HELP: 1995 C280 722.424 transmission troubleshooting after rebuild
 

Hello. Im looking for some help narrowing down the list of suspects.
So the story goes:
Bought the car with bad reverse clutch seal, so eventually reverse has failed in a big way.
I pulled the tranny off and took it apart, the only damage was the exploded reverse clutch, I inspected all other clutch packs and brake bands and they were fine.
Decided to go ahead and rebuild it, I used genuine MB seal kit and MB valve body seal kit to satisfy my OCD. Installed new reverse friction plates, springs, spring plate and circlip. Same time replaced B1 brake band and some cheap plastic pieces. Measured all clearances as per assembly manual, everything checked out. Same time rebuilt engine top and replaced head gasket (had a small oil leak in the back).
If anyone interested I have a youtube channel with these videos.
Installed the tranny back ...
On first test drive it drove fine until the tranny warmed up, it started to slip on take off.
I thought it was the B2 brake band slipping, also a common thing to do in this case is to replace B2 piston pin with a longer one, they come in 0.8 mm increments.
So dropped the tranny and investigated. Measured the B2 band travel, 5.6 mm (spec is 5.5 -6.0 mm), on a closer look I found that the B2 piston clearance was a bit too big to my liking – 0.007”, so I got another piston and a new B2 brake band installed. Put it back together and installed back into the car.
On the test drive it did exactly same thing as before, as soon as it warmed up it started slipping on take off. As it drives it shifts better then before, no kick from 1 to 2, shifts up and down no problems, kickdown works OK.
I don’t know enough about the inner work of a transmission and how the transmission works in every detail, so Im lost. Need to come up with a plan for troubleshooting to narrow down on this problem.
So far I suspect:
1. Low oil pressure on warm transmission at idle?
2. Slipping one way clutch? I had it completely apart, except the actual sprag bearing. Looks like need to test if it slips in reverse as well?
3. Does anyone know what the spec is for 722.424 working pressure, cant find this info ?
4. How do I measure B2 piston pressure?

any help would be appriciated, as I really want to get to the bottom of this problem.

http://www.peachparts.com/shopforum/members/andy_1100-albums-1995-c280-722-424-transmission-picture5814-20170416-111626-large.jpg
http://www.peachparts.com/shopforum/members/andy_1100-albums-1995-c280-722-424-transmission-picture5815-20170416-111805-large.jpg
http://www.peachparts.com/shopforum/members/andy_1100-albums-1995-c280-722-424-transmission-picture5816-20170416-111816-large.jpg
http://www.peachparts.com/shopforum/members/andy_1100-albums-1995-c280-722-424-transmission-picture5817-20170416-111825-large.jpg
http://www.peachparts.com/shopforum/members/andy_1100-albums-1995-c280-722-424-transmission-picture5818-20170416-120653-large.jpg

Finally got some free time to get under the car to connect a pressure gauge. I think I found the problem.
These are working pressure readings:
Cold engine start @ P, 800-900 rpm , modulator vacuum line connected – 100 psi
60 deg engine @ P, 700 rpm, modulator vacuum line connected – 65-70 psi
70 deg engine @ D, 600 rpm, modulator vacuum line connected – 40 psi
70 deg engine @ P, 700 rpm, modulator vacuum line disconnected – 50 psi
70 deg engine @ P, 1000 rpm, modulator vacuum line disconnected – 75 psi
70 deg engine @ D, 600 rpm, modulator vacuum line disconnected – 30 psi
Drove the car for 10 min to warm up the transmission
90 deg engine @ N, 700 rpm, modulator vacuum line connected – 45 psi
90 deg engine @ N, 1000 rpm, modulator vacuum line connected – 75 psi
Drove the car for another 10 min to warm up the transmission
90 deg engine @ P, 1000 rpm, modulator vacuum line connected – 60 psi
90 deg engine @ R, 600 rpm, modulator vacuum line connected – 25 psi
90 deg engine @ D, 600 rpm, modulator vacuum line connected – 20 psi
90 deg engine @ P, 1500 rpm, modulator vacuum line connected – 100 psi

I found some info on 722.XXX transmission, it says I should read 75-90 psi on hot transmission @ D.
Another reference tells me for gas car I should read in Park @ 1000 rpm with modulator vacuum line removed:
E320................174-203 psi
E420 & S420.....160-174 psi
S500 & SL500...186-215 psi
I assume working pressure for C280 should be close to these figures. I'm supprised the car actually drives. Clearly, working pressure is too low, this explains why it slips when is getting hot. The valve body is coming off for inspection. I guess I’ve messed up assembling it.

