Trans experts, join the huddle, I need help with a diagnosis - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 06-08-2014, 05:12 PM

I just got my bro's car running great: Diesel Purge results: This is amazing stuff!
The car is a 1991 300D 2.5 turbo with 91,XXX original miles.
Today on my way to church, about a block before arriving, the trans went into neutral after shifting out of first. I put it in neutral and back in drive, and it shifted into second and then third just fine. After church, I exited the parking lot and it went into neutral every time after shifting from first. I then drove the remaining 14 miles home in first gear, accelerating and then coasting until the governor caught up with the wheel speed and it went back into first (I did this probably 35 times on the trip home).
I have a basic understanding about how an automatic trans works, so I have an idea what could have gone wrong. It has only reverse and first. I believe that the problem is a broken sprag, but that is where you the trans expert comes in. When I got home, I checked the fluid level thinking that it may be just low, but I was surprised to see that it was in fact over full by at least a quart. I talked to my bro, and he said the last time he checked it it was just right (no leaks in the trans). Could the over full condition be caused by expansion of the fluid? Could the over full condition be the cause of the trans only having first and reverse?
I must add that while the engine was having problems with power or the lack thereof (see above thread), the trans would shift really hard in every gear. I checked the modulator and it holds pressure. When the engine is lacking power, the pedal is always to the floor and the modulator sees no vacuum. If I give it easy throttle or let off totally, it would shift smooth, but had no acceleration. After fixing the fuel problem yesterday, it shifted just fine until this morning. Could the hard shifting have contributed to this trans problem? Any diagnosis (expert or otherwise) will be appreciated. I don't want to have to pull and have the trans rebuilt/fixed if I don't have to. Thanks in advance, Rich

Mxfrank · #2 06-08-2014, 06:41 PM

Failure to make 2nd gerar is a B1 problem. In most cases, it's the piston and piston seals, which are accessible with the tranny in the car. In more serious cases, the band itself may be broken, which requires a total teardown.

SD Blue · #3 06-09-2014, 08:27 PM

Over full will cause very strange problems. Been there done that. On mine, I've found that operating temperature before checking the level was critical. Fill only to the lower mark.

Assault · #4 06-10-2014, 09:44 AM

To check your trans fluid follow the PDF in the second post
Speedo cable disconnected - transmission fluid leak.

layback40 · #5 06-10-2014, 09:55 AM

Quote:

Originally Posted by Mxfrank

Failure to make 2nd gerar is a B1 problem. In most cases, it's the piston and piston seals, which are accessible with the tranny in the car. In more serious cases, the band itself may be broken, which requires a total teardown.

X2 on B1 issue. i have heard of the piston breaking up & causing this. its worth removing the cover, just have to remove the spring clip & the circular cover pops out.

JamesDean · #6 06-10-2014, 12:59 PM

Quote:

Originally Posted by Mxfrank

Failure to make 2nd gerar is a B1 problem. In most cases, it's the piston and piston seals, which are accessible with the tranny in the car. In more serious cases, the band itself may be broken, which requires a total teardown.

Quote:

Originally Posted by layback40

X2 on B1 issue. i have heard of the piston breaking up & causing this. its worth removing the cover, just have to remove the spring clip & the circular cover pops out.

The 722.418 thats in the 300D has a plastic gear on the governor. It might have broken. This was the case for my 91 300D. I had reverse, and first gear but nothing beyond that. It did not fall out of gear and go in to neutral though, that might make this different.

If it is the governor its about $10-20 in parts and you can fix it.

'91 300D trans stuck in 1st gear...

91 300D 2.5. Wont Go Over 2,000 rpms!

ROLLGUY · #7 06-10-2014, 08:59 PM

I had my bro check to see if he can get a B1 kit, and Pelican says it is NLA. Does anyone have any part numbers for the parts that might have failed (B1 or governor gear) so I can check elsewhere?

