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Unread 12-17-2010, 07:16 AM   #31
Unlimited04
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Quote:
Originally Posted by cpleasant View Post
I'm currently getting a cheap used rear ds to see if it changes anything. If not I'm going to try some adjustable rear control arms.

In all, I'm in the same boat as you.
I'm still dealing with the vibes right now. mine relates entirely to the rear driveshaft. remove the rear driveshaft, it goes away completely. Driveshaft was completely rebuilt & balanced by the best shop in town. Pinion nut & t-case output nut are torqued to spec, gear pattern looks good, zero pinion slop.

I've tried 1° up - 3° down, in ~0.5-1° increments in pinion angle...little change. Currently at 2° down, with the UCA's at slightly different lengths, and there is little change. Above 55mph, it's less pronounced than it was when I posted this thread, but maybe only decreased by 20%...still very annoying above 68 mph...or maybe I'm just getting used to it.

At this point the only idea I've got is to wait for something to fail and replace it.

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Unread 12-17-2010, 07:42 AM   #32
hustler905
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I have this issue too.

A local guy was selling a used stock rear driveshaft with new u-joints, so I picked it up and the vibes are a lot better. I might be way off track, but it seems to have a tighter fit on the slip yoke (my TC is stock, I have no lift).

The worst it ever was involved poly motor mounts, cold weather, an engine skid, and the old driveshaft with old u-joints.

It's better now with Centramatic wheel balancers, rubber motor mounts, engine skid pulled for the winter, and the other DS.

What I'm getting at is that it might be a cumulative effect of vibe-increasing mods amplifying something that was there all along.


Edit: I'm going in for a 4.88 re-gear in the next 3-4 weeks. If this works as I think it works, I should get the driveline vibes at a lower speed? After the re-gear I will have new front axle shaft joints, a rebuilt front drive shaft, 2 month old joints in the rear shaft, and fresh bearings everywhere. I can update after that.
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Unread 12-17-2010, 07:56 AM   #33
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Quote:
Originally Posted by Unlimited04 View Post
I'm still dealing with the vibes right now. mine relates entirely to the rear driveshaft. remove the rear driveshaft, it goes away completely. Driveshaft was completely rebuilt & balanced by the best shop in town. Pinion nut & t-case output nut are torqued to spec, gear pattern looks good, zero pinion slop.

I've tried 1° up - 3° down, in ~0.5-1° increments in pinion angle...little change. Currently at 2° down, with the UCA's at slightly different lengths, and there is little change. Above 55mph, it's less pronounced than it was when I posted this thread, but maybe only decreased by 20%...still very annoying above 68 mph...or maybe I'm just getting used to it.

At this point the only idea I've got is to wait for something to fail and replace it.
What kind of control arms do you have I can't remember? Do they have solid bushings, poly, or rubber? Cause when I went to solid motor mounts on my Mustang it changed the whole way the car felt. If you control arms are solid you could be feeling a vibe from the engine that pulses through the drive train and you would only be able to feel where there is a solid connection to the body. Since motor and transmission mounts are rubber they would absorb the vibes. Since the engine spinning a higher RPM on the highway might be where it is coming from. My Mustang when it hits 2000 rpm the engine lets off this vibe that is different then any other rpm. I can drive the car without looking at the tach cause I am so used to the vibe I know when I am at that rpm.
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Unread 12-17-2010, 08:34 AM   #34
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Quote:
Originally Posted by Stang5lgt View Post
What kind of control arms do you have I can't remember? Do they have solid bushings, poly, or rubber? Cause when I went to solid motor mounts on my Mustang it changed the whole way the car felt. If you control arms are solid you could be feeling a vibe from the engine that pulses through the drive train and you would only be able to feel where there is a solid connection to the body. Since motor and transmission mounts are rubber they would absorb the vibes. Since the engine spinning a higher RPM on the highway might be where it is coming from. My Mustang when it hits 2000 rpm the engine lets off this vibe that is different then any other rpm. I can drive the car without looking at the tach cause I am so used to the vibe I know when I am at that rpm.
I've got Rokmen control arms - Clevite bushing on one side, Currie JJ on the other. I had them on before the CV shaft, before the regear, and with poly MML. I also ran the CV shaft before the regear, with the poly MML, before the regear with no vibes. Poly MML has actually been on for ~3-4 years with no vibes...even up to 100+mph (which should put the shaft spinning similar speed to me now at 65mph, if not more). Only thing that changed was the regear & rebuild the rear shaft.

I should have some time sunday or monday if you'd like to ride with me or drive it. I love the way it drives, except for this damn vibe.
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Unread 12-17-2010, 08:45 AM   #35
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Quote:
Originally Posted by Unlimited04 View Post
I've got Rokmen control arms - Clevite bushing on one side, Currie JJ on the other. I had them on before the CV shaft, before the regear, and with poly MML. I also ran the CV shaft before the regear, with the poly MML, before the regear with no vibes. Poly MML has actually been on for ~3-4 years with no vibes...even up to 100+mph (which should put the shaft spinning similar speed to me now at 65mph, if not more). Only thing that changed was the regear & rebuild the rear shaft.

