Clutch, transmission (25, 26)
Front axle support (Vorderachsträger, Fahrschemel) Mercedes-Benz type 220S, © Daimler AG
This is how it started, a glass beaded and tumbled clutch housing and then a couple of pictures of the cleaned up release fork with the old, first type of release bearing.
After cleaning up the clutch everything was measured and found to be well within specifications, including the flywheel and its surface. The clutch disc was only slightly worn but I knew I had to do something with since it was “grabbing” when engaged. According to my father it had been like that since he during the 70ies had the disc relined. “They mounted the wrong, too soft, lining!” according to him. A long time ago I found a new clutch for a fair price and bought it in order to remedy this. Unfortunately, it now turned out to be the wrong version of the Ponton clutch; my car had the first version (dowel pin centering) and the new clutch was of the second (cylindrical centering).
The two versions of the Mercedes Ponton clutch; cylindrical centering (second version) and dowel pin centering (first version)
I had a reputable shop in Bromma west of Stockholm (Bil & Industribromsar AB) redo the old clutch disc and its lining. My wish was to have the clutch itself dismantled and gone through as well but according to them it was in perfect condition according to an ocular review. More about that later…
Before assembling the clutch to the flywheel, you need to have the three release levers (fingers) pressed down in order not to force the clutch into place and not to lock the clutch disc prematurely. I had asked the shop to insert three hold-down clamps but that had not been done. Instead I placed the clutch on a steel plate and pressed the fingers down with the help of a threaded rod and a counter hold. I found that the square nuts for the bumpers had an almost perfect height for this. At a later stage I could borrow a set of the original clamps which made the procedure much easier (see picture and drawing in gallery below).
In order to be able to center the clutch disc I borrowed a used transmission drive shaft (see picture in gallery above). After assembling everything I measured the distance between the top of the fingers and the cover plate of the clutch as instructed by the workshop manual. The height was only ~13 mm and one finger even had 0,3 mm less than that (which – according to the workshop manual - could be the reason for the “grabbing”). 13 mm is almost 5 mm under the specified 17,8 mm. A bit strange that the distance was below specification; with a worn disc it ought to be above. I suppose my father had adjusted the clutch pedal as the disc was worn down and when the shop changed the clutch disc lining they didn’t re-adjust that but did the alignment with the fingers only.
Teaching board DBL 204: Type 220 Clutch and transmission, © Daimler AG
On top of that I could not release the clutch with the gearbox in place either (turn the shaft on the coming out of the rear of the gearbox). I was however a bit reluctant to adjust this distance since I had never done a clutch before. I took the clutch down several times, checked it, put it back and engaged the clutch over and over again in order to see if I could get it to settle. In vain. I read a couple of articles on the net (incl the very informative links on the Ponton-site, Clutch Removal and Installation I, Clutch Removal and Installation II and Clutch Removal and Installation III) and also briefly discussed it on some forums. Most of the advises was to leave it, it would settle when the car was used, the clutch worked before I took it down. At the end I did however decide I wanted it to be according to the workshop manual. I didn’t want to risk being forced to remove the gearbox and clutch at a later stage.
After removing the locking nuts, I discovered that the special washers underneath them were heavily worn against the levers and two even had cracks. The clutch obviously wasn’t in such a good shape as the shop thought… Getting new locking nuts was not a problem but the washers were more problematic, I couldn’t find them in Sweden. Firma Karasch did however have them. To be on the safe side I ordered two sets of nuts and washers.
The adjustment was actually very easy to do, just to follow the procedure in the manual. It however took some time and a lot of removing and attaching the clutch, the transmission housing and the gearbox in order to engage the clutch and then readjust the nuts until everything was within specification and stable. The first time it took me 10-15 minutes to remove the housing and gearbox. At the end I did it in 2-3 minutes. After this I could also release the clutch and turn the shaft on the gearbox. Happy!
The pictures below show the assembly of a new release bearing of the first version on the plated and painted release fork and its plated release-unit as well as everything assembled in the clutch housing. Before replacing the release bearing on a Ponton, carefully read Clutch Removal and Installation III. Also, before you pay for the new release bearing, be 110% sure that the grease in it isn’t hard=old stock. To my knowledge there is no way to get the hardened grease out and replaced with new grease. I’ve tried and failed myself.
