Hitch

Well it's time to try and play diagnose that vibration.. The last time ended up with lots of smoke coming out of both side pipes I need to learn to baby it a little more .. The motor is bigger and badder this time and should take some more abuse from me. Here is the back story.

Three years ago I pulled the motor and tranny to rebuild the motor and put a 5 spd in. While doing so I rebuilt the complete front suspension. No problems no vibrations and she was strong to at least 135. Then two years ago I disassembled the rear suspension and rebuilt the differential and the trailing arms. I replaced the halfshaft u-joints, strut rod bushings, shocks, shock mounts, crossmember cushions and the front differential bushing. Then walla I picked up a high speed vibration.

So I've been changing out components and going back thru what I had done. I have changed out the driveshaft and halfshafts and this still has not correct the problem. I jacked the transmission up and am using a poly mount to see if by putting in the new snubber cushion it changed my drive line angle. I've put different tires and wheels on the car and still nothing. So I'm down to Trailing arms, Differential itself or the snubber/front differential cushion. I'm currently leaning towards the snubber cushion is to thick.

If the snubber is to thick it might be pushing the differential yoke angle down thus this is what could be causing the high speed vibration.. Any help is always helpful b/c this one is/has been driving me crazy.. Oh and by highspeed I mean anything over 75 mph.. I know I shouldn't be driving that fast but.. I do.. Dave

vintagecorvette

Have you had the frame checked? Maybe you need a 4 wheel alignment? I see you posted that you changed out you TTII for steel rims and caps. Were the Steel rims 100% balanced?

oWEN

Hitch

I thought that it could be an alignment problem too and took it to two different shops. The first aligned it after the rear suspension rebuild and the second checked it. I had the steel wheels checked before the mounting of the gold lines. I then had them ROADFORCE the wheels and tires after mounting and they were well within spec.. I'm so tired of this stinkin vibration.. Keep em coming....

Vette-66

Can you describe the vibration a little better?
Is there noise associated with it?
Does it seem to be coming from any particular car position?
Does it seem similar to an out of balance type vibration or U-Joint type vibration?
does it always start at the same speed and does it end?

Trying to gather info,
Chuck

Hitch

See I knew I left something out of my post. I can accelerate into the vibration and it starts around 75-80 mph and it continues the faster I go. If I press the clutch in it the vibration remains, well at least until the car slows below 75-80 mph. It is a seat of the pants vibration and I can also feel it thru the gear shifter. It also feels if it's coming from the back of the car. There appears to be no noise associated with it at all just a major vibration.. I'm so confused... There's just not much back there... Dave

Plastic Pig

How are your side pipes mounted ? Are they insulated from the frame with rubber ?


I had a customer that had the same type of vibration that was only in 4th gear. The side pipes were mounted direct to the frame with washers and it set up a resonance/harmonics type vibration.

I've had these types of vibrations before but it is usually RPM related and you can feel it to some extent in every gear at the given RPM.

This guy drove the car from Jersey to Fl. a few times a year and it drove him crazy. The car had it only at highway speeds in fourth gear. We put an real mount kit in and it went away.

Shot in the dark but what the heck.

You don't think your old neighbor's coming over and prying your wheel weights of at night do you ?

Hitch

Bob,
You have me thinking but I do have them mounted with the rubber isolators. I can also feel it in every gear when I'm above 75-80 mph. So that would be 3rd 4th and 5th.

As for the neighbor... He's not that smart..

60vett

Dave, I always like it when you and Duntov exchange messages. Alec

Hitch

Alec you mean our mocker....

Plastic Pig

Are you mocking me.................... That will cause severe repurcussions.

Vette-66

Have you tried swaping tires and wheels, moving the rear to the front and front to the rear. then cross mounting. Just to make sure the vibration does not move around.
you are positive it is not a U-joint (driveshaft or half shaft)?
have you swapped ends of the drive shaft?
has the angle of the trans U-Joint and rear-end U-joint changed? (you did mention a 5 speed)
Did you change the rear leaf or shocks?
are you sure there is no un-necessary brake drag?
does it feel like any of the tires are vibrating or it is some other moving part?

again, just fishing
Chuck

Hitch

Thanks man!

60vett

No, just in general. you both are fun to watch. Duntov always gets me rolling on the floor when he gets going! as far as help with this thread, my 60 is hard pressed to get above 75 with 4.56 rears, so I am just standing by.

