Help needed diagnosing w123 transmission - PeachParts Mercedes-Benz Forum

BlaueReiter · #1 08-08-2008, 09:55 AM

Hey guys,
Complete newbie Mercedes owner here...recently bought an '85 300td w/211,000 miles. Florida car, pretty well maintained (for the most part). I've owned old BMWs for years and years and lately I've gotten smitten with the Mercedes marque. Have a new son and I'm drawn to combination of technological sturdiness, personality and safety. They're beautiful cars, really, and I'm ready for some tinkering. I'm a decent DIYer, as a matter of survival. But I might have stepped into the proverbial crap here.

Here's my situation as way of introduction:
My wife drove the car about 20 miles the other night, and when she got to our block, the car started acting like it had no power--engine ran, but car crept. It got worse, but she was able to park it in front of our house, but not without a lot of effort. She had to really floor it to get forward or reverse. She described it as like having the emergency brake engaged. I went out to the car and experienced the same thing.

here's the thing. I haven't been able to duplicate it. The next morning it shifted fine. I have some slipping/flaring going into 3rd gear, which could be clutch wear, but never any issue upshifting. Rough when its cold, but that seems normal.

I've been poring over the transmission threads to get a clue what might be going on with my new vehicle. I think I might have stepped into it by asking my mechanic to change the tranny fluid--it was dark and dirty. I should have read up some on this, as opinion suggests that if the fluid is dark and dirty, the POs might not have changed it regularly enough, and the fluid provided the extra friction the tranny needed. Now that the new fluid has cleaned the tranny some, I wonder if this could be the source of the flaring (which wasn't so pronounced before the change) and the incident the other night.

Fluid level looks right. Fluid doesn't smell burnt -- at least I don't think so (I'm rather new to autos).

Three mechanics mentioned the clutch wear revealed by the new fluid and said I should just grit my teeth and swap the tranny--it will need one eventually. Of course I want to rule out all possibilities before I plunk out a couple grand or more for a new trans.

should I be thinking about the 3rd gear flaring and the upshifting incident in the same thought bubble?

B2 piston replacment? Is it possible to tighten bands?

any and all suggestions thrown my way are appreciated. Need some education.

TIM
----------------------------
'85 MB 300td
'67 BMW 1600

kerry · #2 08-08-2008, 10:02 AM

Your wife's description does not sound as if the transmission was slipping but that the engine was not producing power. First thing I'd do is replace the fuel filters, air filters,and check the accelerator linkage.
Flaring can usually be modified by adjusting the vacuum (there are a number of good threads on this if you search it) and there is a shift kit available to resolve flaring problems.
I would not condemn the transmission yet.

BlaueReiter · #3 08-08-2008, 10:19 AM

Kerry--thanks for the reply.
All filters were changed, the car is running well.
When I tried it, the car wouldn't move until it got to 3000+ rpm.

the accelerator linkages seem to operating correctly. Some slack, but nothing outrageous.

BlaueReiter · #4 08-08-2008, 10:23 AM

also--I've seen the threads about the shift kit. I would definitely freshen up this tranny if I can rule out impending catastrophic failure

tangofox007 · #5 08-08-2008, 10:27 AM

Did you drain the torque converter and change the transmission filter when you replaced the fluid?

BlaueReiter · #6 08-08-2008, 10:41 AM

yes and yes.

tangofox007 · #7 08-08-2008, 10:49 AM

I am not a big supporter of miracles in a can, but I think that if I had your symptoms I would try a bottle of Lucas Transmission Fix. The fact that the problems started with the fluid change is a significant factor in that recommendation.

Bajaman · #8 08-08-2008, 11:29 AM

I tried Lucas before I swapped in my manual. I was having some pretty significant flaring even with no vacuum signal. It didn't really help that much. Flaring lessened maybe a little. It sounds like a miracle in a can will maybe buy you some more time, but that won't last too long.

BlaueReiter · #9 08-08-2008, 12:32 PM

Thanks for the suggestions.
I'd like to go through a troubleshooting routine before I settle for additives. That would be a last resort, I think.

The no-shifting/power incident could be totally unrelated to the flaring (or not), so I"m thinking I tackle things in this order: 1. check linkages 2. check kickdown/solenoid for wear 3. vacuum testing 4. possible replacement of modulator, b-2 piston, k-1 & k-2 springs. There seems to be plentiful resources on all these tasks. If anyone has another suggestion to fit in this routine, please fire away.

(I love the idea of swapping a 4-speed into this car, and I've read through some of the threads on that topic, but that might be a project for a later date. I expect to receive the finished body of my 1600 soon, and need to get that thing back together.)

jaschanks · #10 08-08-2008, 08:48 PM

Are you sure you checked the tranny fluid level properly? This same thing happened to me after I changed the fluid and filter including draining the torgue converter. I had no forward or reverse. Here I hadn't warmed the engine up properly and was getting false fluid level readings-much too low. Once the fluid was at the proper level everything worked fine. HTH,JEFF

pdxwaker · #11 08-08-2008, 09:19 PM

Your brakes may be getting stuck... if it happens again, try to open the bleed valve at each brake to see if there is built up pressure (look for a squirt of fluid when you open the valve).

I've had the same behavior you describe and it was due to some brake issues...

BlaueReiter · #12 08-08-2008, 10:06 PM

to be honest, I hadn't even thought it could be brake-related, even tho the wife said it felt just like driving with the emergency brake on. Never had such a thing happen before, but I'm guessing it would be due to swollen, older lines? Bad booster? The fact that I haven't duplicated it (yet) is perplexing me.

RE: the fluid--I drove the car about 10 or so miles, getting the temp up to 80c, then I checked it. Looked fine--level was at top mark.

thanks all for the suggestions so far.

BlaueReiter · #13 08-09-2008, 04:55 PM

It is indeed a brake issue. Back brakes (or emergency clutches?) locked up while running some errands today--lots of acrid burning pad smoke, car had to be pulled over to the side of the road til the pressure receded. Limped it home while the pedal slowly returned.

So the thread is incorrectly named. I'm pretty happy that the transmission hinkiness was just a red herring for this much more mundane and cheaply solved problem--just gotta figure out the source. Hopefully a simple caliper swap is all that's needed.

thanks for the ideas and suggestions, folks. I guess all I needed was to drive it enough to duplicate my wife's experience from last week