I Broke my BDR help!

[moneymanager]

Hi Gang.

Friday after Thanksgiving I raced my Backdraft at Firebird and during race #2 I broke something and had to come home early.

I haven't figured out what I broke yet so maybe you can give me some IN-PUT to help me figure it out.

It's something in the drivetrain. It runs, shifts and moves under it's own power but around 2,000 rpm it makes a terrible noise and causes a shuddering effect which can be felt through the whole car, especially in the clutch pedal, every few feet it moves in distance.

It doesn't do it upon first accelerating, only after you get around 2,000 rpm or higher, in any gear. I'm told the brake lights are coming on as well each time it does it, like the brakes are locking up speratically. Although I feel it more in the clutch rather than the brake.

I have a feeling that maybe part of the clutch disc has come apart.

What do you think it might be?

Here are some photos of the race at Firebird:
http://jmichael.info/CobraShowsandRaces.htm

Doc

[Dennis Kelley]

I don't have a clue but have you checked the engine and tranny mounts. Make for sure there good and tight. It sounds like something is loose and when you get to 2000 rpms its really lose. Good luck and let me know what it is.

[tpiini]

Originally posted by Dennis Kelley


I don't have a clue but have you checked the engine and tranny mounts. Make for sure there good and tight. It sounds like something is loose and when you get to 2000 rpms its really lose. Good luck and let me know what it is.

That'd be my first guess also. Broken mount = engine moving = something hitting what it shouldn't. If you carefully cruise past 2k RPM do it do the same thing? If so, my theory is shot to hell, unless it's the rear trans. mount & the driveshaft is starting to flop.

[GeorgiaSnake]

It could be your harmonic damper has given up.

Randy

[Doug I]

Hi Doc

"around 2,000 rpm it makes a terrible noise and causes a shuddering effect which can be felt through the whole car" ok guys were not talking about an instrumentation glitch. Sorry Doc - a play on a movie line involving 3 guys with a problem and the people to solve it were a lonnnnnnng way away.

What I'd do Doc is put her up on some stands and get under there and start looking for anything out of place. We don't want to make anything worse than it already is.

First - as others said look at the engine mounts. I remember your post from a few days ago when you mentioned that a bolt had done a runner on you. Another one could have bailed and the those left could have broken, or worked loose.

Second - as others said tranny mounts. Back end of the tranny would let the front of the driveshaft move around and that'll give you a real bad feeling through the seat. It'd be real bad if you're doing more road work and you get to find out if your new shaft loop really works.

Third - check the driveshaft for anything loose/broken. Could have blown a bearing in a joint or tweaked a pin in there. Try to turn the shaft by hand with it in neutral and the parking brake on, or any way of stopping the rear wheels from turning.

Fourth - check the rear end for any broken bolts etc. Above 2K would be getting to a speed where any slight out of balance in the rear end, wheels and tires would start to show up if anything is loose in the rearend. Check to see that everything appears to work as it should.

Fifth - turn a rear wheel and feel for any tight or firm spots. Listen for any scrapes, clunks etc.

Sixth - do the same to the front.

IF that finds nothing then we've ruled out all the mounts that hold the drivetrain to the car, probably the driveshaft and everything behind that.

The brake lights coming on when this vibration happens made me think that a pad could have come loose, or the pad material could have seperated from the plate. I think that spinning each wheel would show this up.

If nothing shows up by the above then it's a problem that involves dropping the tranny and shaft out. Clutch would be high on my list as it is with the other guys. With the shaft out check that it hasn't thrown any balance weight(s) it may have/ have had.

I'm leaning to something in the brakes as when it happens the system is getting pressurized to trip the lights to come on. I can't really see anything in the clutch side doing that - but with cars about anything is possible .....

I remember many years ago spending a long time checking out the rearend suspension on a car to cure the squeak. Greased everything, checked all the bushes etc, checked the brake drums (it was a while ago) .... still squeaked. Went away when I took the stone out that was jammed between the spring and the shock.

[Dennis Kelley]

Also check and see it your headers are hitting your body. if the motor mount is shot the headers run close to the foot box on the driver side.

good luck man.

[trularin]

The brake lights coming on could be due to excessive vibration. You would have to be the judge of that. If it is really shaking, the brake pedal may be vibrating causing the lights to come on.

Strange, I want to say Synco ring in the trans on top of all the other suggested possibles. There are so mant other suggestions, you will want to check the simple things first.

Let us know what you find.

[relaxinrob]

I think it could be the harmonic balancer.

[Boudy]

Check the differential. There is a bolt that ties the front of the diff to the chassis. This bolt has broken before and mearly needs to be replaced. I broke mine twice before upgrading to a larger bolt. To test this, just push up on the nose of the diff. If this is it, it will allow the spinning driveshaft yoke to hit the chassis.

Boudy

[moneymanager]

Thanks guys for all your input and ideas. I believe from what I have read and the way it feels that at this point my guess is that it could be a brake pad or something in the brakes that's causing the problem. Thanks for that suggestion. That along with your other points will be checked for sure and I'll post here what I find.

Later EDITED- I just got back from taking my BDR into the shop and we figured out what the problem was. The BRAKE BOOSTER is leaking BIG time! When it decelerated it would cause a huge vacuum draw which due to the leaking caused the brakes to pulsate, and is actually activating the brakes. To a point with each vacuum draw the brakes lights are coming on. It's kinda like having a poor man's version of anti-lock electronic brakes that don't work right. Ha

Well at least it's an easy fix and nothing terribly serious. It could have happened anywhere, not just racing so I can put the blame on my racing activiities. The fact that the engine on deceleration from 6,000 rpm repeatedly probably didn't help it much but oh well!

Now I'm off to get a new brake booster!

Thanks again buddies!
"Doc"

[moneymanager]

I just got back from taking my BDR into the shop and we figured out what the problem was. The BRAKE BOOSTER is leaking BIG time! When it decelerated it would cause a huge vacuum draw which due to the leaking caused the brakes to pulsate, and is actually activating the brakes. To a point with each vacuum draw the brakes lights are coming on. It's kinda like having a poor man's version of anti-lock electronic brakes that don't work right. Ha

Well at least it's an easy fix and nothing terribly serious. It could have happened anywhere, not just racing so I can put the blame on my racing activiities. The fact that the engine on deceleration from 6,000 rpm repeatedly probably didn't help it much but oh well!

Now I'm off to get a new brake booster!

Thanks again buddies!
"Doc"

[Doug I]

Glad it was an easy and quick fix

I'd get with Boudy or Reg. and ask about the bolt at the top of the diff.

regards
Doug I