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Hello all,
This is my first time being on any forum for a vehicle, and with how helpful forums have been in the past I figured I'd give it a shot.
So yesterday I got a 1993 40th anniversary C4 Corvette, with the LT1 V8 and the ZF S6-40 manual transmission. I was told the car had transmission issues and it was apparent with the car not wanting to move very easily. I changed out the fluid to AMS Oil's synchromesh fluid and the trans now shifts and moves very well. But when I took it for a test drive, whenever I would give it some gas (a liberal amount I will admit) the transmission would seem to move up and down. At one point I hit WOT and the shifter popped up and stabbed me in the hand. I noticed while I was under the car there didn't seem to be any type of cross brace or anything holding the transmission. Ive seen on some of the autos there's a large x brace that holds the transmission and give support to the body, but I don't seem to have that. And I'm not sure if I have the torque bar/brace either? I can't seem to find any part or reference to a brace from any parts supplier or anything. So should there be a cross brace? Or anything under the transmission? And does anyone have one for sale or know where I can get one?
Thank, have a blessed day.
Hello all,
This is my first time being on any forum for a vehicle, and with how helpful forums have been in the past I figured I'd give it a shot.
So yesterday I got a 1993 40th anniversary C4 Corvette, with the LT1 V8 and the ZF S6-40 manual transmission. I was told the car had transmission issues and it was apparent with the car not wanting to move very easily. I changed out the fluid to AMS Oil's synchromesh fluid and the trans now shifts and moves very well. But when I took it for a test drive, whenever I would give it some gas (a liberal amount I will admit) the transmission would seem to move up and down. At one point I hit WOT and the shifter popped up and stabbed me in the hand. I noticed while I was under the car there didn't seem to be any type of cross brace or anything holding the transmission. Ive seen on some of the autos there's a large x brace that holds the transmission and give support to the body, but I don't seem to have that. And I'm not sure if I have the torque bar/brace either? I can't seem to find any part or reference to a brace from any parts supplier or anything. So should there be a cross brace? Or anything under the transmission? And does anyone have one for sale or know where I can get one?
Thank, have a blessed day.
The rear of the transmission is supported by a c-beam or channel that connects the transmission to the front of the differential housing.
The rear of the transmission is supported by a c-beam or channel that connects the transmission to the front of the differential housing.
When under the car is that an obvious thing to see or would it be above the exhaust or something? And would my trans still bounce up and down with it attached?
The X brace is on verts to stop chassis flex. It has zero contact with the transmission.
The corvette does not have a cross member with a rubber mount like the F-body has.
The C beam is in the trans tunnel. It mounts to the back of the trans, and the front of the Diff. It has 2 bolts at each end. Getting these set to TQ in the trans tunnel is a PITA if you have removed it.
C beam plates have been made to help with install, and the controversy over if they help apply more tq pressure to the beam.
There is also some black rubber/tar stuff on it for whatever reasons at the mounting point. Some speculated it has to do with absorbing any movement/tolerances.
Engines mounts could also be the issue, since that is the other end of the design.
If you remove the exhaust to get in there, you should take the time to find a way to look at the top of the mounting points to make sure someone put it together properly. nuts and washers. Use a iphone camera, or mirror and flash light.
When this is loose, it will move the shifter upwards when you use the car as it should be.
Thanks! So the C-beam is all that supports the transmission? I had a Firebird with the same thing but it still had a trans mount.
The Firebird suspension was a solid live axle rear suspension. The long arm that attached to the transmission from the differential was like a long single ladder bar that controlled axle rotation on acceleration. The trans was supported with a crossmember and rubber mount. I too also had a few Firebirds. Our Corvettes have independent rear suspensions. The differential housing is rigidly mounted to the Batwing mount which is rubber mounted to the frame. Chevrolet then used that mount to support the rear of the transmission using the c-beam.
It sounds very much like the C-beam bolts at either the transmission or the differential are not tight. The shifter should not move all that much. Is there any rattle or clunk when shifting or on and off the throttle?
Once you have the exhaust off, lay an 18mm open end wrench on the top of the beam by the transmission. Place an 18mm socket on a torque wrench and tighten the two front bolts to 55 ft/lbs. do the same with the rear bolts using a 21mm wrench and socket torquing to 65 ft/lbs. It's not really as hard as some claim it is. I have removed these bolts dozens of times in my garage on jack stands with little effort.
OP - the nuts used should be 'prevailing torque' so if someone has done a few removals it's likely the 'prevailing torque' has gone away. You might want to check the mounting holes in the C-beam for elongation, loose C-beam usually creates that issue and results in the 'lift' you experienced.
Fronts should be M12x1.75 and the rears M14x2.0. There should be washers both top and bottom.
Transmission not mounted?
