rexpontius

After fixing the damaged gearbox gasket last week I tried to fine-tune the gearbox 'settings' meaning bowden cable and vacuum modulator.

Shift points are now perfect and harshness/softness is also just the way I like it trough all the gear.

One problem however has been there since I bought the car and I cannot seem to get it resolved:

In 'D' I will not get first gear. Not with WOT/Kickdown not with part throttle, just never. Also not when putting the selector in 2 and then moving it back to 'D'.

I will only get first putting the selector in 2 and leaving it there.

After changing the fluid again when fixing the broken gasket, it suddenly worked with the selector in D, but just as suddenly stopped using it again.
Fluid is standard dexron IID.

Sometimes when the car is cold, it will occassionaly start up in first gear, but very quickly gets back to starting from 2nd gear.

Are there any gearbox-guru's here who can explain what could cause this behavior??

Car is 86.5 with 4-speed (now more like 3-speed ) 722.3 transmission.

Have not tried to fabricate a kick-down bypass switch yet, but would really like to find a solution to avoid having to select ''2" and then back to "D" with longer sprints

Cheers

Maleficio

I think I heard that your model uses first for towing only, but I'm not sure what would inspire the car to downshift to first after you've connected a trailer.

rexpontius

I guess that would have to be the donkey behind the wheel putting the selector in '2'

But seriously, I do not understand why then it sometimes works ??

89FrontPorsche

If I understand correctly, I'll just add that I learned how to start out in first by selecting "2" when slowing and just before the car comes to a stop, it bumps into first. You can feel it. But it will start out in first and stay in first until you move the selector to "3"...but depending on how hard you're accelerating, it will go into third pretty quickly, unless you are about 1/3 throttle or more (or thereabouts).

I hope that helps. So when coming to a stop, somewhere where you'd like to downshift, select "2" and it'll help slow the car, then bump into first just prior to the stop. It's also been my experience that I can get it to do it on my '89 by selecting "2" right away and just crawling, and then it does the bump into first routine. But you have to leave the selector there for it to do it, then when you desire to upshift, move it to "3".

I hope that makes sense. I was told by a factory tech that the 4-speed autos like to start out in 2nd when the selector is in "D". Just the way they engineered it.

You probably know all that, and if so, I'm sorry. Just trying to be helpful.

Landseer

Your 89 is different than his 86. I've got both and know what you mean. (The 89 starts in 2nd unless tromped hard, or if stopped and 2nd position selected.). The 86 should lurch a bit as it downshifts into first whilst coming to a stop, plus, should always start in first.

Suggestion: send an email or PM to the guy here Steve Cattaneo. He is extremely knowledgeable, and despite it being his business, he shares with us.

Another suggestion: Research it from the perspective of it being an 80's Mercedes transmission, one of the heavier versions for the V8 sedans, which it is except for some case adaptations. It has Mercedes marks on it and I have gotten parts at the Mercedes dealer, fyi. You are more likely to find an older Mercedes mechanic in your area that might share with you the reasons. There may be books and even VHS tapes or CD's showing rebuild procedures. I know that the proper diagnosis involves hooking up pressure gauges and driving it and recording pressures. Doesn't look very complicated.

The CD set we recommend here has transmission manuals with it also, if that helps. The WSM has some good descriptions too. I'll look through it for some root causes for you, but didn't see it discussed last time I hunted.

It seems that few regular 928 folks have ventured into the automatic and finished the job of a rebuild, me included.

As they wear-out and age, that will change.

DeWolf

Mine will start in 2nd if left in D. Shift lever to 2nd and it will pull first to redline if the pedal is mashed. Mine is an 85 Euro.

Landseer

So is the ROW model set-up differently?

supercedar

On my 1988 it will stay in 1st gear when selected in 2 before a stop. It will also stay in 1st when pressing hard until I let up and press again, it will then shift to 2nd. It will also shift to second from 1st when it redlineson its own. Another thing I do is start in 1st and run up to about 5,000rpm then select 3rd and back to 2nd quickly and it will stay in second to max out 2nd rpms. I am still working on this trans to figure it out and am confident I will end up liking it.

rexpontius

Steve Cattaneo suspects the B2 piston.
Did some searching on this topic, but cannot quite match the behavior to other B2 piston failures.

Can anyone explain how the B2 piston basically operates and what could cause the behaviour of skipping 1st gear in D?

cheers

rexpontius

Anyone?

SeanR

When the B2 goes, you will loose 1st/2nd gears, but if you can get enough speed for 3rd to engage, then it will operate normally. It's a common failure.

rexpontius

That is not the issue in my case.

Box works fine, exept it will skip first gear in D 99% of the time. With selector in 2 it will start from 1st just fine.

Drewster67

My understanding is if you leave the car in drive and come to a stop. It will not drop to first - only second.

Put the car in second and come to a stop - it will drop to first.

Someone please correct me if I am wrong.

Thanks

rexpontius

This weekend I drove the car for ~150 miles which was a real treat.

Did notice some other gearbox related things which seem to me are not OK.

As explained before, the car will not use first gear when the gearbox oil is warm.

Today after some highway driving I also noticed some vibrations in the driveline with the car in reverse. Like a 'clunking' vibration every 1-2 second when rolling backwards slowly (not when standing still).

A while later at the stoplight I pulled away with the selector in 2, I noticed similar behaviour at low speeds and low load.

It does not occur in D, when the car pulls away in 2nd gear?

Could all this behaviour be B2 piston related???

cheers

rexpontius

Anyone ?