ROLLGUY · #8 07-05-2014, 02:03 PM

I finally got time to pull the pan and look for the problem. I removed the plates for the pistons (one in front, one in back, lower right in photo), and could not find anything amiss.

There were no signs of anything broke or worn. All the springs looked just fine. If this trans had a B1 piston or spring problem, I am sure it would have been evident. I drained about a quart of fluid out of the pan and saw this:

I assume it is part of something that is causing the trans not to shift. Does anyone know what it might be from? All the other plastic parts I can see are a yellowish tan color, and this is closer to white. Would there be a part inside that can be replaced without removing the trans? I hate to take it to my normal trans guy, as he most always says the trans needs to come out. I don't want to have to remove the trans if I can help it. Thanks in advance, Rich

JamesDean · #9 07-05-2014, 03:54 PM

I would pull the cover on the governor and check out the governor. I believe if you rotate the drive shaft the governor should spin as well. If it does not then you've like run into a broken gear.

Check out some pics here from mine:
'91 300D trans stuck in 1st gear...

vstech · #10 07-05-2014, 04:07 PM

really can't see much from that photo.
can you take another out of the sunlight? maybe clean up the part, and get a shot of just it in your hand?

ROLLGUY · #11 07-05-2014, 05:32 PM

Quote:

Originally Posted by JamesDean

I would pull the cover on the governor and check out the governor. I believe if you rotate the drive shaft the governor should spin as well. If it does not then you've like run into a broken gear.

Check out some pics here from mine:
'91 300D trans stuck in 1st gear...

It is definitely worth the effort to check, and worse case, removing the driveshsft and tail housing. I will let you know how it goes.....Rich

Mxfrank · #12 07-05-2014, 05:59 PM

Quote:

Originally Posted by ROLLGUY

I finally got time to pull the pan and look for the problem. I removed the plates for the pistons (one in front, one in back, lower right in photo), and could not find anything amiss.

There were no signs of anything broke or worn. All the springs looked just fine. If this trans had a B1 piston or spring problem, I am sure it would have been evident. I drained about a quart of fluid out of the pan and saw this:

I assume it is part of something that is causing the trans not to shift. Does anyone know what it might be from? All the other plastic parts I can see are a yellowish tan color, and this is closer to white. Would there be a part inside that can be replaced without removing the trans? I hate to take it to my normal trans guy, as he most always says the trans needs to come out. I don't want to have to remove the trans if I can help it. Thanks in advance, Rich

You're looking in the wrong place. The governor is accessed from the left side of the case, the B1 piston from the right. You have to lower the transmission, but I think you access either without removing the entire box. It could be part of the governor gear.

ROLLGUY · #13 07-05-2014, 07:31 PM

Quote:

Originally Posted by Mxfrank

You're looking in the wrong place. The governor is accessed from the left side of the case, the B1 piston from the right. You have to lower the transmission, but I think you access either without removing the entire box. It could be part of the governor gear.

You are right, I was getting the B1 spring and piston mixed up. I was going by other posts that talked about a spring kit. I have actually found the problem, it is exactly what JamesDean described.
I removed the flex disc and used it to hold the driveshaft out of the way:

I found the broken gear in the cavity below the governor:

Now to order the parts and put it back together. Thanks especially to JamesDean, and the rest of this community. Everyone here has been so helpful, and I have saved countless $ on repairs by getting information here and fixing things myself.....Rich

pmckechnie · #14 07-05-2014, 07:33 PM

I had the governor gear problem on my 91 300D also. Part from the dealer was < $3.00. It can be done by lowering the trans by removing the rear crossmember and moving the trans as far as you can to the right side of the car. I tied mine over with a strap to hold it there. I found 1/2 of the gear still on the governor and never found the other 1/2 of it. That was about 10 years ago. Still running great.

Paul

Story of my life, always a minute or 2 late.

ROLLGUY · #15 07-11-2014, 09:31 PM

I finally got the parts today:

Now to find the time to install them when it is not hot or windy (both common occurrences around here).......Rich