1994 S420 Reverse gear issues

39102 Views 125 Replies 15 Participants Last post by Rod Henderson, May 4, 2019

pt80chip

Discussion Starter · Jan 13, 2012

3

Hi all,
I recently joined the forum because I recently bought a 1994 S420! I liked the car before I bought it, but now that I own it I love it!

The car has 102k miles and unfortunately I've inherited some problems. Most of them are not serious but I do have the reverse gear issue. After reading for hours and hours on the forum, I still am not sure what my next step should be.

When I first got the car 6 weeks ago it didn't really have a problem. It quickly started deteriorating and the reverse gear would take 2 seconds, then 4 seconds. Now there are times I wait for 15 seconds and it doesn't engage until I give it gas. Then it jerks into gear. I noticed that it's usually faster to engage when I just turn the car on in the morning. Once I've driven it for a while it becomes either extremely slow or it doesn't engage. I also think being on a hill makes it worse.

In the forum I've found that some people solved the problem by just adding ATF and then I've also seen that some people have had to change out the transmission.

What should my first step be? Should I first try to add transmission fluid? If that doesn't work, should I have the filter changed and the transmission fluid changed completely?
I've read something about a seal potentially being cracked or that the reverse clutch friction material eroded faster than being worn off. I'm hoping not to have to spend a ton of money (like everyone else here) so finding out that my problem is not so serious would be a great relief.

Any ideas?

Also, I know I'd get killed if I didn't add pictures, see my beauty attached.

Regards,
Andy

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tackleberry

· #2 · Jan 13, 2012

I'd start with fluid. Any leaks?
If not, maybe have the fluid quality looked at. The tq converter may have black nasty fluid in it.

Sent from my SGH-T989 using AutoGuide.Com Free

pt80chip

Discussion Starter · #3 · Jan 13, 2012

tackleberry said:
I'd start with fluid. Any leaks?
If not, maybe have the fluid quality looked at. The tq converter may have black nasty fluid in it.

Sent from my SGH-T989 using AutoGuide.Com Free

I'll start with the fluid tonight. I had some sort of leak at one point but never discovered what it was. It also stopped happening. One day I parked the car at a lot and when I came back I saw some fluid. I then drove it home, parked and came out an hour later to find a little more fluid. It wasn't a huge qty but I don't know how many times it happened before that.

My S420 has a dipstick, it seemed to have fluid in it when I checked. Should I be afraid of overfilling it? Do I fill it using a funnel where the dipstick is?

Also, if that doesn't work, what would your next step be?

Thanks,
Andy

Mercedes mechanic

· #4 · Jan 13, 2012 (Edited)

Mafia has the .pdf on fixing the no or slow reverse. Its easy and take about an hour to fix.

YOU DONT NEED A TRANSMISSION. Trust me, you only need to fix the sticking piston in the trans.

If it was slow locking in all the gears, I would agree that its low. But its going into the forward gears ok.

pt80chip

Discussion Starter · #5 · Jan 13, 2012

Mercedes mechanic said:
Mafia has the .pdf on fixing the no or slow reverse. Its easy and take about an hour to fix.

YOU DONT NEED A TRANSMISSION. Trust me, you only need to fix the sticking piston in the trans.

OK, this will be the first time I go to the mafia and ask for anything. Hopefully I'll get to keep my kneecaps.

Mercedes mechanic

· #6 · Jan 13, 2012

pt80chip said:
OK, this will be the first time I go to the mafia and ask for anything. Hopefully I'll get to keep my kneecaps.

lol, no his member name is MafiaDon, he has a copy, Im kinda busy today, but if he dont show up with it by the time I go to bed, I will go fetch it.

And post it up.

pt80chip

Discussion Starter · #7 · Jan 13, 2012

Mercedes mechanic said:
lol, no his member name is MafiaDon, he has a copy, Im kinda busy today, but if he dont show up with it by the time I go to bed, I will go fetch it.

And post it up.

I understood what you meant. I sent him an email and a little after I did a search on the forum and I believe I found it here:

http://www.benzworld.org/forums/w140-s-class/1407863-no-reverse-jerks-reverse-when-cold-3.html

Is that the right one?

pt80chip

Discussion Starter · #8 · Jan 13, 2012

Mercedes mechanic said:
Mafia has the .pdf on fixing the no or slow reverse. Its easy and take about an hour to fix.

