The old problem back again

[Jonathan Lewis]

Doubtless a silly suggestion, but could it possibly be some sort of problem in the cage assembly containing the differential gears themselves?

Just a wild guess based on the apparent source of the noise, the fact that it is a knock rather than a rattle and that it appears to happen only when the car is changing direction (i.e. the condition under which there is likely to be a difference in rotational speed between the two rear wheels)...

Regards,

[Peter Douglas W]

Mike, I have taken to heart all the comments and as soon as I can get the TR through the MOT I will do a very serious look. The twich was there and as I replaced all the silent blocks and diff supports it vanished. It has come back once or twice!!!

But this is happening at 3 to 4 mph.

From the weight feeling you would think the following

1.) the exhaust is swinging in the air and hitting some framework when you go through a curve.
2.) the diff is shifting friom left to right or vica versa.
3.) a spare wheel has just fallen over in the boot
4.) the overdrive mounts have bust and the whole system is moving sideways.
5.) the drive train is so worn out and there is so much play. etc etc.
This is an attemp to give you a feel for the forces involved.

What I don't understand is the Garage could find nothing. I can find nothing and the MOT did not query anything!!!!

As my old garage man told me years ago when I said "Henry it is impossible" he replied "Peter, it is either posssible or impossible but it is something. Go back and have another look" He was right.

[tony]

Give the exhaust a shake.Loose baffle in muffler? Tail pipe hitting subframe where it goes through it? I give up!!!

[Peter Douglas W]

Tony
My very first thought was the exhaust. It moves when the engiine moves, it is heavy, and there is very little space in that hole. I have tried to set it up so that it never touches the subframe. Who knows. If one of the joints was loose the a flop from side to side would explain everything but everything seems to be tight. These are times when I wish I had a formula one car, cameras everywhere.

[TedTaylor]

Peter

With a persistent unidentifiable problem like this that you have done work to fix go back to square one and assume you have done nothing. Sometimes you do a job and do not finish it off properly without realising or even the components did not fit properly - and the MOT man will often look at work you have done, see it is new, and not check it.

Check everything again and get a b****y long lever to help you. Lever everywhere, look at the body mountings area as you lever, and listen for strange sounds. And just because a garage does not pick up on a problem that they should spot does not mean everything is ok.

As an example, back in the '70s a friend of mine had a Spit with a strange vibration. He had taken it back repeatedly to our BIG local BL dealer who could find nothing wrong and so he asked my opinion. We went out for a test drive and the vibration was absolutely classic UJ wear so got it back to the workshop and got underneath to check.

I found that with very heavy leverage there was a barely detectable movement in just one of the prop UJ bearing cups - something that on normal checking (rotating the prop back and forth) was not detectable and so easy to miss. Changed the UJ for him and problem solved ........ he thought I was a genius and I was to modest to disagree with him

Ted

[Richard B]

Have you checked the condition of the Diff mount pins?

They can corrode & snap.

[Peter Douglas W]

Ted I think you are right.
Working alone in a cold dark underground garage one does tend to miss things. Also one does not have that know-all neighbour (who is allways right) putting his head under car when you are laying their and asking you why did you do that, or not do that.
Richard i never realised they could go that bad I know on the TR6 they bust because of the torque being generated but my 50 hp (the others have gone into early retirement) should not be doing much damage. But as Ted says I will get my crowbar out and start all over again.

[Peter Douglas W]

Jonathon
How do I check for this?

[Jonathan Lewis]

Hello Peter,

If you mean checking for problems within the differential, in theory you’d need to remove the final drive and have a look inside. Given that it’s a bit of a long shot, in your place I think that I’d lift the car on the rear left-hand corner only (i.e. leave the rear right-hand wheel firmly on the ground), put the car into gear to lock the propshaft, and gently turn the unloaded wheel to see if you can detect any excess play or roughness in the operation of the diff gears. I have known Triumph final drives to ‘chatter’ when making sharpish turns under power if there is excess play within, but whether it would produce the sort of thump you seem to be encountering is open to question…

One other thought – do I remember from previous posts that your car is equipped with the optional (competition-style) undershields? If so, is it possible that one of these is striking something under some conditions of suspension movement?

Hope this helps!

[Peter Douglas W]

Hi that's a good one I will look. This is one that could make sense.