Anyone has good reference material for valve body rebuild? All I have is not the easiest to read and see the pictures to make sure all valves are installed in the right order?

Re: Pressures

Three items come immediately to mind:
1) Front pump very worn.
2) Defective modulator/modulator valve.
3) Leaking rear pump (if installed).

Before the reverse failed the tranny worked fine, except the slow reverse engagement, but that was due to a rapptured seal I assume.
When i got the car about 3 years ago, I changed the ATF cause it was burned. Took it for a drive the next day and I had a slip in 4 gear 2 or 3 times. Came home and added Lucas transmission fix, after that had no problems at all, just a little kick going from 1 to 2 gear.
On rebuild:
- Valid point, but Front pump didn't show any wear or anything abnormal.
- Modulator valve seems to be OK, no vacuum leak, no oil coming. Transmission had no problem shifting before the rear clutch failure.
- No rear pump installed.

It feels like there's a big oil leak somewhere. I might have messed up the valve body, i'll have to take it apart and check if i got all valves installed in correct order.
Im going tomorror to a wrecker to pull a transmission from a 1995 C280, and i'll take the valve body apart to compare to mine. Hope to find the problem.

The vacuum modulator reduces line pressure when load is light ( high vacuum ) and increases it when load is high. Your tests are with vacuum line attached but your specs are with the line disconnected so we can draw any conclusions from your data.

Buy the $ 30 ATSG service manual ( don't bootleg it as they put lots of effort in to these things. )

Did you air check this trans after it was built / before valve body was installed? This is a way to check for major internal leaks.

97 sl320, i was measuring working pressure, and i did measure with and without modulator vacuum line, didnt see much difference.

If you have any details how to test the transmission for leaks using compressed air could you send it to me, please. aiptech1@gmail.com

To air check a transmission you leave the valve body off, use a diagram to identify the various clutch / band apply ports on the case then apply air using a rubber tipped blow gun. Some transmissions ( not make specific ) need a plate bolted to where the valve body would go as sometimes passages are not round.

When applying air , a slight hiss and a clunk as the element applies is normal. If you get a whoosh, that isn't normal if you are applying air to the correct port.

This isn't used to check pump capacity, the goal is to find something leaking excessively like a cut clutch piston seal / failed piston check valve.

Hello 97 SL320. Thanks for the reply, I do understand the theory behind testing with compressed air, I tried to test B2 piston...not mush suscess. Problem is - Non of the rebuild manuals indicate where to apply the air.
I got a second transmission from a wrecker on the weekend, i might practice on it....

might have found the problem...
 

so yesterday i pulled the valve body off my transmission to swap with a valve body fom the transmission i got from a wrecker, and what i see.....the big paper gasket that should be under the valve body plate is installed on top of the plate, between the valve body and valve body plate. Rooky mistake on my part...
Pulled the valve body plate and installed the gasket on the correct side..under the valve body plate.
Today will install the my valve body back and will see how it goes...keep my fingers crossed this is the only mistake i've made

this is the valve body plate with removed valve body on the tranny i got from wrecker, the papar gasket is under the plate
http://www.peachparts.com/shopforum/...314-custom.jpg

Issue is solved. The transmission works as it should, 70-75 psi working pressure on hot transmission idling in "D".
The only concern i have is when idling in reverse working pressure shoots to 280 psi, and i cant find any info if this is correct.
Otherwise it drives nice, no kicks on shifts.
Case closed.

For some transmissions (in general), reverse pressure is higher because internal gear train leverage is higher. ( not overall ratio ) RE: The way reverse is achieved has higher internal stress than forward gears.

97 SL320
Thanks for the info.
Now ...oil and filter change after an overhaul....after 20k km?

If you want to have a look in the pan for excessive metal / material, that would be fine otherwise just run it.

I just noticed, did you use Permatex Set & Seal on the pan gasket? If so, that is for machined metal surfaces where tight contact precludes the use of silicone. Rubber pan gaskets just need a thin wipe of oil so it doesn't drag as the bolts are tightened down.

