Strange behaviour from GT6 differential that otherwise seems fine.

[RichardS]

I've had a bad vibration from my GT6 above 70mph ever since I bought it. There is slight vibration well below that but it gets bad at higher speeds.

My thinking was that it was something from the front end so I have had all the wheels balanced twice, replaced the front wheel bearings, steering column bushes, track rod ends etc. There is now no play anywhere at the front end and everything turns/spins smoothly. None of this work has made any difference to the vibration!

I then decided to check the rear driveline so I jacked up the rear end of the chassis with two jacks and ran the engine in gear and everything seemed fine. I then dropped the nearside wheel to the ground and repeated the exercise. The offside wheel span freely as expected.

I then raised the nearside wheel and dropped the offside wheel onto the gravel. At idle everything seemed fine but when I increased the revs a little the offside wheel started jerking violently as it tried to spin itself in the gravel. I repeated this exercise several times with the same result. I believe that if I had opened the throttle further, the offside wheel would have driven the car off the jack.

The diff does not have undue backlash when the wheels and prop shaft are spun by hand and I now have the diff on the bench with the drive shafts out and it all appears to be in reasonable condition with just a little scoring on the sun/planet wheel teeth. The crown wheel and pinion look fine. There is no excess backlash or tightness and the bearings all seem to be OK with no obvious rumbling or roughness.

I had expected to see or feel something significantly wrong like a broken tooth or misaligned cog but there is nothing obviously wrong.

Does anyone have any idea why my differential is behaving as if it is limited slip on one side only? 😟

Thanks

Richard

[NonMember]

Diffs always "prefer" one side, just because of tolerances. They're also not designed to spend much time doing high speed on one side only. The grabbing you describe is normal and you wasted your time dismanting it.

If your problem is a vibration above 70mph on a GT6 then it's probably the propshaft.

[Clive]

Ultimately, if the vibration really does get to you, pay a visit to "Vibration free" where they can diagnose anything, and I mean anything, that is causing a vibration. 

But prop is a common issue (had it when a UJ seized 2 years ago) but usually comes in around 60mph, but if just out of balance disappears at higher speeds. 

Diff, I doubt that is the cause. Yours sounds in pretty good condition.

[RichardS]

1 hour ago, Mathew said:

Your lucky you did not have an accident! As for the other side gripping, no idea unless the brake drum is sticking or giving some resistance .

There is a swishing sound as the drum rotates due to the shoes kissing the drum but certainly no binding in the normal sense. However, you have picked up on what I see now as an issue in that I was doing all the tests whilst sitting in the driving seat as I was on my own. I really needed a second person to actually see what was happening on the nearside. 

Unless someone has a better idea, I'm going to rebuild the diff with new ball bearings and oil seals and repeat the tests with a helper. 

If it's not the diff, and I'm now doubting that it is, I'll turn my attention to the prop shaft.

Richard

[RichardS]

50 minutes ago, NonMember said:

Diffs always "prefer" one side, just because of tolerances. They're also not designed to spend much time doing high speed on one side only. The grabbing you describe is normal and you wasted your time dismanting it.

If your problem is a vibration above 70mph on a GT6 then it's probably the propshaft.

You could well be right about the prop shaft. 

Richard

[RichardS]

2 hours ago, clive said:

Ultimately, if the vibration really does get to you, pay a visit to "Vibration free" where they can diagnose anything, and I mean anything, that is causing a vibration. 

But prop is a common issue (had it when a UJ seized 2 years ago) but usually comes in around 60mph, but if just out of balance disappears at higher speeds. 

Diff, I doubt that is the cause. Yours sounds in pretty good condition.

I've never heard of "Vibration Free" but they're not far away from me. I'll email them once I've got the diff refitted.

Edit: Actually, whilst the diff is out I think I'll remove the prop shaft and have a good look at it.

Thanks

Richard

[Colin Lindsay]

4 hours ago, RichardS said:

Unless someone has a better idea, I'm going to rebuild the diff with new ball bearings and oil seals and repeat the tests with a helper. 

That works wonders, if you stand somewhere quiet and someone drives your car past at slow speed. It's amazing what you notice or pick up on. 

[Bob Horner]

I had a vibration in my Gt6 which made it horrible.  Making sure the gearbox mounts were tight helped but there was still a vibration.  Had the prop checked and balanced and completely disappeared.  There is also the issue of changing the way the prop is bolted up - there are two possible orientations front and rear.  
 

Bob

[RichardS]

OK. Whilst the car is up on lift with the diff out, I've used a couple of high-level jacks under the rear drums to try and re-create the "diff grabbing" effect.

