W123 dodgy gearbox

[biodiesel]

Hi there,

The auto box on my 300td is very jerky changing gear. As it changes up there is quite a thump and the car jerks forwards a bit. It seems like it's changing late to me as well. It changes to third at about 35 when cold and 33ish when warm and 50 for fourth.
The ATF looks clean and doesn't smell although the level is slightly high. Could this be the cause? I'm going to sort that tommorow so I'll let you know is it help. Any suggestions would be great.
On a different subject does anyone know a decent indie on the Isle of Wight?
Cheers

 

[Hibbo]

Alright marra, I know exactly what's wrong with your autobox, I'm too pished/tired to explain it tonight, but I'll be back on again tomorrow (in work's time!).

PS. Does your central locking work properly?

 

[television]

Alright marra, I know exactly what's wrong with your autobox, I'm too pished/tired to explain it tonight, but I'll be back on again tomorrow (in work's time!).

PS. Does your central locking work properly?

This will be vacuum related and Hibbo will give you a good answer.

 

[Hibbo]

Hello again mate, as Malcolm has said, it is a vacuum problem. This is a common fault with these cars.

The gearbox uses vacuum to sense pedal position, holding the gears longer and making the changes harder the more you've got your foot down. Lots of vacuum = gentle acceleration = early, soft changes; No/low vacuum = foot to the floor = hard, late changes.

You have a vacuum leak somewhere so your gearbox 'thinks' you are driving everywhere with your foot to the floor.

The gearbox vac system is quite simple, but the car has hunners of other vac systems. If your central locking doesn't work (especially with engine off) then you have a leak somewhere on one of the vac systems and this can be difficult to find. If you central locking is ok then the leak should be isolated to the gearbox system.

The gearbox vac system works by tapping vacuum off the main vac line from the vac pump to brake servo, this then goes though the Proportioning Valve on the side of the Injection Pump (which progressively 'dumps' vacuum to atmosphere (via the vent line that runs to the bulkhead) the more you put your foot down) and then down to the Vacuum Modulator an the side of the 'box.

Check all the pipes around the IP, you might get lucky!

A tenner will get you a vacuum gauge with is a great tool to have if you're running an old Merc.

Hope this helps, let us know how you get on.

PS. Any word on the 2500L duty exemption?

 

[Blobcat]

PS. Any word on the 2500L duty exemption?

http://forums.mercedesclub.org.uk/showthread.php?p=174246#post174246