Ok. Ill just drop the pan in 5000 km

No i didnt use any sealant on my transmission, i just wipe mating surfaces with brake clean and install.
This is a photo of the transmission i got from the wrecker, its a bit messy. Theres sealant all over it. I might keep it and rebuild later.

Got it all sorted out, transmission installed and working as it should.

here's the rebuild video https://youtu.be/eGNElAtNENo

Many thanks for the video Andy,

I have my 722.354 (400E) out and I'll rebuild the original transmission.
The original transmission failed.. I found a piece of spring in the pan and many metal chips.

I want to install a seemingly good donor transmission in order to get the car going asap.

Two questions:
For the donor transmission would you reseal the outside all the many openings (change o-rings and shaft rings) , maybe open up primary pump and check the Reverse B3?

Is there anything to test on the plastic control cable unit where the vacuum hose goes in as well? (I have the two units...one from the original transmission) and the one from donor. The reason for asking: You can't possibly get to the control cable after install. The W124/ 400E is very tight (much tighter than a W126 I have).

Martin

Hi Martin.
Regarding the donor tx, if you want to install it just for the time you will be rebuilding your original tx....
If it looks OK from outside, and you don't see any visible oil leaks I'd leave it as is. You can replace the o-rings on dipstick, pressure control cable and modulator valve, these are easy to replace. Pull the oil pan and inspect the condition of the oil, if it's clean then just replace the oil and filter.
I'd check the modulator valve and pressure control cable to make sure there's no vacuum leaks and I'd do it at the ends where they connnect to the engine to ensure rubber connectors are goos as well.
I can't tell you for sure, but if you have an older tx there are a number of upgrades to be done, i think B2 piston is one of them.
Good luck

From Martin to Martin :)

If you have springs in the pan, or open one of these trannnies, and replace the reverse seals... Replace All THE SPRINGS. The plate holding them if it is not cracked, and replace the spring clip holding the plate..

If you have one of these trannies(722.3-722.5), At the very minimum, replace ALL the perimeter seals on the outside of the case as they just cook. Front seal, Rear seal, B2 piston seal, and reverse seal. Since the 722.3/722.4 has very few frictions it is strained a bit more, so parts tend to really cook, and look burned. These old trannies really cook the Brake Band 1 and 2, but most do not elect to replace them as each Mercedes Band is $300 or so. It is real gamble if you do nothing. The B2 piston seal, and B3 reverse seal just cook really fast on these trannies.



Here are some healthy links with manuals, and photos...

Gearbox 722.368 repair manual / tips - Mercedes-Benz Forum

Martin

Thanks Andy
The donor Transmission looks good. The oil was clean and the seller was confirming that trans worked well before removed. So I could be lucky.
I'll probably get it in sealing at the exterior and done. Not sure if it is worth pulling the primary pump and seal it...look if the pump looks fine?



The transmission to be renovated is a 1992 722.354 , at least this is what I thought. But cleaning the old piece that came out last weekend I saw that the aluminum case was sprayed over in grayish color. They sprayed over modulator, kick down solenoid and plugs/covers...
It looks like this was a re-builder's paint job? I don't think the original trans would be spray painted.
Any hints here?
Probably it does not matter much. It all depends on the inside condition of the parts I guess. If the planetary gears and other hardware are fine it should be rebuild-able.

As the damaged transmission had a few symptoms of dysfunction I'd like to understand why it did behave like it did (before I found the steel chips and chewed up spring in the pan.)

I got a 'Precision' Banner Kit for the 722.3 ..out of interest what is inside.
And I am not very convinced that the frictions are the best available. I'd probably get Borg Warner frictions for the rebuild. I am not sure and I have no idea/experience with friction disks.

You are mentioning updates... like the B2 update... yes...where do I get these parts from?

steel plates are available too but not sure if they are needed for a rebuild
Brake bands B1 and B2 should be installed new or are the old ones typically fine?

Valve body: I think I need to open this one up and clean it from any debris/steel chips inside?

Martin

Martin,
thanks, I really have 2 transmission projects going ( A) old damaged transmission to be fully rebuilt and B) used donor transmission, seemingly in okay shape to go into the car fast to get car going)

for B) the donor transmission to go in fast in order to get the car going....
Are you recommending to changing the exterior seals (so donor transmission does not leak unexpectedly at exterior)? Or would you go deeper and if yes what would be on the list as typical point of attention (B2?)


