Lost 4th gear....
 

Ugh! I lost 4th gear on my '84 W123 this morning. So, last Saturday (a week and a half ago) my wife and I took a hike about 60 miles from our house. Betsie was doing great on our way to the hike. When we got back into the car after the hike to drive home, the first time she was supposed to shift into 4th, she just...wouldn't. The engine is free wheeling and revving up like it's in neutral, but she wouldn't go. I put the gear selector in S, then back into D and she firmly shifted into 4th and was fine. That was the first time I ever had that happen.

Then, last Thursday, the same thing. Right after accelerating and the first time she is supposed to hit 4th after the engine got started, she wouldn't. Engine freewheeling and revving up with no load, I shift into "S", back into "D", and all is well and she confidently and firmly hits 4th each and every time in the next couple of days.

So I kinda forget about it.

And this morning for the third time the same thing happened on my way to work. The first time she's supposed to hit 4th after I've left my driveway she wouldn't. Engine revving up, but no fourth gear. It just isn't there... I shift into "S", I shift back into "D", but still nothing. I kinda go through all the gears (1st, 2nd and 3rd work perfectly and firmly), but no 4th. She's just slipping like crazy.

I mess around for a bit, I ease on the throttle. I have a feeling she's shifting into 4th, but when I hit the throttle she starts slipping again. I can't even keep momentum going, she's slowing down as the engine is hitting 3k.

I curse and cry, put her in "S", drive her home, grab my Mazda and arrive 20 minutes late for work.


So.... I know this is terrible to diagnose over the internet, but does anyone have an idea of what the hell's going on?:disappoin

I have a feeling this might turn out to be something really bad, not just shifter bushings or a tranny fluid change....:mad::(

First things first I assume you have, but I'll ask anyways, have you checked the fluid level and made sure its bang on?

Assuming that's done, and it has fresh fluid and filter in it, it sounds to me like a check valve is sticking. If it was mine, I would:
1. Change the fluid and filter
2. Put in a bottle of either Gunk trans medic or Trans X. They are the same thing. Basically they dissolve all the varnish that builds up inside the transmission. They are not like the Honey think "miracle in a can" ones that make up for leaky seals and the like.

I had a transmission that was slipping into 3rd, fresh fluid, filter, and a bottle of Gunk transmedic and a few miles later it was gone.

The reason I think you might have a chance of this working is that it would intermittently shift into fourth just fine, making me believe that the issue is in the valve body and it could be a sticking valve...

Just my opinion

My 4th shifts were great! Not a SINGLE issue, until last week where it missed 4th once, and after that it was great. Then a few days later missed it again, and after that it was great. Shifted perfectly and firmly into 4th, every single time for days.
Yesterday I changed my power steering fluid and fuel return hoses, and when that was done I took the car on a 60 mile "test drive", 'cause I was bored so why not, right? She was fine! Shifted beautifully. I was barreling down the highway at 70mph, had the radio on as loud as it would go, grinning like a moron, singing as false as I could, and was generally having loads of fun just me and the Benz. I drove a bit...spirited. Parked her in the garage last night, hopped in this morning and 4th gear was just...gone.

I checked the transmissions fluid right after this happened the first time, so a week and a half ago. The transmission level was slightly below the "full" mark. The transmission was hot (just driven 60 miles on a 55mph road) and the engine was running with the car on level ground when I checked, so I know that reading was pretty accurate. I haven't checked the level since then.

I am usually not a big fan of those solutions-in-a-bottle, but I have to admit I've had great success with Lucas oil additives in my Mazda that started burning oil like an idiot and that's been mostly fixed now. So, you just dump a bottle of that stuff in with the normal refill?...

So I'm doing some quick searching on transmissions etc online. I've never owned an automatic, so I don't know anything.
But I'm reading about "valve bodies". Not sure (yet) what they do, but they can easily get plugged up with dirt apparently (lint even, it seems) and that could cause problems.

Could a dirty valve body cause this problem and is there a way to clean it? I would assume you can get to them when you drop the transmission pan?

1984 - I assume a 722.315 transmission which means you have this relationship

http://www.peachparts.com/shopforum/...eenshot-49.jpg

Assuming 3rd still works you could have trouble with your K2 clutch.