Guess what ..... I now believe that it's all down to the GT6 rear suspension geometry which, when the wheel drops down freely to it's maximum travel, partially applies the handbrake as the linkage comes under tension. It seems to happen more obviously on the nearside wheel, perhaps due to it being further from the mechanism or perhaps the adjustment is slightly tighter on that side. This would certainly cause the offside wheel to scrabble on the gravel drive.

I'll forget the diff being the source of the vibration but have already put new drive shaft ball bearings (I'm going to use 9 ball rather than 8 ball versions) and oil seals into my basket as I might as well refurb it.

I've now removed the propshaft and it looks dead straight when checked with a straight edge although I appreciate that does not mean it's balanced. However, there are two welded on balance weights so it has been balanced.

However, the UJ at the diff end is rather "sticky" in one axis and feels as if it wants to self-centralise. I've no idea whether this could set up such a bad vibration but I'll strip it down tomorrow.

Richard

[Pete Lewis]

to get the diff case bearing set with a preload you need to spread the case or its all going to be a bit slack ...- more trouble than you started with

and do you have the dial gauges to check the backlash    very easy to tinker and make a right howler

differential sun and planets are only designed to rotate slowly  spinning one wheel at speed  can end up in a big  Bang    its not advised and proves very little

 diffs do not vibrate   props and drive shafts will  bear in mind the frequency   prop does engine revs   drive shafts  about a 1/4 of that being road wheel revs

Pete

 

 

[RichardS]

57 minutes ago, Pete Lewis said:

to get the diff case bearing set with a preload you need to spread the case or its all going to be a bit slack ...- more trouble than you started with

and do you have the dial gauges to check the backlash    very easy to tinker and make a right howler

differential sun and planets are only designed to rotate slowly  spinning one wheel at speed  can end up in a big  Bang    its not advised and proves very little

 diffs do not vibrate   props and drive shafts will  bear in mind the frequency   prop does engine revs   drive shafts  about a 1/4 of that being road wheel revs

Pete

 

 

Outer ball bearings and seals only.

Richard

[Pete Lewis]

good leave the hard part well alone    Pete

they can be a swine to remove from the short shafts 

good luck 

P

[Jim-GT6]

Very helpful thread, as I appear to have the same on my GT6 mk3. I've had the car for around a year and it's always had a mild wine / vibration when holding a constant motorway speed, but it's recently got FAR worse. It happens over 60mph, isn't there if I'm accelerating or if I take my foot off and there is engine braking, but if I hold a steady speed, it's like I'm scuffing an angle grinder over metal in hops and starts. Terrible sound. Didn't know where to look first. Prop shaft?

Jim

[Jim-GT6]

.... and, what can happen if I don't fix it quickly enough? If it's the prop shaft, what happens when they go? :)

[RichardS]

Hi Jim

I can't answer your specific query but my vibration was always there above 70-ish and never seemed to stop although I don't actually know yet whether the prop shaft is the culprit. I did have an intermittent metal grinding sound but that turned out to be one of the front wheel bearings which was so shot that it allowed the disk to deflect sufficiently to occasionally touch the shield and was instantly cured with new bearings.

My prop shaft is currently at Dave Mac Propshafts in Coventry. The guy there said that the slight misalignment in the yokes would not have been the problem and showed me a new Land Rover propshaft with the yokes misaligned by 45 degrees as prescribed by Land Rover. However, he suspected that the sliding joint was somewhat worn and might the throwing the shaft out of balance and making it impossible to balance. They will either sort it out or suggest a new shaft which they can also supply so we'll see.

Richard

[dougbgt6]

Jim! Is that you?!!! 

I'd check the wheel bearings first. Jack up the front, grip the wheel top and bottom and wiggle. There should be very slight movement. Anymore than slight and it needs adjustment or you got a problem. Adjustment: take off the wheel. Take of the dust cap (lever with a screwdriver) and you'll find the castellated nut with a split pin through it. The bearings are tapered and adjustment is just tightening up the nut and re-inserting the pin. As said before there should be VERY SLIGHT movement. But before that take the nut right off and have a look at the bearing. Is it intact? More grease always welcome!

Doug

[Jim-GT6]

1 hour ago, RichardS said:

Hi Jim

I can't answer your specific query but my vibration was always there above 70-ish and never seemed to stop although I don't actually know yet whether the prop shaft is the culprit. I did have an intermittent metal grinding sound but that turned out to be one of the front wheel bearings which was so shot that it allowed the disk to deflect sufficiently to occasionally touch the shield and was instantly cured with new bearings.

My prop shaft is currently at Dave Mac Propshafts in Coventry. The guy there said that the slight misalignment in the yokes would not have been the problem and showed me a new Land Rover propshaft with the yokes misaligned by 45 degrees as prescribed by Land Rover. However, he suspected that the sliding joint was somewhat worn and might the throwing the shaft out of balance and making it impossible to balance. They will either sort it out or suggest a new shaft which they can also supply so we'll see.

