722.4 transmission now shifts from first to fourth - Page 2 - PeachParts Mercedes-Benz Forum

Walkenvol · #16 10-16-2012, 02:50 PM

Quote:

Originally Posted by mach4

And let me throw the other potential solutions out there for some feedback

1- Replace the 722.4 with a 722.3 which is a substantially stronger transmission
2- Install a manual 4-speed

I vote option #2.

To me, a manual fits with your ride.

mach4 · #17 10-16-2012, 03:28 PM

Quote:

Originally Posted by JamesDean

Eh, that's a lot of time and money.

Perhaps you are in a better spot with more local shops that rebuild MB trans.

I'm in San Diego, right next to Mexico and have a line on a reputable mechanic down there that will do the labor very reasonably, using parts I supply. It's a bit of a risk, but probably less than most of the shops up here.

I've had the engine in and out so many times I actually think it's easier than trying to wrestle the transmission out by itself. Plus I've got some other work to do that will be easier with the engine out of the car. And moving out of the prime top-down driving months it's no big deal to be without the car for a bit.

mach4 · #18 10-16-2012, 03:30 PM

Quote:

Originally Posted by Walkenvol

I vote option #2.
To me, a manual fits with your ride.

I don't disagree, but I think I'm going to get the current tranny rebuilt and collect the parts over time for a manual conversion at some point in the future.

mach4 · #19 10-17-2012, 08:08 PM

Continuing to research my issue and am now wondering if the Bowden Cable, or more accurately, the control pressure cable, is the source of my problems.

This post seems really close to what I'm experiencing

Quote:

Originally Posted by engatwork

I got the cable changed this morning. It is a pretty good job - have to drop the valve body. Anyway, I have it adjusted out and I can't tell where there is any difference. The car is in high gear by the time it gets to 20-30 mph, even when you floor it. While I had the valve body out I looked at everything real good and did not see anything out of the ordinary. The "plunger" that the bowden cable moves looks like it moves alright. Anybody got any other thoughts. The tranny shifts fine manually with just a slight amount of flare between 2-3rd gear. [emphasis added]

While this post describes the function of the bowden cable as controlling shift timing.

Quote:

Originally Posted by C32AMG

The Bowden cable, control pressure cable controls shift timing, early or late shifts in the 722. 3, 722.4, 722.5 transmissions as well as part throttle kick down shifts, WOT kick down shifts is controlled by the kick down solenoid which is activated by the switch under the gas pedal.

Disconnect the Bowden cable from the throttle linkage then Adjust the throttle cable/ gas pedal cable first, make sure you have wide open throttle when you depress the gas pedal to the floor, next Adjust the control pressure cable so the ball can be installed without any tension or looseness in the cable; fine tune the cable to your shift liking on a road test or by the book.

I too am in high gear almost immediately, which seems to mean that my control pressure function in the transmission, handling the timing of shifting is not working, i.e. the bowden cable function is non-existent.

The gears all work and the transmission functions pretty well as long as you start in the 3 position and manually go to D when the rpms are where you would expect the transmission to shift on its own. Under full throttle, it won't stay in 1st more than about 2 seconds and under low throttle it shifts at about 10-15mph. It doesn't seem to be a gear problem per se, but rather a control function.

My latest test was to disconnect the bowden cable at the valve cover and there was no change in operation. This seems to point to a malfunction in the shift timing mechanism in the transmission.

When I initially stated that the bowden cable is working properly, I should describe what that means - when I pull on the bowden cable there is pressure on the cable and releasing the cable returns it to its "rest" position. The adjustment is such that it starts to pull almost immediately off its stop, and at full throttle is fully extended.

The question on the table now is - what does the bowden cable actually control internally, and is it possible that the plunger is stuck even though there is spring pressure from inside the transmission.

Thoughts?

JamesDean · #20 10-17-2012, 08:23 PM

Hmmm. I would experiment. Adjust the cable one way, drive see how it responds, and then adjust the other way. If you go quite a bit one way, you will eventually hold gears out pretty long.

At moderate to low throttle, I do know that my 300SD's shift from 1-2 around 7 mph or so. 2-3 is usually in the teens to mid twenties. 3-4 is 25-30 or so maybe.

mach4 · #21 10-18-2012, 01:29 AM

Quote:

Originally Posted by JamesDean

Hmmm. I would experiment. Adjust the cable one way, drive see how it responds, and then adjust the other way. If you go quite a bit one way, you will eventually hold gears out pretty long.

