Rear end whine

[Mike R]

I’ve had a high pitched whine from the rear of the GT6 at speeds at or over 70mph for some time. Although up to now I’ve just taken it as the Triumphs in the sky telling me not to break the speed limit.

However, it does get quite loud and on the French motorways 80mph is quite legal but not good for my ear drums. (Just returned from Laon Hisorique trip - excellent !)

Very difficult to absolutely pinpoint location amongst all the other noises at that speed but appears to be over my left shoulder so have assumed to be Diff related. Diff was a recon unit around 5 years ago from an excellent Coventry supplier that many will probably know. As I don’t take to those speeds very often can’t really say when it started.

The odd thing is the noise is loudest on partial throttle with it going away on both overrun and quieten on full power.

Does this sound like Diff issues? Could it be wheel bearing? Any solutions?

thanks for any help,

Mike

[NonMember]

I had a diff like that - except FAR worse and not only at speed - which the reconditioner swapped FOC because he was ashamed of it. That was just a bad case of something not right and the chap had been unable to get the clean tolerance marking to confirm the pinion pre-load. If yours has been on there five years and has developed this over time then it might be a similar cause. The hypoid gears don't quite mesh nicely and rub like a violin bow. At low speed this isn't noticeable. At full throttle, or full lift, it's pressing too hard to sound properly (violinists have to develop accurate bow control because the tone of the sound is very dependent on how hard they press). But at high speed and light throttle it "sings" jolly loudly.

Given that yours is not too bad at the moment, you may be able to improve it by replacing the diff oil. Use a good quality heavy GL4 - perhaps EP140 grade (the supplier of my GT6's current diff recommends that).

[Nick Jones]

Bearing pre-loads are not right and letting the contact pattern shift according to load.  Probably worth getting it dealt with before it does itself a mischief.  Just about to try and teach myself how to do it - have a couple of diffs in bits on the bench......

The one in my Vitesse is now similar - noise starts at about 45 and can now be heard at 70mph with the top down...... Kipping built 3.63 - but it has done about 50k hard miles.

Nick

[Mike R]

Many thanks, those replies make perfect sense.

sounds like a job for the winter then.

Is bearing pre-load a reasonable home mechanic can do? Whilst I’ve done things like take diff and gearbox in and out, fiddling with their innards is another thing,

I tried an additive to quieten .... which didn’t work. Replacing the oil would be tricky without a drain plug. Guess the diff has to come out just to drain it, or has anyone tried syphoning the oil out?

Mike

[AidanT]

I have the exact same. At 70 or above I get the same noise. I will try the ep140 thanks 

Aidan 

[NonMember]

As I understand it, the bearing pre-load setting involves some expertise and the use of engineers blue for the final check (you're looking for a clean deposition from pinion to ring with nice central ovals) but can be carried out in a reasonably well equipped garden shed. Never done it myself, though.

I guess syphoning the oil ought to be possible. As has been mentioned elsewhere, while the diff doesn't have a drain plug it does have the flat where said plug hole should be drilled. Probably worth adding one when you take it off the car for any work.

[AidanT]

Not tried yet but I have a large oil syringe to suck out the oil  v cheap on eBay  plus my filler plug is on the side not on the back plate so am hoping that gives a little more room  I believe a previous thread on here said it could be done but they needed to use a thin tube such as screen wash tubing 

Aidan 

[daverclasper]

I removed most of diff oil with a large plastic syringe (about a pound of ebay) and thin tube (helps to run the car to warm the oil a bit)

Dave

[daverclasper]

You beat me to it Aidan

[AidanT]

Dave, did you just drain with the car sitting flat? My plug being on the side is a bit more of a bu**er to get to!

Aidan 

[daverclasper]

From what I remember, the back end, was up on ramps

[trigolf]

For some years now I've had more or less exactly the symptoms that Mike described on my VIt. Mine makes a whine under load from about 45-50 mph upwards,but goes completely quiet on the overrun. As Mike says the noise appears to be from over my left shoulder, although hard to pinpoint in a convertible even with the roof up ! It also started leaking from both output shafts from day 1. Soon after purchase I returned the diff to it's supplier  - the same well known company in Coventry for investigation. The boss reported that he could find nothing wrong with it, but replaced it as a gesture of good will. BTW both diffs had new Crown wheel and pinion fitted. I'm aware that the triumph diff is notorious for being a bit fragile, but the car is not driven hard,so why do Triumph owners have so many noise problems with reconditioned diffs ? I'm pretty sure that if MGB owners had the same sort of regular problems there would be protests ! My car does very few miles each year now and I've got sort of resigned to it. I check the GL4 oil level regularly, but I'm reluctant to try another supplier as I originally went to the no. 1 recommended supplier in the first place ! I've heard rumours that some new crown wheel/pinions are made in Turkey or India ? I'm not sure if that's total b***ls or not, but begs the question over quality control, if true. Whilst I appreciate that the core supply of diffs are now 50 years old, reconditioned ones should be more reliable and better quality in my opinion ! Rant over !

