I am currently chasing down vacuum issues on my car. There are multiple very slow leaks that don't really affect operation here near sea level. But on our tour to Tahoe and Denver, the automatic was shifting really harsh, jerking in the gears, and the recirculation flap did it's flip-flop flapping dance, squeaking happily in the process...

While the recirc flap actuator is tight, the comb and footwell flap actuators have been identified as sources of vacuum loss, and replacement diaphragms are on order.

One other place of slow leakage is the transmission line. I suspect the leak to be wherever that vacuum line connects to the transmission.

I've been trying to locate this piece in PET, but no success.

Where on the transmission does that vacuum line connect? Can this be seen and reached from underneath, or does anything have to be disassembled first before I can get to it?

And while we're at it - has anybody replaced their transmission mounts? If so, what were the symptoms of bad ones? What is the procedure to do this? How many miles were on your car when you did the replacement?

Thanks!

 

Hi Nicole

it's the green thing in this photo. It's on the port side of the box ie LHS looking forwards.

I am pretty certain you can get at it without removing anything just jack up the rear of your 928. Be aware that between the firewall and this conector IIRC the vaccum pipe goes from flexible to solid steel to flexi again and the two connections between the steel and flexi are kinda hidden above the TT




More photos where this came from are at
Erics TT rebuild

Cheers

 

Hmmm... These seem to be quite a few separate parts:

The black rubber piece
The off-white worm-like thingie
The green one
And the black cap

Should I replace all those?

How would I access the other connectors on top of the torque tube? Where about are they located - at the beginning and end of the TT? Would the exhaust have to come out to get to those connectors?

Well, this sounds like it could become a pretty big project... particularly for a rather slow leak.

 

That is the vacuum modulator, remove the black rubber cap and check IT for cracks, if you have a mighty vac also check the modulator for a leaking internal diaphragm. The cap is available thru MB.

 

Mmmmmm my wife commented on that

The black rubber tube above that and the one above that are just chafe protection, and can't leak. I guess the modulator itself could leak as Steve said, but my money would be on the white worm like thingie - it's rubber its at least 15 years old and exposed to the outside world - probably where it connects to the metal pipe above the TT.

Get a mtyvac, disconnect and plug at the Vac mod on the tranny, disconnect at the manifold end draw some vacuum and see if there is any leakdown (or whould that be leakup )

Cheers

 

Nicole,
BTDT last week. Take off the air filter box and find the five way vac connector below it. You will easily see which line goes to the rear of the car. Get a mityvac and test that line for holding vacuum.
Mine was fine and held 20 on the scale for at least 20 mins. If that line holds good I would concentrate on the other lines before touching anything.
Mine turned out to be disconnected at the manifold. Yours could also be bad fuel dampeners.
Good luck.
Roger

 

Nicole,
Mine shifted also pretty hard in Denver and I was not the only owner noticing this. Back in Texas and everting was back to normal.

 

Nicole
I also think to start at the 5 way "T" under the airbox......then work your way back to the tranny! Its very possible the 5 way "T" is old and cracked.....ithat could be causing some leaks...ts a cheap part and easy to replace!

 

Nicole:

A couple of years ago, we tested the vacuum on your car at the 5-way. The line to the vacuum modulator on your car had a very slow leak then. It would lose pressure slowly enough that I did not consider it much of an issue. We did look at the line at the modulator end for cracks and fit, but did not test it further. The modulator end of the line seemed a bit loosely fit. If you are going out for a drive this weekend, come on over and we can put it up on the lift and check more thoroughly. Let me know.

BTW, tomorrow is upper A-arm bushing day, if anybody want to see that operation. Ken Adolf will be over lending his expertise.

 

Nicole... If the vacuum modulator diaphragm leaks you
usually burn ATF and produce white smoke out the exhaust...
Unless the leak is really small, I suppose. But test it anyway.

The lines and 'joints' to it are more suspect most likely.

G'luck.

 

Thanks, everybody! I can't drive the car right now, as the center console is out and I'm waiting for the new actuators to come in. Both had SLOW leaks.

Yes, the leak on the transmission vacuum is not a fast leak, and it's not an emergency. I was just trying to gather information on what to go after next. Bill: I don't remember that we checked the vacuum on the transmission side, but I'm getting old and forgetful...

I definitely want to avoid the recirculation flap from going crazy when I drive in higher altitude. Apparently that flap needs the most vacuum to operate properly, and any leaks or thin air make it go crazy.

And if the shifts get smoother at altitude, that would be purr-fect.

 

Nicole: You're not forgetting. We didn't test the modulator directly. We tested the line at the engine compartment end (slow leakdown), then I just got under the car brioefly and felt the connection at the modulator end. WEe can do the rest later when you get things back together.

 

From experience the line that leads back from the 5way up front to the tranny in the back is spliced at somepoint under the car...near the front bell housing i think. Odds are that little bit of rubber tube they use to splice the line is hard, brittle and has expanded...perhasp source of your slow leak?? Becarefull moving the line around near the 5 way splitter, you can EASILY pull the tranny vacuum tube out from the splice underneath the car!! This happend on my car and Dariens..i ran a new line and splice in both cases.

 

The coupling near the bell housing was my problem. I have no advice for fixing it other than invest in two pairs of very long (10 in. at least) needle nose pliers and prepare to do a lot of cussing. It took me at least 45 min. to get a new coupling on there and reattach the lines. If I ever have to do it again, I'll just replace the whole line from the intake to the modulator and try to reroute it away from the exhaust.

 

Yes I know I am resurrecting an old thread. It is relevant. I pulled the flexi vacuum line out of the hard line fitting today. I took the route of running new vacuum line all the way back to the tranny. Didn't feel like trying to coax the flex line into the hard line connector.

Left the factory stuff there so I can hook it back up when I rebuild my torque tube someday.

Ran the new vac line down and zip tied to the brake line running under the driver's side. Used 1/4" vac line and put 1/2" water hose over the hose in areas where it would be above a heat shield.