mattkoly

I recently did a clutch swap on my 94 cobra, everything is smooth up to 80 then it’s like earthquake city and I can feel it in the rear for sure. my thoughts are it’s got to be from tranny back because it doesn’t change with motor RPM just speed (driveshaft RPM).

So I understand that I could have installed my driveshaft out of phase 180 degrees, what I don’t understand is why it works that way. I have found a couple of posts here and else where that ask the same question but no real answer as to what the balance weights on the driveshaft "balance out" up or down stream.

Does anybody know what is balanced out by driveshaft that would cause vibration if put in incorrectly phased?

67mustang302

Are you sure you didn't somehow knock a weight off while it was out, or forget to tighten the trans mount, and have you checked the u joints?

mattkoly

U joints are new, yes i could have forgotten to tighten a trans mount, that was something I was planning to check but it's not really likely and i will double check the weights but I remember checking to see if they were fastened well before I put it back in.

Tony71502

Well, there are 4 diff positions you could have installed the driveshaft, GM's have two. But regardless, that wouldn't make a difference.

grnstang

if you don't put the shaft in the position that it came out of isn't that out of balance? and cause a vibration? or can you put it in whichever one you want

Tony71502

The driveshafts are balanced outside of the car, therefore there's no way it could have a specific orientation. Just like crankshafts, they are balanced on a machine. I had the driveshaft in my chevelle shortened, balanced in the driveshaft shop, and just threw it in there. No problems. Also, I've pulled the driveshaft out of my mustang when replacing the clutch, and also when installing a new transmission. Once again, we just threw the driveshaft in the car and ran it. No poblems. And I take it well over 80, almost everyday on the way home from work on the highway. At least I did last year before winter hit. It's about to get the same abuse again.

grnstang

i have a vibration at high speeds but i think its because i need an alignment, my tires have feathered edges; and i am willing to bet the guy that balanced my wheels and tires didn't do it right

Tony71502

By feathered edges do you mean the inner sides of teh wheels are worn? The only major vibration that I had above 80 in my car, and I mean serious enough to shake the steering wheel, was a bad ball joint. My buddy has a bad vibration in his car but that is because his transmission has a bad tailshaft.

But, if your insides of your tires are chewed up, you may have an alignment problem and not a tire balance problem, even though the wearing of the inside of the tires will cause them to become unbalanced. I had to buy adjustable caster/camber plates for my mustang, even with stock front suspension, in order to get it aligned properly, so it would stop chewing up tires that were balanced when they were put on the car.

mattkoly

I agree with you Tony71502, that is why I'm having a hard time grasping the whole rotate it 180 or even 90 degrees and having vibration go away. that said, i did rotate the driveshaft and had little results.

One thing I did notice is a had a lot of play in my pinion and it changed with rotataion, so in some spots it had about 10-15 degrees of play and then in others it had very little. could this cause my vibration?

AdderMk2

^^ that could easily be your problem. Have you ever had any rear end work done?