114 Tranny not shifting? - PeachParts Mercedes-Benz Forum

Catrinus · #1 07-07-2002, 02:53 PM

I have a 73 280C that I got about 6 months ago and am going through to get in decent shape. Mechanicaly, it is in very nice shape except for one thing: I know it's supposed to have a 4 speed auto trans, but I'm pretty sure it never shifts into 4th. It also shifts into reverse VERY hard (you really have to keep your foot on the brake to keep it from lurching backward at 15+ MPH). I took it to the local "all brands" tranny shop, but they didn't want anything to do with an old MB. I'm trying to avoid the expense of a specialty shop. The tranny guy mentioned that MB
trannies are vacuum controlled and it sounded to him like a vacuum problem.

How would I check this, and does it normally call for a rebuild? If so, I'll just live with it (I use it for a short commute and don't really get it on the freeway for more than 10 miles a day so it isnt' the end of the world). It doesn't have a tach, or course, so I'm going by feel.

I'm new to this forum, so if there is already another similar thread please let me know so I don't waste anyone's time.
Thanks!
Catrinus Wallet
Portland, OR

ctaylor738 · #2 07-07-2002, 09:01 PM

You may have one non-problem.

If you are in "D" the transmission is supposed to start in 2nd and shift to 3rd and 4th under normal driving. If you stomp it from a standing start, it should shift down into 1st. "S" is similar except no shift to 4th. If you start in "L" you should start in 1st, and stay there. So you may actually have all four gears.

1st gear is very "quick" and the engine is really turning at 20 mph.

However, sometimes the vacuum modulator, which controls some of the shifting goes bad and allows a 1st gear start in "D." Some people like first gear starts, and adjust or change the modulator to do this.

These cars have high rear-end ratios (3.6:1) which means that they run at 3000+ RPM at freeway speeds, and a lot of people think it needs to shift into a higher gear.

Hopefully this gives you the information you need to figure out what gear you're starting in and count from there.

On your reverse problem. You may have a worn clutch pack, which is a rebuild situation. Or you may need to add fluid. Or you may need an adjustment. CTH350 did a post on this. There is a large nut on the (I believe) passenger side of the trans, which controls the timing of the engagement of reverse.

Recommend you check out the "Recommended Shops" forum for one in your area. Be sure to ask if they have someone experienced on your car and make them prove it if they say "yes."

You may also have your cold or hot idle speed set too high.

Anyway - you are in the right place with your questions.

ctaylor738 · #3 07-07-2002, 10:41 PM

I forgot to add that if there is a problem shifting into 4th, then that is likely a modulator adjustment.

cth350 · #4 07-08-2002, 02:52 PM

The band adjustment that Chuck is referring to is very simple. On the passenger side, look for a square headed stud that has a jam nut on it. You can't miss it. Loosen the jam nut 2 turns and then tighten the stud a quarter turn and retighten the jam nut. This is NOT the correct adjustment setting, but it is the fastest way to tell if it's a problem. (The correct setting is done with a torque wrench to set the stud to just the right spot).

However, it's not your problem. The band adjustment fixes a problem with how long it takes to engage. You are not describing it engaging too fast. You are describing the engine turning too fast.

Either you are idling at greater than 800 rpm (likely) or you have a vacuum problem (which would probably make you idle too fast or the idle is raised to compensate for the vacuum problem).

In other words, your tranny is perfect. It's your carb that's hurting. There are LOTS and LOTS of posts about how much we all hate the 4A1 carb.

-CTH

ctaylor738 · #5 07-08-2002, 03:56 PM

Actually, even if the idle is OK, the pump seems to build up pressure as reverse is trying to engage. Then when it does - WHAM - it gives a kick. I think that this is what is being described.

This from personal, current experience.

I'm not sure how I feel about my Solex. Not hatred, but more of a resigned acceptance. I do marvel at how something as simple as a carburetor could be produced with so many problems. And I am fascinated by how it can run lean but smell rich at the same time.

Catrinus · #6 07-11-2002, 09:42 PM

Thanks to both Chuck and cth... you've given me a good list of things to check out. Chuck's description of the problem is the closest -- especially when it's cold. It really does hunt for reverse for a few seconds, and then just slams in. So I'm going to check out some of your suggestions first -- especially the one about the adjustment. It does idle awfully high (again, a bigger problem when it's cold). I think the first thing I have to do is to get a tach so I'm working with objective data. Interesting idea about maybe I've really got 4th after all. But since the top speed seems to be about 75, I doubt it.

Thanks again. I'll keep you updated on my progress.