Auto tranny modulator valve

[AAB]

Anybody out there have much info on the modulator valve (vacuum) for my 74 450SEL ?

It will not hold a vacuum so I assume that it is to go to modulator heaven.

Worrells , my local Benz dealer can get me one from Singapore, $200+ dollars ( none in Australia apparently,..I assumed that that they tried locally )

I have ordered one from Manuel Automatics in Melbourne for $130 plus postage,..in the mail today !!

Manuel did me a recond transmission a few years ago for about $1,500 fitted.

Great service.

Regards,

Alex

 

[TJ 450]

If it doesn't hold vacuum you can pretty well say that it needs replacing, unless it is just the 'o' ring on the cap (unlikely).

The pin needs to be glued in with a retaining compound or epoxy and the unit needs to be screwed in with sealant on the threads.

If you can't measure the fluid pressure with a gauge, the risky business begins... If the spring tension in the valve is too great, you will have neck snapping shifts, too little and you will have slur or flare. The spring tension controls the relative effect of engine vacuum on the valve, controlling its response, which modulates and determines the transmission's operating pressure.

I would err on the side of too little, that is that you can easily push the pin in with your hand. Then it is a matter of road testing and working out which way it needs to go.

Bear in mind that there is potential for damage doing this and it would be worthwhile having the car towed to a workshop after you've installed the valve.

Tim

 

[AAB]

Tim,

Many thanks for your comments.

I have installed the modulator, backed off the adjustment ( anti clockwise) 3 & a half turns, with little improvement,. so I think that I had better get it done properly.

I have done this adjustment on previous occasions with success, but not this time !!

Regards,

Alex

 

[AAB]

Took it to Manuel Automatics ( Ph 03-9466 4499) to be fixed & it turns out that somehow I managed to get the pin jammed during the installation process,..dunno how, because it went in quite easily. Managed to burn my wrist in the process !!

All fixed now,..with it's first service in 120,000 k, ( Manuel was not impressed !!),..I will lift my game & get it serviced every 30,000 or so in future.

Manuel ( he is the owner ) says that if he had to rely on making money on my type of tranny, he would go broke,..the current European ones break !!, not wear out, but have to be replaced.

Regards,

Alex

 

[TJ 450]

That pretty well sums it up. They are brilliant transmissions, if slightly temperamental at times. That all adds to the character though.

The four speed units of the '80s are a little more integrated and a little more troublesome, but on a whole they have stood the test of time. It just went South from there.

Tim

 

[Styria]

Both of you come up with some interesting observations regarding the later type gearboxes. I am unable to comment as I've had no experience neither with late model transmissions nor cars. However, I do know transmissions for both sixties and seventies models like the back of my hand and whilst nowhere near as smooth or seamless when compared with the modern transmissions, I find them robust and quite trouble free.

Getting back to the modulator valves, it is my understanding that the most appropriate way of checking the pressures is to drive the car in top gear at eighty kilometers an hour. Maybe Tim, you might like to comment on that - it is something that I have read in the Gearbox Workshop Manual. Regards Styria

 

[TJ 450]

Yes, I also saw that information in the service manual.

As to the reasons why, I'm not too sure what is special about that speed.

I would speculate that because modulator adjustment is ultimately a compromise, as atmospheric pressure and other transient conditions play a big part in its operation, 80km/h may have the least bias towards any unfavourable condition or influence.

Tim

 

[BAR]

Many of the independent (factory trained and now running their own business) mechanics will say the same thing:

'When the W116 was built it was made to last. Modern Mercedes are made to last - but only 100,000 Kms'