Rear Motor Mount Rubber Issue

chrs1961815

chrs1961815

Well-known member
Yesterday I put my original motor mounts on to replace the floatamotors that were on. I had bought new rubber from Brattons and a bolt set for the frame from Third Gen Automotive (what used to be Roy Nacewicz).

I managed to install everything, but the bratttons rubber was not completely right: the outer plate rubber had ribs to go into the frame holes but those are not right so I shaved them off. Toward the end the nuts were really tight as I was just trying to get enough to get the cotter pin it. That doesn't seem right. Will I have vibration issues when I reinstall my engine?
 
Those rubber protrusions are supposed to be there.Half on one rubber,half on the other.They meet in the middle of the frame.Then the steel sleeves slide through both.Those sleeves are very important.You would not have used them with the floaters.You may just have wrong bolts too.
 
I only ground them off because the L rubber extrusions went all the way through the whole leaving no room for the outer pad extrusions.
 
chrs1961815 said:
I only ground them off because the L rubber extrusions went all the way through the whole leaving no room for the outer pad extrusions.
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They are supposed to be compressed to give just the right amount of tension. Brattons pads are the first correct pads made to print specs.
 
I have tried Bratton's before and 1) they were to thick; and 2) they were hard, 3) has one hell of a time TRYING to get the engine in place.

Got a pair from Snyders...much, MUCH better...slightly thinner, more plyable and had no problem getting the engine into the chassis.

This was 4 years ago...maybe Brattons has changed??? I do not know.

Pluck
 
chrs1961815 said:
Yesterday I put my original motor mounts on to replace the floatamotors that were on. I had bought new rubber from Brattons and a bolt set for the frame from Third Gen Automotive (what used to be Roy Nacewicz).

I managed to install everything, but the Bratton rubber was not completely right: the outer plate rubber had ribs to go into the frame holes but those are not right so I shaved them off. Toward the end the nuts were really tight as I was just trying to get enough to get the cotter pin it. That doesn't seem right. Will I have vibration issues when I reinstall my engine?
Click to expand...



I don't know if you solved your problem but let me give some info that might clear-up some confusion for those searching this later;

The A-5094 Rear Support Cushion (Outer) is a flat piece of rubber with 3 holes that are supposed to be 7/16" inside diameter. There are no ribs or protrusions on this piece. The uncompressed thickness is 0.208"-0.228". The specifications for this material is the same as the A-5092 material, so my guess is that it should compress to a total thickness of 0.1875" when properly installed.

The A-5092 Rear Support Cushion (Inner) has two dimensions shown on the print. The manufactured thickness calls for a finished moulded dimensional tolerance of 0.215"-0.230" -HOWEVER it calls for a compressed installed thickness of 3/16" (0.1875"). This means when the fasteners are tightened, the entire inner rubber is to be 3/16" thick, ...which is where I came up with the installed dimension for the A-5094 piece. The print also calls for the 3 protrusions to be 5/32" (0.1562") with a 5/8" outside diameter and a 7/16" inside diameter. These dimensions are correct for the frame side member and the metal spacers.

The A-5093 metal spacer is spec-ed out at 7/16" outside diameter and having a total length of 0.521"-0.541". I think when you will find when add the thickness of the A-5090 and the A-5015/16 side members, you are going to find that as long as the metal spacer is the proper length, everything will fit fine and there will not be any vibrations.
 
Thanks Brent, now my concerns are put to rest. The odd thing was I did not need a frame spreader for installation.
 
I never knew the outside rubber was flat.I have had to trim them to fit,but only a little bit.You need the protrusions on them for the floaters,as you use the outside rubbers with them.I actually cut the spacers in half to form a bushing for the bolt when installing the floaters.
 
It seems like a lot of frames are crusty in that area depending on time and the elements. That can have an effect. If the rubber is too thick, it may extrude more around the sides when tightening the bolt to bushing fit. If the bushings are too long, that could be a problem. At least one of the pads should protrude into the frame holes to get a good bearing surface for the bushing fit or it could slip off center. A lot of rubber cushion designs will wear through that rubber till they are metal to metal depending on the design of the cushion. The whole pad cushion surface should have some preload.

I just wonder if some are thicker to compensate for frame surface condition. It's kind of risky to assume such things but now days, quality control can be non existent too.
 
CHRS1961815: In going back to your original mounts from the FAMs, did you double check that the originals are crack free? With my engine currently out for rebabbitting I was considering putting the originals back in with new rubber cushions. While the cushions were on order I took the grunge off the old mounts and bead blasted them in preparation for paint. The attached pics show the sort of cracks I then found on both sides of both mounts. Needless to say, I'm now putting in new FAMs!
 

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macdonge said:
CHRS1961815: In going back to your original mounts from the FAMs, did you double check that the originals are crack free? With my engine currently out for rebabbitting I was considering putting the originals back in with new rubber cushions. While the cushions were on order I took the grunge off the old mounts and bead blasted them in preparation for paint. The attached pics show the sort of cracks I then found on both sides of both mounts. Needless to say, I'm now putting in new FAMs!
Click to expand...

I blasted them and welded them up. You just have to v the crack beforehand, and everything should be just as strong as originally.
 
macdonge said:
CHRS1961815: The attached pics show the sort of cracks I then found on both sides of both mounts. Needless to say, I'm now putting in new FAMs!
Click to expand...

Based on past discussions here, Float-A-Motor mounts often controversial topics so I will be generic in my comments, but have you ever thought why these original mounts crack? Have you ever considered exactly what the job of the flywheel housing and the motor mount supports are besides supporting the rear of the engine? If not, these mounts are the sole device that all the power is transmitted through into the vehicle.
 
I buy parts mostly from Bert's, Bratton's, and Snyder's. The last 2 sets or rear motor mount rubbers, just by chance, came from Snyder's, and both sets fit perfectly. Others have reported that the Bratton's rubber was too thick. There was a thread about this problem a couple years ago.
I've only had to use a frame spreader once, and I think that was because my friend's frame had a slight bend in the rear motor mount area.
 
Update - I attempted to install my new motor and it was way too tight to fit in between the two mounts. I guess the Brattons rubber is still too thick - I also guess I have to get some from Snyders.
 
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