722.315 transmision question - PeachParts Mercedes-Benz Forum

turbozeke418 · #1 02-07-2017, 01:28 AM

I have a 1984 300TDT with 292k miles. The trans was rebuilt 2.5 years ago with 277k (previous owner). I have the $2,500 in receipts and looks like the works was done to the trans. You can even see the newer torque converter through the bottom. The trans is now slipping in and out of gear, indecisive of when to shift and flares periodically.

To do a quick fix on it, I'm looking for another trans to throw in it (will prob use my current torque converter). I've been reading many of the threads with trans related cross references. Will any 722.3xx (non electronic speedo) work with my car? I'm talking about bolt right up connect everything with no mods etc. or do i HAVE to find a 722.315?

Stretch · #2 02-07-2017, 04:24 AM

If the rebuild was done properly then I'd expect it to last a wee bit longer than it has.

Before swapping I'd check the fluid level (correctly!) and check the throttle linkage. Measurements of hydraulic pressure are next...

...as to the question...

...yeah some will bolt up. Yeah some have different sized torque converters. Yeah some have different speedos. Yeah some have a throttle linkage - some not. You'll not get anything other than a 722.315 or a 722.303 to shift as it should (as Mercedes designed it to do).

turbozeke418 · #3 02-07-2017, 05:07 AM

Thanks for the info. All of the previous posts I was reading had many write ups from you. THANK YOU!
Today, just for the hell of it, I'm going to drain the trans and torque converter, replace the filter and fill her back up. It can't hurt. Then I'll go from there.
So I should be good with the 722.303 also then?

Stretch · #4 02-07-2017, 05:17 AM

The 722.303 will work and as it has the same valve body as the 722.315 the chances of you getting it to shift as it should are improved! The problem is the electronic speedo. I can't remember for the life of me if you can switch the mechanical tail cone from the .315 to the .303 or not. There's a gear lubrication issue that I think vstech or was it mach4 (?) figured out...

(Sorry to some one else if it was some one else!)

#########

On the whole with transmissions I think it is often a case of "better the devil you know". Sure things will wear out in the end but I get the feeling an awful lot of transmissions get junked because people fail to do the simple things first.

If you are changing the fluid be really really anal about it: And measure in the correct amount! It might be worthwhile measuring the old fluid you remove too. There are many unknowns that need to be ticked off the list to make sure you don't end up chasing your tail.

(I hope I don't need to stress the importance of using dexron II (or III if you have to) do I?)

turbozeke418 · #5 02-07-2017, 05:31 AM

To me fluid is fluid lol. BUT, I have read all the threads and I have dexron iii for it (synthetic).

Carpenterman · #6 02-07-2017, 09:22 AM

Sounds like a pressure problem. Could be excess vacuum. Remove the line from the VCV and see how she shifts. Also turn the T fitting in the modulator clockwise to increase pressure. It would be a good idea as Stretch mentioned to check the pressure at the port. IIRC it should be 32psi.

I've swapped a 303 tail to a 315 transmission with no problem other than a slight mismatch on the housing that I was able to plug with JBweld. Others have reported a perfect fit. Going the other way, yes there is a lubrication problem for the speedo gear, but I don't remember anyone finding a fix. Search around the forum.

Hard to imagine a problem other than adjustments/vacuum on such a rebuilt transmission. Hopefully the pump is not shot.

Diseasel300 · #7 02-07-2017, 09:47 AM

Before replacing the transmission, make sure your vacuum adjustments and bowden cable (if yours has one) are adjusted properly.

I just went through a very stupidly shifting transmission saga in my SDL that turned out to just be a combination of linkage lengths, bowden cable, and vacuum adjustments. I was ready to throw in the towel on it. After doing all the adjustments and piddling with it to get it dialed in, it drives like a completely different car.

tyl604 · #8 02-07-2017, 10:20 AM

Yes, you can remove the vac line going to the vac modulator and it should upshift smoothly. Downshifts will clank. If it is shifting properly, that is.

mach4 · #9 02-07-2017, 11:14 AM

You can go from mechanical to electrical but not the other way....the issue is lubrication for the gears.

sixto · #10 02-07-2017, 10:02 PM

The 722.315 is the most common 722.3 there is in the US. Unless you have a known good .303 in hand, keep looking.

Sixto
83 300SD
98 E320 wagon

vonsmog · #11 02-08-2017, 09:18 AM

I have three good used transmissions for sale if you need one. Two 315's and one 303.

SD Blue · #12 02-08-2017, 06:08 PM

Also, check to make sure your kickdown switch isn't sticking. Mine had carpet fibers, and other crud, in there and was very temperamental! Real easy to get to and cheap to replace.

spock505 · #13 02-11-2017, 12:13 PM

Unusual for the torque converter to fail, perhaps there was more damage than first though at time of rebuild.

Before swapping out I would drain and check pan for fragments, this is often a good indicator if things are a bot more serious and non vacuum related.

As Stretch mentions, measurement of ATF is critical for best performance, I often do two, one when almost cold and the latter when hot.

From cold after 1-2 minutes, MB use a measurement below the minimum level indicator which varies between models, for the 722.4 (mine) it's 12mm.

turbozeke418 · #14 02-12-2017, 11:25 PM

I changed the fluid and the filter. I also replaced the vacuum modulator (I wish I would have done it when I had the trans drained, I didn't realize fluid would pour from it once removed). There were no metal pieces in the pan, but the fluid was more of a dark cherry color, not red. It's not my daily driver so it's still sitting till I can get everything adjust properly.
I checked the bowden cable to make sure it springs back when you pull on it and it does. So I know that it is connected inside the trans. No matter how far in or out I adjust it, everything still shifts the same.

spock505 · #15 02-13-2017, 01:48 AM

That's a good sign, no debris in the pan, worth perhaps continuing with your efforts.

Have you replaced the lower valve body springs, B1,K1 and K2?

These were upgraded several times by MB at various stages depending on model, see thread started sometime ago (click user name).