Transmission Worries

[Zagato]

I've heard many stores about the gearbox needing an eventual overhaul. But how would I know when mine is about to go?

Here's what has been going on with mine:

-I can feel the car squat whenever I switch between Park/Drive/Reverse/etc.
-Second speed literally leaps into gear (You can feel the car squat as well). No grinding or clunking, it just lurches. All the other gear changes are smooth though.
-Upon switching into reverse, the transmission doesn't react right away. Takes about 3  seconds before taking action.

[TJ 450]

As long as the transmission doesn't slip between changes or make any unusual noises, it should just be a matter of adjustment or inspection of the vacuum modulator or other components.

The squatting or lurch is most likely due to an excessively fast idle speed and the delay into reverse is nothing to worry about.

As long as the fluid is good and the modulator checks out OK and all other adjustments are correct there shouldn't be anything to worry about.

The first thing to check RE the modulator is the vacuum line, is it still connected?

Tim

[BAR]

Always be minful to keep up the fluid level as this will stop exaggerated wear and tear.

When mine went, there was a noticeable slipping in top gear, but I was still able to drive the car to the shop.

[Zagato]

As long as the transmission doesn't slip between changes or make any unusual noises, it should just be a matter of adjustment or inspection of the vacuum modulator or other components.

The squatting or lurch is most likely due to an excessively fast idle speed and the delay into reverse is nothing to worry about.

As long as the fluid is good and the modulator checks out OK and all other adjustments are correct there shouldn't be anything to worry about.

The first thing to check RE the modulator is the vacuum line, is it still connected?

Tim

Yeah my W116 has an excessively fast idle speed. The only thing I can do to cure that is pull back the throttle. But that seems to damage the pedal.
So lurching into second gear when accelerating is normal? I try to make it smoother by easing off the throttle when it's about to change gear.
How do I check the vacuum modulator and line? Do I have to check under the vehicle?

Also, would changing the transmission fluid and filter be a good idea, or would be a needless waste of money? I hear I could just add more fluid if it's low, rather than flush the system and change the filter.

[TJ 450]

Hi Zagato,

No, lurch into 2nd isn't normal, although it could be fixed through adjustment/replacement of the modulator etc, if necessary.
If the modulator is defective or requires replacement, you will need to take the car to an MB specialist as special apparatus is required to adjust the modulator pressure.
Otherwise it might just be the vacuum connection as stated before.

Yes, changing the fluid is a very good idea. To be thorough, you should also change the filter, drain the torque converter and replace the pan seal. The parts are the same as a W123 etc.

The modulator is beneath the car on the transmission. It's the white plastic device sticking out the side of the trans. The vacuum connection is the black rubber hose connecting into it, it runs back up to the rear of the intake manifold on the engine.
On your car, the modulator is likely to be the early metal version which has a banjo fitting on it and I'm not quite sure whether it's a rubber hose or what?
If you remove the vac connection, there should not be any liquid emerging from the orifice.

Click for a larger image...


Tim

[Zagato]

Hi Zagato,

No, lurch into 2nd isn't normal, although it could be fixed through adjustment/replacement of the modulator etc, if necessary.
If the modulator is defective or requires replacement, you will need to take the car to an MB specialist as special apparatus is required to adjust the modulator pressure.
Otherwise it might just be the vacuum connection as stated before.

Yes, changing the fluid is a very good idea. To be thorough, you should also change the filter, drain the torque converter and replace the pan seal. The parts are the same as a W123 etc.

The modulator is beneath the car on the transmission. It's the white plastic device sticking out the side of the trans. The vacuum connection is the black rubber hose connecting into it, it runs back up to the rear of the intake manifold on the engine.
On your car, the modulator is likely to be the early metal version which has a banjo fitting on it and I'm not quite sure whether it's a rubber hose or what?
If you remove the vac connection, there should not be any liquid emerging from the orifice.

Click for a larger image...


Tim

Thanks! I'll try to check it out tomorrow. I guess I'll need to take it to a main dealer. Hopefully I can get the transmission fluid and filter changed at the same time for not too much more on $'s.

[TJ 450]

It shouldn't be very expensive, even at a main dealer.