If you want to see where the K2 related stuff is in the valve body then you should look through this thread

http://www.peachparts.com/shopforum/diesel-discussion/323259-722-303-bits-photo-shoot.html

(722.303 has same valve body as the 722.315)

First thing to do with all transmission problems is to

1) Check the fluid level - this is not as easy as it might seem - many people struggle with Mercedes transmissions - temperature and dipsticks

2) Note colour and cleanliness of transmission fluid

3) Take hydraulic pressure measurements before pulling things to pieces (unless you just enjoy that kind of stuff like me)

Hi Strech,
1, 2 and 3rd work good and firm. Absolutely no flaring in between those shifts. I never had flaring going from 3-4 either. It was always nice and firm. Until this morning (and the two times in the previous week and a half...).

I checked the fluid level a week and a half ago. It was good then. Here's how I check it:
1) Make sure transmission is hot (car driven for 30 minutes)
2) Park it in my garage which has a level, cement floor
3) Leave engine running, pull tranny dipstick and wipe clean with my fingers
4) Put dip stick back, pull back out and read level right away.

It was near full a week and a half ago. I can check it again, but I don't know how to get the tranny up to operating temp. I would prefer not driving around for a while, going 40 mph in 3rd... I guess I could, though.

I think the tranny fluid is a bit darker than new fluid, but it doesn't look black on the dipstick or anything. Definitely dark-red, so more than likely due for a change. Which I had planned anyway...

The hydraulic pressure thing doesn't mean a thing to me. How do you take pressure readings and what would I be looking for? I've seen your other topics Stretch, and I know your very capable and take everything to bits.

Me not so much, although I'm more than willing to take stuff apart, as far as someone can guide me through the "how" part. Wish I would have played with mechanical toys more when I was a kid, I feel like I am playing catch-up now that I'm older. I miss that "oh-that-is-how-it-works-and-how-it-comes-apart" thing that other DIY'ers seems to posses. Hence me asking questions constantly...:|


EDIT:
So, since everything works but the 3-4 shift....Would getting the K2 spring kit would be advisable?

I assume you don't have or will have trouble finding pressure gauges then?

If you can't get hold of pressure gauges then you might want to try what most people do =>

"A bit darker than new fluid" probably means it is time to change it. If you can afford the cost of new fluid and then having to chuck it if this doesn't work then I'd go for a fluid and filter change. Whilst the oil the pan is off and you are changing the filter you could use the information in the thread linked above to see if any of the valves for K2 are stuck or the springs are broken.

When you drain the old fluid - measure it. Put back in the same amount in new fluid. Make sure you drain the torque converter. The value you drain / put back in should be the same as that specified in the maintenance manual (which is available on startekinfo - do you need a link?)

Thanks for the response Stretch. I am not rich, but I'm not against spending money. I don't have gauges right now, but what I don't have can be bought.

So....here's just a thought: a K1 spring is 10 bucks. I don't see the K2 spring for sale here, but saw some folks online that put a K1 spring in the K2 spring's place and it was fine.

Idea:
Get the two K1 springs from this website. Grab filter, gasket, crush ring for drain plug etc from this site as well.

Drain tranny, torque converter, drop pan. Replace K1 spring with K1, and replace K2 with K2. of course, I need someone to tell me approximately how to do that, 'cause I haven't got a clue.
Clean pan, put back with new gasket, fill 'r up and all's good in Benz-land?

Yes? No? Maybe? Dumb idea? Great idea?...

I tee was a skeptic when it came to the gunk product. But I figured what did I have to loose, and it worked for me. There are several other threads floating around where members had success with a similar product called transX. TransX wasn't available to me as its not sold in Canada, at least not by me, so I went with the gunk product which was the nearest product I could find.

I wouldn't recommend the lucas transmission product in this instance. Its one of the honey thick ones that compensates for worn seals. I really htink you might have a sticking check valve in the valve body which is why I'm suggesting a product designed to remove the varnish.

If you haven't changed the fluid and filter during your ownership do that first, then yes, you just pour in the bottle in place of a the same amount of ATF. This way you don't over fill.

