Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

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Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

October 11, 2015, 12:31:00 AM

So my Thunderbird has developed an annoying high speed vibration above 68mph. This causes the steering wheel to vibrate up and down between 68 and 80 mph. The vibration is present above 80mph but the harmonics of it smooths out and it is not as violent. It has to be driveline related as:

I've moved the tires from front to back with no change.

I can Rev the engine to 5000rpm in park and it's smooth as glass.

The steering wheel does not shake side to side but instead up and down. Vibration can be felt in the seat as well. It's a rythmic wup, wup, wup feeling.

It does it with both the stock steel driveshaft (which buzzes with the 3.73 gears) and the aluminum driveshaft I normally run.

If the car is run on a lift the vibration is there but not as violent. There has to be a load on the rear wheels for the vibration to be present. The pinion bearing in the rear differential on the car recently started making noise. A lot of noise. The vibration is worse after accelerating above 65mph and letting off the throttle. Again pointing to the pinion bearing or gears. No perceptible vibration is felt on surface roads (below 60mph) only at highway speeds. I've tried shaking the pinion with the driveshaft installed but it's tight. However if I rock the drive shaft from side to side with the transmission in park and the parking brake applied it loudly clunky side to side about .5 inch or so. The clunk noise is coming from the differential. The awful noise when running is definitely coming from the differential, verified by a stethoscope. Is it possible for a bearing or ring and pinion issue to cause a noticeable vibration?

Here is the noise from the pinion bearing/differential at low speed (windows are rolled up).

YouTube video:

Here is the nice and steering wheel vibrating up and down on the highway (again windows rolled up).

YouTube video:

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #1 – October 11, 2015, 05:45:13 PM

I put the car on jack stands. I grabbed the pinion with the driveshaft attached and tried to wiggle it. It did not move and felt tight. I started the car and put it in drive. I let it idle and watched the wheels spin. The passenger side seemed fine. The noise is definitely louder on the driver's side. Watching the wheel it appears to have a slight wobble. I ran the car up to 70+ mph on the stands. It vibrated slightly, almost imperceptibly. When I let off the throttle there was noticeable vibration. I stopped the car. With it off I wiggled the wheel on each side. The drivers side squeaked when I tried to shift it. Is it possible that the axle shaft and bearing are jacked and the ring and pinion are fine?

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #2 – October 12, 2015, 03:50:18 PM

At this point though I'm just going to swap the whole axle out. The current axle is the factory 7.5" unit. Fortunately I happen to have an 88 Cougar XR7 8.8 rear axle sitting in my garage:D. The current 7.5 is factory stock except for a Traction-Lok carrier and 3.73 gears. I'm putting 3.73s, a 31 spline Traction-Lok carrier with carbon fiber clutches, and 31 spline axles in the Cougar XR7 8.8. I'm also replacing the bushings on the axle housing. I figure there is no point throwing money at the 7.5 rear when I've got an 8.8 in the garage.

All I know is it better not vibrate after the rear swap......

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #3 – October 13, 2015, 01:21:56 AM

Holy....well you get the idea. That is awful. Both videos. (Exhaust sounds great though!!! :hick:)
I was going to ask what the frequency was. But at 60-70 mph, the steering wheel shake doesn't correspond to the tires' RPM. And you ruled out the engine. Tranny tailshaft seem okay?

Maybe the 7.5 finally said enough of this mid 300-horse nonsense? That's interesting. You had 3.73's installed, so did I in the red cougar. Several years ago, I feel like both within a year of each other or so. Wasn't too long ago my pinion seal started weeping a bit but it didn't get bad and didn't continue. I think the shop did things right generally. It hummed turning to the right...maybe?? for two weeks initially then went away suddenly. It would also hum at about 90-100 mph and then go away above that. Don't know when that stopped entirely but these days there's no resonance there anymore.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #4 – October 13, 2015, 09:22:50 AM

My first thought was perhaps you'd thrown a balance weight off your drive shaft, but you said it happens with either shaft you use, so that's right out.

If the 8.8 is ready to swap in, and easy enough, GFI(go for it), and let us know!

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #5 – October 13, 2015, 09:29:14 AM

Quote from: ZondaC12;451751

Holy....well you get the idea. That is awful. Both videos. (Exhaust sounds great though!!! :hick:)
I was going to ask what the frequency was. But at 60-70 mph, the steering wheel shake doesn't correspond to the tires' RPM. And you ruled out the engine. Tranny tailshaft seem okay?

Maybe the 7.5 finally said enough of this mid 300-horse nonsense? That's interesting. You had 3.73's installed, so did I in the red cougar. Several years ago, I feel like both within a year of each other or so. Wasn't too long ago my pinion seal started weeping a bit but it didn't get bad and didn't continue. I think the shop did things right generally. It hummed turning to the right...maybe?? for two weeks initially then went away suddenly. It would also hum at about 90-100 mph and then go away above that. Don't know when that stopped entirely but these days there's no resonance there anymore.

