722.6 problem - PeachParts Mercedes-Benz Forum

apb · #1 09-06-2009, 12:11 PM

My transmission shifts hard at higher rpm. I replaced fluid, plug (where the leak to the computer harness takes place), filter. Got the fluid exactly where it should be. It still shifts hard. Btw, it shifts normal below 2500 rpm.

So, I have to bring it in. Does it sound like a seals issue with the gears, or a valve body issue. Anything else I can try before bringing it in for repair.

I have 165k on this transmission, is it best to simply get a completely overhauled transmission rather than to repair whatever this issue is?

Thanks!!

Southern · #2 09-06-2009, 12:31 PM

Sounds like a weak/broken spring, have a look here: 722.6 valve body question

gmercoleza · #3 09-06-2009, 12:50 PM

Southern, replacing the weak or broken spring only fixes a flare (slip) from 2-3 or 3-4. It has nothing to do with shifting hard at higher RPM...

Southern · #4 09-06-2009, 01:07 PM

Quote:

Originally Posted by gmercoleza

Southern, replacing the weak or broken spring only fixes a flare (slip) from 2-3 or 3-4. It has nothing to do with shifting hard at higher RPM...

Your correct, however my trans sometimes slams into gear when I am at full throttle.

APB, another thing to check is your circuit board for the trans: 722.6 Erratic Shifting Problems Solved

It might take awhile for the trans to re-adapt, so don't expect immediate results unless you reset the adaption values.

apb · #5 09-06-2009, 09:53 PM

ok, thanks. How do I reset the adaptation values? So, no reason to replace that spring? I look at the connectors to the transmission control unit and there was no oil.

Southern · #6 09-06-2009, 10:21 PM

To reset do the following steps with the drivers door closed:

1. Turn the ignition key to the on (not start) position.

2. Press the gas pedal to the floor and hold for five seconds.

3. Turn the key to the "off" position (don't remove the key), then release the gas pedal.

4. Wait at least two minutes for ECU to reset.

apb · #7 09-06-2009, 10:32 PM

ok, I will try tomorrow. If this does not fix. Should I try replacing the spring to the valve body, or just give up and bring it in?
Does this sound like a valve body issue or something more serious?

Thanks for all the guidance.

Southern · #8 09-06-2009, 10:35 PM

The posts regarding spring replacement were from flared 2-3/3-4 shifts which usually happens at 1/2 to 2/3 throttle. I have noticed that at full throttle I would experience hard transmission shifts like you have. At 165K miles I would not rule out a worn spring. Once my spring arrives and I install it I can determine if it fixes the hard shifting at full throttle.

I am offering suggestions for you to consider before throwing in the towel and having your transmission rebuilt.

apb · #9 09-06-2009, 11:18 PM

ok, thanks! Keep us/me posted on the performance after replacing the spring. What do you mean by flared? It is slow to engage?

Southern · #10 09-07-2009, 09:31 AM

Flared is when the RMP's go up around 4000-5000 before shifting into the next gear. It's like shifting into neutral with your foot still on the accelerator. This only happens to me when I accelerate from a stop with the throttle from 1/2 to 2/3 holding steady. If I let up on the throttle before the shift point it doesn't happen or if I accelerate less then 1/2 throttle or more then 2/3 throttle.

apb · #11 09-07-2009, 09:59 PM

I decided to order the spring and some oil. I figure I would throw another 60 dollars at the problem, before putting me at the mercy of the repairshop. I really do not know a place to trust in Houston. I used to live in Austin and knew where to go there.

gmercoleza · #12 09-08-2009, 08:30 AM

60 bucks? How is that possible? I think my fluid alone was $130. The filter and gasket are probably another $20 or $30, and the spring with shipping was about $12 or so. All in all, fluid/filter and spring will run you somewhere around $175. That doesn't include the dipstick tool for $35 and an IR thermometer (if you want to do it properly)...

apb · #13 09-08-2009, 10:16 AM

3 liters of fluid, just replaced gasket and filter this weekend (will reuse). I already own the other stuff. So, one spring ($5) and 3 ltrs of fluid.

gmercoleza · #14 09-08-2009, 11:08 AM

When you last changed the fluid, did you change it all, or only 3 liters? The system holds 7.3 liters. I actually put 7.4 into mine, but I did drain the tranny cooler too. You need to change all the fluid to rule it out as the cause of hard shifting. Hard to do ifyou only change 3 liters. As stated previously, changing the spring in the valve body doesn't fix hard shifting. It only fixes slipping between 2-3 or 3-4.

apb · #15 09-08-2009, 11:13 PM

well, I change about 3 liters every 25kmi, so none of the fluid should be all that old. I really thought it could have been a plug adapter problem, the connector had a small amount of oil.... There is no oil in the tcu, and after replacing the connector, it runs about 30% better.
I guess I will change more oil this weekend, replace the spring and then bring it in to check the adaptation values and go from there. I suppose after 165kmi, it could be more than just a spring.

The frustrating thing is that noone else seems to have had those symptoms. A transmission that shifts into all gears, well below 2500 rpm, and very hard at higher rpms...

Anyone knows of a good shop, or how to find a good shop in Houston?