Richard

Thanks Richard, you've clearly had a lot to chase through to find it. I get a metal rubbing sound matched to wheel rotation speed when I'm turning slowly at or near full lock. Heading up the ramps and turns in a multi-story is when I really notice it, as it reverbs around the space. I'll be keen to hear what comes of your latest steps on the prop shaft

[Jim-GT6]

50 minutes ago, dougbgt6 said:

Jim! Is that you?!!! 

I'd check the wheel bearings first. Jack up the front, grip the wheel top and bottom and wiggle. There should be very slight movement. Anymore than slight and it needs adjustment or you got a problem. Adjustment: take off the wheel. Take of the dust cap (lever with a screwdriver) and you'll find the castellated nut with a split pin through it. The bearings are tapered and adjustment is just tightening up the nut and re-inserting the pin. As said before there should be VERY SLIGHT movement. But before that take the nut right off and have a look at the bearing. Is it intact? More grease always welcome!

Doug

Hi Doug! Yes of course it's me! Have I been quiet for a while? There ... I've even updated my picture 😃

Fancy a spin in my car to play guess the noise? Thanks for the wheel bearing tips. Nice and clear (as you know my level of competence!). I'll do just as you suggest.

Cheers,

[dougbgt6]

Jim,

Yes, I have a window of opportunity I could pop round.

Doug 

[Jim-GT6]

58 minutes ago, dougbgt6 said:

Jim,

Yes, I have a window of opportunity I could pop round.

Doug 

Wicked. I'll DM you. Thanks Doug! 

[dougbgt6]

Jim,

Yeh, sounds like rear axel, certainly in the rear centre of the car, top up oil and see if it makes a difference. Certainly sounds like unlubricated gears. Because it's suddenly got worse it may be it's leaking. 

Doug

 

 

[Pete Lewis]

well done Doug  (at least you know he's a member ) if you remember our escapade outing

if this is a low oil level enough to make it howl  dont drive anymore till you have topped it up

EP80/90   GL4   or even a EP140 GL4    works well

simpler way to access the filler is take the N/S wheel off and you can get at the filler plug through 

the gap in the chassis   saves you  going down under on a cold day

the worry is a low oil can seriously wreck the pinion bearings as they require splash , no splash and they  can seize quite quickly

Pete

 

[dougbgt6]

9 minutes ago, Pete Lewis said:

well done Doug  (at least you know he's a member ) if you remember our escapade outing

Yeh, we got BBQ'd bacon sandwiches 

Doug

[Jim-GT6]

On 04/12/2021 at 14:22, dougbgt6 said:

Jim,

Yeh, sounds like rear axel, certainly in the rear centre of the car, top up oil and see if it makes a difference. Certainly sounds like unlubricated gears. Because it's suddenly got worse it may be it's leaking. 

Doug

 

 

Thanks again for the onboard diagnostic Doug! 

I topped it up today and it was almost (or completely) dry. Castrol EP90. I think it took about 400ml. Capacity listed as 1 pint. I tried to poke a flexible tube in first (on a huge syringe) to see if I could pull anything out, but I could only get the tube in about an inch, and certainly nowhere near the level of any fluid left in there.

I wish I'd seen your nearside wheel-off suggestion sooner Pete. I was going to go for ramps and axle stands, as the manual says it should be level, but I've got to do this on gravel so opted for just lifting the rear on stands (on boards) with the ramps in tight under the front as chocks. I took the offside wheel off, as I thought it was on the offside 🙄 and with all this access, I could see how accessible it is from the rear. It's tucked just under the rear sill. I reckon you could do it with the car up just a couple of inches on a jack. I'll know next time. 

Result is a lot quieter. About half as loud. Now I've recognised what the diff sounds like, I realise it's most of the transmission noise I hear. I thought a lot was the gearbox, but I think I have a very noisy diff. I'll be looking at options for refurb / replace I think. Knackered bearings perhaps Pete? Can the diff be quiet?

It's wet with oil, so I'll be checking / filling regularly until it's sorted, particularly now I know how much easier it is than I thought.

[Pete Lewis]

4 hours ago, Jim-GT6 said:

Pete? Can the diff be quiet?

yes they should be    its wear and tear upsetting the very accurate dimensional settings that makes them noisy 

there is a lot of critical settings to control bearing preloads  crownwheel and pinion mounting dostance and backlash all need to be right 

its not any DIY job without special tooling and experience  

as for noises  howls and growls is meshing ,   whines would be more down to  bearings 

maybe  its time to check the gearbox oil as well !!!!!!!

Pete