I would if I could. Whether I run with the Bowden tube connected or disconnected there is no difference....which is why I was asking, in so many words, whether its possible for the Bowden tube to operate without affecting the plunger or whether whatever the plunger does to be plugged, cracked, broken or otherwise inop. And the follow on question would be whether there is an easy way to fix this without a full rebuild.

Stretch · #22 10-18-2012, 03:11 AM

If you post up your transmission type - I need the last two XXs from 722.4XX I should be able to get you a list of the pressures and limits.

You can then attach a (hydraulic) pressure gauge to the test ports and then have a better idea of what is happening. I'm guessing you already have a vacuum gauge to measure that side of the system too?

Govert · #23 10-18-2012, 07:41 AM

If only the bowden cable/plunger doesn't work properly, you will take-off in second gear (instead of first gear) and there will be normal upshifts, only at the lowest possible speed. You will be in fourth gear at around 30 mph. This applies to D. In 3 the upshift will be to 3rd gear only, at lower speed, around 20 mph. If you use L (or 2), the car should start in first and stay in first until the maximum speed of the first gear, then it should shift to second gear.

Now if is something is broken, the transmission can behave unexpectantly, i.e. not as described above. Inspecting the bowden cable can be done easily, it attaches itself on the passenger side of the transmission. By turning the plastic connector, you can pull the cable from the transmission. The cable should be attached by a hook to the plunger. Clean the area before this, you don't want dirt to enter the transmission.

Are you only using the VCV or did you transfer the vacuum transducer too?

JamesDean · #24 10-18-2012, 08:18 AM

Somewhere out there, a google search will reveal it, is a ATSG manual for the 722.3 and 722.4 transmissions that might be of some use to you. They have a nice diagnostics section that you might want to take a look at.

mach4 · #25 10-18-2012, 01:01 PM

Quote:

Originally Posted by Army

If you post up your transmission type - I need the last two XXs from 722.4XX I should be able to get you a list of the pressures and limits.

I plan on swapping in some new motor mounts today, so I'll grab the numbers off the tranny when I'm under there.

Quote:

Originally Posted by Govert

Are you only using the VCV or did you transfer the vacuum transducer too?

I'm using the vacuum transducer as well

JamesDean · #26 10-18-2012, 01:14 PM

Quote:

Originally Posted by mach4

I plan on swapping in some new motor mounts today, so I'll grab the numbers off the tranny when I'm under there.

I'm using the vacuum transducer as well

The vacuum doesnt effect shift points, merely quality. If you unplug it you'll get nice firm hard kick-in-the-pants shifts.

mach4 · #27 10-18-2012, 01:16 PM

While continuing to troubleshoot, I'm concurrently doing the research on what to have rebuilt, if I end up needing to do that.

In addition to what rebuild kits like the one below contain, what else should I consider doing while I've got the transmission in the shop?

I'm thinking of at least the B-2 piston. Brake bands? or are those inspect and replace as needed.

mach4 · #28 10-18-2012, 04:05 PM

Quote:

Originally Posted by Army

If you post up your transmission type - I need the last two XXs from 722.4XX I should be able to get you a list of the pressures and limits.

722.416

Stretch · #29 10-19-2012, 10:33 AM

Quote:

Originally Posted by mach4

722.416

Here's the information I've got. I hope it helps

How's your German? If I remember correctly it isn't a problem for you right?

ROLLGUY · #30 10-19-2012, 10:56 AM

Quote:

Originally Posted by mach4

While continuing to troubleshoot, I'm concurrently doing the research on what to have rebuilt, if I end up needing to do that.

In addition to what rebuild kits like the one below contain, what else should I consider doing while I've got the transmission in the shop?

I'm thinking of at least the B-2 piston. Brake bands? or are those inspect and replace as needed.

I would suggest getting a genuine Mercedes Benz kit. I recently got my 722.1XX (was rebuilt just before I got the '81 CD) back from the shop. It was not shifting out of first. The rebuilder said an aftermarket (Braco?) kit was used, and all the internal seals shrunk. He would not offer any guarantee if a factory kit was not used. A genuine kit is about $100 more than the aftermarket, but seemingly worth every penny.