Update on driveline vibration problem

302Rover

Member
Hello all in Roverland,
a few weeks ago I posted about the vibration problem I've been having in my P6 with the Ford V8. Since then I've done a lot of testing and fiddling but to little avail. Here is what was done and if anyone has any further suggestions, please comment.
1. Put the car up on blocks under the rear suspension and removed the wheels, half shafts, and brake rotors.

2. Started the car, put it in 5th gear and ran it up slowly to 80 mph (yeah, a bit dicey, I know). Vibration started at around 57 mph and stayed at a fairly steady level, annoying but not severe, right on up to 80.

3. Used a digital angle gauge to refine the driveline angles but that did nothing to improve the situation.

4. Noticed that the prop shaft angle in the horizontal plane was fairly severe so built an adapter to move the front diff mount 5/8 inch towards the center of the car, thus getting better prop shaft alignment at the expense of half shaft alignment. No improvement.

5. Removed two 1/8 inch thick washers from between the cast iron halves of the damper system at the front of the diff pinion extension housing and clamped down on the 3 rubber 'disks'. This helped, reducing the amplitude of the vibration and increasing its frequency. The vibration now starts at about 64 mph and stays more or less steady on up to 80. Above that I lost courage with the car up on blocks and the speedo reading 80 mph. If all else fails, this could be acceptable yet still annoying.

6. Removed the prop shaft and took it to the best driveline shop in town. Duane The Driveshaft Guy spun it up and said it was in pretty good balance but he could do some slight improvement by replacing the ujoints with Spicer 'permanent lube, cushioned' u joints and rebalance. After doing this, he told me it was balanced as well as it could be and the best that he has ever done. At least I eliminated prop shaft balance as a root cause. Still no change on the car, however.

7. I replaced the half shafts and ran the car up to speed on the blocks again. No change, which is good news, thereby eliminating the half shafts from the equation. And to be on the safe side, I also had the brake rotors balanced.

8. So what I seem to be left with is the diff itself, which was salvaged from a 3500S. I have been told and read that the pinion extension shaft is suspect and a weak point. I'm wondering if it could be slightly bent or distorted, causing an imbalance at high speeds. Has any one ever come across that problem? Duane The Driveshaft Guy also pointed at the extension shaft as a possible culprit.

9. Classeparts do offer an improved pinion extension shaft and rebuilding the diff using that shaft could be an option, albeit pricey.

10. Another option might be swapping in a Jag diff such as Simon Owen did with his muscle car project. I do have access to a diff from an XJS. But the Forum archive thread covering Simon's project seems to be missing all its photos that were posted on Photobucket. What's happened there?

Right now I am very frustrated so any bright ideas, blinding insight, random thoughts, or anything else that could become "The Straight Word from the Golden Trough" would be greatly appreciated 8)

Cheers,
Tom
 
Hi Tom,

Don't forget that the Rover differential is not a limited slip, and with the car off the ground and running in gear, the two drive shafts within the diff will turn in opposite directions, thus creating an imbalance. On the ground however and under load, both will turn in the same direction.

Ron.
 
SydneyRoverP6B said:
Hi Tim,

Don't forget that the Rover differential is not a limited slip, and with the car off the ground and running in gear, the two drive shafts within the diff will turn in opposite directions, thus creating an imbalance. On the ground however and under load, both will turn in the same direction.

Ron.

Ron,
yes, right. The two wheels turn in the same direction, but at different speeds. But when all is said and done, I took the car out on the freeway for a test run and the vibration is still there. The problem I'm having, I think, is that I'm too close to this and need to step back a bit, view it from a different angle with the help of Forum members. So to that end, thanks for your thoughts.
Cheers,

Tom
 
Does sound like the diff maybe the culprit, however you mention that clamping the diff bracket affected the resonant point which may suggest some issues around mounting point rubbers or the bracket itself. Any other RV8 diffs about to swap out? another possibility given there is a resonance point is engine and gearbox rubber mounts though I think this maybe a bit of a long shot.

