I just did rear ujoints, driveshaft ujoints and rear bearings.

I did install the drive shaft 180* out, so that's been fixed.

What I don't remember is if there is an indexed position for the halfshats... I get this vibration at 72 mph. It's a low, distant rumbler| I have a spare driveshaft... and may just redo it... there is reference in the book that spurs and barbs on the yoke will disrupt operation, leading to vibration.

Does the drive shaft have a front and a rear? If so, that could explain a lot. I realized after the fact that the ends got swapped.

I torqued the bolts on the spindles to 200 ft-pds...

Also, new tires! BFG g-force KDW. The Kumho's were dead... they were nothing but noise factories. There was little change in the vibration from before and after tires, so it's in the drive line.

Thoughts?

Did you posision the black dot on the shaft 180 degress from the yellow dot on the pinion yoke?

There's some prop shaft balancing methods in the book.

No index on the half shafts.

The pinion end is where I had my first problem.

Fixed that one real quick... it was out 180.

But the front? And is there a front or back to the drive shaft?

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I don't think so, nothing in the book. And that really shouldn't affect anything.

Not that it pertains to the C4 but on C2's, there's a balance weight at one end of the shaft, the cars left the factory with that weight usually pointed towards the rear end but some had it pointed towards the trans.

on both my drive shafts, there is a weight, 180* out from the rear yoke... but its still shack'n back there...

Time to run it on jack stands or a lift, try the hose clamp thing. At least that doesn't cost any money.

Anything get bent or running O/R ??

I don't think anything got bent...

I am going to do some testing regarding the driveshaft... that's the wild card.

Did u hav this issue b4 u disassembled the drive line ?

nope... had noises... but that was to be expected. old bearings, old tires... but no vibrations.

I still think it's the drive shaft...

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Did u double check ur installation,sounds like something is off center ??

I am sure that's the issue... either off center or not indexed right.

The biggest concern is the driveshaft and its alignment. very important with the C4... Time to fiddle, just won't happen this week!

did you happen to take the c beam lose when doing the drive shaft ? if so ck you measurements up front that could defiantly cause it .if you turned the driveshaft around while doing the u joints i would put it back as it was .bet it is one of those 2 things .one last thought .ck the tq on thwe mounting straps on the 1/2 shafts . i had a couple work loose after doing u joints or i had a brain cramp and didnt tighten them properly

Brad - your confirming what I was thinking.

The driveshaft is in backwards. The C-beam is torqued, but could be out of alignment. I just don't have the blocks to do that with.

I have the exact same problem, vibration starts at @ 72 or so MPH and climbs/roars from the rear.

I plan on taking my half and drive shaft to have the balance checked in case I twisted something back when I twisted the SCAT crank on a drag launch.

that takes skill to twist a crank, dude.

I never would have believed it, it was the last thin I tested, begrudgingly, I took the crank to the guy that balanced everything and he brought out my balance card and assured me that he did balance the crank to neutral and he was amazed that it was off several grams.. it was a 5140 SCAT not a 4340, he offered to balance everything again for free but I told him to keep the crank, I ordered a 4340 Eagle

I has the ZF 6 speed with a 2500 RPM launch at a prepped drag strip, Indianapolis Raceway Park, home of the US Nationals. The ZF would not come out of gear, I had to pound the shifter to get it out of gear. And the car has vibrated ever since.

It is more of my crappy luck than it was monster TQ, although I had 460RWTQ, can't explain it, I blame Mr. Murphy

That makes me wonder if you didn't bend something inside the gearbox. I would ask ZFDoc.

I bought the TKO after that and the vibration stayed, so it has to be the half shafts, drive shaft or maybe the bearings in the pumpkin since the guy that installed my 3.42's only put the gears in without changing the bearings, but my car only has 93k miles on the body,

Sunday I will pull the shafts and have them balance checked, if it is not that, I'll pull the pumpkin and have it looked at.

i have some measuring pieces that bill made for me to locate the c beam perfect in the tunnel. if you need them just pm me your mailing address and i will drop them in the mail for you .

pm'd! Thanks!

I just realized something about this vibration... it seems to be vehicle speed dependent, not engine speed.

