Chevy parts on a Roadster??? by Dave Brisco aka Dbrick
Published 2010 Updated 2011
UPDATE February 2011: It has been noted by a few who have done this modification that they experienced increased vibration in the driveline. These members went through making sure wheels and tires were balanced, the driveline was balanced and the U-joints were new and were still unable to alleviate the vibration. The ultimate resolution for those cases was to revert back to a standard rubber version of this same mount, or the factory mount and the problem was solved. Please be aware that this could be a potential side effect from use of the Urethane mount!
I wanted to replace the 2 piece trans mount on my car with a stronger unit.
After some sticker shock while pricing mounts I decided to look around and found this unit. The Energy Suspension transmission mount for a Chevy, part # 3.1108 just happens to be almost identical to the Roadster mount with very minor differences and is $20.95 at Summit Racing. I got mine at local Pep Boys, same price. You can get red or black for those who want to color coordinate their undercarriage.
Red Black It’s rated for 8OO HP, so we should be safe.
The only modification required is to drill two 7/16” holes in the trans crossmember for the new mount. On 4 speed cars, its easy enough to reach in and tighten the bolts, 5 speed cars have A LOT less room, so you will need a ratcheting box wrench or lots of patience to tighten the bolts.
Another option would be to drill all the way through and use Allen head bolts. Could not be easier to layout the holes. Make a line between the old holes, find center and make a mark ¾” on each side of center. The mount has a plate that comes with it that goes between the mount and the transmission, as in the picture. This pretensions the mount and must be used.
When I did mine, I was also converting from a 4 speed to a 5 speed and had to modify the cross member. Bill Cole gave me some measurements, so it was time to get out the cutting wheel and learn how to weld. The strip of metal in some of the photos is the cut out piece. I believe the 5 speed cross member has a height of .875”.
More on the tranny mount issue--
Tranny Mount Take 2- by Steve Heimsoth
I used an Energy Suspension polyurethane transmission mount on our racing 5 speed and will be using a Prothane mount for my street roadster 5 speed. As most of you know, the stock 5 speed mount is over $100 new. This is a more cost effective solution. The Energy suspension 3-1108G and Prothane 7-1604-BL are heavy duty polyurethane mounts with fail-safe interlocking cores. Either can be purchased for less than $25.
Energy suspension 3-1108G:
Prothane 7-1604-BL:
The transmission mounting holes on the mount need to be widened about 1/8" on each side in order to bolt to the 5 speed tail housing. You also have to trim the upper plate diagonally as shown so that the mount will clear the X-frame:
New holes inline with the old holes need to be drilled in the cross-member:
On the race car I used the bolts with the 3-1108G to attach the mount to the cross-member. I had to slot the new holes to allow insertion of the bolts sideways into the cross-member and then rotate up inside. I decided to try the 7-1604-BL for my street car because it has studs that can insert from the top. The studs had to be shortened by 1/4" and it is quite a trick to get the washers and nuts on. The finished installation works out real nice.
Note the weld repair on the tail housing boss. I have found many of these bosses are cracked.
Finished:
Since it is so hard to start the washers and nuts inside the cross-member, another option would be drilling the holes all the way through the bottom plate and then opening up the bottom plate holes so that socket head cap screws could be inserted from underneath. I don't mind the nut installation and should not have to mess with it again since the transmission will be installed with the cross-member on it.
_________________ Steve Heimsoth '69 SRL311 '72 S30 (240Z)