Graeme
 
I understand your frustration - my car behaves similarly. I've eliminated far fewer likely sources, have six UJs to fit plus engine mounting rubbers but the PO supplied two lumps of diff internals with the car giving no clear explanation for it. I do suspect the pinion extension on mine. Following with interest!
 
ghce said:
Does sound like the diff maybe the culprit, however you mention that clamping the diff bracket affected the resonant point which may suggest some issues around mounting point rubbers or the bracket itself. Any other RV8 diffs about to swap out? another possibility given there is a resonance point is engine and gearbox rubber mounts though I think this maybe a bit of a long shot.

Graeme

Graeme,
interesting that you should mention the mounts. There have been some posts regarding the 'wimpy' nature of the front mount support and I've been thinking about adding some structure to the front mount. I think that Simon Owen or perhaps someone else on the Forum did that but I've been unable to find any pics showing what was done. Also I do have a front mount for a 3500S which is huge compared to the 2000 mount. This could be another indication that the 2000 front diff mount simply isn't adequate for the job of transmitting the torque that the Ford V8 is capable of developing. Other than that, all mounting rubbers are new and OEM equipment, not aftermarket poly or some such thing.

So far I've been unable to find another diff to swap in. Rovers and Rover parts are very difficult to come by here in Southern California. Most of the good, rust free stuff has been shipped back to the UK due to lack of American interest in the car.
Tom
 
Tor said:
I understand your frustration - my car behaves similarly. I've eliminated far fewer likely sources, have six UJs to fit plus engine mounting rubbers but the PO supplied two lumps of diff internals with the car giving no clear explanation for it. I do suspect the pinion extension on mine. Following with interest!

Tor,
yes, the fact that the PO supplied you with a lot of spare diff parts may be a hint that he finally gave up on the problem and sold the car :? When you look at the drawing of the diff, one can see that the extension shaft is coupled to the pinion input shaft via a spline. I am beginning to wonder if the spline has worn to the point where it begins to 'rattle', thus causing vibration. Also if the shaft gets bent a little bit, it would create an imbalance that could cause vibration.

I did put a dial indicator on the face of the pinion extension shaft input flange and noted about 0.004 inch run out or 'wobble'. Don't know if this is within spec or not. Also there seems to be quite a bit of 'dead band' when one turns the pinion input flange. It moves about 10 or 15 degrees free play. Is this normal? Does anyone know what is acceptable? Part of this free play is probably in the diff itself, between pinion and ring (crown) gear and part of it may be due to a worn spline.

My next ploy may be to remove the pinion shaft extension housing and shaft for a thorough inspection. I wonder if any one else on the Forum has noted either spline wear or a bent pinion extension shaft? An esoteric question, to be sure, but worth asking.
Cheers,
Tom
 
Tom,

The diff is out of my car and won't be needed for quite some time. I am happy to let you "borrow" it to see if that will eliminate or confirm the diff as a suspect.

I am in Garden Grove and the diff assembly is with my mechanic is Bellflower - as far as we can tell it's in pretty good shape. Let me know.

Alan.
 
So Cal V8 said:
Tom,

The diff is out of my car and won't be needed for quite some time. I am happy to let you "borrow" it to see if that will eliminate or confirm the diff as a suspect.

I am in Garden Grove and the diff assembly is with my mechanic is Bellflower - as far as we can tell it's in pretty good shape. Let me know.

Alan.

Alan,
terrific! I would love to swap in your diff to see if that makes a difference. Could you contact me off list with your contact info? I live in the Hollywood Hills near Universal so the trip down to your place would be no problem.
Thanks for the offer.
Cheers,
Tom
 
PM sent.

I know it might "seem" generous, but based on Tom's engineering abilities and the work he has done so far to his car I suspect I will be calling on him for a little help and advice... :shock:
 
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