Follow... if the vibration starts at ~72 MPH, in 5th gear, why doesn't it go away in 6th? If anything, it's getting worse.

Now, is this the nature of the double overdrive? Or is this telling me the vibration is in the rear suspension, and it's lateral to the car and not longitudinal?

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Everything from the trans tailshaft back is spinning at the same RPM @ 72mph no matter what gear you are in.

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If something was loose in the suspension - worn bushings, loose bolts, etc. it may increase you feeling the vibration, new bushings, tightening may decrease your feel of a the vibration, but it won't fix the vibration.

yea... duh... only thought that part of the way through...

hand me my sign.

I swapped driveshafts... No chance to test drive, so I will update tomorrow.

I think it's fixed! The old shaft, with properly installed ujoints and some luck!!! the vibration seems to be gone. Got up to nearly 80 and nothing odd. Lotsa cruise at 70+ in 6th, nothing abnormal!!

Good to hear.

well... the vibration comes and goes at speed... more pronounced in 6th gear than 5th.

It could also be an indicator my motor mounts are toast, which wouldn't surprise me. I have newer ones waiting to go in.

I suspect whatever vibration is left is a result of burrs on the halfshafts causing the ujoints to be overly tight. I will more than likely pull the half shafts next weekend and redo the joints, just to be sure.

Seems strange that the backfire issue happened at the same time.

How did you align the balancer?
(it's NOT keyed for the NOOBs)

the balancer? jeez, that's 3 years ago. I never touched it in this exercise.

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Couldn't be the balancer anyway because the vibration varies with road speed not engine speed.

but the 6th gear thing has me curious...

all I know is this: I have a fresher LT1 just waiting to be dumped in. Do that, and I will fix other ills... AC, etc.

Could it b something in the transmission or converter?

manual trans.

could be in the flywheel, I need to review the TSB on that.

I'm going to go back to what Bill said. The flywheel is tied to the motor. The vibration would vary with motor speed not road speed.

Mike

today, on the drive home, between the vibration and the stumble... ugh...

I will update the stumble in that thread.

However, the vibration is STILL in the rear suspension. I am going to do some reading, but either I still installed the drive shaft 180* out, or, the rear diff half shafts are binding.

I will learn more tomorrow.

That was most interesting... at lunch, the vibration started to feel like a wobble...

And tonight, on the way home, the wobble became a loud BANG! followed by a tinkling sound... I limped to a side street and called a tow.

Got home, jacked it up and found that the front driveshaft ujoint was sheared clean off!!! The cap on the other side is what I heard falling off.

WOW!!!

Damn, Andy

Get some pics if you can.

I will as soon as I get the shaft out. That should be tonite. It's not super hard to do... just annoying I need to go in for the third time.

Glad you got the car home OK. So maybe this was either the cause or result of the vibe?

At this point, Flyboy, I have no clue... none what so ever.

I was hoping the peanut gallery had an idea!

Count yourself lucky.

Could have been a lot more damage

Was that one of your new U-joints? Same thing happened to me once when I "borrowed" my dad's car many years ago (a '68 Chrysler). In my case it was probably the result of winding it out to 70 in first gear too many times.

Brian - you are so right!!! I was barely moving - 40? - when it quit. No body damage, no drive shaft damage (that I can see). I got away with a $30.00 fix.

Brad - yes, new ujoint. And I wasn't hammering on it!

Sheesh, they don't make parts like they used to!

@Brad - you may be right!!

Ok... no work tonight. the weather is a bit iffy. Get this - the remnants of a hurricane are floating of shore of Los Angeles!!! That does not happen much.

Tomorrow I should knock it out.

I'd be inclined to try a new driveshaft between the vibration and u-joint problem.

Matthew

I already tried that... I went back to my original.

Point of reference: NO VIBRATION EXISTED BEFORE I DID THIS PROJECT.

Which means:

1. The replacement front ujoint reintroduced a vibration.

2. The halfshaft ujoints are bound up and need to be reinstalled.

3. The new bearings, the ones I bought from the racer guy (Tommy Morrison, IIRC), could be faulty.

4. cbeam alignment has bit me in the ass.

5. God hates me.