Hello,
I have this vibration coming from the rear of the car at 75 mph plus. It's completely speed (mph) dependent and RPM seems to have no effect on it good or bad. You feel it in your butt and severly in the transmission shifter.

Details on the car...
66 Chevelle big block
Super T-10 trans
10 Bolt rear end
p275r60-15 BFG drag radials

So far I've had the tires and wheels balanced twice. I watched the second time and they looked fine, by that I mean bent rim or such. I've had the driveshaft balanced twice also. Unfortunately everytime I deal with the driveshaft place my confidence seems to sink more and more. The rear end is all new (brakes, drums, axles, gears, everything but the housing). The suspension is all new as far as poly bushings go. The u-joints are new. The output shaft on the trans is new. The only thing I can come up with that it might be at this point is a driveshaft to pinion angle problem. I have not bought an angle finder yet but when you look under the car the driveshaft seems to exit the transmission with almost no angular mis-match. The driveshaft to rear end pinion shaft is not as straight. The pinion shaft seems to be pointing down towards the floor relative to the driveshaft. Is there an adjustment for this angle? I crawled under the car last night looking and couldn't see anyway to adjust this. How perfectly does the driveshaft to pinion angle need to be? Right now I have zero wheel hop or anything undesirable except for this speed limiting vibration at 75 mph. Any ideas or suggestions for something to suspect as to where the vibration is coming from would be greatly appreciated.
Lance

Had a problem like this once before the drive shaft had a twist and the u-joints were out of phase. Try changing the rear tires to a short radial type so the diameter is much smaller. This will tell if it is speed related or engine RPM related. Good luck!

Slo307,
It's definately speed related as you can put the trans in neutral and the problem slowly goes away as the mph slow down long after the rpm's go to idle. Will check the out of phase u-joint thing though.

Lance

Checked the driveshaft last night for the out of phase u-joint thing. Looks fine to me. Still hoping for suggestions or ideas!!!

Lance

Check your trans mount. Then take it to a good chassis shop and have them measure your angles. You may need adjustable upper arms to change the pinion angles. If you do a search there are many discussions on driveline angles.

Andrew

lance

was the the bushing in the tailshaft of the trans replaced? how does the slip yoke look at the spot that rides on the bushing?any slop here may cause a vibration.

what gears are you running and or how many rpms do you run at 60 mph?

at what rpm was the shaft balanced on the shops machine?

Here's how I tracked down the vibration I had. Follow the steps below till you find the culprit.

Put the rear of the car up on jackstands, with them under the axle so the springs are loaded with the cars weight.

Block the front tires.

Hop in, start her up, and put in gear, and take up to speed. Vibration gone means the tires are out of round.

Shut her down, remove a wheel and drum. Vibration gone, that wheel and/or drum is out of balance. Put drum on, use the lug nuts, and try again.

Same for other side.

Still vibrating? now you get to crawl under and remove the drive shaft. With it out, if the vibration is gone, the most likely candidate is the shaft, but it could be internal to the rear end as well.

I don't have any good advice for narrowing that down. If you can borrow a known good shaft, that would help...

Skip
442 Ragtop

Andrew,
I'm using the factory cross member and the rubber mount is new. Yes I might end up searching for a reputable driveline shop. I did the "pinion angle" search and didn't get many hits. Maybe I used the wrong terminology :(

Brandon,
The slip yoke is brand new and I specifically looked at it for some indidcation that it was flopping around when I took the driveshaft back out to return it to the driveshaft builder to "re-balance :rolleyes: ". It looked a-ok to me but then I'm no expert! I'm running 3.73's don't know exactly the rpm at 60 mph but i'd guess 2800? Good question on the rpm that it was balanced at the shop. Don't know. I think my next step is to take the driveshaft to another :rolleyes: shop and get it checked for quality. I have some doubts as to the original driveshaft builders level of quality after all these problems.

Skip,
I had thought of that but the thought of going 80 on a set of jack stands scares the #^%$ out of me. I realize it would be a great way to diagnose the culprit but it's going to take some thought before I do that. I guess I'm just scared hurt my baby.

Thanks for all the responses, other ideas still welcome

Lance

Have you checked the rear itself recently? Worn ring & pinion, worn out bearings will cause it to vibrate as well. Axles could be bent also causing it to vibrate.

Originally posted by lance-w:
Hello,
I have this vibration coming from the rear of the car at 75 mph plus. It's completely speed (mph) dependent and RPM seems to have no effect on it good or bad. You feel it in your butt and severly in the transmission shifter.

Details on the car...
66 Chevelle big block
Super T-10 trans
10 Bolt rear end
p275r60-15 BFG drag radials

So far I've had the tires and wheels balanced twice. I watched the second time and they looked fine, by that I mean bent rim or such. I've had the driveshaft balanced twice also. Unfortunately everytime I deal with the driveshaft place my confidence seems to sink more and more. The rear end is all new (brakes, drums, axles, gears, everything but the housing). The suspension is all new as far as poly bushings go. The u-joints are new. The output shaft on the trans is new. The only thing I can come up with that it might be at this point is a driveshaft to pinion angle problem. I have not bought an angle finder yet but when you look under the car the driveshaft seems to exit the transmission with almost no angular mis-match. The driveshaft to rear end pinion shaft is not as straight. The pinion shaft seems to be pointing down towards the floor relative to the driveshaft. Is there an adjustment for this angle? I crawled under the car last night looking and couldn't see anyway to adjust this. How perfectly does the driveshaft to pinion angle need to be? Right now I have zero wheel hop or anything undesirable except for this speed limiting vibration at 75 mph. Any ideas or suggestions for something to suspect as to where the vibration is coming from would be greatly appreciated.
Lance Tom
he has replaced everything except the housing itself.

Lance
at 60 you would be turning about 2650 rpm. at 75 you would be turning 3350 rpm. im curious to know what rpm the shaft was balanced. a shaft that was balanced at lets say 2000 rpm ??(guessing) might cause vibrations in your case.

check out www.dennysdriveshaft.com (http://www.dennysdriveshaft.com)

all of their shafts are high speed balanced up to 10,000 rpm. they will also check and balance your drive shaft if you desire.

to be honest from your description of the pinion angle it sounds ok. the nose of the housing pointing down is actually desired to an extent, and is used to counter the axle wrapping up under acceleration. too much will cause a vibration so i would still check it before spending a bunch of cash.

i suggest you check the pinion angle, if nothing turns up there send the drive shaft to Dennys driveshaft to be checked and balanced. or find a shop that can balance the shaft at more rpm.

hope this helps
Brandon

Well IT'S GONE YIPPEE!!!!!! :D graemlins/beers.gif

It was a bent driveshaft. Now keep in mind that this was a driveshaft that was built from scratch at a shop in central Simi Valley (feel free to email me for details). They had it back in they're shop twice to "correct/check" it and it was still bent when I took it to the new place. I would like to commend the efforts of the shop that finally fixed it. They were very professional and they're only goal was to fix the problem and make me the proverbial "happy customer". The shop I finally ended up at was WENCO Driveshafts in Van Nuys CA. They are a first class shop. I had used them in the distant past and only went to the other :mad: shop in Simi because it was close to home. So much for convenience. So I would like to thank everyone that made suggestions and had ideas to look at this or that for the source of the vibration. Smooth as silk at 100 mph :D graemlins/beers.gif TEAM CHEVELLE RULES!!!!!!!

Now that is cool! Remember the yingers, dont drink 'em all in 1 place!! graemlins/beers.gif

Glad to hear everything worked out.

graemlins/hurray.gif

Brandon