Or, better than wasting it, put some in the tank to clean and lubricate the pump. Couldn't afford fuel at a point in the past, so burned almost a strait blend, and learned it doesn't smell so good (did have burned clutch smell to original fluid). But, solved the problem of tailgaters. :P

If you need to get the car working as quickly as possible then there's arguably a good reason behind the pre-purchase of the springs. If I were you, however, I'd wait and see if something needs to be fixed before ordering parts. The problem with replacing springs is that once that has been done you should ideally check the pressures - which ends up needing them there pesky gauges (again)...

There are indeed other uses for old transmission oil but it still costs quite a lot of money these days to put good clean stuff in a transmission!

@Stretch
Betsie isn't my daily driver, though I would love to get her back on the road as soon as possible. I drove my Mazda for the first time in two weeks this morning, and it felt strange. I love the Mazda, but I never noticed how small it's puny little steering wheel is, nor did I ever notice how you can feel every bump in the road in that thing. It felt like a toy. :P Having a stick shift was nice though; wish Betsie had one.

Speaking of the transmission: when I came home from work I took Betsie for another spin. And during my 25 mile run, she shifted into 4th every single time! What the f*ck? I shifted from "S" to "D" a bunch of times, I accelerated very slow, normal, and WOT, and she shifted into 4th without hesitation, flaring, slipping, but confidently and firmly every time. I really tried, but I could not make her slip.

Seriously?!

So while this morning it looked like I completely lost 4th gear, that does not seem to be the case.

Here is my game plan for now then:
- Get filter and gasket etc, and drain transmission and torque converter, drop pan, change filter and fill 'r back up. I'll put in a bottle of Trans-X as well, since I read some good things about that online.

What do you guys think?

I think that would be a good first start, because this transmission doesn't seem to be that far gone after all. Shifts from neutral into reverse or drive take 1,2 seconds (measured with a stop-watch). That's apparently a little longer then it should, but not bad for a tranny with almost 300k on it, I think.

So, here comes another question I'm sure has been asked a gazillion times before (I apologize in advance)
- What kind of transmission fluid would you recommend, and how much approximately would I need to get when I drain the torque converter as well?

P.S. After my trip I checked the transmission fluid level with the engine running etc. It should have been at or near operating temperature, I just drove 25 miles. It measured just a tiny bit above minimum, which is pretty much where I expected it to be at.
Weirdly, when I checked the transmission cold and with the engine off (right as I got home from work) she measured a good 3 inches above full (I verified three times...). I thought a cold transmission would read lower, but I assume she was reading high because the engine was off...

What ATF to use? Better than an oil thread!!!

I have had really good luck with the Mobil 1 full synthetic ATF. Rather pricey, and may take 2k - 10k miles of driving to get the full benefit, but in both my '87 wagon and my '95 sedan, transmission shifting improved. In the wagon, it was really pretty amazing how the shift timing and quality improved. In the sedan, which started off shifting pretty well, the improvement was not quite as dramatic.

On the other hand, I know a gentleman whom I have great respect for his MB knowledge, and he swears by the official ATF from MB or the Febi fluid that meets the spec. He's reported results similar to mine.

MB sheet 231.1 says for a 722.3/4/5 transmission, you can use a fluid which meets specs 236.1/6/7/9/10/81. Those seem to all be either Dex II or III. Febi fluid 08971 used to meet 236.6 and .7, but is dropped from the list this time, probably because they didn't pay to have it tested since their last change to the formulation, but I wouldn't hesitate to use it (I still have several bottles on the shelf that were sent to me by mistake when I ordered power steering fluid).

If you can find an ATF locally that has language that it meets MB spec 236.x (where "x" is one of the following: 1/6/7/9/10/81) then I wouldn't hestitate to used that. Note that Mobil1 ATF has never shown up as an approved product, but it meets the Dex. III spec I think, and I've had very good luck with that.

The chances of a k2 spring fixing this are small. The chances of a fluid and filter change fixing this are zero. The problem is that your K2 clutch isn't engaging, or is slipping. If you can get a transmission shop to put a gauge on it and read the working pressure, you'll have an idea of whether it's a hydraulic issue or a friction surface problem. The usual cause of this is worn seals or friction surfaces in the K2 clutch pack. This can only be fixed by rebuilding the transmission.