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M104 300-24 with 722.5 - common issues?

19K views 53 replies 9 participants last post by  LeftCoastGeek 
#1 ·
Hi guys,


I was reading lost and lots of posts here and I finally decided to become a part of the community.

So I have a 1991 200CE. My old m102 is burning more oil than fuel and I really got sick of it. Not to mention that it's slower then some bicycles.

I found a 300CE-24 with a 722.5 gearbox for a very good price, same color as mine and same interior, so I bought it for a donor car. It has a lot more things to be used than just the engine so that's why I didn't stick to searching for the 3.2 version.

I know the 300 m104 is not the best engine, but not that bad ether.

I want to know what should I check before putting this engine into my coupe? What should I inspect and what are the weakest spots in these engines? I really want to make sure the engine is good before installing it.

Next thing is the gearbox, what maintenance does it require and what should I do to properly check it's condition?

I will be able to drive the donor car before disassembling it, but I'm not sure this will be good enough to tell if something is bad.


Thanks.
 
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#2 ·
I believe that 722.5 is the electronically shifted version of the automatic (it would have a 'Winter/Sport" switch near the shift lever), those were never put in 124's in the USA. you'll likely need to swap the whole engine+tranny+control units and wiring harnesses together, pretty much everything under the hood. I'm guessing without knowing that the drive shaft lengths are probably different, as well as different sized flexdisks, so you'll be swapping all that too. probably should swap the differential as they probably have different final drive ratios.

you'll probably want to swap the springs, sway bars, shocks as the 104 is likely heavier than your 2.0. We never got any 4 cyl 124's here in the USA, so I have no idea about stuff like motor mounts etc.

all the 6 cyls suffer from weak head gaskets, so inspect carefully around the head-block seam for signs of seepage. the 3.0L 104.98x motors have a hard-to-find $$$$ EZL electronic ignition module, be sure to clean the mounting surfaces and use a thin layer of fresh heatsink compound when you install it, as keeping it from overheating is the best way of preventing it from failing.

the 300CE might have beefier front brakes than the 200, if so I'd consider swapping the brakes including master cylinder, too.
 
#3 ·
Common issues: 5th gear tends to be problematic as the electronic control takes readings from 7 or 8 sensors & it only takes one misread on any of them & it won't engage 5th, usually is a pain in the ass to sort it out.
The most important issue is when it skips from 3rd to 5th without using 4th, that means the HGS control module(it controls the 4th-5th shift) is broken & can be eigther very expensive or very difficult to find, most probably both, if the transmission shift into 4th but not 5th is simple as a bad sensor or a connector in bad shape.

To get the m104.98x running as it was meant to, you should do a full clean up of your injectors & intake.


& last but not least replace all 3 of the temp sensors on the thermostat housing, only use MB OEM sensors, alternative ones will fit but also give different read outs.
 
#4 ·
Thanks guys,

I've done the CIS cleaning of my m102 last year and I was surprised of the result.

I really intend to replace the whole drivetrain as well as all the wires and electronics. My car will definitely lack most of the wires and most of the existing ones are plastic hard and they shatter everytime you want to bend them. I will only keep the body.

You would probably think why am I doing all that, but the thing is that my car has been driven to the hell and back.
It pretty hard to find a good one in Europe these days. When I bought mine last year I was only looking at the body and the rust. This was the only car within a 1000 miles from me that had absolutely no rust.

The one I bought for a donor is in pretty bad shape as we speak of exterior, but has a very good milage for a 25 year old car and it's interior looks fantastic (on the pictures). I'm still waiting it to be delivered to me because I bought it from Germany.
 
#5 ·
Hello,

Why not use the 200 as the donor car and restore the new 300-24? Or is that too simple? Perhaps I do not understand.

The 4th/5th problems are sometimes very cheap to solve. Mine would skip 4th and go straight to 5th. The solution was to replace the 4th/5th switch (by the gear lever) and delete fault codes.

Both engine and box can be very reliable and a real joy to drive. That 7000 rpm engine can really make things happen. As always, maintenance is very important and regular oil changes using good quality oil and filters is vital for engine and box.

The engine demands the correct spark plugs and the best quality HT components in general. Many people assume that they have serious, expensive problems when only new plugs or rotor arm might be needed.

As with many MB gearboxes, it is vital to empty both the box and the torque converter when changing the oil.

Good luck with your project.

RayH
 
#6 ·
Thanks,

Totally agree with you about the spark plugs and arm! As for the gearbox though It'll be hard to find a good gearbox oil in Bulgaria... I have very very bad experience with fake ATF .. It cost me a whole gearbox back in the days.

Will it be appropriate to leave it with the old oil if it shifts normally? I've heard that these oils are very long lasting.

Main reason to make all the swaps is the rust the new car has, I will inspect the body and decide whether to repair it's rust or just use it for parts... Most important are the areas around the rear fenders and trunk, if they are good, I'll most probably use the new body.

