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  #1  
Old 11-01-2004, 03:58 PM
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Transmission B2 Piston, Governor, KIckdown

My 84 500 SEC (126) with the 722.311 Transmission is refusing to upshift except at redline from what is Either 1st or 2nd gear. Reverse is fine. The engagement of both reverse and the forward gear is without incident. No delay, slippage, clunk or other abnormality. The Kickdown switch under the accelerator pedal is working. Kickdown solenoid that screws into the tail shaft of the transmission is operational; I removed it and bench tested the needle valve while powering up with 12V. Needle valve shifts at the application of power (I was blowing into the valve) allowing passage of air and in the proper location I suspect transmission fluid. Valve closes again as power is interrupted ATF has a flavor a bit like chicken.

Transmission pan was dropped and was as clean as a whistle. I have thus exonerated the valve body for now. The Bowden cable has not come loose and does not appear to be stuck. I can operate the lever inside the pan and feel tension at the firewall as it is connected to the throttle linkage. The plastic governor drive gear was a suspect but I do not believe the car would upshift at all if the governor was malfunctioning. Is this an accurate assumption? The speedometer, which is often indicative of governor failure is working properly. I plan to have the governor pressure tested next week. I believe that I should see pressure drop @10 P.S.I. as R.P.M.'s are increased from 1000 to 3000. If pressures remain constant the governor is the culprit. Can anyone confirm this?

I have read the posts pertaining to B2 piston failure but remain a bit unclear on the matter. Is it the case that with a stuck B2 all forward gears must fail? My understanding is that B2 is engaged in all forward gears except 4th. B2 acting alone in 1st, joined with B1 in 2nd; Dropping B1 and adding K1 for third and allowing K1 and K2 to take over the duties for 4th gear.

Any light that can be shed on these matters would be greatly appreciated. Thank you in advance for any replies.

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  #2  
Old 11-01-2004, 05:28 PM
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Cool

Have you tried driving with the kick-down solenoid DIS-connected? IF not now is the time to disconnect the wire at the solenoid.

IF that resolves the problem take a close look at the "B" lock-out switch on the shifter.
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  #3  
Old 11-01-2004, 08:36 PM
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Thank you for your reply. Yes, I have driven with the kickdown solenoid disconnected and it had no effect on the condition described. When disconnected I understand the electrical system is eliminated as a potential culprit, "B" selector included. Is this correct? I would like to believe at this point it is a failure of the B2 piston but I do not know if my symptoms can be considered indicative of that servo's breakdown.
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  #4  
Old 11-01-2004, 09:48 PM
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Transmission upshift delay

I'm not all too familiar with MB transmissions but on other cars the shift can be delayed to near redline with a disconnected vacume modulator or blown vacume modulator. Check that you have proper vacume at the vacume modulator and then check that the modulator holds vacume using a hand vacume pump.

John Roncallo
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  #5  
Old 11-02-2004, 12:57 AM
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B2 failure usually results in no forward gears, so it's unlike to be that.

The governor drive gear is plastic, it can break, but you are correct, it usually results in no upshift ever.

Upshift at redline only is syptomatic of a stuck kickdown, so if yous is working, I'd suspect a broken spring in the valve body -- the kickdow spool it stuck in kickdown.

you might try running at full throttle while clicking the kickdown on and off on the change whatever is stuck will free up, but I would personally consider a valve body swap. You can check the governor gear at the same time, but I'll be it's fine since you actually get upshifts if you wait long enough.

Peter
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  #6  
Old 11-02-2004, 03:23 PM
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Thank you for your replies. I will test the modulator. It was my understanding that if the vacuum modulator was failing I would experience slippage in all gears and any shifts that did occur would be rather hard. I initially put a flawed valve body on the back burner as I found myself with a very clean oil pan. I imagined that if the valve body was in some way impeded then something would have had to be responsible for such obstruction and some of this debris would be present in the pan. When I refilled the transmission I also added some Trans-X in an effort to free up any unwanted and troublesome elements within the transmision. I contacted German Star and they have one available for $275.00. I have never swapped a valve body. I will conduct a search to dtermine the nature of a valve body swap. Is there anything that immediately springs to mind as particularly challenging about such an operation?