For A) the full rebuilding of the damaged trans I definitively get all parts replaced:
Frictions K1, K2 and B3, (Steel disks if needed) , brake bands B1 and B2,
update on B2 piston.
All seals including the complicated seal rings for the clutches K1 and K2 (remove rivets and replace with bolts).
All gaskets.
I am planning to get the valve body taken apart and cleaned (because I suspect having steel chips all around (as I found in the pan) and I consider these steel chips as one point of failure of the transmission.
As I had chips the transmission cooler was contaminated with chips and also the converter must be contaminated. I hope all the gear sets and primary pump and the bearings are still in good shape.

Question: Are there good sources for replacement parts and if yes what is a good source. Do you have good recommendations for :

clutch frictions, clutch steel disks, brake bands, rubber seals, teflon rings, gaskets, bearings?

Best Martin W

things to think about
 

Hi Martin, i don't want to mislead you, so please note... I don't have an extensive experience with rebuilding MB transmissions, so anything I say or suggest it's just my opinion based on the recent MB transmission rebuild, some information I've gathered during my research on the subject and some knowledge accumulated over the years working as a mechanical engineer designing and building hydromechanical transmissions.
I can give you my opinions, but at the end it your decision how to proceed.
Now that we have this cleared .....

Here, I guess, you need to decide, do you install the donor transmission and leave it for good, or you want to rebuild your old transmission and put it back? Further actions will depend on your decision...

Like I said, if you want the donot TX just as a temporary solution then you can change all exterior o-rings if you want to do that, should be OK they are not hard to replace. Just use high temp grease ot ATF for o-ring installation, make sure you don't cut the o-rings. As for openning the primary pump...my dad used to say "don't fix it if it ain't broke". What do you expect to see? If the donor transmission worked fine and no debriss (metal or aluminum powder) found in the oil pan, 99.9% that the primary pump is OK. If you open the primary pump you'll need to replace the o-ring and the paper gasket and since you are already there I'd suggest the primary pump front lip seal. By opening the pump you can just confirm that it's bad if you see scoring or wear on the gears, but then the TX would not worked well since the pump efficiency would have dropped down.

I don't know...but it doesn't make sence for MB factory to spray the modulator or kick down solenoid...

I think so.

What symptoms?

Usually banner kits contain:Transmission Overhaul Kit (seals and gaskets), and a standard set of friction clutch plates.

You might be OK, Service bulletin "Delay engagement in all forward gears" for B2 piston update applies to MB 722.3 and 722.4 1980-1991, I see your's is 1992. You will know when you pull B2 piston out.

It depends..usually they don't have to be replaced. You will have to inspect them when you take the TX apart. If there's some wear you will fill a ridge when you drag your fingernail across the surface. In this case you might want to replace them.

Depends on the condition, B1 has thin friction layer and is not expensive so I'd change it, B2 is another story...needs to be inspected. Depends what failed in your transmission.


Absolutely 100%. Please note, there's a seal kit for the valve body and it's not included with the rebuild kit, I had to buy it from MB dealer. There are about 25-30 teflon rings in the kit, but you will only need 8.

FEW POINTS:
- you have to flash the transmission oil cooler before you install donor transmission. Ask me how...
- be carefull, B1 piston cap is spring loaded, you better make a tool for removal / install, e-mail me for drawings.
- source ATSG 722.3 722.4 rebuild manual, it's a big help.

Im working on my valve body overhaul video, hope to have it finished soon.

Hi Andy,

I dropped you an email about the cooler flush and tools to build.

symptoms of the failing transmission before I found the steel chips and what looks like piece of a spring in the pan:

it started shifting weird but only sometimes... not real bad but something was off so that I started to readjust the control cable which did not help really. Then it went away. This happened a couple if times and I did not know what was going on. As it shifted fine after a while I didn't payed too much attention to it.

There were also a could of weird up shifts that I didn't expect but nothing crazy.
Went away.

Then the car didn't want to pull off a start easily, Torque converter didn't engage as it should I guess... maybe chips in the oil flow restricting something.

This was getting a bit better but not 100% and I decided to change the oil when I found the chips.

Happy to see you valve body video soon.
I love how you handle the job of the transmission repair without throwing a ton of tools and equipment at it.

Martin

I replied back to your e-mail, maybe it went into spam.