explain this??
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 764
Likes: 13
From: Harvard MA
please explain this
66 L-79 roadster 4 speed 3.70 posi. In the year I've owned it I've been chasing a vibration in the steering wheel under acceleration. I've done alignment, balanced wheels, even balanced the driveshaft. Sometimes I think it's gone then it comes back. Today I noticed that it really is gone when my tank is full of gas, but starts to reappear after I've burned as little as 3 gallons from full. I recall a service bulletin that said set the camber to zero if there is a report of vibration under acceleration. This full tank remedy seems to increase the camber. Can anbody explain why a full tank gets rid of this vibration?
[Modified by brucep, 9:50 PM 4/17/2004]
[Modified by brucep, 9:50 PM 4/17/2004]
Drifting
Joined: Sep 1999
Posts: 1,265
Likes: 0
From: No. 13
Re: explain this?? (brucep)
Well, since vibration is nothing more than a component or components resonating at a given frequency for a given input, I'm guessing that the extra weight from the full tank shifted the resonant frequency of the vibration source to something you wouldn't either feel (higher frequency, usually) or completely decoupled the part in question so that there was no resonance. As you burn fuel, the weight (and center of gravity for that matter) of the car shifts and back comes the vibration.
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Re: please explain this (brucep)
1 get wheels balanced on a Hunter that can detect bad tires. My new Pontiac had 3 bad ones.
2 Check ALL the u joints
3 Reverse thedrive shaft mounting on the pinion yoke
4 balance the half shafts
5 Check the runout on the rear spindles
Tell us when it started and what maintenance has been done lately (that might have provoked the problem.
2 Check ALL the u joints
3 Reverse thedrive shaft mounting on the pinion yoke
4 balance the half shafts
5 Check the runout on the rear spindles
Tell us when it started and what maintenance has been done lately (that might have provoked the problem.
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 764
Likes: 13
From: Harvard MA
Re: please explain this (magicv8)
1 get wheels balanced on a Hunter that can detect bad tires. My new Pontiac had 3 bad ones.
DONE
2 Check ALL the u joints
DONE
3 Reverse thedrive shaft mounting on the pinion yoke
DONE
4 balance the half shafts
NOT DONE
5 Check the runout on the rear spindles
DONE
Tell us when it started and what maintenance has been done lately (that might have provoked the problem.
Been this way since I took it out of moth *****, after being store and restored, but not driven since 1979. Heres what's been done-Rebuilt motor, new shifter linkage, all new springs (front coils, and 9 leaf rear), all new shocks (delco gas), new wheels (bolt-on knockoffs), new tires (Goodyear Regatta), hunter balancing with runout check, balanced driveshaft, (new front driveshaft yoke), new rear camber adjustment cams, new rear struts, new brake Lines, alignment (2 times).
DONE
2 Check ALL the u joints
DONE
3 Reverse thedrive shaft mounting on the pinion yoke
DONE
4 balance the half shafts
NOT DONE
5 Check the runout on the rear spindles
DONE
Tell us when it started and what maintenance has been done lately (that might have provoked the problem.
Been this way since I took it out of moth *****, after being store and restored, but not driven since 1979. Heres what's been done-Rebuilt motor, new shifter linkage, all new springs (front coils, and 9 leaf rear), all new shocks (delco gas), new wheels (bolt-on knockoffs), new tires (Goodyear Regatta), hunter balancing with runout check, balanced driveshaft, (new front driveshaft yoke), new rear camber adjustment cams, new rear struts, new brake Lines, alignment (2 times).
Drifting
Joined: Sep 1999
Posts: 1,265
Likes: 0
From: No. 13
Re: please explain this (brucep)
Guess I could have offered some practical experience to go with the science...dohhh, got wrapped up in the science once again! :D
[Modified by RGGregory, 7:54 PM 4/18/2004]
[Modified by RGGregory, 7:54 PM 4/18/2004]
Le Mans Master
Joined: Nov 2003
Posts: 5,772
Likes: 694
From: Maryland
St. Jude Donor '05, '09, '15
Re: please explain this (brucep)
I wonder if the reduced vibration is due to an increase in positive caster from the increased weight in the rear with a full tank of fuel. What is the caster setting? What is it with a full tank of fuel?
Racer
Joined: Feb 2003
Posts: 442
Likes: 45
From: Reading Pa
Re: please explain this (brucep)
I have a similar problem with my 66 327 4 speed roadster. On hard acceleration I occasionally get a shutter in the steering wheel.
I have replaced the clutch and pressure plate, and even had them balanced with my flywheel when I swapped the M21 for a M20. I had the driveshaft balanced and straightened, and installed new u joints. I also swapped the 4:11 rear for a 3:70. This condition was present ever since I have owned the car. The only thing that made any difference was when I had it aligned. The shake is not as severe since the alignment. I can lessen the shake if I ease up slightly on the throttle.
