Mercedes 7G auto transmission failure

[charlysays]

Sorry to hear about this. I always wondered how much better the 722.9 were than the 722.6. I believe the .6 had some weak-ish bushings on one of the clutches or planetry gear sets, hopefully they strengthened that but sounds unusual for an oil pump to fail?! Oil pump failure in the .6 seems pretty rare.

I once had a 722.6 which started not shifting into higher gears when cold, got worse and worse til I was driving around in 3rd

My daily is a 1997 C250 TD auto with 250k miles on it. I acquired it at 175k miles and I change the fluid approx every 30k miles. I'm gentle with it when pulling away and feather the throttle to ease strain on it when shifting during most driving but I fairly often thrash the hell out of it at higher speeds/ overtaking etc, it's also remapped to about 200hp with some upgrades made to the stock turbo. Other than that I just fitted new O rings on the pilot bushing but not touched anything else. I usually just use the cheapest ATF I can find which meets MB236.10 and usually throw a bottle of lucas transmission fix in with it, so far so good but I have a spare low-ish mileage transmission and torque converter sitting under a bench in case of a rainy day.

 

[JOEPRO]

Update,

Only took 6 months but I got this car jacked up onto my hydraulic ramps so I can have it secure outside and high enough to withdraw the transmission from underneath and out the front.

I did remove a transmission oil cooler line, had my brother start the engine and not a drip was pumping through. So I believe it has to be oil pump failure as suspected.

Only one way to find out. I'll drain some transmission fluid and make sure a decent amount comes out. If so then tomorrow I am going to remove the transmission for diy repair. (I've successfully repaired several before)

 

[JOEPRO]

Transmission removed, wasn't too terrible. Good space in this chassis to reach bolts etc. My new m12 impact 1/2 ratchet is amazing. Was able to buzz out the propshaft bolts with it very quickly and easily.



As I suspected it's looking VERY like pump failure...



Bushing seized to the TC neck



I will steam clean the transmission case now and later should get time to pull the case apart and see what lies inside the oil pump.

Then to take stock of what I need to order. Probably going to be cheaper to buy a good used compatible TC vs sending my own out for refurbishment. I am selling the car as soon as its repaired so not going crazy with it like I would with my other classic cars!

 

[JOEPRO]

I located a good used compatible torque converter from England £90 posted. That will take care of the busted TC nose.

The oil pump isn't supposed to look like this -



I will be making my own 722.6 / 722.9 pump repair plate. And if successful which I fully expect it to be, I'll be offering these for sale too. There are suppliers in USA but none in UK/ Europe.

So this trans will be getting the case emptied and oil gallies flushed out. Replacement used pump and repair plate. New TC radial oil seal. Used torque converter. Service kit (again, only been a couple K miles!!)

 

[premmington]

I located a good used compatible torque converter from England £90 posted. That will take care of the busted TC nose.

The oil pump isn't supposed to look like this -

View attachment 495508

I will be making my own 722.6 / 722.9 pump repair plate. And if successful which I fully expect it to be, I'll be offering these for sale too. There are suppliers in USA but none in UK/ Europe.

So this trans will be getting the case emptied and oil gallies flushed out. Replacement used pump and repair plate. New TC radial oil seal. Used torque converter. Service kit (again, only been a couple K miles!!)

Clear diagnosis - pump pooped itself.

Getting it out on the floor "looked a party" - even with a fully equipped workshop - lifts and gearbox lifting gear - I still whinge like a baby pulling boxes out...

 

[reb78]

Clear diagnosis - pump pooped itself.

Getting it out on the floor "looked a party" - even with a fully equipped workshop - lifts and gearbox lifting gear - I still whinge like a baby pulling boxes out...

Haha. My lift must have paid for itself the first gearbox I did.

 

[JOEPRO]

Clear diagnosis - pump pooped itself.

Getting it out on the floor "looked a party" - even with a fully equipped workshop - lifts and gearbox lifting gear - I still whinge like a baby pulling boxes out...

It's partly why I put if off for 6 months!

But it wasn't near as bad as I thought to remove. Decent amount of room meant I could reach my arm up from below and undo all the bellhousing bolts. The Milwaukee m12 impact ratchet worked wonders at removing all the porpshaft bolts inside a couple of minutes. This jobbie - with 5ah high output battery



My transmission jack is one that mounts onto a 3 tonne trolley jack. But it's too tall really. I had to manhandle the transmission out from the jack onto a dolley under the car which was fun.

