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

mach4 · #1 10-15-2012, 11:31 PM

In the last couple of days, my transmission went from shifting really, really nice to where it will now only use first and fourth in the D position. If I floor it, it will not stay in first but shifts to 4th at like 15 mph. I can feel it trying to hunt for 2 and 3 but only goes to 4th. There is no downshift. It will go into 3rd manually and if starting in 1st manually will stay in 1st.

I've done extensive searching on this board and don't see these symptoms represented.

I've checked the VCV and that is fine. I've checked the modulator line and it holds vacuum fine. I've run it without the modulator vacuum line and there is no difference. The Bowden cable is working as it should. I don't have any vacuum leaks.

This is the 722.4 "one year" transmission that came on the '85 Cali 123 300D. It has about 220k miles and nothing is known about the history of the car. It's been in my 107 diesel conversion and has been running great for the past 7k miles. I've done nothing to the car that I can imagine creating the change in operation.

Any thoughts on the diagnosis or additional tests or things to check? Can I drive it this way while I explore options and fixes or is the next logical step catastrophic, stranding failure?

Stretch · #2 10-16-2012, 02:56 AM

I would look at the governor - it sounds like that mechanical "speed detector" is disfunctional.

Threads that might help =>

Help - stuck on road 722.3 no 3rd/4th gear

722.303 in bits photo shoot

'91 300D trans stuck in 1st gear...

All of these threads have pictures of the governor.

"My" 722.303 thread shows the earlier all metal geared version - I'm pretty sure you'll have the plastic cogs like JamesDean has in the last link. The 722.4 doesn't have the secondary pump on the other end of the governor drive shaft.

I think the governor is the most likely trouble area in these transmissions.

Govert · #3 10-16-2012, 04:51 AM

It could be a problem with the B2 piston, they can fail. B2 is involved in gears 1 to 3.

The 1985 Cali version doesn't use the VCV, but also the vacuum transducer, that has to work too, or else you get very weird shifting behaviour.

mach4 · #4 10-16-2012, 11:41 AM

Quote:

Originally Posted by Army

I would look at the governor - it sounds like that mechanical "speed detector" is disfunctional....

I think the governor is the most likely trouble area in these transmissions.

So let's assume that the problem is the governor - where would one find a replacement? If it's got plastic gears, one would assume that sourcing a junk yard replacement would be trading one problem for another.

One of the solutions on the table is to pull the engine/transmission and take it to be rebuilt. I've got a line on a transmission guy that will rebuild mine for labor and I provide the parts. So from what I can tell things like the governor, B2 and so forth are not part of a "standard" rebuild kit. So, if I'm going to go to all that much trouble, what else should be replaced to take other failure points out of the equation?

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

Zulfiqar · #5 10-16-2012, 11:49 AM

the user jamesdean whose 722.4 transmission had a broken governor gear sourced brand new drive gears from mercedes for very low money. But in his case the trans just stayed in gear 1 - no upshift at any lever position.

If yours can shift that means that it is getting some sort of pressure from the governor - meaning that its spinning.

If your governor unclips and backs out you will lose the ability to shift to R whilst the engine is started and you will most probably lose lower gear starts too. - That was experienced by JamesDean too.

Your problem does not seem to fit in, Govert on the other hand has got pretty nice knowledge.

JamesDean · #6 10-16-2012, 12:54 PM

Army: The 722.4's up to a certain serial all have the secondary pump. Its not the same style mounting as the 722.3's I think. In the 3's I think there was some kind of screw support thing that you had to remove in order to remove the governor. The 4's governor just slides into a keyed shaft on the pump.

mach: I would suspect your problem might be B2 piston related, not governor. As Zulfiqar pointed out if your governor was bad/had broken gears, you would not be able to get out of first. If the gov popped out of its spot like mine did, you would have shifter problems.

if you're going to lower down the back of the trans, I'd pop off the governor governor cover and inspect the area. If you put the trans in neutral (with rear wheels up) the gov should spin nicely.

Just some pricing points:

The two plastic gears for the governor, total about $10. one is ON the governor, one is on the output shaft. You'll also need a new tailshaft seal, $3. All from Mercedes.

A new governor is about $200-250 last time I checked.

A new B2 piston was about $100-115 I think.

