I'm picking up good vibrations...NOT

Gary Morris · #1 (**permalink**) 11-08-2001, 08:04 AM

Ok I need some suggestions for when I can dive into it. Back in June we removed and replaced my engine after having it fixed don't ya know. Put on a new flywheel..after having it balanced to the old one..new clutch etc..etc.... Been taking it easy for a few hundred miles...drives good...runs good. I have a little vibration through the shifter which does not seem to be any different from my old set up. I can rev to 5000+ rpms without any noticeable difference. Out on the road going through the gears everything seems ok...no more vibration than Iwoud expect from a stroked side oiler...........BUT now it's broken in and naturally I want to see if it will RUN! When I really put my FOOT into it from 2nd gear...by the time I hit 5000+ rpms the shifter is almost vibrating out of my hand....same with 3rd....and I'm not ready to hold in 4th to 5000+ to find out if it's still there. We did have the drive shaft out and not sure if we put it back exactly in the same location it came out of but that's about it. If I drive normally through the gears at normal speeds everything seems fine. It's just when you want to go to warp speed that it takes on a different attitude...........BUT it will run..yippeee!! Any suggestions?

Gary

Flyin_Freddie · #2 (**permalink**) 11-08-2001, 08:10 AM

Yo...Gary....sorry to here about your engine needing 'fixing', but Hey...it happens. I'm not expert mechanic...come to think of it, I don't even play one on TV. But, I've had way more experience than most, not as much as some.

When you had your driveshaft out, did you replace U-joints? Sounds to me that one of your U-joints may have packed it in. Had much the same problem with an MGB once...vibration at high RPMs, felt it through the shift lever, wouldn't do it until it was wound up pretty good. Your drive shaft may also need to be balanced, as well.

Just some ideas here...nothing concrete, but certainly some thiings to check when you're into it again. Anyone else....?

CobraEd · #3 (**permalink**) 11-08-2001, 08:31 AM

Even if just one of those tiny needle bearings in the U-joint caps gets lost during dissasembly/assembly, it can cause what you are experiencing.

Ed

Gary Morris · #4 (**permalink**) 11-08-2001, 08:35 AM

No we did not replace any u-joints...just took it out as a unit and put it back in, but it's somewhere to start.

Gary

acaskie · #5 (**permalink**) 11-08-2001, 02:11 PM

When I had a similar problem in a '66 Shelby Mustang with a 4-spd Toploader, it turned out to be an out-of-balance driveshaft. Of course the thing was about four and a half feet long. How an eight-inch driveshaft can get too far out of balance is a stumper, but I suppose it's possible. I would bet its the U-joints as well. --

Cobra20646 · #6 (**permalink**) 11-08-2001, 02:28 PM

Gary,
If I'm understanding your post, the vibrations are severe AFTER the engine has reached 5 grand or so. After shifting to higher gear (3rd), the vibrations are minimal until higher the revs are met agian right?
If that's the case, I'd rule out anything south of the transmission and look at that new clutch. Did you have the flywheel re-serfaced? Clutch plate located DEAD center? Good pilot bearing? All bolts loc-tited and torqued? Sounds like it's engine RPM related to me.
I've had U joints vibrate under acceleration, but they got worse as shaft speed went up and were independent of engine RPM.
- Jim -

Flyin_Freddie · #7 (**permalink**) 11-09-2001, 07:49 AM

Jim's note is pretty much on target, Gary... I should have thought a little more about what you wrote, Gary...if the problem was U-joints, then it wouldn't go away when you up-shifted. The drive shaft maintains the same RPM at the same speed. Therefore, whether you're in 2nd or 3rd, if you're doing 65 MPH your driveshaft is doing so many revs independent of the transmission, flywheel, clutch, pressure plate, etc. There's a formula for calculating drive shaft revs based on your ring and pinion ratio, but I think you get the picture. Engine RPMs are independent of drive shaft RPMs due to different gear ratios, 1st thru 5th. If your vibrations go away when you shift up, then it's not U-joints or driveshaft related, I wouldn't think.

I'd agree with Jim's comments on possibly the clutch disc, pressure plate, or other rotating mass ahead of the drive shaft.

Thanks, Jim, for making us rethink this.

Gary Morris · #8 (**permalink**) 11-09-2001, 08:37 AM

Thank you all for brainstorming for me. As soon as I can get some time I'm going to jump in and take it all apart. I'll let you know how it comes out.

Gary

It's still FUN

hound dog · #9 (**permalink**) 11-10-2001, 05:56 PM

Gary,
Another thing I found out this week after going a round with my engine machinist on internal vs. external balanced engines. If you have an externally balanced engine, and you probably do, the counterbalance weights on the harmonic balancer and the flywheel must be indexed together (aligned). Evidently the weights are used to ofset the throws on the crankshaft when balancing and if you index the flywheel wrong you can upset that balance. If you have the weight on your harmonic balancer you have to have it on the flywheel. Just another thing to check if you do a teardown. Have fun and post the fix!
H Dog