Tom Austin

I've been chasing a wicked speed related driveline vibration in my '66 L79 since last Fall. The vibration comes in @ 65 MPH and is very noticeable @ 70 MPH and higher. It seemed to come on pretty suddenly last Fall. Here are some basics . . . I had the rear trailing arms rebuilt by Van Steel @ 10 years (maybe 3,000 miles) ago. I don't think they could be the issue. I've had the Michelin tires balanced since last Fall - that made no difference. I took the rear suspension apart 2 months ago and had the halfshafts rebuilt - they found one u-joint was very tight and one flange was bent. The rebuilt halfshafts cut the vibration in half! I then moved on to the driveshaft - it turns out it wasn't perfectly straight on one end and wasn't balanced properly - that made a very slight improvement - but the vibration is still present. I've called the guys @ Bairs to inquire @ the vibration possibly coming from the rear end (never been rebuilt - just turned 70,00 miles this weekend) - and they said if the rear end was going bad that I'd hear it before I felt it! . . . it doesn't seem to be making any strange noises.

As I stated - the vibration is at highway speeds - not evident at lower speeds in any other gear. I've even driven @ 70 MPH down hills with the clutch in and the transmission in neutral - and the car still vibrates - so I definitely think it's strictly driveline related.

Anybody have any thoughts at this point??? Thanks in advance!!!

Tom

GTOguy

Tires and wheels need to be checked for axial and lateral run-0ut as well as being in balance. Axle flanges need to be checked for run-out as well. How was the front yoke in the driveshaft? If saddle-worn, it'll cause vibration at higher speeds. Have run into almost zero rear end issues that resulted in vibration. You could always hear a bad one long before failure. Vibration always seems to be driveshaft angle/trueness, excessive run-out on the axle flanges and wheels/tires, etc. (external stuff) Keep us posted!

C2 Hot Cam Guy

[QUOTE=Tom Austin;1594189275]I've been chasing a wicked speed related driveline vibration in my '66 L79 since last Fall. The vibration comes in @ 65 MPH and is very noticeable @ 70 MPH and higher. It seemed to come on pretty suddenly last Fall. Here are some basics . . . I had the rear trailing arms rebuilt by Van Steel @ 10 years (maybe 3,000 miles) ago. I don't think they could be the issue. I've had the Michelin tires balanced since last Fall - that made no difference. I took the rear suspension apart 2 months ago and had the halfshafts rebuilt - they found one u-joint was very tight and one flange was bent. The rebuilt halfshafts cut the vibration in half! I then moved on to the driveshaft - it turns out it wasn't perfectly straight on one end and wasn't balanced properly - that made a very slight improvement - but the vibration is still present. I've called the guys @ Bairs to inquire @ the vibration possibly coming from the rear end (never been rebuilt - just turned 70,00 miles this weekend) - and they said if the rear end was going bad that I'd hear it before I felt it! . . . it doesn't seem to be making any strange noises.

As I stated - the vibration is at highway speeds - not evident at lower speeds in any other gear. I've even driven @ 70 MPH down hills with the clutch in and the transmission in neutral - and the car still vibrates - so I definitely think it's strictly driveline related.

Anybody have any thoughts at this point??? Thanks in advance!!!

If it was differential it would do it at lower speed too I beleive

TCracingCA

Just to speed up the diagnoses-- do you have some place local that speed aligns the car?

For all of the rotating stuff, I paint marks and see what is wobbling or has run out!

Any noise or pitch associated with your vibration?

I played with one car that had the tranny mount off, and the tranny nose wasn't in line with the driveshaft and thus the rear axle. It was a solid mount and the holes were oversized on that problem.

Check also your caps or u-bolts on things like the driveshaft and halfshafts to make sure they were torqued down equal and seating the caps correctly!

Is the exhaust system hitting or vibrating and hitting the body. Is this problem with a passenger or without? Have you check for slop with a dial indicator and a small mallet play in things like the front trailing arm bushings and the inner axles and outer axles? How are the crossmember rubber bushings?

Tigershark3

I'm in

hope2

tire, or wheel causing tire. almost for sure

Jackfit

Blame it on the guy who did all the alterations to your car!......lol

DSR

I haven't heard of "speed aligns the car". Can you elaborate? Especially the part about how you find wobbling or out of round parts.

GUSTO14

Can you or have you tried moving the rear tires to the front and see if the vibration moves to the front?

Good luck... GUSTO

C2 Hot Cam Guy

Good idea

Gary's '66

Have you checked the "snubber" bushing?

Gary

TCracingCA

It is a race car thing! The first place where I had it done was an old black guy in Inglewood CA (he finally died) that was taught the science of speed alignments by his mentor! You probably could check with the local SCCA! I doubt there are many outfits that do it these days, considering all of the lasers and computers, etc!

Kind of dangerous to roll under a car too, with the drivetrain in motion!

Balancing stuff and using strobes etc is kind of a black magic science! I have put like a single perfect round dot, like a white sticker and watched things go round to see if it stayed a line or blurred and got fuzzy looking because something was wobbling out of round or out of balance!

Randy G.

I had a similar vibration on my '62 and it turned out to be a rear axle bearing.

TCracingCA

Also meant as an insult!

But many of the stock cream puffs driven on this forum probably vibrate somewhere if god forbid, driven over a 100 mph! Many with original parts and such probably would look scary from under the cars, with the drivetrains in motion!

The real race car world is all about fresh parts! When I had taken my car, usually everything was new! And I don't know how someone like that old guy would feel about climbing under one that wasn't right, as I truly think about my suggestion! But it would be a way to spot a problem.

John BX NY

I would have all 4 tires checked on a radial force balancing machine like this one if you have not done so already.

http://www.gsp9700.com/how/

warrenmj

Reading your original post, it appears your problem started at the same time you had the tires balanced. I would have all of them checked again.

DSR

Interesting. Thanks

Tom Austin

Yeah, Jack . . . who was that BONEHEAD??? . . . oh, wait . . . never mind!!!

Thanks to everybody that has responded so far . . .

YES - I have moved the rear tires to the front - no affect
YES - the rear snubber is brand new
YES - I had the tires radial forced balanced - no affect

I think GTOguy may be on to part of the issue - that it's driveshaft related . . .but, im my specific case that my diveshaft is simply too short!

Let me explain. When it came time to shorten my stock driveshaft while engineering the installation of my G-Force Street 5 speed, either I took the wrong measurement, or the shop cut it too short (my shaft is too short? . . . the story of my life!). As currently installed there is slightly over an inch ( + 1/16th) of my transmission yoke (this application uses a stock Muncie yoke) protruding from the tailshaft of my transmission. My new theory is that too much of the yoke is exposed and that may be allowing the yoke to wobble ever so slightly! I'm thinking the driveshaft needs to be lengthened by @ 1/2" to work properly. Can you all concur with my latest assumptions? Thanks as always for the input!

Tom

C2 Hot Cam Guy

Please educate me where is the snubber bushing ?

Tom Austin

. . . officially called mounting bushings for the rear differential!