replacing 240D manual transmission - PeachParts Mercedes-Benz Forum

dieseldaddy · #1 07-18-2002, 04:12 PM

I will soon be obtaining a used 4spd transmisison from one of our wonderful members here. (thank you!)

I am also going to attempt to remove the old one and replace it MYSELF. Now what I need is LOTS of help!

1. I am new to this. Maybe I am kidding myself thinking I can do it.

2. While I am under there and the tranny is out, what additional parts, etc. should I just go ahead and replace?
- Transmission mounts?
- driveshaft seal?
- seals/gaskets
- ???
- ??? bushings?? (I have no idea)

3. Also, to anyone who has done this successfully themselves, can you give me any advise as to pitfalls and obstacles that I will run into?

Thanks in advance!
-Brian

leathermang · #2 07-18-2002, 04:59 PM

Clutch, throwout bearing, pilot bearing certainly come to mind....

What do you mean " new to this" ? What else have you done ? What tools do you have ? Are you going to pull the engine/trans as a unit or do it from underneath ? If from underneath what do you have to get the car up in the air safely and keep it there until you are ready for it to come down ?

Do you have an friends with some experience who could help by supervising ? Greg

engatwork · #3 07-18-2002, 07:08 PM

I pulled the tranny out of the E320 in the garage to replace a couple seals about a year and a half ago. The manual 240 has got to be a piece of cake compared to this or any other automatic transmission car. It took me 3 - 6 hour days to do it. Anyway, I would suggest getting a good look at your flex dics while under there. If they look worn go ahead and replace them. Make sure you mark the driveshaft relationship to insure it goes back the same way. You could have balance problems if it doesn't. On most cars you would want to go ahead and replace the rear main seal but unfortunately on the W123's the rear main seal is a "packing" type material and the only way to replace it is to pull the engine and move the oil pan and crank out of the way.
Take you time and take plenty of digital pictures to have a "record" of how everything goes back together. It is a straight forward but physically demanding type of job.

The Warden · #4 07-19-2002, 04:15 AM

Just wondering, why are you replacing the tranny? What's wrong with the old one?

#5 07-19-2002, 06:50 AM

I'm in the same boat as The Warden here. I have'nt seen a manual transmission that needed replacing since my '48 Chevy.

This is a relatively straight forward job, it's just that it is a pain. Around truck shops, mechanics whince when you suggest a clutch job. Speaking of clutch job, make sure you inspect the clutch, pressure plate and throwout bearing while you're there.

Good luck,

dieseldaddy · #6 07-19-2002, 08:42 AM

I am replacing it because it suddenly decided that it didn't like to go into 3rd gear. So it grinds very badly whnever I do.

I have been double-clutching to get it from 2-3, but it does not help going down from 4-3.The only time I can get it into 3rd from 4th is to wait until 20mph or less. (Why would I want to be in 3rd lower than 20mph?)

I have been told by 2 independant MB mechanics and one local dealership that the symptoms all point to the synchro gone bad, and that I would be better off replacing than repairing. My tranny has 202K on it...which I do NOT believe is any indication that the tranny should be starting to fail.

Hey, if any of you can tell me that it is NOT in need of a replacement, please speak up!

This came on VERY suddenly (one night fine, next morning bad) but all the other gears are absolutely fine. Even reverse.

So now what do I do?

I have a guy waiting for me to cut him a check for the replacement tranny... Is a synchro really that "easy" and inexpensive to have repaired? Basically, I found that i could have a used transmission installed for $650, and that includes the transmission from a member here.

janko · #7 07-19-2002, 09:22 AM

the odds that this may help are indeed scant. anyhow, i had trouble with my transmission. i was double clutching to again access to 2nd gear. both on up and down shifts. decided on a lark to drain transmission and refill. well to make a long story short, i drained gear oil. not recommended. refilled with engine oil - mobile 1 10w-30 - and i have a transmission that works perfectly. hope your fix is as easy as mine. good luck.

janko · #8 07-19-2002, 09:25 AM

sorry i should have included this above. question: any chance the clutch is not releasing? given sudden nature and all, perhaps clutch hydraulics need inspection.

dieseldaddy · #9 07-19-2002, 10:39 AM

My first inclination was the clutch.
However, after talking with the mechanics, they all ruled it out seeing that it was only one gear. And the double-clutching works, but only from 2-3, NOT 3-4.

You know, I will change the fluid and see if that helps first.
Always check the cheap stuff first, right?!?!

10w30? My manual says ATF.
There are tons of posts that differ greatly in opinion. What is the BEST to use in my 1983 240D 4spd with 202K miles?

Thanks.

JimSmith · #10 07-19-2002, 10:50 AM

dieseldaddy,

The plugs are both 14mm. Should be available at Sears if you don't have one.

