If it aint broke, Modify it anyway!!
I first want to start off by saying I am extremely pleased with my Ron Morris mounts. They are a quality product and I would recommend them for any one who has a high torque engine in their classic Mustang, because their performance is far superior to the OEM mount.
With that said, it is rare for me to take any new part or tool and not make some change to it. My RM mounts were no exception. As I said in the previous tech article about installing the mounts:
“The only drawback I see to this type of mount and a complaint I have read many times on various Mustang forums is that this mount is not as good at filtering out engine vibration as the OEM mount. Don’t get me wrong I am not saying that this type of mount will cause you car to vibrate it self to pieces, but there is a slight increase in chassis vibration when using this type of mount compared to an OEM mount. There are two factors causing this, the first of which is the stronger design lends it self to more vibration being transmitted from the block to the shock tower. The second issue is the mounts come with a polyurethane bushing which, even though better at keeping the engine more consistently located, is not as good at filtering out vibration.”
There is nothing I can do about the first factor, and frankly I would not want to change the over all design of the mount, as that would reduce its strength and then I might as well go OEM. The second issue however can be addressed by replacing the polyurethane bushings with softer rubber ones.
In order to replace the polyurethane bushings in the RM mounts I first had to remove them. The bushings are a tight fit in to the main connecting body of the mount and then a steel sleeve is pressed in to the center of the bushings to slightly expand the bushing and tighten its fir to the body further. The bushings will not come out until the steel sleeve has been removed, and the easiest way to do that is press the sleeve out.
When dealing with metal on rubber I like to use lubrication. To that end I pressed the bushing out about 1/2”, squirted the exposed 1/2" of rubber and on the other side the 1/2" of exposed sleeve with penetrating oil, then flipped the assembly over, pressed the sleeve back in to the bushing and from there continued pressing until it cam out the other side. Once the steel sleeve was free of the bushing I was able to remove said bushings by pulling on them. They were still a tight fit but was able to get them out by hand.
Once I had the polyurethane bushing pressed out, I went in search of a rubber bushing that would be able to handle the weight of an engine and were the correct size to fit in the mount. After taking some measurements I knew that I was looking for a bushing with a 1.375” OD. To fit in the main body and a .5” I.D. for the mounting bolt. My search was quick as I found that classic Mustang shackle busing were the correct O.D. and I.D. and since I new they could stand up to the weight of a car they would be strong enough for my application.
I called around to several Mustang supply place and the first two were out of 1/2" I.D. rubber bushings. Finally when I called Mustangs unlimited they said they had them in stock so I placed an order. When I got them I was not very happy to find the I.D. was 9/16" rather than the 1/2" I had intended to get, (When I placed the order I did not realize that they only sold the one size, my fault not theirs) but it turned out to be a good thing When I inserted a shackle bushing in to the mount I found that the O.D. of the rubber bushing was about .050 smaller than the I.D. of the engine mount.
To solve the issue I purchased 5/8" O.D. steel sleeves with a 1/2" I.D. this gave me a steel sleeve similar to the ones originally used in the RM mounts and when pressed in to the rubber bushings the larger O.D. of the sleeve expanded the shackle bushings to be a perfect tight fit in the mounts.
I still had to modify the shackle bushing to make them work in the RM mounts. The shackle mounts were .5” longer than the bushings that came with my RM mounts and the shackle bushings were also domed on the outside. You can see this n the comparison between an unmodified bushing on the right and the modified bushing on the left.
To alleviate these issues I started by cutting 1/2" off of the non-flanged end of each bushing. I did this by shoving a 5/8" rod with a slightly rounded tip about 3/4" in to the bushing and then clamped the rod in a vise.
This held the bushing in place so that a serrated butcher knife could be used to cut through the bushing.
I then removed the shortened bushing from the 5/8” rod and took the bushing over to the bench grinder to grind the dome off of the bushing.
The bench grinder removed the rubber very quickly so I was extremely careful to make small light passes on the stone so as not to damage the bushing.
After you are done grinding the domes off make sure you clean up the rubber powder at the base of the grinder before doing any metal grinding. Rubber power is flamable and takes a spark very well. Once I had the bushing roughly shaped I put a piece of 100 grit sand paper on my welding table, grit side up, and run the bushing across the paper to smooth off the uneven surfaces left by grinding and cutting.
The following picture is the original bushing on the left, the modified bushing in the middle and an unmodified shackle bushing on the right
Once I had my bushings modified I turned my attention to the steel sleeves. I got the sleeves from ACE hardware but Lowe’s also has them
The over all length of sleeve I needed was 2.125” but I could not find any sleeves locally that long. To resolve the issue I used a 1.5" long sleeve and then cut a 1" sleeve down to .625". The two sleeves in conjunction gave me the total length of 2.125” that I need and buy having one of them be the full 1.5” rather than two bushings at 1.0625”, the longer sleeve was able to be pressed all the way through one bushing and a little over .5” in to the second bushing which formed a solid connection inside the mount where the two bushing met.
Reassembly was basically the same as disassembly only in reverse order. I started by applying some penetrating oil to the rubber of both bushings. I then pressed the 1.5" sleeve in to one of the bushings and then pressed the bushing sleeve assembly in to the mount. The other bushing was inserted in to the mount and pressed over the sleeve. After I had both bushings and the 1.5” sleeve in place, all I had to do was press in the short sleeve. Had I used a 1-piece sleeve I probably would have inserted both bushings in to the housing and then pressed the sleeve in to both of them at once. If you want a 1-piece sleeve you can get some 5/8" OD .495" ID steel tubing from McMaster-carr.
I purchased some for a future project, and wish that I had had it on hand when I did these mounts.
With the mounts fully reassembled they went back in the car with out issue and the rubber did not seam to deform at all under the weight of the engine. After firing the car up I would say the vibration is about the same as stock OEM engine mounts. There might be just a hare more vibration than with an OEM mount but with the RM mounts using rubber bushings it is barley noticeable.