86 300sdl transmission help - PeachParts Mercedes-Benz Forum

Kevinc2 · #1 06-22-2009, 02:51 AM

Hi,

I have been on the forum for days trying to diagnose my transmission problem to no avail. My transmission will wind up to 4000-4500 sometimes 5000 before it shifts from first to second. You will have to drive 100 yards or so at 4k before it shifts. It seems to shift easier when cold. It will shift up through the other gears without incident, and downshift without incident just a little clunky.

I was working on vacuum issues yesterday and the transmission improved for a minute and then went back to hard shifting. I think my VCU may be bad, but I read in a post by Brian that vacuum does not control shift points.

I disconnected the kickdown switch and that made no difference.

The Bowden Cable is loose, I loosened it more.

The fluid and filter have been changed recently.

Fluid is red and does not smell.

I added some Lucas product to the transmission to see if that helped, it did not.

The transmission was overfilled at one point, by stupidity on my part. I did not know it needed to be up to temperature, figured it out a few days later and took some fluid out, it was a little foamy. Now I check the level with the transmission hot, at idle, in park. The fluid should be at the second mark...correct?

Is there anything else I can do or test?

Thanks for your help, you guidance has been invaluable to me with past issues.

tbomachines · #2 06-22-2009, 09:02 AM

The vacuum controls how firm the shifts are rather than shift points. Too much vacuum and you'll see flaring in between shifts, too little and you'll get back-breaking firmness. The Bowden cable changes the shift points. Before going any further MAKE SURE that these are properly tuned or else you'll be throwing time and money away.

Once you're completely confident that your vacuum and bowden cable are properly adjusted, you can move on to more involved work. If all is okay with the vacuum/bowden, my guess is that the B1 spring is either too slack or more likely, one of the little springs in the valve body is getting loose with age (or could have broken) causing your flaring. To solve you'd take off the valve body and clean clean clean while inspecting all the little springs and balls. You might want to consider the "superior shift kit" (search for this term, also in DIY section) which replaces all the springs which tend to stretch over time.

Here is a thread with great pictures and descriptions of the valve body:

http://www.peachparts.com/shopforum/showthread.php?t=250153&highlight=B1+accumulator

Brian Carlton · #3 06-22-2009, 09:16 AM

Quote:

Originally Posted by Kevinc2

The Bowden Cable is loose, I loosened it more.

Here's your last shot:

Have another person assist you to check this cable. It might be loose at the throttle linkage but be binding internally and preventing the transmission from reducing the throttle pressure.

See if you can verify that it's working properly at the transmission...........not an easy task, but necessary in this case.

You've covered all other bases..........and you're out of viable options at this point. Despite the multitude of "vacuum" claims, it's not going to help your specific situation.

Kevinc2 · #4 06-23-2009, 06:40 PM

Spoke to a transmission shop today on the phone.

They said symptoms sound like the B2 clutch pac nothing a $2400 rebuild can not solve. Or possibly a governor issue $700 or so.

What do you guys think? If this is the case should I buy a rebuilt transmission and install myself? My skills are ok, I have never pulled or installed a transmission before.

I may sell as is. A shame the car has 188K and is in mint condition.

What would be a reasonable price to ask?

Thanks

mplafleur · #5 06-23-2009, 10:29 PM

I paid $1150 for my last transmission rebuild.

As for DIY, the trans I don't think is that hard to take out and put in. We had one member a couple of months ago get pretty good at it once he got a transmission jack at Harbor Freight. I think he could pull it in about 1/2 hour.

I'm not sure it's the B2 that is the problem, although I'm no transmission expert. It's odd that it worked at some times.

Disconnect the bowden cable and see what happens

tbomachines · #6 06-23-2009, 11:45 PM

How long was this mechanic looking at it? I would definitely look at the B2 piston before suspecting the clutch pack. I doubt the mechanic opened it up and inspected the piston and bushing. I replaced the B2 piston in my car, it cost about $120 in parts and 5-6 hours of work, probably something you can look into before dropping a ton of money on a new trans.

LUVMBDiesels · #7 06-24-2009, 07:02 AM

First of all loosening the bowden cable sets the shift points higher. Try tightening it to the point where there is hardly any play at idle. Then drive it and see if this helps. If the shift points go down in RPM, you can then adjust the cable so that the trans shifts at 3700 RPM floored.

mplafleur · #8 06-24-2009, 08:51 AM

Quote:

Originally Posted by LUVMBDiesels

First of all loosening the bowden cable sets the shift points higher.

Sorry, had it backwards.

Woops, I didn't have it backwards.

Brian Carlton · #9 06-24-2009, 10:25 PM

Quote:

Originally Posted by LUVMBDiesels

First of all loosening the bowden cable sets the shift points higher.

Incorrectamundo...........tightening the cable sets the shift points higher.

With the cable disconnected, the shift points are at the lowest possible points.

LUVMBDiesels · #10 06-25-2009, 07:26 AM

Quote:

Originally Posted by Brian Carlton

Incorrectamundo...........tightening the cable sets the shift points higher.

With the cable disconnected, the shift points are at the lowest possible points.

Oops... I always thought looser = higher as you need to move the linkage more to get the cable to the same position. That seemed to work on my 300SD If I am wrong I apologize.

Brian Carlton · #11 06-25-2009, 09:33 AM

Quote:

Originally Posted by LUVMBDiesels

Oops... I always thought looser = higher as you need to move the linkage more to get the cable to the same position. That seemed to work on my 300SD If I am wrong I apologize.

If you loosen the cable, you reduce the throttle pressure for any given position of the go pedal. Accordingly, the shifts will be earlier. Tightening the cable has the opposite effect.

mplafleur · #12 06-27-2009, 03:08 PM

Any new info in this????

Today, I plugged the kickdown switch back in.

While driving I engaged the kickdown switch and it downshifted one gear and I accelerated forward. The problem is now, the trans only shifts at 4500 rpm ALL THE TIME.

I disconnected the kickdown switch and it didn't eliminate the problem. I drove home like that and I will let the trans cool down and the fluid pressures return to normal and try again.

So something is stuck? What does the kickdown switch actually do to the transmission?

mplafleur · #13 06-27-2009, 08:13 PM

So no one on this forum knows how this works?

Brian Carlton · #14 06-27-2009, 08:26 PM

Quote:

Originally Posted by mplafleur

So no one on this forum knows how this works?

Can you check the Bowden cable for freedom of movement? If bound up, it will stick in the open throttle position and cause the problem you have.

mplafleur · #15 06-27-2009, 09:05 PM

How nuch movement should I have with the cable? I removed the Bowden cable connection and it had no effect.

I also pulled on the cable a few time to see if is was bound up. I was able to pull out the cable an inch or so and it retracted.

I searched Benzworld for a while and while some people have had this problem, no one ever posted a resolution.