Lumpy overrun

[rjaxe]

My S130 with Weber Carbs becomes decidedly lumpy on the overrun. I can feel the engine rocking through the gear lever and the hear load coming on and off in the transmission, put on just a slight amount of throttle and all is smooth again. I am not sure this behavour will do the transmission a lot of good in the long run. Anyone with any ideas please?

[Jason1]

Hi Richard

Not sure if you mean normal noise you get through the exhaust or drive train noise?

If you are talking about the noise through the exhaust when you are coming down a hill at great speed and let off the gas, this is normal for Webers and great fun when you pass a group of old ladies at a bus stop The Webers are lumpy on overrun, which is part of their charm.

If the engine or gearbox is rocking in it's mounts (worn mounts) then the gearlever will move about when you accelerate or deccelerate. Or is the donuts are gone they will bang about?

Hope this helps

Jason

[rjaxe]

Thanks Jason, the noise is definitely from the transmission its as if the load is cycling rapidly between overrun and drive at around 1-2 cycles per second. If I throttle back very very gently and come onto the overrun smoothly the noise is much less suggesting that the sudden application of load sets up some oscillation.
The exhaust does pop a bit on overrun but I believe this is normal behavour.
The engine and gearbox mounts were all replaced around a year ago (2500miles) and the car is fitted with CV joints in place of donuts. I have not yet changed the diff mounts could part of the problem be here?
I have tried to locate any excess movement in the mounts or slack in the drive components but only by hand even so I cannot detect anything unusual.
Maybe I should try some new mounts as I have heard that the quality of some are suspect. Any other ideas please?

[rjaxe]

A belated update on the "diff noise" problem I posted in January. I have finally got round to refurbishing the rear end and changing the diff to a 3.54 ratio version all which I had intended to do during the winter. Its amazing what you uncover in these exercises:
The diff top mounts were in quite a state, the inner steel sleeve was almost completely worn away.
The RH diff output shaft bearing had lost its shield and hence its grease and was merrily rusting away.
Potentially v. serious, there lying in the bottom of the housing was the broken off head of one of the crownwheel bolts .
Luckily there was no damage to the diff internals and the backlash was still in spec but the pinion preload was very low. A rebuild needed at some point.
The noise has gone and the suspension works fine