GuardsRedHammerhead

I know this was covered here, some time ago, and yes I have read through all of those old threads. Maybe looking for a bit different perspective.

I have a 1985 32V US 4-speed car that has a very hard shift. Like my old 1972 Monte Carlo with a shift kit in it. I have had it in to my mechanic three times to try and weed it out. My mech is a competent 911 air cooled guy, and big 951 tuner in Daytona Beach. He also does a lot of old Mercedes stuff, so I would think he knows these trans.

I have replaced the filter and changed the fluid, twice. Both times, it was quite clean. While my guy was in there, he put a new Green Top modulator in the car. He has supposedly vacuum tested the car. The car had a complete vacuum replacement UNDER THE HOOD about ten years ago. I do not know if the line was changed between the manifold area and through the firewall back to the trans. He has recently tried to soften it for me, by dialing back at the transmission, but as you guessed it, I am now getting 2nd gear to 3rd gear fanning. After my final visit to him, he is telling me it is either valve body replacement time or possibly a complete rebuild. It is a high mileage (160,000) car that has been very well cared for. So, I guess a rebuild is plausible, and if I must do it, so be it. I am thinking about buying the vacuum kit from Roger and running an new line all the way back, as one final last ditch before buying a new box.

Do any of you Auto guys have experience with this, and have you successfully repaired them by replacing the vacuum? Most people that know these transmissions say that they are very resilient, and they see few if any fail.

I would appreciate some last chance suggestions before I head down the replacement path.

Thanking you in advance.

Speedtoys

Put a vacuum guage on the hose at the modulator with the car idling.

Do YOU see vacuum?

GregBBRD

Do you have to lift off of the throttle slightly to get it to shift?
If not, what happens if you do lift off slightly, before it shifts automatically?
The 1st to 2nd shift should occur at a very low rpm, under light throttle. (Before it gets through the pedestrian cross walk.)
Is your shift normal or late?

GuardsRedHammerhead

Yes, lifting off the throttle shifts it. EVERY time.

GuardsRedHammerhead

My shift is always a bit late. As a matter of fact, I frequently find myself cursing at the thing to shift, because the high REVS in the neighborhood is driving me nuts. So, I lift up on the throttle and then it shifts.

Speedtoys

Adjust the Bowden Cable?

GuardsRedHammerhead

My mechanic says he did do that, but I guess I will not know until I just do it myself. I take it to him because I am only competent with things like fuel systems, electrical and timing belt swaps. From many years of doing it myself, but never delved into the transmission stuff. I will have to just get it on stands and go through it myself. I know he is a very competent guy, but some of the things that he doesn't know about 928 sort of bother me. Certain things throw him for a loop. Odd that a guy can rebuild 911 Turbos all day, but get confused by 928 tensioners? Not knocking him, as he treated me very fairly, but I just think his knowledge is quite specific to other cars.

Speedtoys

The adjustment is...quite simple.


It shouldnt be tight, or loose...see what it is right now. I bet its TIGHT, and if you remove it, it will go back away from the ball.

Constantine

I'll throw this in just because I can't understand if it was covered or not.

If the line from the engine to the transmission modulator becomes disconnected, it will have hard shifts.

The rubber line comes from under the engine manifold then goes behind the engine and under the front bulkhead on the driver's side where it attaches to the hard line which goes along the top of the torque tube (TT). The hard line then changes back to a rubber line at the back when it leaves the top of the TT and goes over to the transmission modulator. Suggest your tech check all these connections starting at the engine.

I hard hard shifts on my 1986.5 after I did a lot of work to the car. Found the rubber line became disconnected at the front where it first connects to the hard line. Very difficult to see but once it was reconnected, it shifted normally again.

HTH.

GuardsRedHammerhead

Thank you. Cannot wait to check this tomorrow.

The Forgotten On

I bet that rear line has cracked. If it is the original cloth hose it is definitely toast that this point. Silicone hose goes on very easy compared to the original stuff...

Landseer

The modulator valve, into which the vac line connects at trans, can fail a couple ways. One mode is the black cap that covers the adjustment thingy can crack or leak.

Speedtoys

He has a new one there already, I think I read in the original post.

GuardsRedHammerhead

Correct. Fresh Mercedes Green Top Modulator.

Speedtoys

So, its check bowden cable tension on the throttle quadrant and check vacuum presense with a vacuum gauge at the end of the hose at the modulator.

Both trivial driveway jobs.