I believe we are correct regarding the governor gear. I do not think there would be any upshift at all if it has been sheared off. A pressure test should bear this out. I understand that upon inspection, if you can rotate the governor by hand the gear is damaged. Will a pressure test also be able to relieve the B2 piston of any responsibility for the maladies that I am experiencing? Thank you again for your help and I apologize if any of you gentlemen get stuck driving behind me. 20 m.p.h. will try any man's patience. With your kind efforts to assist me I believe I will be back up to speed soon. Cheers.
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  #7  
Old 11-02-2004, 05:26 PM
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You are correct on both items! The modulator doesn't have any effect real on WHEN the trans shifts BUT on how hard!

IF The governor are stripped you have only first OR first & second gear.

Have you disconnected the shift cable completely & then driven the car?

VALVE body control pressure plunger may be stuck.
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  #8  
Old 11-02-2004, 07:00 PM
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It does upshift at redline but I am not sure what gear it places me in. I have not driven with the shift cable disconnected. What is to be expected when performing this test? Can the valve body pressure valve become stuck without a foreign entity being introduced? Is there a spring or some other mechanical element that can fail? This problem began suddenly, after I engaged the kickdown switch to pass a slower motorist and I have been unable to upshift (except at redline, which gives me some anxiety) since. At first I thought it was as simple as the KD switch being stuck or perhaps a stuck needle valve in the solenoid, but alas it was not. It would be too coincidental for it to be unrelated. What would the kickdown and in turn wide open throttle disturb to such a degree that would leave me scratching my head? I will be quite pleased to unravel this mystery provided it does not call for a transmission rebuild. Interesting to know that a failed governor could allow 1st and 2nd gear. I wonder if it could merely be upshifting from 1st to 2nd. I have only redlined it once and had to quickly come off the accelerator as traffic demanded it. I remain scratching. I must determine the governor's state of affairs. Cheers.
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  #9  
Old 11-03-2004, 01:30 AM
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The failed governor usually leaves some plastic bits in the pan, the gear comes all to pieces. Green plastic with spiral gear teeth. Stevebfl, I think, has posted some pics about six months or so ago, worth a search to look at them. If it upshifts eventually, it's working as the tranny will NOT leave the inital starting gear if it's broken, the hydraulics "think" the car is stationary,.

1st or 2nd would be determined by which gear the tranny normally takes off in -- my TE starts in 2nd unless you operate the kickdown switch on takeoff, so a similar situation might leave it in second rather than first.

There is a counter spring on the spool valve and on the pressure control valve, either could break and cause the condition you describe, and sometimes spool valves can get burrs on them in normal use that break off and make them stick. I believe there are also a couple check valves with plastic cages that can break that you should probably replace at the same time.

Valve body just bolts to the bottom of the oil passage casting, it' shown in the posted pics as well.

Peter
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1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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  #10  
Old 11-03-2004, 08:22 AM
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Cool

To start with the 722.3 trans DOESN'T have plastic governor gears!! ONLY the 722.4(small trans) has plastic gears!

With the cable disconnected the trans should shift into 4th by 25MPH under light throttle.

YES springs in the VB can break & pistons will seize as well for NO apparent reason.

You can check governor operation if you want (send private message to me if you wany more info about that test!).
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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  #11  
Old 11-03-2004, 06:20 PM
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Noupshift till redline

Enough has been said all things point to faulty valve body shift spool/spring causing shift points to be 'wide open'. Tranny is 'thinking' you have your right foot resting against the front bumper.

Not the governor
Not the vac modulator
Not the B-2 piston
Not other clutches
Not kick down solenoidpressure control

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