1996 Mercedes SL 600

[Krikkit]

With the gunson bleeders I've found that a latex glove can be used to get a better seal if the thread on the reservoir doesn't match the thread on the lid quite perfectly. You can also dig out a spare lid and drill the small hole needed for the pressure line if needs be.

I've also started reducing the supply pressure to 10psi instead of 15+, it still bleeds fine, but it stops things getting blasted everywhere. If you do get some rogue brake fluid wash it with plenty of good old H2O straight away and it should come clean without damaging the paint.

[illmonkey]

I ended up using the missus, it's the only time I ask her to do something and she does it. Brake! ... off.... brake!

[alabbasi]

Hereward said:

I have also noticed the 722.6 gearbox kickdown sometimes results in a long pause before a rough engagement of the lower gear so I am wondering if I should check out the conductor plate solenoids. Perhaps I should replace the kickdown switch first. I can't really be arsed to delve back in to the gearbox again but it may be a Winter project.

There's a common issue with the electrical plug on those 722.6 transmissions which can leak at the pins. ATF would then travel up the wires and onto the TCU which I think is in the passenger side foot well on the left hand drive cars (not sure about RHD). Remove it and inspect it to see if it's oily at the pins. The plug should be replaced every time you change the fluid . It costs about $15 for a replacement here in the US.

[SpeckledJim]

r129sl said:

I'd vouch for the maintenance-as-therapy angle. I'd also say to anyone who, like me, drives a desk and is generally a mechanical spaz, that you just need to start somewhere. Anywhere. Start with oil and filter changes. The hardest part is getting the under tray off. And go from there. Slowly. Expect to cock it up first time you try. I think I started with oil and filter, progressed to shocks, and now can do many things including brakes. Shocks make a good example. The first side takes two hours; the second takes 15 minutes. It has taken me seven years to get confident with stuff.

You don't need much gear. A good jack, good axle stands, one of the big Halfords Professional socket sets, a breaker bar, a drain bucket. And lots of latex gloves. A big rubber mat for lying on the floor is useful. It really helps if you don't need the car tomorrow. It is also quite physical. Finally, make friends with the garagiste in the village: when you do cock it up, and we all do, he will fix it for only twice what it would have cost you to take it to him in the first place.

Agree with this. You can build a useful set of tools and kit for the equivalent of 10 hours of garage labour.


PRICE LIST

£40 an hour
£45 an hour - If you want to watch
£50 an hour - If you want to help
£80 an hour - If you've already had a go

[Hereward]

alabbasi said:

Hereward said:

I have also noticed the 722.6 gearbox kickdown sometimes results in a long pause before a rough engagement of the lower gear so I am wondering if I should check out the conductor plate solenoids. Perhaps I should replace the kickdown switch first. I can't really be arsed to delve back in to the gearbox again but it may be a Winter project.

There's a common issue with the electrical plug on those 722.6 transmissions which can leak at the pins. ATF would then travel up the wires and onto the TCU which I think is in the passenger side foot well on the left hand drive cars (not sure about RHD). Remove it and inspect it to see if it's oily at the pins. The plug should be replaced every time you change the fluid . It costs about $15 for a replacement here in the US.

Many thanks. My pilot bushing and the transmission control module under the footwell (front left footwell in my car) are bone dry. However, studying the below picture do I detect a slight oily sheen on the right-side wiring and under the unit?!

This is the control module under the front left carpet:


The gearbox does seem a bit smoother since I topped up the ATF but it still occasionally pauses then clonks in to gear on kickdown from what I think is 5 to 3. No issues when dropping a single gear.

[Hereward]

Interesting...I've had a another look and there is a slight oily residue in the area. I have cleaned all the connectors with electrical contact cleaner and will test the gearbox again. The pilot bushing is definitely dry, I inspected that a few weekends ago.

This is a 5 minute job - slide back the seat, peel back the footwell carpet and remove the plastic protective cover to reveal the modules:


Note the oily residue on the black plastic:


Thanks for raising this, alabbasi, I had ruled it out. Definitely easier access than the conductor plate solenoids! Let's see if the degreasing made any difference...