Gav

[Pete Lewis]

If you get noise changes between drive overun and coast I would suspect the pinion pre load is rather light  and a tweek on the nut if collapsible spacer or a shim removal on fixed spacer between the pinion bearing may improve things 

Pre loads are  used to maintain pinion position during the changing loads 

Theres lots of things that affect the mounting distance of pinion and crownwheel, and the tooth marking will move up or down the tooth 

on drive to overun,

the need for a case spreader is so you can achieve the correct shims to get the tooth  backlash and achieve a preload

You dont want the crown wheel and diff case moving left to right or the pinion moving in or outwards

The mounting distancd is the dimension the projected cone of the pinion meets the centre line of thd crown wheel hence the shims under the main pinion thrust bearing  with any variance being etched on the end of the pinion

Theres a lot to getting this all sweet and quiet

Pete

[daverclasper]

Wow Pete. Sounds like, not a DIY job, or even not professional fool proof.

Dave 

[Pete Lewis]

Its easy to make a screamer , 

The manual spels it out, short cuts only work if your very lucky.

And being a hypoid adds to the accuracy as the centre line of the pinion is offset to the centre  of the crownwheel.

This gives a longer tooth contact to make it  quieter

Pete

[Clive]

On 30/05/2018 at 9:25 AM, trigolf said:

For some years now I've had more or less exactly the symptoms that Mike described on my VIt. Mine makes a whine under load from about 45-50 mph upwards,but goes completely quiet on the overrun. As Mike says the noise appears to be from over my left shoulder, although hard to pinpoint in a convertible even with the roof up ! It also started leaking from both output shafts from day 1. Soon after purchase I returned the diff to it's supplier  - the same well known company in Coventry for investigation. The boss reported that he could find nothing wrong with it, but replaced it as a gesture of good will. BTW both diffs had new Crown wheel and pinion fitted. I'm aware that the triumph diff is notorious for being a bit fragile, but the car is not driven hard,so why do Triumph owners have so many noise problems with reconditioned diffs ? I'm pretty sure that if MGB owners had the same sort of regular problems there would be protests ! My car does very few miles each year now and I've got sort of resigned to it. I check the GL4 oil level regularly, but I'm reluctant to try another supplier as I originally went to the no. 1 recommended supplier in the first place ! I've heard rumours that some new crown wheel/pinions are made in Turkey or India ? I'm not sure if that's total b***ls or not, but begs the question over quality control, if true. Whilst I appreciate that the core supply of diffs are now 50 years old, reconditioned ones should be more reliable and better quality in my opinion ! Rant over !

Gav

MGB diffs are massively strong, our small chassis diffs are puny little things.....

A recon diff without a new CWP is a real gamble, if the CWP are whining before it will likely whine to a lesser (or greater!) extent after a rebuild and setup. And yes, I believe some of the new CWP are from Turkey, though that was a few years ago, and I doubt the situation has improved. The best bet is to try some of specialists who never seem to advertise. Some of them (eg Tony Lindsey Dean) seem to have stock of genuine bearings etc, and possibly CWP too.

I changed to a subaru diff, I won't break it(I have tried, it will lock both wheels up at 50mph if I am an animal and change down to second at that speed, no complaints) However, they are not immune to issues, like me not checking the oil level often enough and I suspect loosing a little oil out the breather at high speeds Still, replacements are not expensive and always work perfectly, having played with a few ratios. The issue is the conversion to fit it in a triumph with the breather being inline with the CW, whoever did that ought to be shot. And me being lazy.... However, it did have about 100ml of oil left, and it has just done 3 trackdays like that, and the whine is very slight. 

