350SE trans failure

[s class]

I am about to reinstall a freshly rebuilt engine into a W116 350SE, and in discussion with the owner, we agreed that it would make sense to provide the transmission with a new filter. Due diligence also dictated that I wanted to replace the radial torque converter seal, and front pump seal (since these always end up leaking, and require transmission removal to address).

I removed the bellhousing in order to extract the primary oil pump from behind, and replace the seals. All went well, and I reassembled after cleaning the parts :



With the transmission on a stand, then rotated it onto its side to remove the pan and access the filter.

As the trans rotated, there was the unpleasant sound of loose spares rattling around in the pan...

 

[s class]

The loose piece retrieved appears to be part of one of a locking ring. I then removed the filter and valve body to see if I could fish out any more bits :



Some more bits were duly found :



Removing the reverse-gear actuator piston revealed more debris, plus damage to the piston caused by the spares floating around in its cavity :



The plan now is to disassemble the complete transmission, as I have not managed to recover enough debris to account for the complete locking ring, so there must be bits still hiding in the guts of the unit. One of the pieces removed shows clear evidence of having gone through a gear set, so it is quite likely that there is additional damage.

Once completely stripped a decision will be made as to the way forward. I have a 90% complete spares unit that can donate any bits needed to repair this trans unit.

 

[Helmet]

Seen that many times, I always replace that ring and give clutch minimum clearance so that it won't fall out when it breaks next time.

 

[Styria]

I can speak from experience with this sort of breakage occurring in a 6.9 gearbox. Unfortunately, the clutch plates basically destroyed the drum. Obviously, the whole transmission had to be dismantled, and carefully examined for any additional damage to other components within the box. It was indeed fortunate that a replacement drum from a 450 could be used as a replacement.

Incidentally, that very same car also suffered from a catastrophic differential failure, with one of the bolts securing the crown wheel actually becoming dislodged and punching a hole in the differential casing. That was messy, and I believe the noise when it happened was something else to experience. Incidentally, I have also come across this potential failure on a 6.3 differential, with perhaps three or four bolts being just a little more than finger tight. Luckily enough, that one was caught in time.

At one stage, I even contemplated as normal servicing to remove the cover plate on the diff. housing and checking the tightness of all of those bolts. However, as with some items, one never seems to follow through. It is a matter of 'out of sight, out of mind' - until something happens. Regards Styria

N.B. Ryan, nice to see you back on TK after a lengthy absence. Good to have you back.

 

[Andrew280SEL]

Nice to see you again, Ryan.

As for the trans, it's a little over my head but sounds like a lot of work Envious of the owner getting a nice fresh rebuilt M116 engine though.

 

[sean sherry]

Not knowing anything about Mercedes Transmissions in particular
I wonder if the large engines are blighted with basically the same transmissions in the smaller engines ?
Lincon Continentals I know something about, and their 7 litre Engine models had a much stronger version of the Borg Warner 12 Unit
( called Duel Range Ford- o- matics ) Like an extra bolt connecting the larger bell housing to the larger stronger Case.. duel double acting servos for 2nd gear band...a heaver centre web to take the load of the rear band servo etc. Probably more metal in the clutch drums as well , but I don't remember. I never had a failing in one save for hard seals from over heating the convertor when stuck in the snow. The Yanks philosophy is to build it bigger, eg., their Engines , more Cubic Inches.

 

[Styria]

Sean, there is basically not all that much different between the various boxes, even comparing sixties to seventies, or indeed the early E type boxes and, indeed, the 722.002/3/4 boxes from the seventies. There were obviously many little variations that were effected over the years. For instance, early six cylinder models may only have three clutch plates as compared with the five platers from the 6.9.

Other variations related to clutch bands specifically. 6.3s had (from memory) double 'looped' bands (one or two), as did the 6.9s. 450s had normal bands only. Incidentally, the 6.3 double loopers used to cost the proverbial "bank vault" until now (I believe) you can no longer buy them. Servo units also differed greatly between the various boxes, with the 6.9 having the highest capacity servo units. In my opinion, the box that Ryan is rebuilding for the 350 is a particularly well constructed and designed box, probably just that little bit more sophisticated than the boxes fitted to the six cylinder models. Valve bodies, of course, differ greatly between the various models - just about none are interchangeable, sometimes even between similar boxes. I must admit that my knowledge does not extend to valve bodies - you've got to be pretty well crash hot to understand those. I used to make the mistake of dismantling those as part of rebuilding the boxes - probably the worst mistake you can make. Re-assembly is tricky, and some of the workshop literature does not fully illustrate the cross sections of the valve bodies, and the location of the various valves, together with varying spring pressures. I am sure that one or two of my grey hairs have their origin from those valve bodies.

Having said all that, rebuilding a box is fascinating - you actually have to use any wisdom you may have accumulated in your melonhead. Regards Styria

 

[sean sherry]

Yes I agree with you Styria about not stripping valve bodies unless there is metal in the box from an internal failure. In these cases we always reverse flushed the oil cooler and put a temporary filter in the return line for 1000Ks. Then removed it.
We had had a lot of trouble, especially with Ford C4 transmissions , with customers complaining that cold upshifts were delayed after an o/haul.
The fine particles still hiding in crevices in the radiator oil cooler went straight to the Governor Valve. New hot clean oil dislodged them. Also splitting a valve body that had been subject to excessive heat, meant relieving stress in the two half's and allowing them to warp. We had to face all such body half's by hand using a machined surface with emery paper glued onto it.
We learnt the hard way ! It was always thus .

 

[Styria]

Sean, I know where you're coming from as far as warped valve bodies are concerned. However, I tend to think that MB valve bodies were probably a little stronger and possibly subject to less distortion than the Ford boxes you are talking about. Also, as you'd know, the MB valve bodies come in (I think) four quarters (?) and this makes them difficult to assemble. Usually you have either eleven or thirteen ball bearings of two different sizes, tiny little springs, and tiny little valves that govern the various functions of the valve body that needs to respond to road speeds, loads and gear selections, so all in all, best to leave alone.

Of course, that's what I am preaching today - over the years, unfortunately I did not follow that philosophy. Experience, experience, or lack thereof.......Regards Styria

 

[s class]

Interesting that you guys are advocating not disassembling the valve bodoes - I've done a few without issue - maybe I've been lucky. These units have 4-layer valve bodies.

Recently I had to strip the valve body on my own 350SE due to failure - I had a quite unexpected in-service falure where I could not get any forward motion, only reverse. I stripped the valve body and found the fault in the form of a broken spring. Replaced the spring, reassembled the valve body and all was good.

BTW styria, I am also developing grey hairs, probably from the valve bodies. It is quite a task to get them together with every spring and ball in the correct place.

 

[sean sherry]

Yes Mercedes Valve Bodies are very complex, and probably why they have from time to time , sagging or broken springs. As opposed to simple 2 speed Automatics behind high torque low revving American engines. Fewer springs with much less work to do.
Design philosophy is two sided , a balance between Mercedes efficiency and American simplicity.

 

[sean sherry]

This thread has jogged my memory way back to 1961 when I worked in London for a Ford Dealer...A Mercedes Parts Man remarked to me that Auto Trans Boxes were his fastest moving Part.

To Quote him ...." Why didn't Mercedes just go to Ford and buy in 3 speed C4's " ?

Probably the best Ford Auto has ever produced .. and afterwards the larger C6 for their V8s.

Not meaning to offend our die hard Mercedes friends...... but nobody has a monopoly on brains.