The steering wheel shaking up and down corresponds to that awful noise. If it was a front wheel, front wheel bearing, spindle, or rotor issue the wheel would shimmy from side to side. Being that the vibration is lessened by accelerating and amplified by decelerating it points to something in the rear. It seems to be either the pinion bearings or an axle bearing. Transmission is fine and was rebuilt 5 years ago. Oddly enough accelerating/constant speed vibration is only very slight with the car on jack stands at speed. Letting off the throttle at 80mph on jack stands causes the whole car to shake. What ever is fubar in the rear needs the weight of the car on it to be really severe.

The 3.73 and Traction-Lok was the first mod I did to the car. That was 12 years ago. It used to have some slight gear whine on deceleration but it hasn't done that in years.

At this point I figure if it's the pinion bearing the rear would need a complete rebuild. New bearings, ring and pinion, and possibly axles. All those replacement parts cost more than the same components and a 31 Spline Traction-Lok carrier for the 8.8 rear. Plus I would end up with the same weak 7.5 rear end.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #6 – October 13, 2015, 01:01:28 PM

With the drivetrain loaded/bound-up due to acceleration and power being applied, things stay tight. I don't fully grasp the mechanism but obviously closed throttle causes opportunities on decel for the engine's output to roughen a little and so whatever slop there is, contributes. I'd be interested to know just what you find when you take that rear end apart. If you do.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #7 – October 14, 2015, 08:56:11 AM

Well I think the driver's side axle is bent/the axle bearing is toast. See here https://www.youtube.com/watch?v=AeicDZ8EaVU

I filmed the driver side axle followed by the passenger side axle. The driver side has a wobble when letting it spin with the motor at idle in drive and shakes bad when I let off the throttle at 75mph.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #8 – October 16, 2015, 02:32:21 PM

Just to verify but there is no way that vibration can be caused by anything in the front end correct? Everything in the front end (rack, rack bushings, inner/outer tie rods, control arm bushings, ball joints, strut mounts, struts, wheel bearings, and rotors) has been replaced in the last 5 years and has maybe 6K miles on it. The front end alignment is fine and even when vibrating the car tracks straight with no steering input. I did swap tires front to back with no change as well.

I just find it hard to believe that a rear end issue (bent axle, axle bearing, pinion bearing, etc) can cause a vibration that is felt like that in the wheel, dash, and seat.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #9 – October 19, 2015, 12:33:48 AM

At first I said "oh that looks okay" and THEN saw the actual decel part. ! I think the axle is alright...unless you smacked a curb? Bad pothole? I'm thinking bearing or the carrier.

I *did* drift into a curb with my 'Vic in snow thinking I was a badass and could shoot the gap. Chunk out of an AR Type 39 wheel and bent the and backing plate good. Above 10-15 mph, yeah whole car shook pretty good :hick: Differnent scenario but still the victim of really bad runout in the vertical plane.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #10 – October 19, 2015, 02:51:24 PM

Haven't smacked anything with the wheels, not even a pothole. I'm leaning toward an axle or carrier bearing.

I should be picking up the rebuilt XR7 8.8 tomorrow and swapping it in a few days later. After I do I'm going to break into the 7.5 and figure out what broke.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #11 – October 19, 2015, 03:18:19 PM

Definitely let us know! Good luck! Thankfully you have rust-free components underneath to work with :) The convenience simply can't be overstated....

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #12 – October 19, 2015, 04:05:33 PM

Yeah the rust free thing helps. The bolts on the control arms should just spin right off. Heck the control arms are still that factory grayish color.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #13 – October 21, 2015, 10:27:22 AM

Well I picked up the rear this morning. I'll hopefully do the swap in the next few days and report back. I'm hoping I don't break this rear end as it's an 88 XR7 8.8 with 3.73 gears, 31 Spline Traction-Lok with carbon fiber clutches, and 31 spline Moser axle shafts. Before I race the car again in the spring (track closes this weekend and there is no way I'll break in the gears by then) I'm going to slap some CHE upper and lower arms on the car as well as quad shocks. I don't want wheel hop tearing up the new rear end :hick:.

Vibration shakes steering wheel up and down. Speed related. Pinion bearing?

Reply #14 – October 21, 2015, 01:17:11 PM

With an automatic if it hooks up OK you probably shouldn't hop much. Do you run a sticky tire on it?
In any case that is a stout 8.8 setup, black cougar has that exactly. Well, I don't know about the clutches but there is very little slippage. It feels like it's binding going around turns. I was told it had an aftermarket Eaton carrier.