part is thinner than stock and it is all held together with bolts. You could cut or grind the rivets out of your stock unit and just bolt it back together with a suitable piece of rubber between. The stall mats used for horses might work, maybe a little too thick but would hold up to oil. I put my stock mount back in last time I had everything apart. If you would like to try the aftermarket mount I will send it to you for the price of shipping.

I installed one that I purchased from Classic Parts that was riveted and not bolted. It was missing when I bought my truck so when I reinstalled the engine and tranny after a recent rebuild, I also installed the new rear tranny mount. I personally was impressed with the quality and it was one of the only aftermarket parts I bought that did not have to be tweaked.

Try using pieces of sidewall material cut from a worn out 18-wheeler tire. The stuff is as tough as woodpecker lips, and layers can be stacked if a thicker cushion is required.
Jerry

You do have a way with words. 😆

The thickness of the rubber I believe is critical. Once you install the front and rear engine mounts, the rear of the transmission where the mount is attached, does not have allot of movement. If you change the thickness one direction or the other too much, I believe you would put undue stress on the other mounts.

Cutting the rivets is an option that I may use, but the issue is that sandwiching flat rubber between the plates wouldn't deal with the horizontal positioning that having the space between the rivets/bolts filled with material would. It's possible that it could slip and make metal-to-metal contact.
Chuck, I will keep that in mind.
Phil, I agree that it should be in the same position as original, which wouldn't be that hard to do with pourable polyurethane.
I'm not sure if tire sidewall would be the right softness/hardness to cushion things properly. I think tires are around 70 Shore hardness, which might be too hard. No-one knows what the hardness of the original rubber is? That's probably lost to time. The rubber in my existing mount is pretty soft, but may have been affected by the oil soaking it.

What is the correct thickness of the rubber?

I just measured my original. 1/4" on either side of the plate that bolts to the crossmember. I have some 2 part polyurethane that's Shore 40 on order. I'm going to try that. If it doesn't pan out. I'll go another approach.

kilhansen In the fifties for flat mount work we used coal belt,it is tuff,kind of hard to punch holes in, butwith a tuff belt punch you can do it. I have some homemade flex couplings made 20 years ago still OK. Have one my Dad made in the fifties still good. These however are not oil soaked,a racing pal said if it didnt leak oil it wouldn't be a chevy LOL !!

Measuring the gap in my spare transmission support I get around 3/8" to 5/16". Can't say ever remember replacing the rubber pad. Need to crawl under my truck....

The rubber supports are 3/8" thick. No idea where I got them, but it was apparently back in 2004. Remind me of a piece of tire sidewall. Has belt material in the middle.

I stand corrected. I went under my truck to find two rubber pieces about 1/4" thick. One between the upper bolt to tranny plate and the main plate which attaches to the cross member and the other rubber piece between the main plate and the smaller plate underneath.

Bills truck parts sells the rubber for the mount ,the price is not listed but may be feasible with the low Canadian dollar. Page 137 or 139 price 8.50 thinking Canadian if so about 5 .00 US dollars

KEVINSKI,
Thanks for the info. Here's what I copied from their website.

Rear Transmission Mount Repair Pads w/Bolts # 40-216 - 2 pads/2 bolts 47-55 $8.50

I have sent them an email to confirm the thickness of the rubber but now that I've studied this a little more, with bolts and nuts replacing the rivets, I think some rubber pads pads a little thicker, will probably do the job.

Cleaned up the tranny mount and poured some polyurethane rubber in the space between the plates today.
Pic 1 - Burning out the old rubber. It was about half rotted away.
Pic 2 - Mold made of a piece of 1/4" plywood for the top side. Used silicone grease around the edges so I can get it back off.
Pic 3 - Mold for the bottom side out of 3/8" plywood
Pic 4 - What I used for the molding. I mixed 6 ounces, but only needed a little over 1 ounce.
Pic 5 - Rubber poured in from the top side with the mount vertical and front down.

Pic 1 - Photo of the bottom with rubber poured in. Had a slight leak around the front side, so had to stick a shop rag in there to stop it from oozing out.

It's setting up now. I'll post more pics once I get the molds stripped off. I think it's going to work well.

Looks like it should work. Nice job!

Thanks, Phil

Here's the finished product. I think the hardness of the rubber is perfect. Doesn't squish a lot, but does allow some movement, so should be a good vibration isolator. The same company sells a harder rubber product, but I think it would be too hard for this application. If this stuff could be colored (don't know if it can) it would be good for tool handle dipping. Feels real durable.

The material cost me under $40, and just a couple hours of work. I'd recommend it for others who need to fix their tranny mount.

Which Durometer did you use?

Supposed to be Shore 40 A. The other option was Shore 80 A, which is harder than a typical shoe heel. Not enough give.

This is what I bought

Good to know. When you get it installed and have a few miles on her, let us know if it was a success or not. Thanks!