you could be right about the c-beam having no effect on the chassis rigidity, but after fitting torque beam plates I am convinced the c beam must have some affect on torque being transferred through the drive train,
i compete in hillclimb events with my car, it used to squirm when turning and accelerating hard, after fitting torque beam plates it doesnt do it anymore, its as solid as a rock, before the plates i put urethane bushes and 2 new sets of rear shocks in and no difference, put beam plates in - cured !
It would be interesting to hear some input from someone with an automotive engineering background on this subject ?

Having made my own , my take on it is the stock bolts do not have enough area under the bolt head to clamp the beam tight enough to withstand the twisting/ lifting motions ; especially in manual cars.
Witness the number of owners including myself that have found the bolt holes in the beam elongated when the beam is removed, indicating that alot of movement has occurred
To my mind the plates extend the clamping forces over a much greater area thereby reducing or even eliminating any movement between the beam and it's mounting points

......... Are you hill-climbing with a Corvette ? ..... Don't you need ground clearance for that ? ........ The factory applied an epoxy glue to the diff end of the C-beam ... more than likely to prevent / diminish squeaks .... that's the grayish-white stuff you find all over the bolt waffles on the front of the diff .........

I submit the C-Beam be identical in function to a torque tube. The C5 and C6 simply completed the circle [ bad pun?].

While providing zip " frame strength", it does transmit power from the rear wheels through this independent rear suspension system, to the motor mounts.

A "hard" cross motor mount at the trans snout would help, but then you would have drive shaft joint issues....

This is exactly why I put in the plates. IMO they act as sort or a much needed heavy duty fender washer.

Hi guys, I'm a Licensed Professiona Structural Engineer by trade and the author of this thread is 100% Correct.

The C Beam is basically a channel shaped member that transfers a portion of the weight of the engine and transmission to the rear bat wing through the differential housing. Without it, the rear of the engine and tranny would drag on the ground :)

A channel section is a very poor conductor of torque. Round sections are used to do that i.e. the round shape of a hollow drive shaft.

One other thing, the rocker beams are vey effective in resolving the torque exerted by the engine and differential through the engine mounts and bat wing as the rails are far apart from the center of the car. The torque gets resolved into a force couple that is extered up and down on each side of the frame rails.

This car is very well engineered in that the forces are carried very specifically to well beefed up sections of the frame where it is needed.

The upper and lower suspension tracking arms prevent the differential housing from twisting opposite from the rotation of the rear wheels, so there is no additional torque added to the C beam in that direction which would cause additional bending loads in the beam. No it simply is there to support the rear of the engine and tranny weight. BTW, this gets quite a large load when the car is airborne then slams back down on the pavement when coming off a good bump in the road.....mechanical engineering 101.

Just my 2 cents.....great article :thumbs:

I'm no engineer, but this is dead on.
The C-beam replaced the traditional cross member allowing the exhuast to be routed under the car and free up interior room and allow the seats to be lower, and the car as a whole height wise.

Time for some schooling from Corvette From the Inside by Dave McLellan

Paraphrasing:
Originally the C4 was to have a torque tube like the C5/C6. They where not sure how they where going to service the drive-line without a major tear down for even minor repairs. Hehehe.....have fun C5/C6 guys. Your welcome a C4 idea that was delayed a generation till it had a transaxle out back. Which is another C4 idea, that was delayed. Seeing a pattern here. The C4 was so different that it took a incomplete revolutionary step (C4) to get to the C5. Not all of Dave's ideas where feasible at the time, money, time, technology, had yet to catch up.

The torque tube they had exhibited a vibration in en-sync with the engines firing frequency. They understood why the Porshe 928 has a battery mounted on the end of the trans-axle, its a damper for this vibration in its drive line. The C4 engineers could not chase this vibration that occurred at all normal driving speeds out of the engines operating range without a damper or extra weight. They took the easy route, make the drive-line less stiff=C beam. Solved the service issue=regular prop shaft with u-joints.

:lurk:

Great Thread!

ha ha, yes ground clearance is desirable but not essential !
in this clip you can hear what my c4 sounds like on an uneven surface,

[url]http://www.youtube.com/watch?v=Te4-x_3OzDk[/url

I think you and rodj are right that cleaning it up and using the plates with a clamping action on the torque beam tightens everything up, its not surprising things might start getting a bit loose after 25 years !

what is the proper procedure for installing the c beam when replacing a 4 + 3 in a 1985 model?