YOU DONT NEED A TRANSMISSION. Trust me, you only need to fix the sticking piston in the trans.

If it was slow locking in all the gears, I would agree that its low. But its going into the forward gears ok.

By the way, what is the difficulty level of this project? I usually end up getting in over my head with these types of things and this is the car which I use on a daily basis, I don't have a second car.
It's how I learn, but sometimes it's at the expense of not using whatever I'm fixing.

Mercedes mechanic

· #9 · Jan 13, 2012

pt80chip said:
I understood what you meant. I sent him an email and a little after I did a search on the forum and I believe I found it here:

http://www.benzworld.org/forums/w140-s-class/1407863-no-reverse-jerks-reverse-when-cold-3.html

Is that the right one?

No its a single page .pdf. It explains simply whats wrong and how to fix it.

Its a pretty easy job, but its messy. And you will need fluid and a filter for the trans.

MafiaDON

· #10 · Jan 14, 2012

I believe the PDF in question the one in this post:

http://www.benzworld.org/forums/w14...-pictures-current-project-49.html#post4944119

All the best!

(I have not attempted to do this repair yet though, still driving with no reverse lol)

Mercedes mechanic

· #11 · Jan 14, 2012

MafiaDON said:
I believe the PDF in question the one in this post:

http://www.benzworld.org/forums/w14...-pictures-current-project-49.html#post4944119

All the best!

(I have not attempted to do this repair yet though, still driving with no reverse lol)

Thanks, you can always count of Mafia.

television

· #12 · Jan 14, 2012

The fault could also be the Ks leaky gasket or clutch for slow to engage or no reverse gear

Peter Guenther

· #13 · Jan 14, 2012

I had the identical issue with my 92, it worked fine when cold, but hesitated when warm. MB did a trans drain and filter, did not help and got worse. They finally replaced the transmission with a MB rebuilt, no converter, two years ago. This seems to be common on the 722.3 but more so on the ones MB deleted the rear pump on

aboynton

· #14 · Jan 14, 2012

pt80chip said:
I'll start with the fluid tonight. I had some sort of leak at one point but never discovered what it was. It also stopped happening.

Hopefully it didn't stop because all the fluid leaked out. In my experience, that's the only time leaks stop on their own but maybe you're just lucky and the leak healed.

Sent from my Autoguide iPhone app

gyrate

· #15 · Jan 15, 2012

the valve body job is an optimistic solution.

the burnt clutches (what usually happens).. trans is getting overhauled. and it is coming off the car (enjoy that job). if you are getting consistently no reverse, or slipping (or starts to slip) it's clutch packs. hard to know without having the car when the issue developed

leaks stop when fluid drops below the leaking location

glenlloyd

· #16 · Jan 15, 2012

The problem is in the reverse frictions, which deteriorate faster than they wear. The material used originally was different from the forward frictions but new replacement reverse frictions use the same material as the forward gears.

It's 7 hrs r&r plus an hour on the bench to repair the problem. It does not require a full rebuild unless you really want to take the time to do it.

Rarely will a valve body cleaning do much of anything to resolve this problem. While a valve body cleaning is a good thing it's a separate issue.

Mercedes mechanic

· #17 · Jan 15, 2012

At 100,000 miles?, you guys are telling me you think the transmission friction bands are burned up? On a 18 year old Benz that has been that well taken care of? Really?

I bet the both of you right now $1.00 each that its not the friction material.

television

· #18 · Jan 15, 2012

Well ignore it all you like but the Ks leaky gasket or clutch is the most common reason for this fault, it a rotten job and the box need to dismantled a long way to get to it.

I have all of the work sheets if anyone wants them

pt80chip

Discussion Starter · #19 · Jan 15, 2012

I went to Auto Zone and they told me they don't carry the ATF for an S420 1994. The guy said they don't carry mineral oil and that is the only thing the car will use.
I've seen on the forum that some people don't use the recommended oil. What does everyone think about this?

Also, where can I get a list of MB approved oils? I'd like to pick it up today and see if it helps any. If not I'm going to move onto the mafia PDF.

Regards,
Andy

television

· #20 · Jan 15, 2012

Oil type
Shell Donax TA D-21666,21774.....Castrol TQD 22256.......BP Autran MBX

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