Drive Shaft Thunking

[MrMagoo]

Hey guys. I've got a Venom 427 with a 351 connected to a late aftermarket Tremec T5. When I apply the clutch in 1st gear from a compete stop, I get a loud chattering thunk from the drive train behind the tranny, presumably from the driveshaft. The only way to avoid it is to release the clutch quickly, give it gas and spin the tires. Sometimes (like when there's a cop looking at you) that kind of thing attracts more attention than I want, so I was wondering if anyone has any ideas. Mike Forte thought clutch/flywheel, quickly noticed that I dont know anything about cars, and cautioned me against having the driveshaft wack me in my naughty bits. The Team-C guys thought slave cylinder.

Anybody out there have any ideas?

[blykins]

If it just does it on taking off when letting the clutch out...sounds like a clutch chatter...

[MrMagoo]

If I were to replace the clutch, and possibly the flywheel too, do you think it's a good idea to go with a lakewood style steel bellhousing?
During my research on this problem I have been reading a lot about exploding clutch assemblies, etc.

[DAVID GAGNARD]

MrMagoo;

I had a very similar thing happen to me in 1996 when I finished my Mustang,had no less than 10 people look at it,drive it,tried 9 suggestions,they did not work,last one was right,I,the great mechanic that I am,left out the bushing/bearing in the rear of the crankshaft,causing all my problems,pulled the trans.,put in a bushing,no more problems 20,000+ miles later..... Could it be that?????

David

[blykins]

Magoo, you should definitely think about a scattershield. Cheap insurance for your legs. There isn't much between the clutch and your body.

[MrMagoo]

Dave, Since I didnt assemble this motor, I guess all bets are off. I'll certainly check that out. Since the clutch seems to work in all other cases (2-3, 3-4, 4-5) it's possible that it's not a clutch problem, I suppose.

[MrMagoo]

blykins,

The scattershield does seem like a good idea. I think I'll do that no matter what.

[decooney]

The simplest thing to do is have a qualified mechanic diagnose it for you for one hours shop time. That way you can try to rule a few things out before randomly pulling things apart.

A good/trustworthy troubleshooter with a lift/rack can usally isolate things to a particular area quickly, and save you a lot of grief if you find yourself wandering about... Good Luck.

[Ibr8k4vetts]

Sounds like input bushing/bearing IMHO
Mike

[MrMagoo]

have a mechanic who will be checking it all out. I am going to tell him to be sure to check the bearings. Thanks to all.

[MrMagoo]

One crucial piece of info I forgot to include is that in order to pass CT inspection, I raised adjustable shocks in the rear to the max setting, and forgot to put them back. I returned it to close to its original settings, and the problem is MUCH reduced, now just a slight buck if I let the clutch in too fast. I may lower it even more, just to see if I can make it even smoother, but now I am in tweak mode rather than "holy s**t my back end is about to fall out of the car" mode.

Thanks again to all.

[DavidWard]

Sounds like u-joint bind. The drive shaft is so short on these cars that alignment is critical. FFR's are notorious for u-joints binding, as the drive shaft is only about 10.5 inches.

David

[MrMagoo]

What's the best way to check for proper alignment. Just eyeballing it?

[Bruce Edwards]

The angle from the rear of the trans to the front of the rear end should be almost straight with the suspension loaded, the car on the ground. The rear end pinion should be pointed just a few degrees down but darn near straight.
You can check it in the air if you put jack stands on the suspension. Just be careful you do not put it on a part that will move as you let the car down on the stands. Wrong place and they can shoot out from under the car or cause the car to "jump" on the stands and may cause it to fall.

[MrMagoo]

Thanks for the tip. A lift would be nice, eh? Can I put the rear tires on ramps to get the effect, as I happen to have a pair?

[DavidWard]

Inspect the u-joints. If they have been binding you will see shiny spots where the bind is occuring. If you have adjustable upper control arms, they can be adjusted to fix the bind. Without adjustable arms, you can either space the tranny mount up, or cut the mount, depending on which way you need to go. Another fix that has been done is to use a dremel and remove a small amount of metal from the area where the binding is occurring. Adjusting rear ride height will also have an effect.

David

[Bruce Edwards]

Sure that will work. The idea is to get a good look at the angle from the trans to the pinion. You may also want to be sure the drive shaft is not to long. You should see some of the slip yoke bearing surface hanging out the rear of the trans. Depending on your rear end set up it can be as little as an inch if your rear end is solidly mounted like a Vette or Jag and more than an inch for a standard 4 bar or leaf spring style.
You want to be sure as the rear end winds up that it is not making the drive shaft bottom on the output shaft. That will give you a banging noise till the car starts rolling and the drive shaft levels back out. You may also hear it if you hit a speed bump to fast.
Just another thing to check.

[DC COBRA]

Mr Magoo
I thought the Team C cars was similar to the Backdrafts, they both used BMW rear IRS suspension. If that is the case, then changing cars height will not change driveshaft angle that is fixed position. It would change the c-v axles angles so might possibly have a bad joint there. Might also check main driveshaft joints and differential.

DON

[MrMagoo]

I checked the CV joints by rotating the driveshaft and wheels and checking for play. I found play on the inboard drivers side CV, which I am going to have replaced. I'll let you all know if that improves things significantly.

[rob frink]

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