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Dodgy clonk at the back end


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Hi Folks,

I have recently got a clonk when taking up drive or lifting the throttle.

The diff was looked at in May to sort out a faint whine and oil leaks.

 

With the GB in 2nd gear and the hand brake on

No play in either drive shaft

No play in the prop shaft

Prop UJ's are new

Inboard UJ's on the drive shafts are new

Hubs are 1 year old with associated UJ's

 

Handbrake on and in Neutral.

The propshaft can now be rotated >5mm measured at the diff front pinion.

 

How much free play is normal/allowed at the front of the diff.

 

The input pinion flange was changed due to wear at the oil seal #37 https://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/clutch-transmission-drivetrain/axles-differentials/irs-rear-axle-differential-tr4a.html

 

 

If I can't find the cause I will have to drop the diff and return to the builder but am reluctant to do this.

 

Any ideas !!.

 

 

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Are you sure its from that area Roger, have you checked shock mounts and trailing arm mounts?

Stuart.

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Roger,

 

TR IRS cars have a very close clearance between the diff INPUT flange where the prop shaft attaches and the side of the transmission tunnel underneath the rear seat area. The diff is offset (various IRS cars are different) reducing the clearance and under torque loading either way as the diff mounts allow movement. It can contact sometimes with a graunching rubbing noise or a knock if the contact is only marginal, could it be that is the culprit.

 

Mick Richards

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Hi Folks,

there appears to be no torque twisting contact. The shocks and TA's are secure.

The forward inboard diff mount structure is very close to the brake/multiway union

Both are secure and was probably like it when I removed the diff the other month.

 

I shall pop the silencer back on and do a test run.

 

Any consensus on the diff front pinion free play.

 

Roger

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5mm at the pinion input flange sounds a bit much for a TR diff to me.

 

A totally different car, but perhaps relevant/perhaps not... My Scimitar GTE has a Salisbury axle which is well know for having a lot of play, and that shows about 5mm on the input flange. Driving at about 60mph on very light throttle, I can hear the Scimitar diff 'chattering' when it's really hot and the oil is thin. Does your TR have any faint chattering from the diff under similar conditions? If so, I would suspect it hasn't be set up perfectly.

 

 

Nigel

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Test drive with empty boot - still had the clonk, may be not as bad.

 

If I change gear without a smooth pick-up then it clonks.
if I lift the throttle and then stamp it down it does not clonk !!!

 

Roger

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Hello Roger

Someone in the boot trying to get out??

Seriously though - check the diff mounting points - I had one (offside front) split once, and wasn't easy to see until the diff was removed. Also check that dampers are ok - had fixing bolts on one of those loose once. Exhaust knocking onto floor somewhere - had that as well, it was knocking when taking up drive as you describe. Also check that floor pan is fixed to chassis securely at rear mounting points.

Might be play between propshaft and diff as you describe but as you say - not an option you want to go down yet.

Good luck

Keith

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Reger, Check the pressed steel front diff support for cracking just inboard of the offside pin. Mine clonked once on and once again going off throttle in first gear. Its a weak point and has been disturbed.

Peter

Edited by Peter Cobbold
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Roger,

 

I would be checking the diff mounts for cracking around the top of the pin. Front offside is usually the first to go.

 

Cheers

Graeme

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Hi Folks,

I've checked all the areas offered by your good selves. They all appear to be OK.

Just did apprx 1000 miles in Cornwall and with excellent clutch control and cotton wool in the lug 'oles I kept the clunk down to a minimum.

 

My next guess is to change the drive shafts. They feel excellent but are 10+ years old. Then the prop.

 

Roger

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Hi Folks,

I've checked all the areas offered by your good selves. They all appear to be OK.

Just did apprx 1000 miles in Cornwall and with excellent clutch control and cotton wool in the lug 'oles I kept the clunk down to a minimum.

 

My next guess is to change the drive shafts. They feel excellent but are 10+ years old. Then the prop.

 

Roger

You must have been going round and round in circles to do that amount of miles in this county and you didnt bother to come and say hello either!

Stuart.

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Hi Stuart,

we were not ignoring you - honest. We had so many little areas to go to on the North coast.

 

We got down to Mevagissey .and on the way back to Camborne (don't ask) we kept passing signs for Grampound Road - we couldn't escape.

 

We did about 900 miles in 4 days.

 

Roger

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You must have been going round and round in circles to do that amount of miles in this county and you didnt bother to come and say hello either!

Stuart.

If Roger was "going round and round in circles" might the cause be a broken drive shaft, and the "going round and round in circles" direction indicate which one is broken??!!

:D :D :D

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  • 3 weeks later...

Hi Folks,

I bit the bullet last week and ordered an new propshaft from Proptech in Kidderminster.

The old one had significant wear in the splines.

 

Fitted it yesterday and went for a very short (rain interrupted) run. It definitely felt & sounded better but need a longer run to be positive.

 

Out this PM for a late lunch - proof of the pudding in at least two ways.

 

Roger

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Hi Folks,

I bit the bullet last week and ordered an new propshaft from Proptech in Kidderminster.

The old one had significant wear in the splines.

 

Fitted it yesterday and went for a very short (rain interrupted) run. It definitely felt & sounded better but need a longer run to be positive.

 

Out this PM for a late lunch - proof of the pudding in at least two ways.

 

Roger

IRS Props do wear much more than solid axle car ones as they dont utilise the sliding joint so the wear is all in one spot on the splines. Cheaper get out is a s/hand earlier prop.

Stuart.

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Hi Stuart,

I'm not overly concerned by the wear as the prop has been there for nearly 300K miles.

 

It is finding the clonks that is my goal.

 

Tomorrow I shall remove the O/S driveshaft and strip it down and see what the wear is like.

 

Roger

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Roger

 

I'm trying to ascertain how much play in the sliding joint constitutes unacceptable wear - if I clean off all the grease, there obviously has to be some tolerance between the the two splines, otherwise they couldn't slide, but can you "feel" this tolerance if you twist both ends?

 

If you can't, then they must be very close - if you can feel a tiny amount of play and this disappears if you then grease up the joints, I assume that should be OK.

 

But is there a simple way of gauging how much play is acceptable/not acceptable or is it just years of experience - I have quite a large pile of props, all displaying some play, and I can't believe they are all scrap - forget the UJs, I've got a large box of GKN ones which I got for a bargain and will last me several lifetimes, if I'm lucky ( or is it unlucky!).

 

Cheers

Rich

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