[DerekS]

This may be a bit of an essay, bear with me please. I've been reading postings like this with interest for a while as I haven't been too happy with the diff on my 1500 Spit, not too noisy exactly but making it has been making it's presence known. Also, I haven't been overly impressed with the blue grade polybush diff mounts, I think they're too soft, especially when hot. The diff didn't have a drain plug; I changed the oil earlier this year by using a vacuum pump but started having afterthoughts about if all the old oil was out. So yesterday I changed the mounts back to standard grade black rubber, then bit the bullet and drilled and tapped the diff to take a plug. The position for the plug is obvious as there was a simple in the casting. I've gone for a 5/16" UNF size, I had a short unused setscrew with a washer and dealing washer. The casting at that point is 1/2" or more in thickness and cast iron is lovely stuff to drill, just take it easy with drill speed and pressure and the pilot went through a treat. I had the tapping -size drill ready with the clear top of of an old aerosol on it to catch the oil while drilling. It's surprising how quickly the oil drops through a small hole but I managed to catch it in a drain tub and as the flow eased off did the tapping of the thread. I put some unused oil through the filler hole afterwards to flush out any possible flakes of metal but there was nothing. This time I've refilled using 140 grade GL4. We'll see how it goes long term of course but on a test run today it was lovely and quiet, a big improvement indeed with virtually no noise, especially on the overrun. When I looked at the drained oil there are small traces of what looks like water in it.

[AidanT]

That's great news. I have still to change the oil but oh have now spurred me on

What did you use to get the oil back in?

Aidan

[Pete Lewis]

It was quite common to use 140 in diffs but drifted to 90 when hypoids replaced bevel pinions  as hypoids have a longer tooth contact

And loading is less and  should be  quieter   ,   good result Derek     we all like a cheap fix that works 

Dilling cast iron is quite therapeutic

Pete

[DerekS]

Hello, Aidan, I used a small 1/4 pint oil can to refill, it gave the old fingers and wrists a workout but we got there eventually; no waste and no mess.

Yes, very forgiving stuff to drill,  Pete. I was wary of the drills snatching on breakthrough; a broken drill would have been fun. The other thing I was worrying about was if there was a gear or whatever running close to where the drill broke through. Poking an allen key in afterwards showed there wasn't. Two more points: using a cordless drill gave far better control, drilling cast is easier with a lower speed range. Also I did have a couple of small BSP tapered plugs and taps ready but changed to the UNF setscrew at the last minute and am pleased I did. For one thing the setscrew doesn't present the possibility of raking yourself on the projecting head of it...

[trigolf]

Derek,

I'm very interested in trying some 140 grade oil in my diff, to possibly quieten the whine ( see my rant of May 30th ). Probably a daft question, but does putting 140 grade oil in make any noticeable difference to mpg figs -  such as it is !?

Gav

[Pete Lewis]

I dont think putting a 140 vs 90 in the diff will have much effect on the efficiency ratings of 60/70s economy ratings 

Adding 2 psi to the tyre pressures has more influence than having a goo in the mincer

And if its quieter you will drive faster ..   right foot has the biggest contribution

Pete

[Mike R]

A little update on this topic ....

a reminder .... I had a whine on the diff when at 70 or more which was worse on part throttle.

Opinion is that pinion bearing pre- load is wrong and this agrees with other online research I’ve done.

I’ve just had the rear suspension apart to do the rotoflexes. Whilst I was there, thought I’d take a look at the diff. Its a collapsable spacer type with the Nyloc nut under the tamper proof cover. I thought about giving the pinion nut the smallest of tweaks to increase pre-load, but lost my nerve as no way of knowing what is correct.

Then I checked the casing bolts, and found every one slightly loose. About a quater of turn brought them to the correct torque (based on my calibrated arm!).

It got me thinking ... is it possible that slightly loose casing bolts has meant that the casing gasket isn’t fully squeezed leading to lower bearing pre-load? I.e. the 2 halves of the casing were sitting slightly apart?

Well with the casing bolts tightened I took her for a spin on the A180 up to 80 ... and it appears much improved. Although that was a quick 5 minute test .... time will tell on a longer run.

what do you think?

Mike

 

[johny]

hmmm sorry cant see the casing bolts making much difference as the pinion and CW is all held in the front half so movement of the rear casing could affect only the alignment of the stub shafts and their bearings....

[RogerH]

The loose bolts could have a small affect on the audio dynamics.

The rear casing amplifying any noises in that area.

 

But the problem lies elsewhere.

Roger