Stretch · #7 10-16-2012, 01:43 PM

Quote:

Originally Posted by JamesDean

Army: The 722.4's up to a certain serial all have the secondary pump. Its not the same style mounting as the 722.3's I think. In the 3's I think there was some kind of screw support thing that you had to remove in order to remove the governor. The 4's governor just slides into a keyed shaft on the pump.

...

I didn't realise that thanks - thinking about it, it must be a date thing rather than a series thing as some later 722.3s lost the secondary pump too...

mach4 · #8 10-16-2012, 01:44 PM

Quote:

Originally Posted by JamesDean

I would suspect your problem might be B2 piston related, not governor. As Zulfiqar pointed out if your governor was bad/had broken gears, you would not be able to get out of first. If the gov popped out of its spot like mine did, you would have shifter problems.

if you're going to lower down the back of the trans, I'd pop off the governor governor cover and inspect the area. If you put the trans in neutral (with rear wheels up) the gov should spin nicely.

Assuming the B2 is the problem (or part of the problem ) I did did some searching on how to replace the B2. If this article [The (infamous) B2 Piston] is correct it would suggest that it's not necessarily the B2

Quote:

From article about that Infamous B2 Piston

The symptoms of a B2 piston failure are unmistakable:

Fails without any warning whatsoever
Slips out of gear in 1st with any load
Massive flaring going into second
3rd and 4th work normally
Reverse works normally

They fail anywhere between 100K and (in my case) 400K miles; chances are very high your first major problem with this transmission will be this one.

Mine does not "slip out of gear with any load" and does not have "massive flaring going into second (it skips second altogether). Third and fourth work normally, but only with manual shifting, not in D.

The article makes a good point in saying "There is a school of thought that says any pre 1994 MB with one of these should be replaced as preventative maintenance." So makes sense to change this out regardless.

Army's write up on the 722.3 rebuild shows this chart

Which shows the K1 is involved in 3rd gear as well.

In fact, I'm now questioning my impression that I'm starting out in first gear after all. Maybe I'm actually starting in second and just skipping 3rd gear.

Based on my symptoms, is it consensus that doing a 'rebuild' plus the B2 would solve the problem, or is there something else that might be involved?

Stretch · #9 10-16-2012, 01:49 PM

Valid points about the B2 piston folks but the B2 is needed for first gear and if first gear works...

...don't you think that that kind of suggests that the B2 is working?

I don't know for sure - I can't know for sure - and I don't want to steer anyone the wrong way.

Stretch · #10 10-16-2012, 01:50 PM

Ha you beat me to it

I love that chart!

Stretch · #11 10-16-2012, 01:53 PM

Quote:

Originally Posted by mach4

...
Based on my symptoms, is it consensus that doing a 'rebuild' plus the B2 would solve the problem, or is there something else that might be involved?

I can tell you for sure that a rebuild will fix it what ever it is!

(Small print - has to be a good rebuild!)

JamesDean · #12 10-16-2012, 01:54 PM

Quote:

Originally Posted by Army

I didn't realise that thanks - thinking about it, it must be a date thing rather than a series thing as some later 722.3s lost the secondary pump too...

I was told it was 1991 but my 1991 300D 2.5 has one. I looked it up in the EPC, they list out serial numbers for the break point. So maybe its somewhere in 1991's serial numbers. I've since disabled the whole pump..

JamesDean · #13 10-16-2012, 01:56 PM

I have a thread around here somewhere about my B2 experience.. I cant remember everything about it but it didnt show every symptom listed there.

You could always just take the cover off and inspect the B2...

mach4 · #14 10-16-2012, 02:33 PM

Quote:

Originally Posted by JamesDean

I have a thread around here somewhere about my B2 experience.. I cant remember everything about it but it didn't show every symptom listed there.

You could always just take the cover off and inspect the B2...

If I'm going that far, I might as well pull the tranny and get it rebuilt. It's got 225k mi, so something else is probably worn and ready to let go. No need to do it twice.

Everything that has been said clearly indicates that it's not something fixable with any of the external control stuff that's an easy DIY fix, but rather something internal, with varying degrees of complexity.

JamesDean · #15 10-16-2012, 02:38 PM

Eh, thats a lot of time and money.

The B2 work on my one 300SD only took like 2-3 hours and cost $100. Perhaps you are in a better spot with more local shops that rebuild MB trans. I was not. They are nothing but scam artists locally.