I just recently checked the rear spindle runout and it is ok. I haven't checked the halfshaft u-joints yet. I will have to take note of how it acts in relation to fuel level. I have wondered how the alignment might have affected this condition. Does anybody have any info on that service bulletin relative to camber or any other ideas?
Thanks
Brian
I have replaced the clutch and pressure plate, and even had them balanced with my flywheel when I swapped the M21 for a M20. I had the driveshaft balanced and straightened, and installed new u joints. I also swapped the 4:11 rear for a 3:70. This condition was present ever since I have owned the car. The only thing that made any difference was when I had it aligned. The shake is not as severe since the alignment. I can lessen the shake if I ease up slightly on the throttle.
I just recently checked the rear spindle runout and it is ok. I haven't checked the halfshaft u-joints yet. I will have to take note of how it acts in relation to fuel level. I have wondered how the alignment might have affected this condition. Does anybody have any info on that service bulletin relative to camber or any other ideas?
Thanks
Brian
Race Director
Joined: Jan 2003
Posts: 17,659
Likes: 3,666
From: Central Arkansas
Re: please explain this (66ragtop owner)
Maybe it's a slight U-joint (driveshaft) misalighnment that is improved with a full load of fuel and slightly lower heigth in the rear. Seems like a long shot that it would be that sensitive for what couldn't be a very big change in U-joint alighnment - but who knows? Good luck. :seeya
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Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 764
Likes: 13
From: Harvard MA
Re: please explain this (DansYellow66)
What about a worn transmission tailshaft bushing that gets "unloaded" when the driveshaft postion changes slightly? I replaced the front yoke because it had visible wear, but not the tailshaft bushing.
Racer
Joined: Feb 2003
Posts: 442
Likes: 45
From: Reading Pa
Re: please explain this (brucep)
My tailshaft busing is new, plus the shake has been the same with 3 different transmissions in the car.
I drove it again today and the shake is very visible in the steering wheel. You really don't feel it in your seat or the driveline, but alomost all in the steering wheel. Also trans and engine mounts are new.
I am interested in any info anybody has about the alignment settings causing vibration on acceleration.
Thanks
Brian
I drove it again today and the shake is very visible in the steering wheel. You really don't feel it in your seat or the driveline, but alomost all in the steering wheel. Also trans and engine mounts are new.
I am interested in any info anybody has about the alignment settings causing vibration on acceleration.
Thanks
Brian
Racer
Joined: Feb 2003
Posts: 442
Likes: 45
From: Reading Pa
Re: please explain this (JohnZ)
The mounts are OEM type rubber. It is definitely not an engine miss, it pulls strong and smooth all the way up the RPM,s. I'll try to list the alignmet specs per the print out.
left front right front
actual before actual before
camber 0.5 0.7 0.7 -0.4
caster 1.0 1.3 1.2 0.1
toe 0.26 0.39 0.25 0.38
left rear right rear
actual before actual before
camber -0.7 -3.2 -0.4 -2.6
toe 0.11 -0.21 0.12 -0.37
Thanks to all for your input.
Brian
left front right front
actual before actual before
camber 0.5 0.7 0.7 -0.4
caster 1.0 1.3 1.2 0.1
toe 0.26 0.39 0.25 0.38
left rear right rear
actual before actual before
camber -0.7 -3.2 -0.4 -2.6
toe 0.11 -0.21 0.12 -0.37
Thanks to all for your input.
Brian
Racer
Joined: Feb 2003
Posts: 442
Likes: 45
From: Reading Pa
Re: please explain this (66ragtop owner)
Looks like my specs didn't come out like I typed them. They should read like this. The first set of numbers after camber are as follows. left front 0.5 is the actual(new) spec and 0.7 is the before spec. right front 0.7 is actual and -0.4 is before. They read the same way for caster, toe and again fro the rear. I hope this makes sense.
Thanks
Brian
Thanks
Brian
Instructor
Joined: Sep 2002
Posts: 227
Likes: 0
From: Marysville WA
Re: please explain this (brucep)
As long as were throwing things out.....Steering wheel vibration on acceleration....weight shift off the front wheels.....make sure the basics are not overlooked... be sure the front tires (if belted) do not have a broken or shifted belt.
Intermediate
Joined: May 2002
Posts: 49
Likes: 0
From: Kanata Ontario
Re: please explain this (66ragtop owner)
Hi Bruce, this may or may not help, but it sounds like you can narrow it down pretty quickly. If you don't feel the vibration in your hand on the shifter, or in the seat of your pants, then it's highly unlikely to be anything other than front end related. I think you're on the right track with the full tank of fuel. Why don't you get a set of long bolts for the rear spring, and play with the rear ride height (simulate the effect of a full tank of gas). You can probably do two extremes fairly quickly, and see if that has a real effect. Then get your alignment guy to read the alignment on the front end with the two extremes (assuming, of course, this works :confused: ). Good luck, I hate these mystery vibration problems.
Bruce
[Modified by 63bruce, 11:44 PM 4/25/2004]
Bruce
[Modified by 63bruce, 11:44 PM 4/25/2004]
