TR6 Out of balance

[Peter Douglas Winn]

Yesterday I went to a big classic car show. Long motorway drive and some fast normal roads. Every so often I had an unbalance. Foot on the clutch no difference. The unbalance came in mostly when pullling under load or when overdrive being switch in, or even when changing from 3rd to 4th. Some times it was extreem and others times just rough running.

So now the question. Knowing the O/D is new the G/B is good the Engine is brand new, the mounts are new, where do we start looking? For me that means the minimal of effort.

Ok I can swap the tyres back to front. I can wiggle the prop and drive shafts all very technical. The revs are between 2000 and 2500. I cannot think out why it is sometimes there and on other days there is nothing.

Can drive/prop shafts have this effect?

 

[PGB BME]

Hi Peter

Have you looked at the propshaft UJ's

Regards

Phil

[Peter Cobbold]

Could it be temporary loss of sparks on some cylinders? - misfiring will be more obvious under load.

I doubt its mechanical if it comes and goes.

Minimal effort:

- change rotor arm for a red one from Distributor Doctor, and fit one of his condensers too.

- look for stray sparks around cap and leads in the dark at tickover.

- swap for another coil

- new plugs

- 2000-2500rpm is where the cetrifugal swing is 'all in'. Listen for disy noises

Peter

Edited June 4, 2016 by Peter Cobbold

[TriumphV8]

Propshaft does a humming, driveshafts, wheel bearings and

imbalance in wheels do something like shaking but if realy

related to apply power I would expect a universal joint close to fail.

 

Try out if its realy under load or only because you are just passing

a speed border. Mine starts trouble at 80Km/h and at 90 its gone

what is an indication that the wire wheels need attention.

[Peter Douglas Winn]

Peter

Any ideas? When declutching it is still there. So it is not the motor or forwards. It feels to be from the back end and is pretty heavy. As I said before the G/B mounts are new, O/D new, G/B ingood running condition. Hence for me it can only be one or more of four things. Tyres, driveshafts, Propshaft or the telescopic shockers konis. I think if it is a wheel bearing I would hear and notice it at other speeds. If it was swing arm rubbers it would exüect to notice it at other speeds. I am just trying to think it out and hoping for ideas, that I have overseen.

[Deggers]

Morning Peter,

 

Had a similar problem once. I'd suggest heading down to your local friendly tyre shop this afternoon, and having them rebalanced. Always worthwhile doing occasionally, but especially so at the moment.

 

Cheers, Deggers

[Peter Cobbold]

Peter

Any ideas? When declutching it is still there. So it is not the motor or forwards. It feels to be from the back end and is pretty heavy. As I said before the G/B mounts are new, O/D new, G/B ingood running condition. Hence for me it can only be one or more of four things. Tyres, driveshafts, Propshaft or the telescopic shockers konis. I think if it is a wheel bearing I would hear and notice it at other speeds. If it was swing arm rubbers it would exüect to notice it at other speeds. I am just trying to think it out and hoping for ideas, that I have overseen.

Peter, OK its not engine. I have only had a prop shaft UJ go once in 280K miles so that's perhaps less likely. Drive shaft UJs usually clunk when the drive is first taken up from stationary,as would a fractured diff mounting and perhaps ( not certain) and bolted drive shaft joint in need of tightening. If you can drive through the vibration and it appears and goes with road speed then it might be a wheel balance issue.

But it is odd that it comes and goes and does not do it all the time.

I think I'd check the front prop shaft flange bolts - the gearbox has been out recently ? and on the basis its something that has been disturbed.... just a guess. And listen for clunks on take-off.

Peter

Edited June 4, 2016 by Peter Cobbold

[Peter Douglas Winn]

I have just had a look at the car. As you say the propshaft is OK. The only thing I can find is a slight movement on the RH drive shaft inside UJ. Also with the nonsence Shocker test (jumping up and down), I had the feeling one was very, very slightly softer as the others. As they are adjustables I wil get a MoT test house to check the dampers. and if OK give the screw a tweak. I am pretty sure the wheels are ok because I have always in the past, been able to drive through the unbalance period, this time not.

[Penfold]

Definitely get the wheels re-balanced. You can get some very odd things going on if more than one wheel is out of whack and the effect can vary depending on speed and road conditions depending on how much each wheel is out-of-balance. Also....if you have wire wheels - don't let the muppets at the mainstream tyre fitters do the re-balancing (or tyre fitting for that matter) - the wheels will 'seem' balanced but be far from it...Wire wheel balancing requires specialist gear and know-how.

[Peter Douglas Winn]

Quote "I cannot think out why it is sometimes there and on other days there is nothing." Anyone with some sensible or even silly ideas who knows?

[Andy Moltu]

I had this after a chassis rebuild and it turned out the diff pins were too long - or more the section that wasn't threaded resulting in the nut coming to the bottom of the threads without clamping up the diff mounts, at times it would feel fine then vibrate hugely.

It was a matter of packing out the mounts with washers to get them clamped up tightly and all was well again.

Before I found this I had checked UJs, prop and wheels with no joy.

[Peter Douglas Winn]

Andy

That's a new one I can look at that and see.

[Trever the rever]

I've just had a o/s drive shaft inner UJ fail on the way back from Le Mans near Beauvais. I had noticed a slight klonk (whats unusual you may ask!) just a few miles before. I have the newer uprated shafts fitted about 4/5 years ago, but they still have UJs (these ones have grease nipples too). Stopping at a junction at low speed I noticed a scratching higher pitch groan. I was in a convoy and help was at hand. Soon I was taking the O/S rear wheel off hoping to find a loose shock absorber bracket for the telescopic spax but could quickly see one aspect of the UJ was knacked, end off and circlip long gone but yoke looked okay. I took a photo and sent it to a well known TR specialist and had a quick chat; 20 miles maybe but 200 certainly not! So recovery it was to a local garage which amazingly was classic car friendly, and I hear today the job has been done. So I travel (C/O the insurers) next Monday and pick it up.

 

So - was it early life failure of the UJ, (8-10k max), lack of grease, undue vibration from my 20 year old wire wheels. I'm not sure at this stage. The wheels do vibrate slightly at 50 mph. I've been told they are out of true, so a refurb is probably on the cards, if I can find someone, MWS maybe? Certainly make sure the UJs are greased where need be. I had had the prop balanced professionally about 3 years ago.

 

watch this space, Regards Trevor Hughes - !972 TR6 - goes to Le Mans on annual pilgrimage every year since 1998!

[rcreweread]

Trevor

 

Try Tudor Wheels in the New Forest - they refurb and retrue all sorts of wire wheels at a very reasonable price - proprietor is a Richard Skinner on 07801 069261 - website is www.tudorwheels.co.uk.

 

He is currently refurbing a full set of wires for me - seems to be a good set up and know what they are doing.

 

cheers

 

Rich

[Trever the rever]

Thanks Rich, appreciated. I'll put some feedback after my return on how the car felt after uj repair. Regards.