Jack60

If it isn't RPM related, but speed related??? Did you change ride height that changed air flow over car, anything loose that the air is catching at speed to cause resonance/harmonics type vibration.
I fly to Raleigh Monday, staying in Garner for work till Friday, another set of ears mite help.

Hitch

It's definately speed related... If you want a better way to spend an evening then sitting in a hotel room I'd be greatful for another set of eyes and ears... I don't live very far from Garner... Dave

Jack60

I'll be in Tripps every night for dinner, I'm the old hippy at the bar.
My cell 410-596-3624

rgs

Mis-matching of the angle of the transmission to the differential certainly will cause exactly what you describe. The best way to check this is with a magnetic angle finder. Remove the driveshaft and the yolk from the driveshaft. Re-insert it into the transmission tail shaft. Position both the transmission yolk and the differential yolk exactly perpendicular. Use a level if necessary. Check the angle of each. They should be EXACTLY parallel (complementary angles). If not, shim either the tail of the transmission, or the nose of the differential till they are. Also, check the parallel alignment of the output shaft to input shaft along the car centerline. Rotate the yolks to exactly horizontal. I clamp a pair of straight lengths of square tubing to each yolk and measure the distance apart at each end. Shift the transmission tailshaft as necessary. They must be exactly parallel also.
It is an interesting phenomenon. The angular velocity of a rotating shaft after a universal joint will accellerate and decellerate proportionally to the angle of deflection. An exactly equal and opposite universal joint will reverse this accel/decel resulting with a restored constant velocity, but they must be both in phase, and exactly opposite. Setting the output shaft/input shaft parallelism is half of it, the other is to verify that they are in phase by verifying the yolks on each end of the driveshaft are exactly inline with each other. I use a pipe the inside diameter of the yolks. I clamp the driveshaft in a pipe vise with one end close to perpendicular. I place the pipe through a yolk and measure the angle the yolk is attached to the driveshaft with the magnetic angle finder. I duplicate this at the other end and the angle should be exactly the same.
An interesting historical point. The first 63's had a problem with vibration that was tracked back to the production of the half shafts not having the yolks aligned.

wombvette

WoW, man you lost me. How could you ever get a drive shaft really aligned back there? The shaft is not exactly level and the the transmission is offset with the body with the rear being basically in the center. Not exactly though, it is offset the amount of the ring gear and pinion. So you have an angle both vertically and side to side. Certainly U-joints are capable of handling that much especially since it was designed that way and it is basically bolted solid with the independent rear of a corvette. Deflection in this design is nothing like the deflection of the driveline in a normal solid axle car. I will now offer my two cents, for what it is worth. First, I would change the snubber cushion to the original style. I know that the urethane bushings will change the angle and have been known to make the U-joint contact the frame. If nothing else the urethane mounts transfer more vibrations to the frame of the car. Secondly, I would look at the alignment of the rear and the relationship to the rear axles. Too much downward angle of the half shafts have been known to cause the vibrations that you describe. Thirdly, If you are unsure of the balance of the shafts, I would definitely have them balanced to make sure.

rgs

Simply put, the input and output shafts need to be parallel. They can be offset both horizontally and vertically, but need to be parallel. I wouldn't change a thing till I knew what I already had, hence take some measurements.

ctjackster

I have no technical advice to offer, but I do have some general experience on the matter of "I worked on this part of my car/boat/motorcycle, and now I have an issue, so I must have f-ed something up during that last project" - the conclusion [that the problem vibrtion has something to do with the work you did just before it appeared] is valid, but not exclusive. Don't be fooled into focusing just on what you worked on - my favorite example of this phenomenom is when my dad rebuilt the carb in his 1970 Opel Gt (a real Corvette wanna be if evr there was one) back when I was a kid - he did the job right, he was methodical, laid everything out, and put the car back together to specs, etc. - and then the car would not start at all once he put that carb back on. Had to be something he did wrong with the carb, right? Off it comes, re-rebuilt it, put it back on, still no go (did that a few times) - we never bothered to check on other basic tests (like spark at the spark plug wires?) because we were so sure of the cause being his faulty work on the carb.

Turns out the distributor had decided to develop a short by the points - a simple check for spark at the spark plugs would have told us something else was causing the problem.

Good luck, you'll track the vibration down, just don't be so sure it relates to what you did in the rear, perform "standard" diagnotics as if it just appeared.