I should have some time sunday or monday if you'd like to ride with me or drive it. I love the way it drives, except for this damn vibe.
Monday will probably work. I build axles pretty much full time at home now so I am always around. I understand you had the arms and sye before. But what I am saying is the engine never revved that high before at that speed. Bring it by I will take ride with ya.
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Unread 12-17-2010, 11:03 AM   #36
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Tough one!

Probably a dumb question on my part but are you absolutely sure you are getting correct DS/pinion angle readings? If you say you went 2 degrees down (BTW, how do you do that degree sign on the keyboard?!) and it helped, maybe try a few more degrees?


One of my old setups had a very similar pulsating vibe. (RE3.5, SYE, D35 4.88 gears, 33s). I never did track it down and it would almost go away sometimes and sometimes it would be very noticable. I just figured at the time it was the harmonics of everything. In early '08 when I switched to the current rear axle and t-case (same lift and gear ratio), it took a little playing with the pinion angle but now it is smooth. I *think*, especially with a rubber bushing on the control arm end and any "slop" anywhere else that it may affect the pinion angle when driving down the road just enough to vibe. My 241 T-case still has the factory harmonic dampener on it, not sure if it is helping or not but might be worth mentioning.
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Unread 12-17-2010, 12:02 PM   #37
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Quote:
Originally Posted by WAC_Jeeper View Post
Tough one!

Probably a dumb question on my part but are you absolutely sure you are getting correct DS/pinion angle readings? If you say you went 2 degrees down (BTW, how do you do that degree sign on the keyboard?!) and it helped, maybe try a few more degrees?
Yup degree measurements are correct, taken in the same exact spot every time. Digital angle finder from harbor freight, with a nylon washer and a rare earth magnet to hold it to the u-joint cap.

here's an example:


This is before regear & shaft rebuild...you can see the HP D30 in the background (no vibes in other words)

The keyboard sign is Alt+num pad 248 (thank mrblaine for teaching me that one)

EDIT: It's also not the tires...those were road force balanced and rotated...no change.
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Unread 12-17-2010, 12:12 PM   #38
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The º is option and 0 on a Mac.

I don't think there is much else to balance ... sounds like you've done all of it.
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Unread 12-17-2010, 03:10 PM   #39
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I have a similiar vibe in mine though it doesn't sound as pronounced. One of the things that was recommended to me was to get my tires road force balanced. I know you said the vibe goes away when the rear driveshaft is removed but could that be because one of the rear wheels is out of balance and it stops vibrating when there is no power to it?

Maybe you could try swapping your front wheels to the rear and see if that changes anything?
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Unread 12-17-2010, 03:35 PM   #40
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I have the same type of issue on 4.88's as well. It was fine then all of a sudden it was there. I got some water in it and have changed the fluid a few times. I also have a brand new Tom Woods shaft in the rear and the front was only rebuild about a year ago. Its definetly coming from my rear axle because I can hear it behind me. Im also running the balance beads in the tires so they are balanced correctly.
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Unread 12-17-2010, 03:50 PM   #41
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went to 4.56's and a very similar problem

since then i have changed sye's (my hack and tap would actually wobble) front ds, rear ds, front control arms to setup the pinion, re set my rear pinion, as well as torqued everything down. my vibe is almost a resonating one, it comes and goes at lower speeds, but becomes a real driveline vibe at 60 plus, the last things i have left to change that i can think will help will be motor mounts, trans mount, re torque-ing the t-case outputs and modifying my exhaust hangers to get the cat off my tub. Im also sending my driveshaft back in to tom woods to rebalance it as well as lengthen it.

good luck, i've been dealing with mine since my regear in june, and with a 1hour college commute each way everyday it hasnt been the best of fun, im just hoping and praying i can resolve it all before the start of next semester
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Unread 12-17-2010, 05:12 PM   #42
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Quote:
Originally Posted by Stang5lgt View Post
If the rear axle isn't making any noise it shouldn't be the problem. If it was the rear axle I think you would have still noticed it when the shaft was off.
I understand that this post is a few month old, but I must point out that this is completely incorrect. Removing the rear DS takes the load off the rear gears on the drive side, thus removing the vibe. I would be willing to bet that it is a bad install. There is either too much backlash, incorrect pinion depth or not enough preload on the carrier bearings.
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Unread 12-17-2010, 05:25 PM   #43
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if you measure the pinion angle from the front face of the diff, the flat spot with the hole in it next to the diff cover on each side forget what its called, do u get the same angle as measuring from the ujoint cap?
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Unread 12-17-2010, 06:59 PM   #44
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Sounds like something in the t-case is bent a miniscule amount or the case is not torqued properly...If you remove the rear DS and the problem goes away. That is IF your tires arent the problem and everything else is good to go.
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Unread 12-17-2010, 08:44 PM   #45
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Originally Posted by williambmac View Post
I understand that this post is a few month old, but I must point out that this is completely incorrect. Removing the rear DS takes the load off the rear gears on the drive side, thus removing the vibe. I would be willing to bet that it is a bad install. There is either too much backlash, incorrect pinion depth or not enough preload on the carrier bearings.
I'll have him check it on Monday. Thanks!
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