1983 300SD Lost 4th Gear - PeachParts Mercedes-Benz Forum

eatont9999 · #1 04-04-2016, 10:46 PM

Here's the story. I was driving my 300SD that has 255K on the clock to work last week when I lost 4th gear. As I was driving, the car attempted to make a 3-4 shift when it flared where I would expect it to pick up 4th gear. I thought it very odd, so I shifted down to 3rd and back up to Drive. The transmission took 4th gear again and I kept going. After a few miles of doing this procedure, the transmission stopped shifting to 4th and stayed in 3rd without attempting a shift to 4th when it normally would have; the selector being in Drive. After driving stuck in 3rd for a while, it went back to flaring where 4th would be, so I had to shift down to 3rd to keep the car going the rest of the way to work. The transmission continued this behavior the whole way home, so I kept it in 3rd and took the back roads. Previous to this incident, the car was shifting through all gears without jerking or flaring. The car still has a strong reverse and shifts normally through 1-2-3.

I searched and read many articles related to this problem and they either had no solution posted or the solution had to do with a faulty piston, broken band or the use of Trans-X. I do know the difference between shifting into 4th and not shifting into 4th.

I have not made any changes to the transmission recently, so I can't say it is related to something I did. I thought about the kickdown switch being stuck but then the transmission is flaring 4th, so it is attempting the shift that it would not if the switch were stuck.

Please leave any thoughts or comments. I really want to fix this issue without having to rebuild the transmission. If I find a solution, I will be sure to post it.

tyl604 · #2 04-04-2016, 10:50 PM

Sounds like you are low on transmission fluid.

Mxfrank · #3 04-05-2016, 07:52 AM

The problem is that your K2 clutch isn't engaging. Unfortunately, the most likely cause is a fatal failure of the clutch seals or friction elements. Short of that, there could be something causing a lack of working pressure...very low fluid level, clogged filter, a faulty pump, a leak. If you can get a pressure gauge on the job, it would give you more information.

First aid is to change fluid and filter. Throw in a viscosity enhancing additive, and hope for the best. If that doesn't work, plan on a transmission swap or rebuild.

eatont9999 · #4 04-09-2016, 06:57 PM

The fluid was a little low, so I added half a quart to bring it back up. Still no change in 4th gear flaring. I will hook up a gauge and test the pressure before reporting back.

Zacharias · #5 04-11-2016, 04:39 PM

Try a fluid and filter change and add Seafoam.

eatont9999 · #6 04-11-2016, 10:08 PM

Quote:

Originally Posted by Zacharias

Try a fluid and filter change and add Seafoam.

Seafoam - like the stuff you add to the fuel tank?

Ceristimo · #7 04-11-2016, 11:00 PM

This sounds eerily similar to when I lost 4th gear in my W123. The whole thread is here if you want to read through it all:
http://www.peachparts.com/shopforum/diesel-discussion/369151-lost-4th-gear.html

But if you don't: The solution was a fluid flush+bottle of TransX and (this is the most important part) the transmission filter.

The transmission filter looked pretty bad, and was most likely restricting flow and thus killing 4th gear.

Haven't had a single transmission related problem since...

*knock on wood*

Also, when this happened Betsie would indeed stay in 3rd longer than usual and attempt the 4th shift later, and the 4th shift was almost like going in neutral. The engine would rev up high (you can call this flaring I suppose) and it would kind of be in 4th, but she wouldn't accelerate in 4th at all. Was just slipping like crazy.

eatont9999 · #8 04-11-2016, 11:52 PM

Quote:

Originally Posted by Ceristimo

This sounds eerily similar to when I lost 4th gear in my W123. The whole thread is here if you want to read through it all:
http://www.peachparts.com/shopforum/diesel-discussion/369151-lost-4th-gear.html

But if you don't: The solution was a fluid flush+bottle of TransX and (this is the most important part) the transmission filter.