Edited by Hereward on Saturday 23 March 11:30

[alabbasi]

If you've got over 60k miles and the conductor plate has not been replaced. It's due. Swap it out when you do the fluid and do the torque converter too. Make sure that you use approved 236.10 ATF fluid. The cheapest I've found is valvoline maxlife atf here in the US but double check this as the chemistry could be different for the Euro market.

Also consider doing the brake switch as it will cause the trans to act out (as well as trip the ASR and BAS lights). Another cheapy fix.

I'm enjoying this thread. I have a 98 SL500 (M119) and a 90 300SL with a manual gearbox.

[Stegel]

Another vote for spannering as therapy here too - a few hours figuring out what’s wrong, what to do and where to get the parts, and the actual doing, makes any thoughts of the day job recede completely. I was really into working on cars in my teens and very early twenties, rebuilt engines, gas welded bodywork, but then just stopped - so much so, that 20-30 years later changing a wheel gave me a sense of satisfaction. Over the last 5 years I’ve regained confidence in taking on brakes, suspension and the like - we have the benefit of forums, Youtube etc. now which helps massively. If I can buy the parts and perhaps a special tool more cheaply than I can let a professional have a go (and perhaps codge it up) I’ll think about having a go! Little extra jobs, like applying some rust proofing wax when changing shock absorbers, which a garage would not do, give a real sense of doing the car good too!

On the brake bleeding, I bought a Sealey pressure bleeder, and used it for the first time on my SL. Unthinking, I disconnnected the line from the cap without depressurising it first - brake fluid everywhere, with frantic squirting of Surfex and a hosepipe into the scuttle (fortunately I was doing the job outdoors) to save the paint.

Returning to topic, my code reader picked up problems in the gearbox when the connector plug was leaking - there was no leak evident externally, but the plug on the end of the cable was soaked in oil when pulled, so that was washed repeatedly in contact cleaner and allowed to dry before reassembly. With regards ATF fluid, and I hate to get into debate over MB fluid specs, 236.10 was the recommendation for (I presume) a 722.6 box, but they’ve now change that to 236.14 (see sheet 231.1 - that fluid was introduced for the 7G box originally) - I used it (Fuchs) in my 97 SL and it made a great difference to smoothness.

Edited by Stegel on Sunday 24th March 09:41

[Hereward]

Today I tested a spare Adaptive Damping System (ADS) ECU that I purchased a few years ago. I assume these parts are going to get harder to source as the years go by so I purchased a used ECU on Ebay from Germany for 255 Euros so that I would have a spare.

My existing ECU is totally fine. It's the original unit, manufactured in Week 40 of 1996. The spare ECU was manufactured in Week 44 of Year 2000.

The ADS control module is mounted in an engine bay bulkhead housing next to the 38 pin diagnostics socket (My car is Dec 1996 build):


Prise it out gently and simply push the new one in:


Original and replacement:


There is no need to calibrate or synchronise replacement control modules, just plug and play. A test drive confirmed no issues.

There is so much incorrect information about ADS on the internet. It's simple hydraulic principles. I don't understand how owners and professionals alike can get it so wrong when diagnosing issues.

[Hereward]

alabbasi said:

If you've got over 60k miles and the conductor plate has not been replaced. It's due.

I replaced the conductor plate in my thread update of 18th April 2017. I may have to delve back in there to test the solenoids

[SilverStar]

Fantastic thread. I've just read everything from the beginning.

[alpinab3]

Euro car parts sell MB236.14 Triple QX oil

[bolidemichael]

Hi Hereward, have you undertaken any more tinkering of late?

[leef44]

r129sl said:

I'd vouch for the maintenance-as-therapy angle. I'd also say to anyone who, like me, drives a desk and is generally a mechanical spaz, that you just need to start somewhere. Anywhere. Start with oil and filter changes. The hardest part is getting the under tray off. And go from there. Slowly. Expect to cock it up first time you try. I think I started with oil and filter, progressed to shocks, and now can do many things including brakes. Shocks make a good example. The first side takes two hours; the second takes 15 minutes. It has taken me seven years to get confident with stuff.

