Grumble from LSD

[ratty]

Or maybe not... I've noticed two things occuring on my Chim 500. First is that when I accelerate in a low gear (eg 4th) there appears to be a momentary shudder in transmission accompanied by a slipping noise from the rear end - doesn't appear to actually slip (like a duff clutch) but just gives the impression of some sort of take up when pressure applied. Second is that there appears to be a slight hum from the rear end at 100mph+ V slight at the moment - I wondered whether the prop shaft might be out of balance (?). Does anyone have any ideas or has had similar experience. Is it possibly the LSD ? Would like to get some ideas before going to a dealer. Many thanks Ratty ps car has not been abused, last main service 4k miles ago (24k)

[GreenV8S]

Is it just a small amount of backlash in the transmission as you take up the drive? A certain amount is normal, although it gets worse of the CV joints or diff are worn. 24k is a bit low for trouble with either of these. If it was like that when it was serviced and the dealer didn't mention it, it's probably nothing to worry about. BTW I'm astonished if you can hear a 'slight hum' at those speeds - you must have really good hearing! Cheers, Peter Humphries (and a green V8S)

quote:Or maybe not... I've noticed two things occuring on my Chim 500. First is that when I accelerate in a low gear (eg 4th) there appears to be a momentary shudder in transmission accompanied by a slipping noise from the rear end - doesn't appear to actually slip (like a duff clutch) but just gives the impression of some sort of take up when pressure applied. Second is that there appears to be a slight hum from the rear end at 100mph+ V slight at the moment - I wondered whether the prop shaft might be out of balance (?). Does anyone have any ideas or has had similar experience. Is it possibly the LSD ? Would like to get some ideas before going to a dealer. Many thanks Ratty ps car has not been abused, last main service 4k miles ago (24k)

[ratty]

Peter, thanks once again for the feedback. As you suggest, the symptoms under acceleration give the impression of take up of slack in the rear end somewhere. Having had the car for 18 months I can say it wasn't the same when I bought it although it's not appearing to get any worse. Are there any simple tests I can do to check where the slack may be? As for the hum you're right it could be in my mind or even from the radio (the exhausts have been modified by the dealer so are even louder than normal) by I'm sure there's something not quite right. It doesn't sound like diff whine, more the sound of something not quite in balance (if such a state has a sound!). Has anyone experienced similar? Rgds Ratty

[GreenV8S]

The slack is most likely to be in the diff, although worn CV joints can have a small amount of slack. If there's any significant slack elsewhere you've got a problem that you need to sort ASAP. You can get a general idea of where the slack is by jacking up one rear wheel with the handbrake OFF (safely chocked, of course) and watching the half shafts, CV joints and drive flange to the prop shaft as you move the wheel to and fro. Check for movement of the inner CV joint relative to the wheel i.e. if you move the wheel does the inner CV move immediately, or is there any slack? There shouldn't be enough slack to be noticeable, if you can see it this indicates a badly worn CV joint. (You can get an indication of whether it is the inner or outer CV by looking at the half shaft itself.) You can do the same test on the other side by rotating the wheel until all the slack in the rest of the system has been taken up and the half shaft connected to the 'grounded' wheel starts to take up torque. Again there should be no relative movement between the inner CV joint and the corresponding wheel. I've always noticed worn CV joints by the knocking noises they produce, even in very worn ones the backlash should be very small. Finally watch the inner CV joint and the output flange to the prop shaft while you move the wheel, and note how far you can move the inner UJ before the prop shaft starts to move. This shows you the internal backlash within the diff gears. You may be surprised just how much backlash there is, typically this will correspond to at least an inch of travel at the tyre. If it's more than two inches the diff may be on the way out. You will probably notice other symptoms like a growling noise that is highly throttle dependant. I've been through two diffs now and in my experience the symptoms get very obvious indeed before it finally 'lets go'. If you're hearing/feeling a low frequency vibration at about 15-20 Hz this is wheel frequency and probably indicates a wheel out of balance, bent rim or a flat spot. But if the symptoms are subtle enough that you aren't sure there is a problem - there probably isn't, and if there is it can probably wait until the next service. Hope this helps, Peter Humphries (and a green V8S)

quote:Peter, thanks once again for the feedback. As you suggest, the symptoms under acceleration give the impression of take up of slack in the rear end somewhere. Having had the car for 18 months I can say it wasn't the same when I bought it although it's not appearing to get any worse. Are there any simple tests I can do to check where the slack may be? As for the hum you're right it could be in my mind or even from the radio (the exhausts have been modified by the dealer so are even louder than normal) by I'm sure there's something not quite right. It doesn't sound like diff whine, more the sound of something not quite in balance (if such a state has a sound!). Has anyone experienced similar? Rgds Ratty

[trefor]

Maybe I'm been too simple here, but the rumblecould be the rear wheel bearings - mine were replaced last year around 32,000 miles. You might also want to check the bushes are all OK. If it makes you feel better my diff has a bit of backlash in it, but hasn't got any worse in the past 12 months. Trefor/.