In the workshop manual, under “Installation” there are two phrases that are strange:
- “Do not forget the snap rings” (Sprengring in the German version). No-one I’ve been in contact with understand what this could be. The only snap ring (or C-clips) we could come up with is in the release fork. We however agreed that it is probably the clamps mentioned above that are meant. They are present only for purposes of shipping and assembling the pressure plate and must be removed and discarded at the proper time. Probably a typo.
- “Only the prescribed special screws should be used”. I had standard, not hardened but 8.8 (lower quality you wont find in a Ponton), screws and the spare parts list only states standard screws in two different dimensions depending on chassis number. So "special screws" is probably a typo as well.
Also, the clutch housing belongs to group 25. But if you are looking for the M10 screws that holds the clutch housing to the engine block/crank case you have to go to group 26 to find them and their specifications.
Assembled Mercedes-Benz Ponton clutch and transmission
The gearbox was restored many years ago by Bernats Bil and one of their old-school mechanics, close to retirement, so I felt very sure everything would go smoothly with this item when I was preparing to attach it to the engine during the spring 2017. Unfortunately, this (too…) turned into a lengthy sub-project. The short version of this story can be read below.
I realized that the parts on the gearbox cover was untouched, i.e. unrestored. The rubber/plastic bushings in the shifting and selector levers as well as the ball sockets on the shifting and selector rods were not replaced. The sealing on the shifting shaft also looked old but since it didn’t seem to leak I decided to focus on the bushings and sockets. I had the levers and rods sandblasted, plated and finally painted. Bushings were renewed and even though I fixed the old ball sockets, I ordered new ones with plastic bushings instead.
Everything nicely photographed and published below.
Before doing this, I had however noticed that I had problems putting the gearbox into reverse so to speak. I either had to use a lot of force or it didn’t work at all. I had a spare gearbox cover where I didn’t have this problem. There should be some resistance since there is a “shoulder” on the guiding plate inside the cover (see group of pictures below where you can see the guiding plate and its “shoulder”) that prevents you from putting the car into reverse by mistake. Since we’ve never had problem with putting into reverse when the car was in traffic and the gearbox had been restored I didn’t really pay attention to this, thought it was ok.
When assembling the levers again I didn’t know that the selector finger (see picture 2 below) wasn’t locked in its vertical position (but see the note under the assembly chapters below). That is not a problem per se because you don’t damage anything if you push it down and you can lift it up. Since I didn’t know that this happened, I tried to shift with lever when the selector finger was actually in the “pushed down”-position. With the selector finger in that position you easily get it out of its seat in the shifting finger (see picture 2 below) that sits on the shifting shaft in the cover. That is also not a problem since you with some fiddling can get it back in its correct position which I managed to do.
Now I again noticed I had problems getting the box into reverse. Hmmmm, maybe I had damaged something when I fiddled with the selector finger!? Slept on it a couple of times and fiddled with the reverse light switch (see picture 3 above and the pictures in the group below), its bar and spring and tried to exchange the original ones with the ones from the spare cover to see if I could get it to work. It didn’t.
Taking the cover apart
Hence, I took the cover off, so that I could continue fiddle with the things visible. Didn’t get it to work anyway and I couldn’t make any sense out of it. Nothing seemed wrong. Took the cover apart to see if I could find any wear or play in the mechanism that caused the problem. I couldn’t. Took the spare cover apart and started to compare and exchange the parts (having 110% control over what cover the parts belonged to) to see if I could find the reason. I couldn’t. So, I started to terrorize the Ponton mailing list and VHD Mercedes Club’s forum again as well as took direct contacts with knowledgeable MB-people all over the globe.
I have spent many hours exchanging mails and photos. I disassembled my transmission cover several times and assembled it with parts from other covers and I have tried my parts in the other covers. I have thought I have found the cause in shafts, switches, guiding plates, springs, washers, bushings, bars, pins or fingers but after a couple of new tries and tests concluded I hadn’t. I have spent a couple of evenings going through the same steps with an old, very experienced, technically skilled and practical MB friend here in Stockholm to see if two brains would succeed. We didn’t. He got as confused as me.
Having tried a couple of gearboxes, as well as covers, I also learnt that the force required to put them into reverse differed a lot, from very hard to veeery easy. I learnt that a newly assembled cover is, due to unknown reason (at least for me), hard or impossible to put into reverse. Fiddling with it for 5-10 minutes makes it easier and more dependable. Probably it needs to settle.