The body of my car though is in incredibly good shape .. it's a rare thing especially in Europe and that's why I wanna keep it. If you have tried to repair rusty fenders you'll know that for 2-3 years all the paint over the rust spots will peal no matter what you do... I don't want to spend tons of hours and money for something that won't last long...
 
#9 · (Edited)
Fuchs Titan ATF 4000 is a ultra high performance Dexron 3(H), which is very common to find. It has MB 236.1 and 236.9 approvals

rayhennig, Titan ATF 5005 is a premium Dexron 3(H). It only meets 236.6. It is best suited for vehicles that see regular or year round cold (sub 0 Celsius) temperatures.
 
#10 ·
Guys, the donor car has finally been delivered and I immediately took it for a spin.

My first impressions are that it's got quite hard throttle pedal compared to my 200 m102, don't know if that's normal? The other thing is that the transition from neutral to drive is not very smooth and feels like someone bumps at me. The shifting is smoother, but not smooth enough compared to other automatics that I've driven. Since the car is not street legal I couldn't take it to the open road and I still don't know if it will shift to 5th.
Also when it's on drive at a standstill position there is quite a vibration inside and feels like the engine is struggling to run, the handbrake barely handles it.

Could the gearbox oil be too thick? I checked it's level and I was surprised to see that it was golden/brown (mineral oil color), I expected to see red oil.. I hope someone of you has experience with these boxes and their strange behavior.

I could see some white smoke from the exhaust and it smelled like burnt oil. From what I know an indication for bad piston rings is crankcase pressure so I opened the oil cap with engine running to see if there is any, but I felt none. I assume the valves O-ring seals are old and they need to be replaced.

Like the German grandpa said, the car has tons of rust and it's no good for restoration, I will follow my initial plan of engine and gearbox swap.
 
#13 ·
Hi Geo.

Could your vibration issues be related to sagging engine mounts allowing the sump to hit the cross member? Does it change when going from drive to reverse and back again, at standstill of course.

The modulator on the left of the autobox is vacuum controlled from the inlet manifold. If the modulator diaphragm is burst/ripped then shift patterns are affected and the engine sucks up and burns atf.

Boyd
 
#14 ·
I doubt that vibrations are due to bad mounts, it's just the rpm going really low when switched to D or R. For me it seems like the torque converter provides really high tension and it's not loose enough due to the bad oil. I will give an update after doing all the maintenance.
 
#17 ·
Hmmm. Does the car roll forward with the engine turned off? If so, it is gravity.

If it doesn't, then there is likely a problem with the torque converter or a transmission problem. Under normal conditions, the car should never move when the transmission is in neutral hence the name.
 
#18 ·
I would suspect clutch/bands not disengaging, rather than the torque converter. the torque converter always spins the input shaft... in neutral (or park), all the bands should be disengaged, so the planetary gears freewheel and the input shaft isn't 'connected' to the output shaft.
 
#19 ·
The car is on a completely flat surface with no slope and it moves only an inch or two when I rev the engine. I have experienced such thing with another car before, but in that case I really had to smash the pedal down just to feel a tiny forward movement (it wasn't a Merc). In my case I only rev the engine to about 2000 rpm and it tries to go.

I just wanted to make sure that this thing isn't normal because I haven't driven an automatic w124 and I don't know what to expect.

My main concern is the quality of the trans fluid. In automatic gearboxes the gears never fully disengage like they do in manual boxes. There is always a tiny bit of friction between the gears clutch disks inside caused by the fluid. That's a part of the reason why automatics are not as efficient as manual boxes. Minimizing this friction is the main reason why the fluid is so important. The golden oil in my box can most probably be the reason why the friction is so huge.
 
#22 ·
My main concern is the quality of the trans fluid. In automatic gearboxes the gears never fully disengage like they do in manual boxes. There is always a tiny bit of friction between the gears clutch disks inside caused by the fluid. That's a part of the reason why automatics are not as efficient as manual boxes. Minimizing this friction is the main reason why the fluid is so important. The golden oil in my box can most probably be the reason why the friction is so huge.
virtually all ATF is cherry red as several have said.

your description of the power loss in a AT is incorrect. its not the planetary bands that cause power loss, its the torque converter, which is a propeller driving an impeller. Once you're past the torque converter, the actual gearing is several sets of planetary gears, each with a clutch band that either locks the outer ring gear, whereupon the gears are driven, or it doesn't, whereupon that gearset spins free and are in neutral
 
#26 ·
I'm not where the car is for the moment, I only spent a few hours there and had to take off to the city I work at. I will be able to start the project and see it again no earlier than March. That's why I only talk about it, I'm a bit anxious and just wanted to share my initial impressions of the car and hear some thoughts.

Aren't thease forums meant for that ?
 
#25 ·
M104 in 1990 R129

I have the M104.981 engine and 722.500 transmission in my 1990 300-SL (24 valve) and they have been a very reliable combination.

