722.4 fault finding - PeachParts Mercedes-Benz Forum

spock505 · #1 07-06-2016, 05:16 AM

Hi folks,

I am pretty familiar with the 722.4 box which has a lumpy shift under moderate to hard acceleration.

On previous boxes this has always turned out to be a vacuum leak somewhere so out came the Mity Vac. tested all line whilst sealing up butterfly valves with golf tee's but no luck, i did however come across this green valve.

From other posts I understand it regulates the vacuum pressure, blowing from both ends it appears to be empty, no restriction at all?

Could anyone confirm if this is correct?

Modulator is next on the list followed by K1 spring.

Thanks,

BillGrissom · #2 07-06-2016, 09:24 AM

My 1985 CA 300D has the 722.4 transmission. It has a similar green cylinder (smaller) off the "Vacuum Control Valve" on the injection pump (don't know if yours has a VCV). I think the green cylinder is a "damper", which works in conjunction with the in-line orifices (brown in your photo) to add a time lag to the vacuum signal to the transmission modulator. I think you are correct that it is just a volume, with no restriction. My 1985 also has the "blue moon" vacuum amplifier of yours.

My 1984 300D w. 722.3 transmission has a similar green cylinder. It also has the "blue moon" amplifier since I installed one from a junkyard 1985 CA car. Seemed a good idea, though haven't noticed any difference in shifting. I didn't add the other feature of the blue moon, which is a switched intake manifold pressure signal so the shifting is affected by turbo boost.

spock505 · #3 07-06-2016, 12:54 PM

..ahh okay, thanks - it's fine when cold but once warm it becomes a pain, I find myself anticpating shifts and lifting off the throttle which is okay short term.

Someone mentioned adjusting the bowden cable, anyone had experience of this?

Zulfiqar · #4 07-07-2016, 11:20 AM

how old is your ATF? worn out ATF can cause sticky shifts which exhibit themselves as bump shifts.

By the looks of the engine here Im assuming you have a 606 diesel. There is a vacuum tank inside the right front wing, mine was disconnected for a while and what I considered normal shifts were corrected once I connected that tank back to the system.

spock505 · #5 07-07-2016, 11:34 AM

ATF and filter new, drained TC too.

The vacuum circuit seems to be holding okay, I wold like to check the vac tank though - is it on the inner wing as both front wings removed and refitted.

OM606.910 '96 S124

Thanks,

Zulfiqar · #6 07-07-2016, 01:20 PM

Quote:

Originally Posted by spock505

ATF and filter new, drained TC too.

The vacuum circuit seems to be holding okay, I wold like to check the vac tank though - is it on the inner wing as both front wings removed and refitted.

OM606.910 '96 S124

Thanks,

The tank should be visible if you remove either items below

1 - the entire wing
2 - inner splash shield

its shaped like two married spheres and has one vacuum line in it.

spock505 · #7 07-07-2016, 04:38 PM

Thanks, I remember seeing those before, will investigate further. I watched one or two clips on bowden cable adjustment, might try this also but suspect this is not the problem.

This is one very unusual S124, last of the line in '96 with mostly documented miles at 126k. The body rust wise is in extremely good shape, almost zero rust except for suspension linkages, what is really puzzling me though is how many parts have needed to be replaced.

Wheel bearings (front), center bearing, differential - all seemingly worn out, my thoughts are being the end of run they may have used sub-standard parts or something, someone mentioned they were made in other locations such as Mexico - not sure but I have just removed the rubber flange from prop/differential only yo find one of the bolts is not a match, different size head and thread pitch - this thing has never been touched so it must be factory??

Zulfiqar · #8 07-07-2016, 05:10 PM

the last W124s had japanese wheel bearings in them - NTN brand and they work ok provided they are installed correctly.

The problem usually seen is that it is assumed that the UFO green mercedes grease is considered to be something from a superman novel. Its not, its usual disc brake wheel bearing grease which you can buy from a motor factors (called parts shop in USA). It has a finite life and is affected by moisture.

the old grease the bearings slathering is required in these bearings on regular bases unless you fill some really unique and good grease in them.

The rubber coupling bolts in the prop shaft are never different, the nuts can be different (this is a balancing technique in the service literature) and MB actually sell the heavy nuts as spare parts.

spock505 · #9 07-07-2016, 05:16 PM

Spot on, they were NTN branded bearings, these were yellow due to over tightening so popped those in the bin.

My concern with having one large non standard bolt is vibration, this might account in part at least for worn out diff or perhaps shortened life of center bearing?

Zulfiqar · #10 07-07-2016, 05:23 PM

You would have to get one bolt and nut from a scrap yard wrecker because the bolts are sold with a new coupling only.

You should not have a larger/heavier bolt as it surely can induce a vibration. When I work on the driveline of my cars I make sure I mark them with spray paint first and use the right thick grease on the middle splines and also in the end bushings. A dry spline can make an irritating clunking noise.

btw - dont always assume the bearings are bad by color, I removed a bearing set from one of my cars and it was brownish yellow, which I could not clean with regular cleaning and I assumed it was an overheated bearing, a dunking in acetone removed that staining completely. - But bearings are very low cost for the front of these cars.