I verified that the different parts in my gearbox cover had no or very little wear and play, at least on surfaces involved in the shifting. We concluded that there was no way that one part by itself could be the cause. This was proven by extensive testing, measuring and comparisons. Replacing all parts involved with new, would cost me at least €500. A new cover €1000. Of course, I could go for a used “fully functional” cover but would still want to replace bearings, gaskets etc as well as alignment of the forks against my gearbox. Since that would mean a disassembly of the cover, who knows how that cover would work after that. My experience pointed towards that risk that the same problem would show up was very high.
The solution I found came from a MB300d -62 gearbox with a cover marked “111 260 03 14” which wasn’t fitted with a reverse light switch (the switch is located elsewhere in the shifting mechanism), only a screw holding the bar and its spring. Putting this gearbox into reverse was extremely easy, almost too easy. The spring in this cover, behind the screw, was a bit longer than the ones I had seen so far but much weaker. Using that spring in my cover made it fairly easy to put my cover into reverse. Putting my spring in the MB300d gearbox made the force required to put that into reverse moderate, but definitely not hard.
So, that will be my solution. I hope and believe that whatever is the problem behind this won't ruin my driving the coming 20 years...
Any thoughts on that? Pleeeease, contact me!!!
Above you can see the two springs and the bar as well as the pin for the brake light switch. As you can see the “new” spring is a bit longer but also weaker. The second and third picture show the result of intense polishing of the “shoulder” in order to really see to that the guiding plate moves freely and that there is nothing that the bar, also polished, can be stuck on. The fourth and last picture I just throw in to show that I’ve leveled the base of the cover.
Then we come to the process of assembling everything. First, I made a tool for assembling the forks. It is based on a tip from the American 190SL Group’s forum (many thanks to H Magno for giving me this link!). As you can see in the link as well in the first picture above, it consists of three parts, an M6 screw, a smaller piece with a 45-degree cut off half of the cylinder diameter and a small cut off on the other half (at least that is how I understood the link’s instruction) and finally a longer piece which you use to push the smaller piece into the fork (picture 2 above). The length of the smaller piece allows it to be removed when you assemble the fork and its shaft in the gearbox cover.
The instruction from the 190SL Group-link above says, more or less:
Press the ball into the spring with the 6 mm bolt (picture 3 above). Slide the small tool into the shaft hole and press it into the ball with the longer bolt while pressing down with the 6mm bolt. When the ball is contained (picture 4 above), remove the 6mm bolt and the long piece. Put everything in place in the cover and press the shift rod into the small tool, pushing it through (picture 5 above). Be careful about releasing the ball. It will fly into a great hiding place.
This worked perfectly!
Gearbox cover assembly
I made the decision not to paint the housing or clean the covers of the gearbox. At this stage I didn't want to spend this time or risk damaging anything. This means that the gearbox won't look like new which is sad but with a little luck not many people will study the engine compartment that thoroughly. In this case function goes before looks.
First I saw to that the cover was leveled where after the locking plate (in which the locking finger goes, following the typical shifting pattern) was put in place. New needle bearings was pressed in as well as a new shifting shaft sealing.
According to the spare parts manual there should be a sealing on the sifting finger, on the "interior side" of the cover so to speak. When I took apart my covers there was no sealing. That doesn't mean that there was none from the beginning. It may have worn out, fallen apart and disappeared when the gearbox oil was changed. I really can't see that there's a need for this sealing since the finger itself sits very close to the cover, "sealing" the very tight hole. I can't see how oil would be able to travel vertically, at least not in larger amounts. My gearbox, without this sealing has not leaked. Any way, I installed one and of course there is another advantage with that; the selector finger now sits in a correct position and you can not move it up and down vertically as I could in the beginning (see above)! Don't over tighten the selector lever assembly!
Next came the guiding plate with new washers and nuts. Also the reverse gear lock parts (bar, the "new" spring, pressure pin and the light switch). The shifting lever was installed in its correct position.
With the help of the tool it was then very easy to install the rails and ends for the different gears. Be careful so that you get all the shims into their correct places!
Finally the "key for shifting rail mounting" was pressed into position.
The housing got a small amount of sealant and the cover a touch of Vaseline before the new paper gasket was put in place. And Voila!, I finally had a completely restored Mercedes-Benz Ponton gearbox in front of me!
See "Engine suspension (22/24)" for my discoveries around a new rear engine suspension, the one that sits on the rear end of transmission on some Pontons.