Bad sounds coming from the tunnel to the rear of car

Dinobyte · #1 (**permalink**) 03-28-2007, 11:16 PM

I was out today for a mini tour of the area, and when entering an on ramp to the 280, I got on it and heard a terrible sound from the rear end...

It is a major vibration every time I push the gas down, and it seems to be coming from the transmission tunnel or from just behind the seats...maybe even from the rear end.

The car still drives fine, but this sound and vibration is diffinitely not normal.

I have not done any burnout starts in the car...but have had spirited driving...so there has not been any dropping of the clutch to take off. Rolling take offs are the M.O. for the car.j

Does anyone have any ideas as to what might be happening before I put it up on jack stand and take a look.

Thanks
Michael

DonC · #2 (**permalink**) 03-28-2007, 11:30 PM

Were you getting the vibration when coasting with the clutch in?
My first thought would be either the drive shaft or (if you have independant rear suspension) the half shafts. Check the flange bolts and also, if it's been balanced with weights, check drive shaft to make sure you haven't thrown a weight.
Ditto the wheels. I'd also look at the side pipe mountings.
Is the rear end still securely bolted down?
A lot of potential areas to look at and not a lot of information from you at this point. Just throwing stuff out there.
DonC

Dinobyte · #3 (**permalink**) 03-28-2007, 11:39 PM

Quote:

Originally Posted by DonC

Were you getting the vibration when coasting with the clutch in?
My first thought would be either the drive shaft or (if you have independant rear suspension) the half shafts. Check the flange bolts and also, if it's been balanced with weights, check drive shaft to make sure you haven't thrown a weight.
Ditto the wheels. I'd also look at the side pipe mountings.
Is the rear end still securely bolted down?
A lot of potential areas to look at and not a lot of information from you at this point. Just throwing stuff out there.
DonC

Don,

Thanks for the input. No vibration with the clutch in and coasting. I do have an independant rear suspension...and the half shafts did cross my mind. Interesting you mentioned the side pipes...because i was thinking about that too. The car does not make the sound in just average driving...but any quick acceleration and the sound/vibration comes back.

I will update tomorrow after I have had a chance to put it up on jacks.

Thanks
Michael

6t8stang · #4 (**permalink**) 03-29-2007, 05:34 AM

Also, do you have an open rear, LSD, etc?

madmaxx · #5 (**permalink**) 03-29-2007, 06:03 AM

drive shaft bolts are loose. tighten and use locktite

Cashburn · #6 (**permalink**) 03-29-2007, 07:17 AM

Michael,
Maxx has a good suggestion. Give us a call today and we can get you sorted out. Does not sound major since it is only at very high revs. and not across the board.

Don't break that thing before Sean's car gets there.

Doug I · #7 (**permalink**) 03-29-2007, 09:17 AM

Any weights on the driveshaft that could have got tossed ? Wheel weights ?

jp65cobra · #8 (**permalink**) 03-29-2007, 09:39 AM

Michael,

My half shaft bolts loosened up and I had a similar sensation. Tightened them up and used lock tight and all is well after 6K more miles.

JP

1985 CCX · #9 (**permalink**) 03-29-2007, 10:49 AM

Not trying to offend here:

Isn't the BDR IRS from BMW? If so, can that handle power and torque from Southern Auto FE? I would be concerned about differential component structural integrity using the FE for power. Beamers are usually 6 bangers with lots of power but hp is not always the same when compared to V8.

Please inform as I would like to be better versed.
Jeff

pmfranke · #10 (**permalink**) 03-29-2007, 10:58 AM

sounds just like a pinion bearing.happened to me just 800 bucks ago.

CHANMADD · #11 (**permalink**) 03-29-2007, 11:16 AM

Could also be a bad engine or tranny mount!

Doug I · #12 (**permalink**) 03-29-2007, 12:37 PM

1985 .... Torque is what brakes parts. X amount of torque goes in to produce acceleration but there is Y amount of dead weight and traction resisting that torque. If either are to great compared to the other something has to give. That'll either be a weak point in the drivetrain or traction. Traction almost always looses. It doesn't matter how many cylinders are producing that torque, it's just a number.

The question of the ability of the BMW rear to withstand the power of a V8 has long since been put to bed. In race trim Bemmer engines produce a lot more power than the V8's used here, and the rears handle those without problems. These cars are also lighter than the original Beemers, so that reduces the dead weight, and in some cases traction that resist the torque. Yes with enough abuse anything can be broken, it's just a case of keeping everything within the limits. BDR's have been running with 600+ HP and the rears have stood up to it, the tires ..... well that's different

Bottom line is the rears don't break with the power and traction available, even with an FE.

Dino - sounds like it MAY be an easy fix.

Dinobyte · #13 (**permalink**) 03-29-2007, 06:15 PM

Checked the trans mounts, the driveshaft bolts, the half shafts...all tight. The drive shaft is not missing it's balance weights either...

Out of ideas other than to the shop.

aldersonjames20 · #14 (**permalink**) 03-29-2007, 06:29 PM

How much play was there in your driveshaft? I don't have a BDR, but the problem sounds awfully familar to something I experienced on my car. When I got on it it started to get a pretty loud noise and some vibration... turned out to be worn U-Joints. With the angle of the driveshaft that these cars have (at least SPF's, but I think most all of them) and the power we put through them (especially with that monster you have under the hood) they wear out if not lubricated properly. It only cost me about 200 bucks to have new ones put on and properly set up. I hope thats all it is... or one of the other simple fixes listed above.... nothing worse than you child being sick and you cant do anything for them...

James

maurice19 · #15 (**permalink**) 03-29-2007, 06:32 PM

My first thought was u joint

Maurice

badrich · #16 (**permalink**) 03-29-2007, 06:41 PM

Michael: I had a similar issue before my rear U-joint fasteners gave up.

I now have a new heavy duty $650 drive shaft with loop, etc. Very pretty. I see you have just checked those fasteners, but just in case... Rich

Dinobyte · #17 (**permalink**) 03-29-2007, 07:12 PM

The u-joints look okay...not loose, not oozing grease...any tell tell signs they are worn?

Dinobyte · #18 (**permalink**) 03-29-2007, 08:47 PM

Found the issue...left rear trailing arm...the bolt came out.

How in the heck do I get this bolt back in without taking the entire left rear end off? I have tried jacking up the trailing arm to line the bolt up, but no good. There is no room to work, and I can't seem to get the bolt to grab a thread on the other side, provided the other sides thread is not striped out.

jschiller · #19 (**permalink**) 03-29-2007, 09:07 PM

Cut the bolt with a cutoff wheel or Dremel, right near the mounting bracket, then drift or push the rest out from the outside. There probably won't be much left after you cut it off.

John

Dinobyte · #20 (**permalink**) 03-29-2007, 10:40 PM

Thanks guys for all the advice.

This looks like a simple fix...however I have been tyring to sead the bolt into the threaded nut with no luck. I tried putting my floor jack under the trailing arm to lift it so the holes line up, but there is not enough room to make it work. I fear I am going to have drop the entire rear end, or at least the left side, just to thread the bolt back in.

I might try taking this to a local shop that can fit me in tomorrow...any ideas Bay Area Cobra Club members?

Thanks
Michael