The transmission filter looked pretty bad, and was most likely restricting flow and thus killing 4th gear.

Haven't had a single transmission related problem since...

*knock on wood*

Also, when this happened Betsie would indeed stay in 3rd longer than usual and attempt the 4th shift later, and the 4th shift was almost like going in neutral. The engine would rev up high (you can call this flaring I suppose) and it would kind of be in 4th, but she wouldn't accelerate in 4th at all. Was just slipping like crazy.

Thanks for posting! Your symptoms sound just like what happened to me. I have a filter kit on order right now. Hopefully it arrives before the weekend so I can get ATF in my hair again. Fun times.

If anyone has a rebuild manual for the 722.3xx, could you PM me so I can obtain a copy? I might pickup a spare tranny to rebuild and make a how-to series on it.

Mxfrank · #9 04-12-2016, 08:23 AM

Corteco rebuild instructions:

http://www.transtec.com/downloads/tech_inserts/mercedes/94642.pdf

Internal images:

http://www.shinseiauto.com/japanese/transtar/atmercedes.pdf

Disassembly video:

https://www.youtube.com/watch?v=_Whlh51VUZ0&nohtml5=False

oldsinner111 · #10 04-12-2016, 10:13 AM

you did check the kickdown switch under pedal right?

eatont9999 · #11 04-17-2016, 11:22 PM

I replaced the filter, fluid and added Trans-X today. I also checked the K2 spring in the valve body and it looks like someone had previously installed a Superior Shift Kit as the spring was pink. The issue still persists with no change in symptoms. Maybe I can pull the cover and check the K2 piston and band for issues.

Mxfrank · #12 04-18-2016, 09:46 AM

There is no K2 piston or band. The K2 system is a clutch pack and drum, and it's deep inside the transmission. You won't be able to inspect it without tearing down the entire box.

cho · #13 04-19-2016, 03:39 AM

Quote:

Originally Posted by Mxfrank

The problem is that your K2 clutch isn't engaging. Unfortunately, the most likely cause is a fatal failure of the clutch seals or friction elements. Short of that, there could be something causing a lack of working pressure...very low fluid level, clogged filter, a faulty pump, a leak. If you can get a pressure gauge on the job, it would give you more information.

First aid is to change fluid and filter. Throw in a viscosity enhancing additive, and hope for the best. If that doesn't work, plan on a transmission swap or rebuild.

I second what Mxfrank said... my symptoms were not identical..ie
mine was dropping from 4th on highway,city driving was ok
I did all simple things and no help,friction plates were worn...ended swapping 280se tranny...all fine now

note: yes w126 280 gasser tranny is perfect match for 617a

.

.

eatont9999 · #14 04-25-2016, 12:15 AM

Update: I am almost done rebuilding a 722.315 tranny. I plan to swap the tail shaft with my 722.303 once I pull that tranny out of the car. I wound up breaking the B1 clutch pack spring retainer, so I am on the hunt for a new one and possibly the tool used to install it. That said, I am about 3/4 of the way through a complete disassembly and cleaning of the valve body. Every valve, screw and ball gets cleaned up.

eatont9999 · #15 05-29-2016, 09:56 PM

Talk about auto trans hell, the transmission in my other car lost 3rd and 4th. It is a 722.309 which is not the 722.303 I thought would be in there. From what I have read, the .309 is an early transmission fitted to the 300SD. That or someone swapped it into that car at one point. Either way, it always shifted way too hard no matter how much adjustment I put into it. Long story short, I bought a used but working 722.303 from a guy on Craigslist and swapped it in earlier this weekend. If anyone one here is looking for a fun, interesting, time consuming and dirty project, this is for you! To my relief, the new trans works beautifully and I have a drive-able car again or at least once I fix the AC.

The parts came in from Germany, so I can continue the rebuild of the transmission for the original car. Once it is rebuilt, I will decide if it is too hot out to swap it in or not. AC for the DD is taking priority over everything else, though.