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Old 06-16-2010, 08:00 AM
Registered User
Join Date: Jun 2010
Location: Bahrain
Posts: 21
AT Modulator Valve + Hi-speed fan.

hello everyone...

Just registered on the forum and I'm seeking for some help around here.

I just got my hands on a 1993 500SEC in Almandine Red Metallic and I just got my hands on a whole set of new goodies for the front linkages in genuine form (I hope I did the correct move by getting genuine MBZ parts) and got the Bilstein HDs on it... I've got a couple of stuff to do here and there and DIY.

I'm having quite some rough gear changes. Went down under the car and my car has the WHITE AT Modulator Valve OR known as the Transmission Vacuum... Started playing around it to make it change a bit better but didn't work THAT well but it was a significant change.

My parts vendor told me that there are 4 types. The Black, White, Yellow and Red. He doesn't know what's the difference neither the mechanic does but he said that it's only a matter of difference in pressure. The mechanic said that the best one is the Black one. So, I got my hands on that but I'm not quite certain if it's the correct one as my car has the white one and I don't know within the time frame of my car's life if it was actually changed.

My car has been overheating amazingly because the High speed fan has not been working unless I disconnect the switch. What seems to be the problem? Is it a damaged switch or is there any other problem?.

Hopefully, the car will run great now after I take it to Bosch Service Center and it will be running like a dream. I do need some tips about types of OIL that I could use for the engine + transmission + diff.

I'm going to drain the engine + diff after a couple of days because I have no idea what the car is running. The tranny has the Liqui Molli.

ONE more thing, that I believe is the diff not having oil in it.. Whenever I slow down when I'm coming up to a roundabout or something but not coming to a complete halt, I hit the gas and there is this strong "DUM" sound but nothing happens to the car.. no bogging no nothing.. except for that DUM and the car feels like someone is kicking it.

I hope that I would get some help regarding this!

Thanx all.

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Old 06-16-2010, 08:18 PM
hey_allen's Avatar
greasy fingered tinkerer
Join Date: May 2006
Location: Tacoma, WA
Posts: 728
Regarding the overheating, what condition is the main engine fan in?

With my auxiliary fan not working at all, the engine temp will only occasionally creep up the temperature gauge beyond the normal operating range, now that it has a good viscous clutch on the fan.
Testing the cheap Mercedes axiom, one bolt at a time...
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Old 06-16-2010, 09:21 PM
Registered User
Join Date: Jun 2010
Location: Bahrain
Posts: 21
The fan is in good condition, I don't think it's a clutch problem but the thing overheated CRAZILY....It was exactly under the 120 degrees margin!....

I think I will be able to solve the fan problem, should take time to tackle the problem...

I just want to make sure that I made the right choice by getting the Black ATMV instead of the White one that is already on the car..

and one more thing, the gear changed takes a lot of time to actually change... somewhat sort of SPORT mode lol...Any hints about what I'm suffering from?
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Old 07-10-2010, 12:57 PM
Registered User
Join Date: Jun 2010
Location: Bahrain
Posts: 21
Any help regarding the AT Modulator Valve??

What's the difference between Black, White, Blue and Red?????????????????????????????

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