Quote:
Originally Posted by Zacharias
Thanks for all the input. I did try a variety of searches, but I didn't catch many posts having to do with the 1980 vacuum-only control transmission.
|
Typical failure mode for the vacuum control valve -- the bulb on top of the
IP behind where the ALDA would be on a turbo -- is lack of "last" upshift. I've had 3
of these "vacuum only" shifters and they're actually fun to tune when you get the
hang of it.
Put in in L and hear it shift once.>
If the VCV is holding vacuum for the 20? seconds spec'd in the manual, it will
have enough capacity to force the last upshift. Some times people mess with
the governor setting in an attempt to fix a failing VCV. Some times people
swap the orifice in the VCV supply line -- in an attempt to get shift points back.
Some times the transmssion ages and drifts, requiring a new orifice AND VCV
setup.
The VCV acts as a vacuum "dashpot" slowing the onset of vacuum -- actually
drawing down the leakage level over time through a bellows. leakage is ideally
back to cabin atmospheric, although i've never noticed a difference on an old
car leaking it to underhood air.
I think I posted last year some time on messing with this, and what I'd learned
from the list and trying all 5 orifices to optimize shift points back in a 79 240D.
It had exactly the same 'misses last shift' problem, and was instantly
repeatable by disco'g the VCV. At the other end of failure
-- too little leakage -- it shifts like a soggy dog -- all over the place, with a lot of flare "mud".
Typically this happens when the VCV is filled with oil, sucked
from the IP around its seal. Stops leaking and starts acting like a shock absorber.
The switchover valve only controls the EGR setup, and has NOTHING to do
with the transmssion on 722.11? cars, approx 1978-1980 normally aspirated
616 and 617s. It can be confused with bowden cables because they share a bracket on later models.
On some models, the EGR vacuum is parallel to the VC vacuum, which can make a mess of troubleshooting.
Disconnect it temporarily. Pay the planet back by turning off a light bulb. Re-connect it after your tranny is sorted.
A new, correct VCV can be acquired by taking the IP serial number to your local Bosch repair site.
There are several dozen? types, apparently. I've seen a chart somewhere, and its mind-boggling.
So, I'd skip that "ebay and hope" model that looks the same.
hth.