A little air in the clutch hydraulics will make the clutch operation less than what was designed. Look at the back of the brake fluid reservoir and see if it is low. If it is you might have a fluid leak, and the first gear exchange to show is your 3rd gear one. This is a very frequently used synchro (into and out of 3rd) so it may in fact be worn. Like others here, I have never seen it, and based on how hard it works (not as severe as the lower gears in terms of what it must do at every gear change it is involved with) if you have good fluid you should not expect to see it go bad. Good luck, Jim

janko · #11 07-19-2002, 10:52 AM

i read a plethora of posts - automatic transmission fluid/ engine oil - and for whatever reason went with the engine oil. no regrets. and no leaks. maybe that was the deciding factor. transmission fluid now adays no longer friendly to 20 years old seals. who knows?

#12 07-19-2002, 11:01 AM

I am assuming that you or your technician have checked the shift linkage bushings. I also would triple check the clutch release. I have changed a clutch before, only to find that the problem was hydraulic. There, I admitted it!

Good luck,

dieseldaddy · #13 07-23-2002, 08:42 AM

I drained the fluid last night.
It was dark red, with metallic swirls and shiny sparkles in it. Almost looked like red metallic paint!!

So, I refilled with ATF (per my owners manual) and still grinds.
Well, at least I know I have good fluid now! But for how long...?

I am taking it in this week for a real good look over.

Larry: I have only talked with the mechanics face to face at this point, and only one of them has ever been under my car. Probably not a good idea, huh?

Thanks guys! I will let you know how it turns out. I would really like it if it was NOT the transmisison and only an auxillary part.

leathermang · #14 07-23-2002, 10:03 AM

Transmissions are an ideal candidate for Magnetic drainplugs... both to capture steel particles to keep them out of suspension and if the trans is drained regularly to give advance notice that things are starting to wear...

JimSmith · #15 07-23-2002, 12:15 PM

Sounds like someone should have changed the fluid a few times in the last ten years and didn't. However, the transmission is a synchromesh unit and that means the gear teeth on all the gears are always meshed, but freewheeling on the drive shaft when they are not selected. Selecting a gear to drive the wheels involves moving a cylindrical block that is splined to the drive shaft and never freewheels so some pretty robust nubs on the face of the block engage some pretty robust nubs on the face of the freewheeling gear. Only one gear can be selected by the shift linkage at a time.

Anyway, the point of this is to note the grinding and clunking is the whacking of the nubs against each other, which is supposed to be limited by the synchonizers that are intended to match the speed of the freewheeling gear to the speed of the cylinder with the facial nubs (called a dog clutch) before they actually engage. This is usually not a big deal, but if the main, foot pedal actuated clutch is not working correctly and the anticipated load on the synchros goes up because now the synchro is trying to adjust the engine speed or road speed to allow the dog clutch to engage, it is a big deal and the synchros give up. And you get a grinding sound which is really the dog clutch nubs being banged up. It can also cause premature wear of the synchros. Which is likely what you see as the metallic particles in the red auto transmission fluid you drained out. The nubs on the dog clutch face are pretty robust, so some clunking is not fatal. Prolonged clunking will round off the corners and could chip the interface with the gear face nubs, which would be bad and result in the transmission popping out of gear as load increased or decreased. You have not reported popping out of gear as a problem, so I think you probably have yet to take a big chunk out of the nubs on either part.

So, I think Larry and I agree you need to rule out the clutch mechanism first, even if you have already done some damage to the transmission, so you don't prematurely wear down the synchros in the next transmission. And, if you find the clutch hydraulics are not working right and fix it, that may be enough to make the car driveable again. A little driver assist to the matching of the wheel and engine speeds, involving double clutching, should help stop the problem and make the car driveable too.

The clutch is actuated by a hydraulic system that gets it fluid from the rear partition of the brake fluid reservoir. Any leak that might have let air into the system will cause the clutch to move less than the design stroke, and possibly not disengage fully, leading to the higher load on the synchos scenario I described earlier, and to the clunking and grinding you are experiencing. This is because air is compressible and hydraulic fluid is not, so as you push the pedal the bulk of the travel goes to squashing bubbles of air, and when that is all done, the clutch begins to move if you have any pedal travel left.

I would also try RedLine Manual Transmission Fluid from RedLine Oil Company at www.redlineoil.com. This stuff has a friction modifier to help your synchros get a little traction, and if yours are heavily worn (which is how it sounds) I would give the stuff a try. I am not sure what ATF has in it that addresses the need for the synchros to be cooled but not develop too slippery an interface, as too low a coefficient of friction makes the synchro unable to apply torque to the slower element.

I use RedLine MTF in all my transmissions (manuals that is) and find it works very well. I am in no way associated with RedLine, just a satisfied customer.

Good luck, and I hope this helps. Jim