Home made rubber mounts

[Zoobi]

Last fall I broke my transfer-case mount and found my motor mounts had sagged horribly. I replaced the motor mounts with the Brown dog and tried to find something for the transfer-case. I have the Nth degree skid so the mount is custom and very poorly built. Short version is five month's later, I couldn't find a suitable mount, adapting others didn't work well enough and I didn't want to make a solid mount. The mount couldn't be higher than 1 inch and shorter than 3/4 inch.

After several weeks of research I found mixable urethane. Odds are most of the people on this forum probably already know about these, the knowledge base here is very good. So here's what I found.

After reading forums and talking to tech people at different companies, I settled on a company named "smooth-on". Their tech line was fantastic and they have something for everyone.

First the spec's. The hardness is rated in whats called "shore". The category's give ratings that range from something softer than an eraser to harder than wood. The category I chose was "shore A". What I found was most rubber mounts are "shore A 70" and urethane mounts are around "shore A 90" So I bought one of each.


I started with the "70" and thought it was too soft so I made the mounts with "90". What I should have done was let it cure for 18 hours like the instructions said because "70" would have been perfect and "90" was harder than I wanted. Oh well.

Here's step by step.


Lower half. The plastic sleeves are to create a cavity where the lower bolts will screw in. The bolts and sleeves are sprayed with "mold release" to keep the rubber from sticking. The center hole is where the transfer-case mount bolt will recess up inside the mount. This will allow me to tighten it separately from the bottom and give a little adjust ability.



Upper half.


Assembled for fitting. The upper plate is sitting on a bushing made of aluminum foil. When done the upper plate has to be no higher than 1 inch. I'm using foil as a "crush sleeve". The outer bolt's will be mounted to the skid and the center bolt will recess upward and bolt to the transfer-case mount. The case will rest on the upper plate with 1/2 inch of rubber isolating the bottom.

Continued.

[Zoobi]

Mount side view


Here you can see the foil and bolt covers. At the last minuet, I turned the upper mount upside down before I poured the rubber. I feel that having the bigger plate submerged will help it from being puled apart.




Ready to pour. The mix is 2 parts to 1 part. The quantities are critical. I used cardboard and packing tape to seal the sides and bottom. I didn't spray release agent on the sides because I didn't want to take the chance of it causing something critical to not stick. When mixing and pouring It's critical to do it slowly. You cannot have air bubbles. I poured it from one side and let the compound flow evenly. It mixes to the constancy of honey.


After curing, 16 hours. As you can see they came out slightly clear.


Bottom view. You can see the center recess with the foil pulled out.


Side view. You can see the center plate.

Over all Ive been happy with the way they came out. According to what Ive read they should hold up very well. Most of the forum posts I read were from people making their own urethane motor mounts because either no one made performance mounts or they needed a replacement mount and the mounts were no longer available. What they would do is take the stock mount and using a propane torch, burn the old rubber out then use the stock frame and pour the new rubber in. Looking at the two types I bought the "Shore A 70" is real close to factory rubber and the "Shore A 90" is harder like the poly mounts and wont isolate vibration as well.
Now for the "lets see how they hold up over time" test.


Scott

[Zoobi]

Driving around today I stressed them pretty hard. Holding up well. I feel a slight vibration at real low speed. I actually thought it would be worse.

Scott

[daniel_buck]

very cool!

[TipsE-Z]

I'm curious to see how they hold up over time but it looks freaking sweet. I'm sure, as you said, that others have already done this but I would have never even thought of it.

[Zoobi]

Update

One week of driving hard, including some high torque low range on a local trail.
90A compound is a little too harsh for me. The vibration wasn't bad but with the AC on at idle, it irritated me. Remade the mounts with the 70 A. I replaced them yesterday and much better. I measured the old mounts to see if they distorted in any way and you cant even tell they were mounted except where the paint rubbed. The strength spec's for both are the same so I don't expect any problems.
Based on what I can tell from this project is, 90A is a little harder than urethane and 70A is a little harder than normal rubber mounts. So say 60A-70A for stock application and 80A-90A for something more ridged.

Scott

[4wheelinmike]

Nice job Scott!

-Mike

[USMC 0369]

[COLOR="#800000"]I'll need to remember this. I'm sure the CJ will have lots of 'custom' mounts before too long. [/COLOR]

[RAT]

Nice. I can think of a bunch of applications for this stuff. Rock on Scott.