[ZBall]

I'm trying to hunt down a vacuum leak and I hooked up a hand vacuum pump to the Trans Modulator vac line in the engine bay. I pumped it up to about 20 psi and it slowly (15-20 secs) leaked out. My tranny does shift hard occasionally... So because it doesn't hold vacuum does that prove the modulator to be bad?

 

[slk230red]

I'm trying to hunt down a vacuum leak and I hooked up a hand vacuum pump to the Trans Modulator vac line in the engine bay. I pumped it up to about 20 psi and it slowly (15-20 secs) leaked out. My tranny does shift hard occasionally... So because it doesn't hold vacuum does that prove the modulator to be bad?

When my vacuum modulator started leaking, it was sucking transmission fluid. I replaced the VM and it still shifts better than when the car was new.

 

[ZBall]

When my vacuum modulator started leaking, it was sucking transmission fluid. I replaced the VM and it still shifts better than when the car was new.

That's good to hear... I'm working up the nerve to replace it if I have to. :|

I read the instructions about using a "banjo bolt" for the pressure test. Did you use a banjo bolt or just a normal fitting? If a fitting, do you remember the thread size? I don't want to spend more time than I need under the car... And any other advice would be helpful.

 

[slk230red]

That's good to hear... I'm working up the nerve to replace it if I have to. :|

I read the instructions about using a "banjo bolt" for the pressure test. Did you use a banjo bolt or just a normal fitting? If a fitting, do you remember the thread size? I don't want to spend more time than I need under the car... And any other advice would be helpful.

When I checked my transmission fluid and it was low and no leak, my first thought was to check the VM. When I disconnected the vacuum line near the intake, I saw trans. fluid in the line. I knew then it was the VM. When I put my mighty vac on the line it didn't hold vacuum so I replaced it.
Now here's the hard part. I had to lower the exhaust system and lower the transmission to have enough room/space to remove and install the VM. I got this information from a MB mechanic on one of the forums. I didn't do any pressure testing on the new VM, I just installed the new one, took it for a drive and was amazed at how smoothly the transmission shifted. No more hard shifts after engine warm up.

If you decide to replace the VM yourself, it would be a good idea to inspect the shifter bushings while you have access to the linkage.

 

[ZBall]

Well I just ordered a new modulator and I hope to have as good luck as slk230red did! Not sure when I'll put it in but I'll try to remember to take pictures...:smile

 

[slk230red]

Well I just ordered a new modulator and I hope to have as good luck as slk230red did! Not sure when I'll put it in but I'll try to remember to take pictures...:smile

Good luck ZBall!

My wife and I made a cruise ship stop in Seattle in May. Went to the Chihuly Garden and Glass Exhibit, the Pop Culture Museum, the Aquarium, and of course Pike Place Market, but my favorite place was the Old Stove Brewing Co. Great beer! We haven't been to Seattle since the late '80's....still a great place to visit.

 

[ZBall]

I'm trying to hunt down a vacuum leak and I hooked up a hand vacuum pump to the Trans Modulator vac line in the engine bay. I pumped it up to about 20 psi and it slowly (15-20 secs) leaked out.

I got the new modulator the other day and i hooked up the mighty-vac to it and got the same slow leakage. So the vac test wasn't conclusive, but i'm gonna try installing the new one anyway.

 

[Dan300]

I need to replace my modulator too, but have no idea on how to lower the transmission.

 

[ZBall]

I haven't done this yet but from what i've read... Well basically put your car on ramps and put a jack under the tranny. Theres a bracket (rear trans mount) you'll have to remove. Also the exhaust has to be disconnected. Then you can lower the tranny enough to get to it. Heres a thread about it, but theres others around.

http://www.benzworld.org/forums/w20...1-transmission-modulator-removal-replace.html

 

[ZBall]

I need to replace my modulator too, but have no idea on how to lower the transmission.

Well I'm attempting to change mine at this moment and I have the exhaust hangers all disconnected and the rear tranny mount removed but the tranny is only coming down an inch or so. I can pry it down another inch or so but nowhere near enough. The drive line looks like it has another inch or so but it seems something else is holding it up? any ideas? I'll probably put it back together for another day...sigh.

 

[A.Cabral]

Well I'm attempting to change mine at this moment and I have the exhaust hangers all disconnected and the rear tranny mount removed but the tranny is only coming down an inch or so. I can pry it down another inch or so but nowhere near enough. The drive line looks like it has another inch or so but it seems something else is holding it up? any ideas? I'll probably put it back together for another day...sigh.

Remove the heat shields about the exhaust and unbolt the front brace that rides below the propshaft. Then unbolt the center carrier bearing of the driveshaft. This should give you the clearance you need.

I got the new modulator the other day and i hooked up the mighty-vac to it and got the same slow leakage. So the vac test wasn't conclusive, but i'm gonna try installing the new one anyway.

Sometimes Mityvacs leak down. I know mine does slightly. The best way to test is to hook up a line and run it into the car with a gauge and then back out to the intake manifold as depicted in the FSM.

 

[ZBall]

Remove the heat shields about the exhaust and unbolt the front brace that rides below the propshaft. Then unbolt the center carrier bearing of the driveshaft. This should give you the clearance you need.

Well I gave it another go the other day, with no luck... I had everything unbolted including the center driveshaft bearing and the exhaust system hanging free. Unless there's something under the hood holding it up it must have something to do with the drive shaft? It doesn't seem to have u-joints like a regular vehicle. Will it separate at the tranny and come free or will it have to be removed completely?

 

[A.Cabral]

Well I gave it another go the other day, with no luck... I had everything unbolted including the center driveshaft bearing and the exhaust system hanging free. Unless there's something under the hood holding it up it must have something to do with the drive shaft? It doesn't seem to have u-joints like a regular vehicle. Will it separate at the tranny and come free or will it have to be removed completely?

It can separate at both the transmission and differential, however if your driveshaft is like mine, it likely wont telescope properly which means it may have to be completely removed.

 

[ZBall]

Yeah, thats what I was afraid of... well maybe I'll put this to bed til next spring.

 

[A.Cabral]

Yeah, thats what I was afraid of... well maybe I'll put this to bed til next spring.

Not hard to remove the driveshaft since you're basically almost there already. Gotta just unbolt the flex discs. Make sure you renew the locking nuts if you do.