Touch wood, I've had fantastic results with the 5-speed tranny and have changed ATF three times in 120,000 miles. Most recent change made a huge difference shifting into overdrive (5th gear) and the shift is now almost imperceptible, even with some acceleration. I have some slight transmission seepage that need sorting but nothing that drips on the floor. Maybe 1 time in 40 (usually while cold) the tranny flares between 2nd and 3rd but again it's very minor...if I let the car warm up properly there are very few concerns.

The M104 is a superb engine! Plenty of power and with careful maintenance it purrs like almost new. Mine could use new injectors (or a cleaning) but it gets good gas mileage (20+mpg around town/25+ highway). The only issue with the dirty injectors is that it doesn't start instantly, usually takes two to three seconds when cold and MB spec is four seconds so I ignore that minor issue.

If the head gasket hasn't been replaced it surely will need to some day. Mine was replaced at ~40K miles and has been solid since. Make sure to use new motor mounts. Those can fail early in the engine's life. I've been through at least three rear flex discs. Be sure to install new ones, especially at the interface from the transmission as that one requires you to drop the exhaust system for replacement.

ONLY use MB/OE components for ignition, oils, etc. Anything else you are inviting problems as this is a high performance engine, engineered for high performance parts.

Good luck in your frankenBenz!
 
#27 ·
Hi again,


I promised to pick that thread up when I have something done and here it is. The swap is almost completed.

Some of the things done include replacing the engine's valve stem seals and the valve cover gasket. I repainted the valve cover and now the engine looks like new. I don't have any problems with the engine, but I cannot say the same for the tranny.

Since the car is road legal I took it for a spin on the open road.

I immediately noticed that the tranny doesn't like to downshift very much. I really have to put the hammer down and press the kick down switch to have it downshift or I have to go real slow and when it does, it'll spin the wheels.. I don't think it's normal to have to use the kick-down every time I need to accelerate. Another problem is that the car won't stay at 4-th gear for more than a second. I expected it won't even go to fifth, but it actually doesn't wanna go out of fifth very often. Moving the lever left to engage 4-th does nothing.. when moved further back to third will engage third, but the electronic switch itself won't do the job of disengaging 5-th.

One more thing which I don't know if it's odd or not .. I don't ever start in first gear no matter where the standard/economy switch is. It's always second and if I want to go faster again I smash the gas pedal and after a couple of seconds it goes to first and I see tire smoke in the back.

Most of you already think about the bowden cable, but it's not the issue, I played around with it, and it has influence on the upshifts. I could get the car to upshift later, but still the downshifts are late and inconsistent.

I read a lot about this and found a guy who described the very same case. He solved it by reading the MAS module fault codes and reseting them. This will be my next move!

Can any of you provide a table with all error codes for pin 13? I couldn't find error codes listing anywhere..

I changed the ATF with Fuchs Titan ATF 4000 as proposed by you, also changed the filter. Yet again the car tries to go forward even in neutral, so the assumption is that it wasn't the ATF responsible for that problem. I also still have harsh engagement to D or R when the car is warmed up. It's smooth as silk when cold.

The bad thing is that I'll be out of town for the next 10 days, and all I will be able to do is read and search for ideas, so if any of you has any - you're welcome!
 
#29 ·
There's a tranny expert who goes by MAVA on the R129 forum. Search and read his posts on the 722.500. He's rebuilt one recently and has posted many pictures and how to information. PM his for advice if you like.
 
#32 ·
Hello people! I am trying desperately to find the HGS unit in my 300CE -24 (104.980 CIS-e) (722.501 trans)
it is NOT in the engine bay near MAS... i have to diagnode no 5th gear (electric problem)
Somebody please know here did they put it? I can get blink back at diagnostic socket 13, so it must be there somewhere... but not in the trunk
 
#34 ·
I believe all 722.501 have HGS units for 4<>5 shifting as mine does.

dav781 said:
Hello people! I am trying desperately to find the HGS unit in my 300CE -24 (104.980 CIS-e) (722.501 trans)
it is NOT in the engine bay near MAS... i have to diagnode no 5th gear (electric problem)
Somebody please know here did they put it? I can get blink back at diagnostic socket 13, so it must be there somewhere... but not in the trunk
As for the missing 5-th gear - the most common issue is disconnected throttle position sensor and/or missing connection to the VSS(vehicle speed sensor). Note: Malfunctioning HGS causes the tranny to skip 4-th gear!

Some pictures of the area behind the battery might help me telling you where to look at. I've stripped down my whole car a while ago so I know where the wiring goes so I can be in favor.
 
#36 ·
fyi, the automatics I've seen with simple electric overdrives, such as the venerable Toyota A43D and BorgWarner 03-71 and Volvo AW7x transmissions, are NOT really like the older brit cars (and certain volvos) with their laycock J units.... the laycock overdrives were behind the transmission on the output shaft, while the automatic overdrives are internal to the transmissions on the intake shaft.
 
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