6-speed W123 - PeachParts Mercedes-Benz Forum

juanesoto · #1 11-08-2011, 03:51 PM

Hello folks!

After looking for a 5-speed tranny for my W123 for several years with no luck whatsoever, I decided to go down the transmission adaptation road. I found some really useful data created by Dropnosky (at STD forum) of a W201 transmission modification he did for his 61X application.

However, since I'll be going through all the bellhousing cutting/welding process, I have decided to go for the big fish! Therefore, I bought a W203 C230 Kompressor 6-speed manual transmission and gear selector. The transmission code is 716.648.

I have several concerns though. This transmission has no mechanical speedometer output, so I need to figure out a way to make my speedometer work. Also, I have to figure out a way of adapting the output flange of a W123 tranmission to this transmission, so I can use the original flexdisc intended for my car.

I'm waiting for the 6-speed to arrive, so I can do a side by side comparison with a 4-speed.

Any thoughts, tips or advice you can share with me will be highly appreciated!

Happy driving!

gatorblue92 · #2 11-08-2011, 03:59 PM

No advice however I'm very interested to see how this project turns out.

vstech · #3 11-08-2011, 04:40 PM

my only advice is to take LOTS of pictures...

shadetree77 · #4 11-08-2011, 06:07 PM

you could just use a permanent GPS for the speedometer; i was tinkering with the idea for my old truck. there are lots of programs that can take the data feed off a gps receiver and display it on a small screen ( i was going to sacrifice my old HP IPAQ as the screen, but never got around to it). there might also be a program that will show the speed and keep up with the mileage (haven't checked though, but it seems fairly simply for a program to do that)

shadetree77 · #5 11-08-2011, 06:15 PM

i just poked around amazon and turns out they actually make gps speedometers; primarily made for boats though but would still work in a car. there's an IPOD gps speedo app too...oh my, i think you might be able to take one of those gps speedos apart and stick it in the back of your instrument cluster with the MB factory needle attached to it and make it look totally stock (just nerdy thinking on my part, the actual gps receiver would have to mounted somewhere in the top of the dash or perhaps on the sun deck, though with modifications i bet it will work)

juanesoto · #6 11-08-2011, 06:47 PM

You can bet I will take lots of pictures! I've learned so much from the forum in the past years, that documeting the process and sharing it with you is the least I can do to pay it forward.

Regarding the speedo, the GPS idea sound pretty good. I've been reading about the electronic speedometer that the 81 300TD used and it seems this is a good "factory" option. However, I need to find out exactly how that system worked. I know there was some sort of magnetic sensor in the output shaft of the tranny in that particular car. I just need to figure out how to set up that sensor in the 6-speed tranny and wire it into an electronic speedometer. Besides this, I need to find out the diff gear ratio that particular car had, so I can replace the faceplate of the speedo to get an accurate reading based on my current diff ratio. Anyone with some advice on this setup?

vstech · #7 11-08-2011, 07:58 PM

... only available the one year, not likely to be an easy find.
the gear ratio would have been 3.07

juanesoto · #8 11-08-2011, 08:23 PM

That's going to be a tough one... Perhaps I can adapt the speedo mechanism of a W126 behind the faceplate of a W123 speedometer. However I would need to know which sort of input signal it requires to work. The good thing is that since I'm going to need to modifiy the output flange in the 6-speed tranny, I can weld a splined wheel on the flange to work as a pulse generator for the speedometer sensor. However, I need to know how many pulses per flange revolution where used in the factory setup.

Anyone has a 1981 300TD Electronic Speedometer for sale? If not, at least the part number to try to find it somewhere? I tried looking in the EPC, but without an specific VIN, I get several part numbers and the description does not specify if its electronic or not...

Regarding the final ratio, currently I have the 3.46 ratio, but I guess I'll have to change it if I happen to be able to get a speedometer funtioning accordingly...

I knew the transmission cutting/welding was going to be the "easy" part and the rest of the details would be the culprit...

4x4_Welder · #9 11-08-2011, 08:34 PM

You would be best off figuring out pulses per mile for the old system, then translate that into a number your car can generate (tire revolutions per mile x gear ratio). Make the ring bolt onto the back of the flange, so it can be changed if you later change your gear ratio. I have the tools to make a tone wheel, or you can have a local machine shop do it. All you need to provide would be the OD ID and number of teeth needed.

juanesoto · #10 11-08-2011, 11:15 PM

Quote:

Originally Posted by 4x4_Welder

You would be best off figuring out pulses per mile for the old system, then translate that into a number your car can generate (tire revolutions per mile x gear ratio). Make the ring bolt onto the back of the flange, so it can be changed if you later change your gear ratio. I have the tools to make a tone wheel, or you can have a local machine shop do it. All you need to provide would be the OD ID and number of teeth needed.

You're right! Pulses per mile would be much easier to deal with and having a replaceable tone wheel will be great for future mods in the driveline. Does anyone know the type of signal used by the electronic speedometers? My WIS does not work in Windows 7, so I can´t get the inspection procedure for electronic speedometers. BTW, anyone knows where I can buy an updated WIS that will run on this Windows?

