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  #1  
Old 08-27-2013, 01:24 AM
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Looks like I ruined my transmission

Last week Charmalu and I performed an engine swap in my driveway on the 300SD. My transmission had a small leak coming from somewhere up front, so I decided to change the front seal, front pump gasket and o-ring. I followed the instructions from some very good links that Stretch sent me and I thought that I did a good job on it.

My transmission only shifts up to 2nd gear and can't get to 3rd no matter what I disconnect or adjust. After doing a fluid and filter change with no luck, I took it to a respectable MB shop here in Alameda to see if they could find something that I'm missing. They said that it must be something internal because everything on the outside looks fine. All I can think of is that the first time I tried to spin the torque converter, it was tight and I had to back off on the 13mm bolts that hold the front pump and then re-torque them in order to get the torque converter to spin freely. Could I have done the damage during that first trial on the torque converter?

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Old 08-27-2013, 11:18 AM
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Did you take apart the front pump?

Normally a front transmission pump installed on the 722.3 transmission will look like this:



Removed from the transmission (eight bolts) it will look like this:



and on the inside it will look like this:



You can take it further apart, but did you do that?

You replaced the old front seal, this one?



the pump gasket, did you remove the old gasket? It took me one hour (or more) of delicate scraping to remove the gasket from the transmission:

Before:



After:



Which O-ring did you replace? There are several.

The eight bolts that hold the pump housing to the transmission wouldn't impair the working of the pump I should guess. If overtorqued, the pump might leak.

You could measure pressure of the transmission: working pressure mainly, but the other pressures: modulating pressure and regulating and control pressures. That should give you information. I'm guessing that it is either pump or torque converter. Low working pressure means pump is bad or badly assembled. Pressures OK, than probably TC.

Whether something is damaged can only be assessed if the transmission is taken off the engine again.
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Old 08-27-2013, 11:32 AM
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Yes, I took apart the front pump and replaced the largest o-ring that's closest to the front.

What gauges and fittings would I need to check the pressure?

When you say the torque converter could be bad, how does it go bad, what damages it? Thanks,

Otto
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Last edited by otto huber; 08-27-2013 at 11:44 AM.
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Old 08-27-2013, 02:15 PM
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If you have 1st and 2nd gears then I would think that the pump and converter are good. When I bought my 300D, it wouldn't change out of 1st, and the governor gear was broken.
Does park and reverse work? When it won't go past 2nd, does it just not change at all, or does it go into neutral? If it won't even try to shift, but stays in 2nd then there is a problem with the governor or the valve body. Both can be serviced with the trans in the car. If it goes into neutral instead of 3rd then it could be a clutch problem or valve body problem. The first test I would do is disconnect the kick down sol AT the transmission, remove any vacuum lines from the transmission and disconnect the bowden cable going down to the transmission. Check the cable and make sure it pulls out a couple inches and returns on its own. With the 3 things disconnected, it should still shift, early and hard through all gears.

Paul
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Old 08-27-2013, 02:45 PM
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I've already tried disconnecting everything; Bowden, modulator, and kick down. It's good to know that a shop might be able to do the necessary repairs without pulling the transmission.
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Old 08-27-2013, 05:26 PM
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Below you can the measuring points for the oil pressures inside the transmission.



At the top at A you measure the working pressure, that is the pressure from the pump. Use a pressure gauge up to 25 bar. Measuring is done by disconnecting the vacuum line at the modulator and running the engine up to 1000 rpm with the transmission in D. Use both parking brake and normal brake to stop the car. The pressure should be 12.5 bar plusminus 1 bar.

At R you can measure governor pressure, that is the pressure which pmckechnie is talking about. Use a pressure gauge up to 10 bar. At 30 km/h the pressure should be 1.2 bar; at 90 km/h it should be 2.8 bar. There is of course a problem, as that speed is not obtainable at the moment. But the pressure at 30 km/h should give you an indication.

At M you can measure the modulation pressure. Use a pressure gauge up to 10 bar. Disconnect the vacuum line and drive in D at 50 km/h. The pressure should be 2.9 bar.

I'm thinking that the pump isn't pumping out its full working pressure, that affects the other pressures too, as other pressures are derived from the working pressure.

All this info is from the German FSM.

Here is a close-up of the measuring points M and R:



To the below-right of #60 is M. Below #12 is R.

If the car isn't running, you can remove a screw to get the fitting. Oil will not stream out. You need a pressure line too, long enough so that it can be fed into the car interior

There are two teflon rings too, below one old one:



and some more O rings:



Did you torque the bolts of the oil pump to 20 Nm?

