P38a RR "Clunks"

[briang8789]

I have a 2001 P38a 4.6l V8 RR Auto done 86000Km. When moving gear selector from 'Park' to 'Reverse' from a dead-cold engine start and waiting for initial revs to subside, a loud 'Clunk'rocks the vehicle from the transmission area and can be felt through the selector. Slightly less dramatic when going from 'Park' to 'Drive'.

However within 2-3 mins of engine start both symptoms vanish.The transmission behaves normally in all other respects in terms of gear shift,kickdown etc.Transmission fluid only 6mths old and symptoms were around before fluid change.Ambient temperatures 15-20Deg Celsius.

Any ideas please?

It's probably unconnected but a very soft clunk from the rear wheel area occurs (regardless of engine temperature) when moving from stopped after selecting 'Drive' or accelerating from a very low speed to any speed.No symptoms when accelerating to overtake etc.

Is this experienced by other P38a owners?

There was a service bulletin went out in 1995 concerning a 'click' when engaging 'Drive' (cured by a Loctite product in a drive pinion)but this surely would have been cured by 2001.

[David Sparkes]

Wait and see what other responses you get here, but at some point in your investigation I suggest a chat with Ashcroft Transmissions regarding the loud clunk.

For both clunks, have you checked for play in the propshaft UJs, and for play in the rear differential? Best check the oil level as well.

The comment "dead-cold engine start and waiting for initial revs to subside" might be an indication of an engine fault. You quote no numbers, and because I run neither a petrol engine or an automatic gearbox I don't know what the speed should be, but "waiting for initial revs to subside" makes me a little uneasy. The engine speed may be too high, in which case the loud clunk is more a natural reaction than a fault.

[briang8789]

Thanks David,

I have had a cursory look at the UJs and diff with nothing obvious but a serious revisit is a good idea.I know of Ashcroft but unfortunately they are 12,000 miles away from us here in NZ!

The 4.6L V8s >MY99 have a Bosch Motronic 5.1 Engine management system and it's not given me a problem since new.According to the workshop Manual,the "Idle Air Control Valve IACV during cold start conditions,will hold the idle speed at 1200rpm in neutral for 20 seconds.Ignition timing is retarded as a catalyst heating strategy." It then drops to 660rpm.My one does exactly that.I have no faults showing on the Rovercom for the Engine ECM or the transmission ECM. Curious.

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[vougese39]

first start is a worn viscous unit or chain in the t box if after changing these it is still there investigate the diffs been though 5 cars and know always start at the centre and work out on the p38a the diffs arnt good but neither is the t box usualy it is the chain but have has one with a worn gearbox mainshaft splines

[argonaut]

I think I may be on the way to passing some money to Ashcroft Transmissions soon - I have a noticable tyre squeal when turning - I initially thought this might be due to tyre pressures since the car has been off the road for the last 3 months but after checking and correcting tyre pressures the squeal is still there. I have yet to do the test (jack up one front wheel and try to turn it as I understand the procedure) but I have another issue which I think might be related: when pulling away from an engine re-start (makes no difference if hot or cold) there's a noticable "click" coming from what sounds to be under the front half of the car. It's there where moving from Reverse to Drive or from Dirve to Reverse - the click only occurs once each time and doesn't repeat and it only clicks once the vehicle initially moves, i.e. simply moving the gear selector doesn't cause the click. It doesn't sound very heavy just a light sort of "click". Any ideas from anyone? I know this is a rubbish description but I wondered if one of the RR guru's out there might have experienced this in possible coneection with dying Transfer box/Viscous coupler problems.

Cheers