Nokones

I am looking for information on the C4 Torque Arm. I figured a Drag Racer would know his/her stuff so I am posting this to the Drag Racing Section. I am an Autocrosser with an 89 C4. I am running a Lingenfelter SBC with 560 horsepower at the wheels. I have been having problems with the shifter rising up under load when the car gets underway.

I am running with a Tremec TKO600 and I have an adapter mount to tie the torque arm to the tranny. The bolts are tight to 90 ft pounds of torque. The rear diff bolts are also torqued to 90 pounds.

Today I learned from a fellow Corvette Forum member, C409, that the rear diff maybe rising/rotating up thus causing the tailshaft of the tranny to also rise up.

Has anyone run into this situation and what did you do to resolve this problem?

Does anyone know if the the torque arm is flexing under extreme load?

I am assuming if the diff is torquing up that the batwing must be pivoting at the chassis. Has anyone modify the batwing bushings/mounts to keep the diff/batwing wing from pivoting?

Any help would be appreciated.

Here is a picture of the adapter/tranny mount that I had modified to help keep things tight.

STEVEN13

Things that I would check are the mounting points for the batwing (bushings)-damaged batwing (batwing is the rear housing)-damaged C-Beam (its called a C-Beam not torque arm) or engine mounts.

Nice car! Any photos of the TKO 600 mounted in the car?

Steve

Nokones

Thanks for the reply Steve. It would probably best to change out the Batwing bushings. I thought about the poly bushings but, I wonder if the poly bushing would, in time, contribute to undo stress on the chassis mounts where the batwing mounts to.

In the many years dealing with C4 Corvettes, I only found that people on this forum call the C Beam a C Beam. In many Corvette circles and Corvette Performance Shops, the beam is referred to it as a Torque Arm, in generic terms, because that is what it is, and the F Bodies have the same setup. Technically speaking and in accordance with the Factory Service Manual, the C Beam is a Support Beam or Carrier Support Beam. It all means the same thing.

I don't have any pictures of the TKO600 in the car but, I'll take some the next time I am under the car. However, I do have a lot of pictures of the car with the TKO600 in it.

383vett

Your tranny to c-beam mount looks stout. As long as the bolt holes are not elongated and the beam is tight, it shouldn't be moving at that junction. The stock torque at the tranny is 55 ft/lbs for an 84. As mentioned, I would check the batwing bushings; if they are shot, your rearend will be moving around a lot. Also it may be possible that you have a bad motor mount. That will cause the shifter to rise up. I had my car in the low 11's before I switched to a straight axle and a true torque arm. I never had any shifter movement with a manual or automatic launching on slicks.

Nokones

Thanks for the response. The bolt holes are definitely not elongated. The bolt is a tight fit.

The motor mounts are good. Lingenfelter did some custom chassis work for me in order to get the dry sump pump to fit the chassis.
Looks like I don't have any photo files on the chassis modifications on this computer. When I get home on Thursday, I'll post a couple on what they did.

rklessdriver

What kind of bushings are in the batwing? Poly or some made from PVC or Derilin would take alot of the deflection out if your still running factory rubber.

On my old 92 6spd I had resorted to putting a bar from the roll cage down to the pinion of the diff because the C Beam flexed so bad that it kept cracking the nose on D44 housings. I broke the entire nose off on a particularly nasty 1-2 gear change..... That car had just under 500 at the rear wheels with a very aggressive clutch. I called it a "snubber bar"..... Worked really well because after installing it, I didn't crack the nose of the rear end housing again.

The cars new owner cut the bar off so it wouldn't contact the C Beam anymore. The C Beam had permantly bent a little and the bar contacted it pretty much all the time..... the drive train noise transferred thru the main hoop was too much for him to deal with. He doesn't race the car like I did so I told him it wouldn't be a problem.

Pics of how I did mine.







And FYI I am not the originator of this idea.... I copied the snubber bar idea from this guy.

https://www.corvetteforum.com/forums...-rear-end.html

Will

Nokones

As promised, here are the pictures on the custom motor mount and chassis work that Lingenfelter did on my 89.

The poly Batwing bushings are on order.

STEVEN13

Why did they change the chassis mount for the engine? Is it due to the transmission?


Steve

Nokones

To make room for the Dry Sump Oil Pump.

Nokones

I received my new Poly Bushings yesterday. Can anyone tell me if the old batwing bushings are press-fitted in and do they need to be pressed out, air chisled, or if they can be easily removed. I'm curious on what I am up against before I start the work.

Any help would be appreciated. Thanks

STEVEN13

You can drill holes in the rubber or burn them out with a torch. The metal sleeves will require a little work to remove. Carefully cave them in and hammer out or use a press. Search the C4 Tech section for more info. Good luck.

Nokones

Thanks Steven:

I read a bunch of the postings. Drop one side at a time, drill out the rubber, hacksaw a tad on the outer metal sleeve and don't touch the batwing inner-housing, chisel out carefully, or do the sockets with C-Clamp procedure. Got it, should be a piece-of-cake, it should be fun.

Nokones

The batwing bushings were replaced with poly bushings and that did help a lot. The shifter only moves about a 1/4" now. Thanks guys for all the help.

I kinda wonder if the batwing was moving laterally under load in the turns and changing the rear toe? Anyone know if this could have been happening? Just curious.

STEVEN13

I guess anything is possible-But I am thinking if the whole batwing was moving it would just change the tracking of the tires-It's all connected together minus the 4-link bars to the chassis.

Steve

Nokones

I know that this forum is for drag racing posts. Although I am an Autocrosser,, I knew I could get some help from a drag racer for the right info regarding my problem. The info was a big help and I really appreciate all of the help on this matter.

Replacing the Batwing bushings not only resolve the rising shifter problem, the rear of the car handles a lot better and I can get into the gas and put the power to the ground a lot better.

This past weekend, I attended my first event since replacing the bushings and my times were a significant improvement. It was a night and day difference.

Thanks again guys.