All -

I am continuing my efforts to keep the Wayward Woman, my rescued 380SL on the road. My current problem as described in an earlier post is that the transmission behaves very badly from a stop after warming up. See the following for details:

722.3 Transmission Troubles

I have bought the book published by ATSG, which is helpful, and I found an even better reference in a PDF on the web:

http://w126.pp.ru/akp722.pdf

Anyway, I believe (always the optimist) is that the problem is caused by the transmission not shifting correctly into first gear when coming to a stop. If I shift to Neutral, even for a second, then first gear is correctly engaged and everything is fine. And, again the optimist, I am hoping that this is a correctible problem not needing a rebuild.

According to the Mitchell Guide:

"In 1st gear, brake band B-2 is applied, and one-way clutch is locked. Both planetary gear sets are involved in gear reduction."

and -

"When the selector is moved from the "N" position to "D" position, brake bands B-1 and B-2 are controlled."

That's about all the information that seems to exist in the Washington DC area. The general response is "hmm, better get a factory rebuild." Maybe that's what I need, but I would at least like to satisfy myself that there is not a simpler solution.

Does anyone have an idea why the transmission would shift well after a quick pop to Neutral, but go completely to crap when left in Drive or shifted manually into low?

Dirt in the governor and a broken pressure relief valve have been suggested. The governor sort of makes sense because it runs off the tailshaft and could prevent a downshift to Low if it "thought" the car was moving too fast?

As always, any suggestions are appreciated.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

If you have big cajones pull and overhaul/clean the valvebody. If you dont, get a reman valve body. Personally I'd swap one just to see if there was a change in it reaction. Sounds to me like there is a sticking command valve, either 1-2 or 2-3. The balls, (look in the book) will also erode some and leak like a sieve as will the apply piston seals.




Joe

__________________
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

When it comes to this stuff, my cajones aren't much bigger than the check balls. But I will give it a try - a rebuilt valve body and an autopsy of the current one.

Thanks.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

go to howstuffworks.com and you can find a nice explanation of how auto trannies work. generically, of course; nothing specific to any make or model.

As you slow down the trans also changes gears, sounds like you have a problem with B1 engagement & then dis-engaging. MB offers an "auto-adjusting" B1 piston that usually helps with that problem. You can retro-fit that part to your transmission.

You will need (1) 124-270-12-32, 140-277-08-40, & 005-997-86-48. ALL 3 parts have a total list price of $65.

Installing that takes about 2-3 hrs, w/o removing the trans.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

The primary pump, supplies pressurized fluid to the hydraulic circuit. This pressure applies bands, clutches and lubrication for all moving parts. The most hydraulic circuits are found in the valve body. As the fluid moves into the valve body it has the potential to actuate every single valve. When the valves move they redirect the pumps pressure to control the application of bands and clutches thus providing up and down shifts and different ratios through the planetary system. The pumps working pressure is always the highest pressure in the hydraulic system.

All other pressures are derived from this maximum pressure and is reduced and controlled by regulating valves. The primary control valve is the pressure regulator valve. Mercedes calls this valve the control valve working pressure. It controls and regulates the amount of working pressure in the transmission. This pressure varies depending on which way the valve moves. If the valve moves towards the spring, which sometimes breaks, we have low working pressure. If it does not move, or moves a little, we have high working pressure. There are other pressures that balance and regulate the pressure regulator but when we have 210 pounds of working pressure in a vehicle in drive, the problem is usually the pressure regulator.

The governor is the road speed input from the transmission. It has no regulating pressure from a stop and does not control a first gear start in any valve body. In a Mercedes first gear start valve body, the 1-2 command valve is stroked in the first gear start position; by design once the car is started, commanding the B2 band on and the F, one way clutch locked. If the valve body were a second gear start, then the one two command valve would be stroked in the 2nd gear start position commanding the B1 and B2 bands on.

The description of operation in that PDF is for a 1996 C22, which Is a 722.4 transmission that starts in second gear.

What they are referring to by the engagement dampening circuit, is the accumulator cutting in oil circuit wish is a dampening system designed to soften shift engagements from a dead stop (not at road speed):

The dampening circuit just cushions the selected gear engagement.

