240d trans into 300td? - PeachParts Mercedes-Benz Forum

Zacharias · #1 11-04-2010, 12:23 AM

Hi folks, I have a 1980 300td (that is, non-turbo) with a trans that won't shift up from second gear. I can't find any external reason for it.

I happen to have a 1982 240d automatic parts car.

Can anyone advise me: can I use the 240d trans for the 300td?

I looked in the Nitske book and the gear ratios are identical, so I am wondering if it's actually the same transmission.

Thanks

kerry · #2 11-04-2010, 01:03 AM

Have you checked the kickdown switch and bowden cable for malfunctions. These are typical reasons why the transmission will not upshift. How many rpm's have you run it up to without shifting? Have you tried shifting it manually?

vstech · #3 11-04-2010, 09:56 AM

the trans should be same.
however, are you SURE it won't shift up from 2nd? how long did you hold the motor in 2nd? past the II tick marks on the speedo? (around 45 or 50 IIRC) you could just have a stuck kickdown switch. is 1st to 2nd a long time? like around 25 before it shifts?

Zacharias · #4 11-04-2010, 09:59 AM

Hi Kerry, it's a non-turbo so I have no tachometer, but I have wound it up over 45 mph for sure. It was screaming.

I was under the impression the bowden cable was only on turbo models. Is the bowden the cable running from the linkages on the valve cover, down to the transmission?

Tks

Quote:

Originally Posted by kerry

Have you checked the kickdown switch and bowden cable for malfunctions. These are typical reasons why the transmission will not upshift. How many rpm's have you run it up to without shifting? Have you tried shifting it manually?

Zacharias · #5 11-04-2010, 10:03 AM

I have driven it for about 20 minutes this way on back roads, and I held it until it was absolutely wailing. Its a non-turbo so I have no tacho, but it was over 45 mph for sure on one run.

I have checked the kickdown switch... it seems to be functioning normally.

It shifts normally from 1st to 2nd, very quickly and smoothly actually (compared to the three SDs and the 240d I've owned in the past).

BTW, the vacuum line to the transmission is connected.

Tks

Quote:

Originally Posted by vstech

the trans should be same.
however, are you SURE it won't shift up from 2nd? how long did you hold the motor in 2nd? past the II tick marks on the speedo? (around 45 or 50 IIRC) you could just have a stuck kickdown switch. is 1st to 2nd a long time? like around 25 before it shifts?

kerry · #6 11-04-2010, 10:28 AM

Yes, the bowden cable is the one from the valve cover to the right side of the transmission. On earlier models it is a rod and not a cable. On some models there is no rod or cable just vacuum control. If yours is a vacuum controlled only model, I would remove the vacuum and see what happens.
I can't remember a case on this forum where a failure to upshift necessitated the replacement of the transmission. Perhaps other members can.
Have you tried manually shifting it?

Zacharias · #7 11-04-2010, 11:02 AM

I did try manually shifting it at first, but nothing changed. The car sat for over a year before I got it, and I had kind of hoped this was an issue related to non-use. (I had an SD that wouldn't shift into 4th for the first week after I put it back on the road after long inactivity.)

I will look over everything on the weekend.

Tks

Quote:

Originally Posted by kerry

Yes, the bowden cable is the one from the valve cover to the right side of the transmission. On earlier models it is a rod and not a cable. On some models there is no rod or cable just vacuum control. If yours is a vacuum controlled only model, I would remove the vacuum and see what happens.
I can't remember a case on this forum where a failure to upshift necessitated the replacement of the transmission. Perhaps other members can.
Have you tried manually shifting it?

babyjames · #8 11-04-2010, 05:49 PM

Worst year for the 123, for me anyway. Vacuum ONLY to the transmission. I've put a transmission from an '82 240 into a '79 sedan before, and that went perfectly. Not saying you won't be able to use the transmission from your 240D in that '80 TD, necessarily, but you may have to find the appropriate throttle linkage from another car. You'll have to get under there and look.

Jay.

kerry · #9 11-04-2010, 06:32 PM

I would begin my monitoring the vacuum in the line going to the transmission as you drive to see what is happening. You could T in a Mity Vac and leave it sitting on the cowl in front of the windshield to monitor the vacuum levels.

I'd do a search on a 1980 transmission or a vacuum controlled only transmission to see if there are troubleshooting procedures for it on here.

Zacharias · #10 11-07-2010, 10:17 PM

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.

I did read one post on switching over the connections on the vacuum switch (on the valve cover) as an experiment.

I tried it: immediately I got all my upshifts back, but all except 1 --> 2 flare like mad.

This is good news, as I can't see it being a mechanical failure issue now, it's a vacuum troubleshooting issue.

I'm going to order a new vacuum switch and try to dig out my old vacuum tester. It's been a while since I messed with an old Mercedes.

Thanks for the help. Any further advice at this point?

kerry · #11 11-08-2010, 08:38 AM

That's good news. Maybe starting a separate thread on 80 Vacuum controlled transmission troubleshooting might be good since there isn't much on here. I would do two things. 1--monitor existing vacuum in the configuration where it wasn't shifting. 2--monitor vacuum in your new experimental configuration. 3--disconnect all vacuum connctions to the transmission except for the Mity Vac and feed the mity vac into the passenger compartment and drive around pumping different amounts of vacuum into the mity vac to see how the shift patterns change.
What would be very useful on the forum would be a conceptual analysis of how the transmission is controlled strictly by vacuum? On bowden/vacuum systems, vacuum controls harshness of shift and bowden controls shift points. Vacuum must do both on your model. Given the fact that you're now flaring, I'm assuming that your experiment increased vacuum to the transmission. You could simply remove the vacuum line fromthe transmission so it is getting no vacuum and see what happens. Given what has already happened, I'm guessing it wont upshift at all.
Another possibility is that the modulator is failing but I would think it is far more likely that the problem is in the amount of vacuum--which could also be a failing VCV if you have one.

franklynb · #12 11-08-2010, 05:04 PM

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.

franklynb · #13 11-08-2010, 05:11 PM

Quote:

Originally Posted by kerry

What would be very useful on the forum would be a conceptual analysis of how the transmission is controlled strictly by vacuum? .

here's my start:

http://www.peachparts.com/shopforum/showthread.php?t=261946

Zacharias · #14 11-09-2010, 03:41 PM

Quote:

Originally Posted by franklynb

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.

Thanks for all the info. Two questions:

1. Is there any way to clean out the VCV? I did notice oil sitting inside the top vacuum line connection. I was hoping it was residue from my recent oil change. Perhaps not.

2. When you refer to the switchover valve, that is a new term to me. You don't mean the white, 3-port vacuum switch on top of the valve cover, do you? If so I don't understand what you are saying... on my '80, the vacuum supply from the main line runs to that, with an offshoot line then supplying vaccum to the VCV....

Cheers