Tim

[Zagato]

I don't think the dealer in my area has the 'special apparatus' required to adjust the modulator pressure. When I phoned the serviceman, he said that in order to adjust the modulator pressure, frequent adjusting and road tests will be required to get it just right. So a few hours of work. Bad when it is $120 per hour.

I haven't made the appointment yet and not sure if I ever should. Maybe just changing the transmission fluid and filter would do it? I just noticed today what smells like burning transmission fluid in the cabin when driving long distances.

[TJ 450]

Maybe just changing the transmission fluid and filter would do it? I just noticed today what smells like burning transmission fluid in the cabin when driving long distances.

That's where I would start.

How is the fluid level?

Tim

[oscar]

Being a 74 model I don't think any adjustment can be done unless it's changing the size of the modulator pin.  With your modulator zagato it's worth visually checking it and the vacuum line going to it.  A new filer and fluid change isn't going to cure your problem I reckon.  You'll have to jack the front of the car up and get right under there.  The modulator is where TJ says it is but it will be an all metal gadget like mine pictured below.  In that picture you'll see the vacuum hose has cracked open and was leading to abrupt shifting.  Check that hose of yours and also note if there's any A/T fluid around it because you need to know if the modulator has a perforated diaphragm which will alter the the modulator's characteristics and hence shift characteristics.  Another sign common to perforated diaphragms in the modulator is caused by the engine sucking up A/T fluid through the diaphragm into the engine where it burns and causes white smoke at the tailpipe and that burning A/T fluid smell.  Depends on how big the perforation is and the strength of engine vacuum.

If you find that the modulator is cactus, renew it.  Mine cost me about 40-50 USD a few years ago.  But be careful when removing the old modulator.  There's a pin connected to the diaphragm which needs to be used in the new modulator.

[Big_Richard]

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[Zagato]

Checked out the vacuum modulator today. It's still connected and the vacuum line looks solid with no cracks or holes:

Sorry about the poor picture. Was in a hurry and couldn't find a good position to take the photo.
I think that the fluid is causing the poor changes. I checked the fluid and found it very difficult to read. There's no obvious fluid soaking on the stick to differ from the thin film of moisture stuck to the level. I assumed it's low and poured a bit in. So right now I'm unsure if the fluid level is normal or nearly empty.

Also, I asked the boys at Kal Tire if they could change my transmission fluid and filter. However, they told me it ain't a good idea for old, high mileage cars because the old fluid may be helping the gearbox hold together. He's afraid that once it's drained, new fluid would ruin the gears. He says he's seen it happen a few times before to other high mileage vehicles.
This true or a weird urban myth?

[oscar]

........the old fluid may be helping the gearbox hold together. He's afraid that once it's drained, new fluid would ruin the gears...........

Is it any wonder why so many of us end up getting our own hands dirty.  I'm trying to restrain myself from making fun of the quote.  He's obviously said it for a reason zagato but why.  Unless he's worried about new fluid cleaning the insides of the seals and causing leaks and.... I don't know.   Have I got it wrong?  Can someone else back me up if that is just a BS reason not to change fluid? 

If you're happy with the modulator that it's not leaking, go ahead with the filter and oil change I reckon and if you're going to get someone else to do it, source out an MB independant shop pleeeease!  Someone who knows these mercs.

[TJ 450]

They probably don't know how to, or couldn't be bothered doing it. Whichever way you look at it, that is complete BS.
The fluid needs to be changed as well as the pan seal and the filter.

If you are on an extreme budget, I would just drain the fluid at the dipstick tube fitting and refill it to the correct level to go on with.

Checking the fluid level is something that takes a bit of getting used to. Correct me if I'm wrong, but I bring the car to operating temp, cycle the shifter back and forth, leave in Park for a minute and check the level three of four times. I then perform the process again to be satisfied that the level is correct and within the markings. One must avoid overfilling at all costs, which is very easy to do. Adding fluid and checking the fluid level are all done with the engine running.

Tim

[Zagato]

Sure hope it's complete BS.
I'll try to take the car to a shop and have the fluid and filter (+rubber seals) changed as soon as I can. Next to the timing chain, a dying transmission is my biggest worry.