You don't need much gear. A good jack, good axle stands, one of the big Halfords Professional socket sets, a breaker bar, a drain bucket. And lots of latex gloves. A big rubber mat for lying on the floor is useful. It really helps if you don't need the car tomorrow. It is also quite physical. Finally, make friends with the garagiste in the village: when you do cock it up, and we all do, he will fix it for only twice what it would have cost you to take it to him in the first place.

nice thread resurrection. Very inspirational, coming from you r129sl. I had no idea you started out as a "numpty", you're a bit of a legend on here when it comes to these cars.

[Hereward]

Hello. Very little tinkering to report.

Maintenance-wise I pulled out a spark plug to check the condition and that has been it.

This engine has one spark plug and one pencil coil per cylinder. Other Merc V12 variants have (I think) 2 plugs per cylinder (dual spark) and also coil packs, which is a rail of 6 coils combined as a single unit, one for each bank of the V. The coil packs are known to fail and are expensive to replace. Luckily my car's engine is basic tech and access is easy to all 12 plugs.

My pencil coils are all original 1996 components so have done well.

This is a pencil coil unplugged, unclipped and carefully pulled out:



I removed a spark plug for a visual check. Looks to be in beautiful condition so I simply refitted it. Replacement plugs are basic Bosch F8DC4; they cost less than 2 quid each. Who says these engines are expensive to maintain?! Going forward I will simply inspect a plug once every year or so.

Edited by Hereward on Saturday 1st June 11:36

[Hereward]

What a bizarre day. Having not posted for a few months and then providing a dull spark plug update this morning, I can report I have cured the kickdown issue that I have suffered for a year or two.

I started the car this afternoon and it immediately went in to limp mode, with the BAS/ESP light illuminated and a rough high idle. I turned the engine off then turned the key to position 2 and looked under the bonnet. I could only hear one of the two throttle bodies humming, the nearside one was dead. Pre-facelift throttle bodies are problematic but these ones were meant to be very reliable. A few taps with rubber mallet didn't wake it up.

I then noticed an external plastic portion of the butterfly valve housing stuck open against a bolt and it all made sense.

A few years ago I had replaced the cracked rubber boot between the MAF and the throttle body. At the same time I replaced the threaded bolt on the jubilee clip that attached the boot to the throttle body since the head on the original one was rounding off. I had used a bolt that was 1cm too long and it had been catching on the external spring-loaded plastic portion butterfly valve, preventing or slowing the opening of the valve.

I moved the bolt out of the way and re-started the car and all was fine. I went for a drive and used aggressive kickdown and the gearchanges are now instant and totally smooth - the throttle body butterfly valve is now free to move instantly to wide-open throttle position with no delay as it fights against the tip of the bolt.

Nearside throttle body with the affected area circled:




Close-up showing gouged butterfly valve and offending bolt:

[bolidemichael]

Excellent stuff! How satisfying... so is the next step to replace the bolt and the gouged our butterfly valve? Is there a part number for the bolt?

[Hereward]

bolidemichael said:

Excellent stuff! How satisfying... so is the next step to replace the bolt and the gouged our butterfly valve? Is there a part number for the bolt?

Hello. Nope, it's all sorted. I simply rotated the jubilee clip a few cm so the bolt no longer fouls on the valve components and all is good. I had a few minutes of imagining having to source a new/refurbed throttle body, so this is a massive relief.

[Yogioes]

I love that.
It's great when you find a simple solution to what was a potentially expensive problem.
Yes, these cars have some complex stuff on them, but as with most cars, a lot of the problems can be quite simple.
It's easy for the pleasure of ownership to be spoiled by the fear of something failing. I often have to say to myself that it's just a car, nuts, bolts and wires.

I don't usually enjoy problem solving at the time, but I do enjoy looking back after a fix and realising that the clues were there.

Thanks for sharing

[tobinen]

Great result, must be satisfying