300DTurbo tranny hard shifts
 

Hello all:
New owner here. I just bought a 1987 300D Turbo for a daughters' first car. I'm new to Mercedes, foreign cars and Diesels. Been a backyard Mechanic for 30 Years though, and the car does run. It has really hard shift points though, shove you thru the seat hard. The kid who owned it siad it was normal, but I don't buy that. Any Ideas? What tests do I need to do to see where the problem lies. I have the haynes and Owner's Bibles on the way. And I'm not in any huge hurry to get it on the road either, so I can take my time.
mike

try reseting the computer back to factory shift points
 

I don't know if it'll work on an 87 D, but it defintley works on my 90 300TE.

I have a 1992 300D that had the same problem , so I had all the rubber vacuum lines changed and the problem was solved. Also check all the vacuum connection. Cheap and easy fix and it will fix other problems also.

Hope it works.

I second the vacuum lines motion! R&R them for easy peace of mind:cool:

Hard shifting is a symptom of no vacuum (or low vacuum) to the transmission. Usually a simple vacuum leak, it takes a tiny leak to cause this. Another thing that causes hard shifts is low off-boost enrichment, search ALDA if you don't seem to get any power at all until ~2000rpm.

BTW, the "124 owner's bible" is useless IMO, the Haynes might be a little better, but you need the Factory Service Manual ("FSM") for any really useful information, available I believe for around $40 from Mercedes on CD.

I'll second the endorsement on the factory manual. The bible is nice reading but not very helpful for repair. You will also need Steve Nervig's index, which makes finding your way around the manual much nicer (the factory CD interface leaves a lot to be desired).

http://web.mac.com/dakota/Mercedes/Home.html

Shift timing is controlled by a cable that runs from the tranny to the engine throttle linkage, and shift quality (hard or soft) is determined by vacuum. If your power brakes are working fine, then you probably have good vacuum output from the vacuum pump (more on that pump later), so as suggested you probably need to track down and fix vacuum leaks. On the transmission itself there is a vacuum modulator that can be adjusted, but you really need to first fix the leaks to make sure the proper vacuum signal is getting to the transmision.

Here is a nice link to describe your challenge:

http://www.continentalimports.com/ser_ic20242.html

Now, your vacuum pump. If it is original, you need to replace it. The original pumps have a crimped-on cover, the replacements have a screws holding the cover down. The original pump design is flawed and the pump can fail in as little as 125k miles (by 250k miles the odds of failure are very high); when failure occurs, parts get dropped into the front engine cover, which is also where the timing chain lives. Those metal parts will break the timing chain if they get caught and that will destroy the engine. You can find your vacuum pump by following the big plastic line from the power brake booster to the front of the engine.

I think Jeff is right. You've got a vacuum problem somewhere. Often times the problem is not in the transmission circuit per se, but a leak elsewhere causing a general low vacuum condition. You'll need a MityVac to trace it down.

Emissions control and HVAC are known vacuum leak points, after all the rubber connectors are replaced.

There's a black plastic line that runs from the round blue thing on the driver inner fender to the drive side of the transmission. It attaches to the top fitting that's not at the center of the round blue thing. At the other end, it attaches to a round metal device attached to the transmission just above the pan and ahead of the where the rod from the shift lever attaches to the transmission. There's a green cylinder about 2cm in diameter by 3cm long along the plastic line. Not uncommon for this line to be knocked loose during an oil change.

And of course there's all the other vacuum lines :)

Sixto
87 300D

You can find sites hosting the complete FSM that go up and down from time to time on here. I found 1 and copied the whole site to my hard drive, site was shut down few days later. Google copy website and you will find a bunch of freeware tools to do it. Best hour Ive spent on here.

Can you see this without timing covers removed? Is ther a pic somewhere of what new style versus old style looks like installed? Ive been worrying about this since I read the thread on pump failure, and have been wondering if Im due for for $400 investment.

This is what the new style pump looks like from the outside. Note the exposed screw heads -

http://www.w124performance.com/image.../vac_pump1.jpg

The screws keep even pressure on the gasket. As the gasket ages and gets dry and brittle, the crimps aren't enough to keep oil from leaking all over the front of the engine.

The more relevant change is inside as told by this sequence -

http://www.w124performance.com/image...p_failing1.jpg

http://www.w124performance.com/image...p_failing2.jpg

Without the cage, the balls fall out of the bearing. The roller makes skewed contact with the driving cam on the IP timer damaging that uncheap item. Complete failure sends shrapnel into the timing chain and eventually the oil pump. You can guess what happens next.

The redesigned bearing looks like this -

http://www.w124performance.com/image.../vac_pump6.jpg

There are vacuum pumps with screws on the front cover but old style bearings. I've seen used ones on eBay. I've yet to see a new one. Otherwise I'd save money on a used latest style pump.

Images courtesy of DaveM/gsxr

Sixto
87 300D

Thanks again Sixto. I owe you at least 3 beers by now.

All this means Ive got the old style pump in there...and 280k miles...

Re: 300DTurbo tranny hard shifts
 

Thanks all, Well I've been downloading, and checked what I can see easily. It looks like a new cover Vacuum pump. The brakes do work well. I removed a vacuum line connector, and have good vacuum, now I just have to get under there and look by the tranny.
Mike