P38 Drivetrain vibration - no prop fitted!

What started out a couple of weeks ago as a gentle vibration / shudder at around 30mph has got the beating of me. Symptoms have gradually got worse which prompted 'pit inspection' yesterday afternoon. Good news is we found 2 x badly worn/seized uj's on the front prop. Having replaced both joints the clicking and squeaking has gone but not the vibration. After checking rear prop (fine and free movement), have now taken front prop off completely and vibration gone. I've read that chatter about vibration dampers and harmonic balancers, is there where I should be going next?

Have a look for a propshaft specialist, they can check the balance for you. Start with the obvious before running from one thing to another like a headless chicken.

balancers dont do alot ,check front prop diff flange brg behind prone for wear ,put 30mm socket on t/box front flange and see if it turns (not in park or gear) if its locked viscous coupling seized causing wind up between axles should turn slowly with some effort

When you took the front prop off, did you mark the flanges so you could put it back in the same place? Also, did you take the prop apart, i.e. pull the splined sliding bits out giving you 2 pieces of prop? If you did, did you get it back with the UJ's correctly aligned?

wont matter which way prop goes on diff or t/box flange,it will only go on two ways but prop alignment is important if split on splines

Aargh, been there with this one. Never did get a final decision on whether to have the joints parallel or phased by two splines. Mine is still phased slightly and any vibe is barely noticeable which is a lot better than a bearingless joint half out the yoke and rubbing on the nuts!!

jamesmartin said:

balancers dont do alot ,check front prop diff flange brg behind prone for wear ,put 30mm socket on t/box front flange and see if it turns (not in park or gear) if its locked viscous coupling seized causing wind up between axles should turn slowly with some effort

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90 degrees in a minute with 27lb feet of torque applied. That's from memory so don't slate me if it's a bit wrong.

ive never measured it for years so cant remember you can feel whats right with experience but thats hard to pass on as advice

jamesmartin said:

balancers dont do alot ,check front prop diff flange brg behind prone for wear ,put 30mm socket on t/box front flange and see if it turns (not in park or gear) if its locked viscous coupling seized causing wind up between axles should turn slowly with some effort

Click to expand...

Balance as in dynamic balance of the propshaft itself. They are balanced at manufacture with small weights...look like small plates, welded on.

no i meant the wieghts on diff not prop

jamesmartin said:

ive never measured it for years so cant remember you can feel whats right with experience but thats hard to pass on as advice

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Yeah that is true, trying to pass on experienced feel on here in words is hard work. But the official testing method i quoted is a good way to go if you have not got that experience. It can be tested on centre nut of a front driveshaft with that wheel off floor, but using about 95 lb feet with that method. But the wheel only needs to move about 25 degrees in the same time scale. If it moves less than that there is too much resistance on VC if it moves more not enough. If it spins freely VC caput if it does not move at all same senario.

Thank you Gentlemen for all your advice.

The prop has been split and re-assembled in the correct manner. (it only fits comfortably one way on the splines). I'm presuming that a poorly front diff is what took the uj's out in the first place. Will conduct test as soon as I can get back underneath it.

Tired Old Girl said:

Thank you Gentlemen for all your advice.

The prop has been split and re-assembled in the correct manner. (it only fits comfortably one way on the splines). I'm presuming that a poorly front diff is what took the uj's out in the first place. Will conduct test as soon as I can get back underneath it.

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If the front UJ's and the diff are shot, most likely cause is the VCU.

Hi Guys

Sorry for the delay in replying. Thanks for all your advice, your assistance has led me to establishing that the VCU is seized. Have this morning ordered a replacement from Ashcroft Transmissions and will look forward to fitting this next week.

Regards

Ian