[W126 Coupe] Re: 87 SEC hard shift

[Richard Hesek]

  Thanks for the reply Dick,
 I have had this same behavior in 2 diesels which are quite different due
to the vacuum system.
 I have tested modulators exactly the way you describe. I have a vac pump
but a Mity Vac would be ideal. Modulators fail when the diaphragm tears. A
large tear will cause a harder shift and also cause trans fluid to be
pulled upstream towards the intake manifold.
  I have also replaced a B2 piston, tranny in the car, on my '81 300SD. It
was easy provided you have good instructions. I am not sure about the
coupe. Although it is a 126 chassis car, there are tight spaces where the
sedans have room.
  I will replace the modulator since it is cheap the car has 200k+ miles on
it. I will let you know what goes on.

Rick Hesek
===================

Hi Rick:

A couple of similar events to the one you described:
I've experienced a firm hard shift in all gears when the vacuum to
modulator is lost or absent.  In my case the vac line was disconnected.
This would be easy to check visually and with a vac guage in line while
driving.  I imagine you could put a vacuum on the modulator to see if
the diaphragm is holding the pressure too.

I am experiencing in another MB a firm hard shift from 2nd to 3rd and
suspect it is the B2 piston.  In my case when slowing down but not fully
stopping and then accelerating again I get a pause then the hard shift
from 2nd to 3rd.  I do have the procedure for replacing the B2 piston
and the nylon sleeve with the transmission mounted to the car chassis.
It looks like very tight quarters to me so I have waited until I do the
front engine mounts where I can tilt the engine up and lower the
transmission valve body in the hopes the B2 is accessible from the side.

I 'd be very curious to learn what you discover on your SEC and maybe
you can ask to see if the B2 is even a factor on your model year.

Good luck, Dick

Richard Hesek wrote:

>  Hi Coupers,
>  My '87 560 has developed a firm, even hard, shift from 2 to 3rd gear
>under normal acceleration. This happens only when warm and after driving
at
>least 20 miles.
>My transmission fluid and filter have right around 7k miles on them.
> I suspect the modulator has failed and I will pull that out and test it.
>I just wondered if there were any other thoughts as to what might cause
>this.
>
>Thanks,
>Rick Hesek