So a low profile transmission jack is on my shopping list.

 

[JOEPRO]

Ps I have a 2 post lift to install yet. And a scissor lift which I immediately perched a project car on top of and removed its engine


Still lying on tarmac outside. I'll never learn.

 

[premmington]

It's partly why I put if off for 6 months!

But it wasn't near as bad as I thought to remove. Decent amount of room meant I could reach my arm up from below and undo all the bellhousing bolts. The Milwaukee m12 impact ratchet worked wonders at removing all the porpshaft bolts inside a couple of minutes. This jobbie - with 5ah high output battery

View attachment 495509

My transmission jack is one that mounts onto a 3 tonne trolley jack. But it's too tall really. I had to manhandle the transmission out from the jack onto a dolley under the car which was fun.

So a low profile transmission jack is on my shopping list.

I got one of those 3/8ths 12v right angled impact wrenches with a 6ah battery on it. I like mine too...

I got rubber boot for mine as well...

 

[JOEPRO]

At least I'll have some expensive garage wall art now

I'll clean and mount the pump on the wall. I also plan to cut the old damaged TC in half, parts wash it and display the 2x halves of that on the wall too. Why not. Always wanted to see inside one first hand.

 

[premmington]

At least I'll have some expensive garage wall art now

I'll clean and mount the pump on the wall. I also plan to cut the old damaged TC in half, parts wash it and display the 2x halves of that on the wall too. Why not. Always wanted to see inside one first hand.

I seen plenty that have split - mostly when they tried to escape the bell housing...

 

[JOEPRO]

Update. I'll summarise in bulletpoints - there has been decent progress!

Obtained a good used torque converter. Thoroughly cleaned transmission internals including splitting the valve body. Checked frictions and all are in good condition. Cleaned up the damaged metal in the bellhousing. I am waiting on my first custom oil pump repair plate being ready. Test fitted replacement oil pump to replacement TC and feels like a good tight fit no binding.

Some photos -



I am 100% confident all metal material is now fully removed from the transmission internals. I hope to collect the repair plate tomorrow after work. All transmission parts are wrapped in plastic awaiting final assembly. It has to have the oil pump next, then that put into the transmission before valve body goes on so that's as far as I can take it for now.

 

[dobbslc]

That's an impressive looking piece of engineering!

 

[JOEPRO]

I picked up the first pump repair plate sample watercut to my drawing. Fits 100% although I will make a couple of tiny adjustments then send the new file and get a small run of them cut.



Polished side with film on it still - goes against the pump gears so they ride on a super smooth surface.



It has a very fine burr on the back side so I will carefully sand that off with 1200 grit then this one will be going into this transmission now.

 

[dobbslc]

What actually failed?
I want to see exploded things!

 

[8ob]

I am 100% confident all metal material is now fully removed from the transmission internals. I hope to collect the repair plate tomorrow after work. All transmission parts are wrapped in plastic awaiting final assembly. It has to have the oil pump next, then that put into the transmission before valve body goes on so that's as far as I can take it for now.

Don't forget the trans cooler and pipes, doesn’t take much in the way of swarf to wipe out another transmission.

Bob

 

[JOEPRO]

Don't forget the trans cooler and pipes, doesn’t take much in the way of swarf to wipe out another transmission.

Bob

Yes I will be flushing the trans cooler oil lines through before starting back up

 

[JOEPRO]

This plate is a great job. Damaged bellhousing cleaned up but not usable -



Pump repair plate offered into place



Ultra smooth flat surface for the oil pump gears.

 

[JOEPRO]

I got just enough time after work tonight to re install the oil pump, B1 frictions and the geartrain. Some pics of that, didn't cover it all.





Then the case goes back on and bellhousing bolts torqued.



Test fitted the torque converter and it spins with my pinky so all good, nice and smooth.

Next up tomorrow I'll pull the pan again and re install the valve body and new filter etc and pan on for the last time before install into car which will commence Saturday morning early.

 

[JOEPRO]

What actually failed?
I want to see exploded things!

The oil pump bushing spun then the oil pump gear went off centre and destroyed itself