After c beam plates what are people doing to stiffen it up? Or are they just making a steel/tube version?

 

What problems are you having?

 

Exhaust maybe hitting rearend. I built a heat shield for the spring when I did the exhaust and it has bent down a few times. It's new and pretty stiff so I know the exhaust isn't moving around on it's own and it's not hitting the ground.

When the car hooks up too good sometimes I get noises. Had a thud noise that sounded like something hitting the fiberglass and just recently a nice groan/rubbing sound on launch. I looked and looked but can't find any other witness marks than the bent heat shield. Always sounds like it's behind me. Car still gets squirmy some with the plates too sometimes, but not as bad.

Need a gopro and it's on my winter buy list.

 

Nothing. The C-beam is more than stiff enough. It's strong enough to lift the front wheels off the car off the ground, from reaction torque imparted it by the diff housing. IDK why it would need to be stronger than that.

GoPro works. You could check your bat-wing to frame bolts too...

 

Your diff doesn't move up and down at all unless your rearend bushings are completely shot. Noises are part of owning a C4 check shock mounts etc. Have someone push the rear up and down while your under it.
Why do you need a heat shield and are you sure your exhaust isn't hitting it?

 

Didn't say the rearend was moving it could be the engine/trans since that is what the exhaust is bolted to(I know solid mounts or chain the engine), but I imagine the c beam is distorting some too then. I've also read about some who fabbed a pinion snubber deal to keep the nose of the rearend from rising, some forget the ring gear is trying to climb the pinion with good traction.

Shocks are used with brand new poly bushings.

 

No way is your C-beam distorting....unless it's been previously damaged somehow.


That is all wrong. Pinion is "trying to climb" the ring gear.

Don't need a snubber, b/c the C-beam handles all of that force.

There is NO WAY, there should be any noise created by anything that a snubber would help. If you have noise from your diff hitting the chassis/body, then your C-beam bolts are loose, or your c-beam is damaged and has lost it's strength in that direction. Additionally, your engine shouldn't be moving much (again, just deflection in motor mounts) and there is no need for a chain or solid mounts. If you motor is moving enough that exhaust is hitting things (due to engine movement), then you need new motor mounts.

You need to get under the car and look, push, pry, etc. Nothing should hit, nothing should move (more than deflection in bushings), and there shouldn't be any "thuds" or "banging" noises.

 

Stuff flexes/distorts period! It's alum I've seen moly/steel stuff move around that shouldn't.

LOL that was my edit I couldn't rem how it went pinion or ring and I changed it. You get the idea the front of the diff is trying to rise.

Been under the car looking a lot and today when I change my gov I'm gonna check some more.

If I listen to everything people say that shouldn't happen based on what they think about how my cars should perform, I'd loose a lot of races

Still thx for your input!

 

well, ya gotta start somewhere, and I'd start by replacing the batwing bushings with poly bushings; once that's done the rear end has a solid foundation to work off of; after that it's usually a loose c-beam; tightening it is good, beam plates are better, but best of all is to verify that the mounting holes in the c-beam haven't been worn oversize and then repair or replace as necessary. Also check the c-beam mounting webs on the differential nose piece, they can...and do...crack and collapse.

 

Yah I'd like to do poly or make some solid in spring, I'm bout done messing with this car for the year. I'll check the c-beam by the diff better next time I have it up.

 

I think they still sell C-beam plates, that is all I know of.

http://zfdoc.com/c4beamplate.htm

 

Heres a real easy test for c beam movement....

Watch your shifter **** when you accelerate/ decelerate...

Does it move up and down? Thats what mine did when i didnt tighten my c beam bolts enough. The shift **** moved up and down about 3/4" when id accelerate and decelerate...
Note i have the zf 6 spd not sure if the auto would do the same


All this said.... I have poly bat wing bushings, beam plates, solid motor mounts, a new c beam (im that **** i figures i might have elongated the holes from driving with the c beam loose) and know to tighten the heck out of the c beam bolts.... And i still get maybe 1/8" to 1/4" of up/ down movement in my shift **** during accel / let off the gas (decel)

So there is def some movement and with clearance being so tight between dif and exhaust, i could see an issue

 

Auto cars the shifter bolts to the floor and uses a cable(usually but I have seen some other vehicles that don't). Still good advise for manual guys.