N to D = B1 and B2 = 2nd Gear
N to 3 = B1 and B2 = 2nd gear
N to 2 = K1 and b2 and f is locked = 1st gear
N to R = K2 and B3 = Reverse




In the neutral position there is no power flow between the engine and transmission, no bands or clutches are applied. This is also the towing and push start feature of the car.

By moving the transmission lever from neutral to drive at road speeds, you are going from a pressure less system (neutral) to a high pressure system (drive). At that high pressure you are probably freeing up whatever is stuck in the valve body.

I think the problem is in the valve body. If that car was at my shop I would change it.


In any 722.3-4-5 MB or Porsche 928 if you move the selector lever manually to second, the transmission will start in first gear. This is engine breaking. Try that as a test.


Good luck

Thanks for the explanation and the suggestion about the valve body and the B1 piston kit.

I am on the road this week (damn day job), but I will look into a rebuilt valve body and the B1 kit. WRT the latter, it seems like the trick would be compressing the cover enough to get the snap ring and the rest of the stuff out in the close quarters of the transmission tunnel.

I will keep you posted.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks for the explanation and the suggestion about the valve body and the B1 piston kit.

I am on the road this week (damn day job), but I will look into a rebuilt valve body and the B1 kit. WRT the latter, it seems like the trick would be compressing the cover enough to get the snap ring and the rest of the stuff out in the close quarters of the transmission tunnel.

I will keep you posted.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I would guess a sticking valve or leaking check ball, possibly a leaking servo, but that's not likely.

The reason it works properly when you shift to neutral first is that you dump all the control pressure off the shift valves when you take it out of gear, and I'd bet it's hanging on the downshift to first.

Auto trannies work by applying hydraulic pressure to either clutch packs made up of disks coated with friction material interleaved with steel plates or by servos clamping a band on a drum. MB uses two or three bands (for the three planetary sets) and three clutches -- the bands clamp around the ring gear "bucket" and the clutch packs are splined inside and out -- one side for the frictions, the other for the steels. In modern practice, there are also several "overrunning clutches" (also known as sprag clutches) that only allow free rotation in one direction. Much lighter that a clutch pack, and no hydraulics needed.

Pressure is applied to the correct band servos or clutch pistons by a "mechanical computer" consisting of spool valves and springs. The spool valves open and close hydraulic passages as they move back and forth under the influence of springs and hydraulic pressure (or the shifter linkage). If the spool valves are dirty, they will stick, so the correct pressures aren't applied.

The check balls serve to "cushion" the pressure changes so the tranny doesn't slam the clutches or servos on -- Torqueflites were well known for snapping the low/reverse band actuator end off if downshifted manually at high speed -- police cars had the first gear position blocked to prevent this. When the tranny gets worn and the pistons in the servos and clutches have to move a long way to engage, the tranny "flares" between gears since it is in netural with no clutches engaged. Some will shift VERY hard under these conditions if something is allowe dto turn backwards momentarily.

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

You might add some transmission cleaner, such as from 'BG'. Sometimes a build up a crud and varnish causes problems.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Just finished ordering a MB-rebuilt valve body and B1 kit, plus new filter and gaskets. My rationale is that I can at least use these if I end up with a used tranmission if this doesn't fix the problem.

Thanks again for the help. Any words of advice on the install?

CT

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Clean, clean, clean, clean.

Any grit in the valve body will cause the spool valves to stick or leak.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Decided to go with the B1 kit and a rebuilt valve body.

I have ordered and received the B1 kit. Mercedes does not sell rebuilt valve bodies anymore, only new ones. I finally found one for $275 at German Star, but they need the P/N off the old unit. So last night I dropped the pan, got the number (126 270 86 07) and ordered the valve body.

Stay tuned.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I ended up having to send my valve body to German Star's rebuilders in Texas. It came back today, shrink-wrapped in plastic but otherwise not looking much different. So tonight I installed it, and put everything back together.

Took a test drive and observed (with some pleasure) totally normal operation. In addition to not doing the awful stuff, I noticed other improvements

- no more flare into 4th when cold
- no more "clunk" downshifting when coming to a stop
- better downshift from 4th to 3rd (climbing a hill under light throttle)

So I am thinking that I will quit while I'm ahead and not do the B1 kit. Opinions?

Thanks for all the support. I never would have tried this without the suggestions.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I a glad it work out well, of all the hydraulic Transmissions, the MB is the most complicated to diagnose and repair. I would not use B1 piston; it has a problem with the self adjustment.