tranny shifts hard/late and flares, aamco "fixed" it and now the problem is back
 

about 6 months ago, my dad took the car to aamco for a tranny diagnosis. It was shifting late/hard and flaring once in a blue moon. They said the problem was just a loose vacuum line. Now it is doing the same thing again. It seems to shift smoother when it is driven harder (i.e., quick starts and fast acceleration). My question is, is there a specific vacuum line that tends to be the culprit in this type of situation? Also, how are the lines secured to the tranny? I have no idea what to look for, other than 40 bucks to have aamco "fix" the problem again :rolleyes:

Thanks in advance,

John

Loose line producing a hard shift makes sense. You need vacuum going to the modulator in order to get a soft shift.

Now, where in the chain from booster line/ vacuum control valve/ modulator is the line disconnected? Don't know. Have you looked under the hood?

John, steve brotherton has many great threads on this site about the magic of mb trannys. use the search at the top of the page and you will find what you need. hope this helps steve 83sd

i have, however i have no idea what to look for, or even where to look.

tried doing an advanced search using both "steve brotherton" and "steve 83sd" as filters, but it said no such user

http://www.continentalimports.com/ser_ic20242.html

oh, duh. dang, i must be tired. thanks ;-)

Hey I like that link! You need to make sure you have not vacuum leak and then start checking other components. That link Brian gave is an excellent resource. If you have any more questions, just ask.

Anytime. Don't feel bad. The search function is very difficult to use here. It takes years to blow over all the threads that are worthless. However, note that we (WHunter specifically) have been attempting to get around this problem by listing all of the most important threads on the forum for specific tasks.

Check out the Do-It-Yourself Resources Forum.

1980 SD with Same problem
 

hey guys, my '80 SD has that same shifting problem. I bought the car in September, havn't had a great amount of time to get into trouble.

Here's what I know about the health of my vaccum system.

At Tempuratures ABOVE -5c My vaccum system works flawlessly, with the exception of the transmission.
Below -5c however is another story. The door locks are slow, sometimes non-functional, the "AUTO LO" and "AUTO HI" will not function automatically even at 85*. I thaw the car for one night and everythng will work for about two days and them the problems re-occur. It will also not shut off, under the hood I go to press the "oh ****" lever

Overall, the Vaccum system DOES leak down when the car is off, I'll shut it off (when it's working) and lock the doors, then 15 minutes later, come out and unlock the doors and there isn't enough vaccum to raise the dook lock knobs.

That's minor stuff, I can diagnose vaccume leaks no problem. I DO need to know how much vaccum the Mechanical pump produces at idle, and what the Vaccume should read on both sides of the tranny dash pot, and vaccum regulator on the back of the IP. I can isolate that circuit to test it..


So....how much Hg on either side of the components making their way down to the transmission from the main line to the vaccume "thing" (can't think of the word right now) on the tramnsmission itself.


Thanks a BILLION....GTB

Have you changed any of the flex lines?
 

This problem sounds like a flex line leaking somewhere. On mine, changing out all of the 3-way, 2-way, etc. flex fittings (~$10) cured a lot of vacuum woes in one shot. Gives you a base to start from for easier troubleshooting also.;)