Stretch · #11 11-09-2011, 03:42 AM

Exciting project this one!

For your flex disc problem:-

I think it is best to wait and see how different the two transmissions are when you've got them side by side. I wouldn't be surprised if you need to make up a custom front propshaft anyway so perhaps the whole flex disc problem will kind of solve itself in the end!

For the mechanical speedo problem:-

I have no idea how it is on a manual transmission that was designed to be fitted to a W123 but here is a picture of an automatic transmission mechanical speedo drive:-

722.118 governor and plastic gear for the speedo

As for the welding and cutting and shutting - is the starter motor bell housing hole on the wrong side for an OM617 (again)? Can you "just" make a custom adapter plate and then "just" move the oil filter housing out of the way so you can fit in a starter motor?

juanesoto · #12 11-09-2011, 11:51 AM

Army, what you said about the flex disc might be right. I'll figure that out once I have the tranny here. It's going to take a couple of days, since I got the tranny in USA and the shipping will take 3-4 weeks as its coming by sea freight. We'll see what happens.

In the manual tranny, there is a plastic gear just like the one in the picture you posted. However, its located in the ouptup shaft of the tranny, close the the rear retainer. I think that the electronic speedo is the best "factory" option, but I still need to find out the type of pulse and so.

About the bell housing, it's the same old issue with 617 engines and the starter location. I really don't know if the oil filter can actually be relocated. I've never heard of that mod. On the other hand, we have the input shaft length and spline pattern issue. I have the 617 engine flywheel and clutch components, so I'm planning on keeping that stock. The main advantage of doing the mods to the tranny instead of the engine, flywheel, clutch, etc. is that if at some point the tranny fails and I need to go back to the 4-speed tranny, it will be bolt out bolt in work. At least in my case this is better since I have 2 complete manual drivelines; the one currently on the car plus a complete spare.

I'm getting quite excited about this project!! It's going to be a fun christmas!

Stretch · #13 11-09-2011, 12:52 PM

Quote:

Originally Posted by juanesoto

Army, what you said about the flex disc might be right. I'll figure that out once I have the tranny here. It's going to take a couple of days, since I got the tranny in USA and the shipping will take 3-4 weeks as its coming by sea freight. We'll see what happens.

In the manual tranny, there is a plastic gear just like the one in the picture you posted. However, its located in the ouptup shaft of the tranny, close the the rear retainer. I think that the electronic speedo is the best "factory" option, but I still need to find out the type of pulse and so.

About the bell housing, it's the same old issue with 617 engines and the starter location. I really don't know if the oil filter can actually be relocated. I've never heard of that mod. On the other hand, we have the input shaft length and spline pattern issue. I have the 617 engine flywheel and clutch components, so I'm planning on keeping that stock. The main advantage of doing the mods to the tranny instead of the engine, flywheel, clutch, etc. is that if at some point the tranny fails and I need to go back to the 4-speed tranny, it will be bolt out bolt in work. At least in my case this is better since I have 2 complete manual drivelines; the one currently on the car plus a complete spare.

I'm getting quite excited about this project!! It's going to be a fun christmas!

How common the oil filter repositioning actually is remains to be confirmed by others! But it seems to be the thing to do if you want a newer OM617a in a W115 240D...

see

http://www.peachparts.com/shopforum/video-forum/278403-1975-mercedes-benz-300d-om617-turbo-w115.html

for example...

Perhaps there is something to be learned there? There are also some "kits" that allow you to use a spin on /off filter instead of the two stage (fine and coarse) filtering designed by MB - I don't know how they actually get on with oil coolers though. That in my opinion is worth researching =>

http://www.peachparts.com/shopforum/diesel-discussion/297630-will-i-still-get-filtered-oil-if-i-block-off-my-oil-cooler-lines-ports.html

Spline matching => hmmm measure and design your own shaft? I'm sure you're a whiz with CAD packages...

EDIT how much was the shipping? If you don't mind me asking...

aaa · #14 11-09-2011, 05:40 PM

Oil filter relocation you say? Pic:

juanesoto · #15 11-09-2011, 07:34 PM

Thanks for the info on the filter relocation! I'll think about it. Not really sure if I want to mess around with that, but worth of considering.

About the spline matching and so, the main downside of leaving the W203 tranny stock and using an adaptor plate is that the input shaft is quite short, as the W203 uses a dual mass flywheel. This means that I would have to get a custom made flywheel. If I stick to the 617 flywheel/clutch set up, I can compensate the input shaft length issue during the cutting/welding/process. Please consider that I will be cutting the input shaft of the frankentranny and welding the splined part of the 4-speed input shaft to it. This is going to be interesting...

About the shipping, yes, you may ask! I still don't have the final cost, as my freight forwarder charges upon delivery, but according to their freight calculator, the shipping from Miami, FL to my front door via sea freight, including handling fees, customs clearance and so will be somewhere around $300. Not cheap, but not dreamkiller expensive!