I talked about how the car was after the plates, but didn't really say I have them. I do and they are torqued to spec per directions & been checked.

 

That is stating the obvious. Everything has some flex to it -even granite, but the flex is so small that it is meaningless. Insignificant. So we don't waste our time discussing that which is not related to the root problem. Know what I mean?

I get it. As I stated earlier in the thread, the C-beam is so strong and rigid, it will lift the front of the car off the ground during a launch, in a high HP car. See "Rklessdrvr" (sp?) threads. If it can do that, how could it possibly flex enough to allow contact in your stock or stockish car? It can't unless it was previously damaged and already bent.

 

One test you could do is safely support the car, have someone inside, set the parking brake, have them throttle it on/off, while you watch underneath. Movement should be readily obvious at that point.

.

 

The C Beam does flex some depending. 6spd cars that leave hard are harder on them than an Automatic car.

I do have a pinion snubber built off the roll bar in my 1992 6spd but that car has a bad *** clutch in it, a lot of power and I did this is to keep it from breaking another diff housing. You got to think with a 6spd the diff is getting hit with a ton of bricks on every gear change.... The 92 also has ZF Doc beam plates. It's really not that fast of a car... 480RWHP with a 6psd... It barley gets in the high 10's @128MPH on it's best day but man it's rough on rear end parts with the 6spd and SPEC Stage 3 clutch. I quit racing the car all together because of that. I need to remove the pinion snubber bar because all it does on the street is transmit rear end and tranny noise inside the car.....

When I still had IRS under my 1984 I never did anything to keep the C-Beam from flexing. No beam plates, no snubber... nothing. The car eventually had over 700HP N/A + 200HP on a nitrous plate.... But with the TH350 auto and PTC soft hit converter, it never broke anything but the halfshaft U Joints so I never saw a reason to "fix it" like the 92....I'll have to take a pic some time of the driveshaft out of the 84.... you can see where the C Beam flexed so much that after 3-4 yrs of racing the car it wore away part of the driveshaft yolk where the rear U Joint is.... No matter I went mid 8's @ nearly 160MPH with it like that last year - so it held on long enough.

My advice would be to get your camera under there and see what's moving around then see what you can do to fix it.
Will

 

Knew I read someone had a pinion snubber deal. I've done a lot of mods to make it launch on a less than ideal surface and the car leaves well, but not perfect. Something is moving and hopefully in spring I'll figure out what before it breaks.

 

...depending on the power, gear, weight, traction. I have no doubt that with a ~900 HP car, or a ~550 HP car w/a stick....or ANY car that "hits" the rear end hard and/or lifts the front end of the car, that the C-bean will deflect some. The C beam definitely wasn't designed with picking up the front of the car, in mind.

HOWEVER, I think Boot77's car is pretty stock. Is it not?

I took a vid of the diff movement (governed by the flexing of the C-beam, if any). My vid shows about what I'd expect to see for flex/movement...not much. I didn't edit the vid, so the "high torque situations" occur at:
3:38 - 4:00 -I am in 1st gear going from no throttle to full throttle.
7:25 - 7:36 -I do a minor clutch dump in first gear, then do some mild drag type shifts to 3rd gear.
8:50 - 8:56 -I do a couple little clutch dumps and tire squeaks. Didn't want to go too crazy in my neighborhood and also didn't want to shake the camera loose.
9:55 > -I'm backing up a pretty steep driveway. Nothing major there, but the same thing in our Caddy (which has atypical 3 point/pinion bushing mounting) and the diff would be flopping all over the place!



One additional note: IDK how much tq the OP is making, but my car is stock and I'm at 7000' elevation. So...330tq x .21 = 69. 330-69=261 ft lbs is about the max my car will make here.
X 2.68 (ZF first gear), x 3.45 (rear gear) = 2413 ft-lbs at the diff.

 

Video evidence that it does NOT flop all over the place when installed correctly and one that is not having issues. Seems solid enough.

Recklessdrivers car yeah I would expect some movement its running times WAY faster than ever designed to do. On a fairly stock car or even one mildly modified if its moving anything more than Tom's you have a problem not just "C Beam" flex.