Last edited by Govert; 08-28-2013 at 09:17 AM. Reason: spelling
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  #7  
Old 08-27-2013, 06:39 PM
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I torqued the bolts to 20nm according to my old style needle torque wrench. It may not have been accurate enough, but I remembered what those bolts felt like to be loosened and it seemed like my wrench was close.

This car is my daily driver, and I'm running out of time with gigs coming up and losing money on rental cars. I've decided to install the donor car's transmission to get me on the road for a while, and then sometime soon I'll take this transmission to a place in Fremont called MB exchange where they can test it and give me an estimate on what needs to be done. Thanks for all of your input.
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Old 08-27-2013, 10:26 PM
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I found some transmission manuals when I was working on trans manuals and wondering why the parts car is without reverse. Mitchell had one of them. It comes up with something like "722.3 site: mitchell or whateverthe site is"

I also remember some reasonably priced remans with 12 or 24 month warranties.

try rtpartsco.com He sells OE surplus & may have something. I bought OE steering for my dodge ram. Not exceptionally cheap but reasonable for OE retail.
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Old 08-29-2013, 07:16 PM
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I have the donor car transmission bolted up to the engine, but have one last question before I finish up. Is the yoke at the back of the transmission supposed to rotate with the torque converter?

Last week when I had both transmissions sitting on my garage floor, the yoke turned as my torque converter turned. Right now the original transmission that won't shift into third is in the garage and the yoke doesn't spin with the TC even though the TC went 3 steps back into place and is well behind the tab on the side that holds it in place. I tried spinning the yoke on the transmission that is in the car so as to line up the TC bolts with the flywheel and the TC isn't spinning. I tried putting the transmission that's in the garage into the different shift positions to see if that would get the yoke spinning but no luck. I haven't tried shifting the other transmission yet.
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Old 08-29-2013, 10:09 PM
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The TC won't spin when you turn the output shaft by hand. If it did, something in the stack up is wrong and the TC is also binding internally. If the TC is removed, sometimes the input shaft will spin but this is due to internal friction between the clutch plates.
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Old 08-30-2013, 04:47 AM
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Thanks 97. I went to install the 13mm bolts that connect the TC to the flywheel and the TC is stuck. It moved easily when the transmission was outside of the car. I currently do not have all of the 17mm bolts that mate the transmission to the engine tightened all the way. I tried leveraging a screwdriver against one of the teeth that are on the perimeter of the TC and couldn't get it to budge.
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Old 08-30-2013, 02:06 PM
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A couple of things.

Does the trans actually fit your engine? ( designed to fit )

Was the pilot on the front of the TC and the hole in the back of the crankshaft clean ( just generally clean will do ) ? A bit of grease ( just a thin swipe ) is a good idea to prevent fretting in the long term but won't cause your install problem.

Make sure the dowel pins are in the back of the engine, sometimes these get stuck to the old trans during removal. These pins keep everything in line.

If the TC isn't fully seated in to the front pump, you will have a bind during install.

How loose are the trans to engine bolts? ( space between engine and trans )

Don't force anything, it will cause problems.
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Old 08-30-2013, 02:12 PM
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Quote:
Originally Posted by otto huber View Post
Thanks 97. I went to install the 13mm bolts that connect the TC to the flywheel and the TC is stuck. It moved easily when the transmission was outside of the car. I currently do not have all of the 17mm bolts that mate the transmission to the engine tightened all the way. I tried leveraging a screwdriver against one of the teeth that are on the perimeter of the TC and couldn't get it to budge.
Sounds to me like you aren't getting the TC seated on the shaft correctly. Did you check the "Installed height in the bell housing"? This is between bell housing flat that mates to engine and a high ear on the TC. See attached pic. It should be 8.7 mm or 0.34252 inches.

It is a bit tricky and it feels like it seats but really it has to line up and slide on another part of the shaft. I did 3 of these transmissions this summer and I feel your pain. It gets old R&Ring trannies. Good luck. Also i can email you full R&R doc if you don't have it.
Attached Thumbnails
Looks like I ruined my transmission-tcseat722.jpg  
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  #14  
Old 08-30-2013, 03:53 PM
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Thanks for the input guys. This is the transmission that originally came with the engine, so everything should bolt up fine. The tab on the driver's side is still in place and can only be inserted if the TC has gone 3 steps back. It was spinning just fine in the garage, so unless something came ajar while Charmalu and I were struggling with it underneath the car, it should be in place. As of now, the 17mm bolts and starter bolts are not all tight. Should I tighten everything up in order to get the transmission flush with the engine. or should I loosen everything up and then pull it back a little to see if the TC will spin?

Biopete, if you could send me that R&R document, I would greatly appreciate it.

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