2 cars in one week, won't shift into 4th gear - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 08-24-2015, 11:11 AM

Both of my niece's cars ('82 300CD & '81 300D) quit shifting into 4th gear in the same week, that is just weird. They both will shift just fine up to and into 3rd, but stay there. The cars will only go about 45 MPH without revving them too much. The CD has a 722.3 (I think), and the D has a 722.1 (vacuum only). I have not had the time to look at either car, and my brother has no idea about transmissions (I'm not far behind him). I have heard that a fluid change and adding Trans-X or the Lucas product will help, but I am not sure if that will fix the problem. Both girls love their cars, and would not like driving anything else. Anyone have an idea of what to do? Is the fluid change worth the effort and expense? Thanks in advance, Rich

greazzer · #2 08-24-2015, 11:18 AM

That is bizarre ... but those coincidences happen. Cannot hurt with a fluid change and I like Trans X. Gave my wife's Voyager van another few years of life. Sort of miss the minivan at times.

Zulfiqar · #3 08-24-2015, 11:59 AM

my 95 did that once and then worked ok after a mile or so.

It did that once or twice after that, then I changed the ATF and put in a bottle of lubegard (as I had it on the shelf). The car never did it again. The ATF that came out was not exactly cherry syrup, it was opaque.

dude99 · #4 08-24-2015, 12:05 PM

MAke sure the kick down switches aren't stuck\jammed by a floor mat.

X2 on the fluid change and a bottle of trans-X\Gunk trans-medic (whichever you can source) and see if the issue goes away. Could just be a stuck gravity check valve. I would avoid the lucus product initially. It's a thick honey like fluid designed to work on transmissions with worn out pistons and leaky valves to allow them to build up more internal pressure.

leathermang · #5 08-24-2015, 12:08 PM

On this particular complaint....
the nice thing about Trans x is that it is a CHEAP TRY...
with no downsides except it might not work....as build up of varnish may not be the problem...
If you have a top sucker you can attempt it without even getting under the car... although the best actual try , giving the best chance at a fix, is to pull enough out to put one or two cans into the system.... drive it long enough , or run it in the driveway going through the gears... instruction in the archives.... and then change out the trans fluid and filter... and add back in 10 percent of the Trans X forever...
Mainly ... give it plenty of chance to WORK....50-100 miles if it is driveable.... it is just a varnish solvent... and that stuff has had thousands of miles to build up.... like a stalagmite ...
I told about my Rambler I bought cheap which would only drive in ONE GEAR... and was fixed by trans x... and I only tried it because a family friend mechanic suggested it.. I had no confidence in it... sure changed my mind...

tyl604 · #6 08-24-2015, 12:51 PM

Could it possibly be that the shifter bushings are worn and the gear shift lever is not exactly in gear?

Ceristimo · #7 08-24-2015, 12:54 PM

My car lost 4th gear suddenly about 2 months ago. One minute it was there, the next...it wasn't,
Instead of not shifting into 4th though mine would try to at higher RPM's (around 55 mph), but it would slip like crazy. As if the car was put in neutral.

Anyway, drained transmission, changed filter, and dumped in a bottle of Trans-X, and it's been fine since.
Lost 4th gear....

And when it happened I thought my transmission was toast!

Most definitely worth a try to just drain and fill, replace the filter and gasket and put some Trans-X in.
If you Google this issue you'll notice a lot of folks that suddenly lose 4th gear on their Benz. Doesn't seem too uncommon on these cars now that they get older. A slightly clogged filter or transmission fluid with impurities seems to affect 4th gear the most.

Tyl604 has a good point though: definitely check the shifter bushings for excessive play. Should be easy to spot when looking underneath and having someone use the shifter.

One would think a stuck kick-down shift is easily determined to be the culrprit, as the car will nearly redline in every gear. If it shifts at normal points when going 1-2 and 2-3, I don't think the kick-down could be the issue. Then again, unplugging it will let you know for sure...

ROLLGUY · #8 08-25-2015, 10:22 AM

Thanks all for the input. It looks like a trip to the auto parts store for some TransX and ATF is in my future. Ceristimo, I did read your entire thread before posting my query. I knew the cars had a different problem, but still a lot of good info on your thread. Yes I am aware of the shifter bushings, and have them in stock. I am waiting on the tool to install them. I have tried installing them without the tool, and it is very hard. Although the coupe definitely needs new bushings, the lack of 4th gear is still there......Rich

leathermang · #9 08-25-2015, 10:26 AM

What does the ' shifter bushing install tool ' look like ? Where can it be found ? Is one available in the tool rental section of this forum ?

dude99 · #10 08-25-2015, 10:33 AM

I know that Kent makes and sells one

Zacharias · #11 08-25-2015, 10:35 AM

Different suggestions for the two cars:

- CD: Check that the adjuster assembly for the Bowden cable, on the valve cover, is intact. The adjuster can sometimes break and this will start producing weird transmission issues.

- 300d: (1) Start with the vacuum system. Check that the pump is producing the correct vacuum. If that's okay, proceed down the vacuum control line: check the post-VCV vacuum going to the transmission. If the VCV spring has gone out of adjustment, it may not be bleeding off enough vacuum to allow the 3-4 shift at the normal speed range. Also of course check that the modulator cap is holding vacuum. Also check that all the rubber junctions for the vacuum hoses are intact, no ballooning or splits (one guy recently found his issue was that a junction had split underneath, where it was not visible).

VCV link: Transmission flaring or clunking? VCV DIY - Mercedes-Benz Forum

- 300d: (2) Also check that the 3/2 valves (the little white lever valves on the valve cover, the car should have one or two) are working properly.

leathermang · #12 08-25-2015, 10:41 AM

Interesting that in that reference to ' Flaring' ....which I define as too slow actuation of an auto trans clutch mechanism resulting in engine rpm rising during the process. ..
that no mention is made of the possibility of the varnish problem in the one way valves in the auto trans valve body.

ROLLGUY · #13 08-25-2015, 04:27 PM

Quote:

Originally Posted by leathermang

What does the ' shifter bushing install tool ' look like ? Where can it be found ? Is one available in the tool rental section of this forum ?

It is available from our sponsor, and also Amazon (a little more than half the price).

Zulfiqar · #14 08-25-2015, 05:27 PM

so the hot water in a cup doesnt work for you guys?

you can also cut and push it on with a screwdriver all the way, apply some silicone lube to the bushing and push the rod in it.

VA-Merc · #15 08-26-2015, 08:46 AM

The 722.3 in my 87 did the same thing a couple years ago. I thought the tranny was shot. Drained the fluid and added fresh stuff like others here have mentioned, changed the filter too. Not a problem since...still shifting great as I am approaching 300,000 miles on the original tranny. Hopefully a fluid change will be all you need.