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1980 300 sd tranny question

Started by dizzyD, 04 November 2005, 12:46 AM

dizzyD

Hello everyone, first post to this board.
My 1st question is; Does anyone know what causes the transmission not to go into reverse when it is cold, cold start, after it runs 5-10 miles it will go into reverse!
Thanks for any input, I love my black 300 SD, It was well taken care of. BTW It has 130K miles when I bought it but think the miles are way wrong, but still got it at a very good price, I will post pics soon,

Brian

Mforcer

Hello and welcome to the forum. We are all glad to have you here :)

I am not sure what is wrong with your car and I am sure someone else here will be able to help but I have heard of people having strange problems with enganging gears becasue of vacuum leaks and if this is the case is easy to fix. Sorry I can't offer any more help on this.

Have you had a chance to post some pics yet? We can never get enough photos of great looking W116 :)
Michael
1977 450SE [Brilliant Red]
2006 B200

boneheaddoctor

Quote from: dizzyD on 04 November 2005, 12:46 AM
Hello everyone, first post to this board.
My 1st question is; Does anyone know what causes the transmission not to go into reverse when it is cold, cold start, after it runs 5-10 miles it will go into reverse!
Thanks for any input, I love my black 300 SD, It was well taken care of. BTW It has 130K miles when I bought it but think the miles are way wrong, but still got it at a very good price, I will post pics soon,

Brian
This may or may not help....but if you siphon off 1 or two quarts of transmission fluid and replace with trans-X if its availible in your area.  drive it a few hundred miles then replace the fluid and filter. If its due to a varnish buildup it may cure your problem. Worst case is it won't help.

John Hubertz

I have some better news....

Since it engages in forward well, the only the cause can only be:

1.  Dirty filter and/or trash in the fluid causing improper pressure in the valve body or intermittent/erratic piston or valve body valve action

2.  Dirt or obstruction of a valve body passage due to "varnishing" due to old trans fluid or dirt

3.  Worn or leaking seal on the reverse actuator "piston" that actually puts the car "in gear" when you call for it using the lever - this is unlikely.

First of all, if forward is working and reverse doesn't engage, it is likely working, just not as efficiently when cold.  Change the fluid and try it before adding anything else.  Clean fluid can work wonders, and a clogged filter screen can also cause low pressures in the valve body and on the piston that engages the gear.


Generally, not a lot of driving can cause these conditions, so drive the PISS out of that car all through this process.  Drive it HARD.  Transmissions HATE driving slowly because pressures build SO slowly.  Think of a really aggravating, really slow lover.  It drives transmissions INSANE because they ALMOST get to shift........then don't.  The throttle pedal is designed to PUSH.

Then if it still isn't working after driving the car A LOT for a couple days, add the trans medic stuff mentioned earlier.  Then:


1.  Try engaging it when cold by revving the car up to about 1500 RPM when first trying to back.  That should make it engage due to higher hydraulic pressure from the RPM driven pump and torque converter that create all the "power" that operates this transmission.  Apply the brake firmly and do it ten or twenty times.... after you use the trans medic so the goo gets a chance to work.


2.  It is possible your valve body has a stuck valve - and because it does engage well in forward it is a likely culprit.  Valve bodies are cheap to replace used.....  but first

CHANGE your fluid, and when you do pull the valve body off (it just bolts on with a couple bolts.... (10mm?).

Take it to a trans shop and ask them to clean it, or ask them what to use and carefully try to clean it yourself.  Be aware there are little "ball bearings" and springs that glide back and forth inside the passages of that little cast worm farm....  Any lacquered passages or nasty bits stuck in those wormy little tubes in that thing will cause the condition you describe.

Be careful though, they can sometimes go "sproing" when you dissassemble them, but are safe to handle to remove and reinstall....just be careful.  If you start trying to remove and clean the little balls etc just be SUPER careful.

3.  Reinstall and test.  If it still is doing it, buy a used valve body and try it.  If this isnt' working, a used transmission is the next alternative.

Oh - and because it is a diesel I'm assuming you have good vacuum....  if the vacuum system is lousy I think it might affect upshifts - does anyone know if it can effect engagement of reverse?

John
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

Bratman47

Lucas Transmission Fix after you have changed the oil and filter. This additive works and you can get it at Auto Zone or almost any automotive store. Do not over fill! I have owned and driven my 300SD for 24 years.

John Hubertz

The correct amount of fluid is listed on this site in the specifications section.  Remove the pan all the way - if there is any crud you can clean it out with the pan off...and without pulling the pan off you can't be sure you are filling it accurately.

I'd recommend buying the gasket and filter at your M-B dealer so you know the filter creates the correct amount of resistance to fluid flow.

Good luck!  Let us know how it is working out!

Accelerate!  Accelerate!  Accelerate! 

John
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

Tomi

Possibly only the shift leaver linkage needs some adjustment
(better try simple things first)

dizzyD

Well since it has warmed up here in southern California, it has been going into reverse cold, with alittle help. (accelerating slowly in reverse). BTW, this was a used tranny I got installed after the old tranny broke the 2 torque converter "tangs" that go to the pump. I still have the old tranny, which worked great b4 it broke, I had possibly overfilled the tranny a couple of weeks before it broke. Make sure tranny is in neutral when checking the dip stick, not park.

Thanks for all the info everyone has provided!!!!!!!!

Brian

John Hubertz

Richard,

Based on your experience, I'd then assume the lucas goo in the fluid/filter change is the best/only recourse other then internal work...correct?

Re the valve body, I understand your reluctance on the dissassembly because of their complexity, but removal and reinstall I've always perceived as easy - is there something about M-Bs that I don't know but should?

John
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

John Hubertz

Richard,

Thanks for the info.  If I'm hearing you correctly you're saying that (as is true for most cars) 

1.  Valve bodies are like gigantic mechanical watches - only a very skilled or very foolish amateur would dissassemble

2.  The MB valve body is not the easiest to remove and replace from the transmission as the gasket is hard to align...is that correct?

Also, I'll be proud to help you locate a perfect used one.  There are jillions of those in the recycling network here - and they will USPS by snail boat to Aussieland no problems.  Your experience is very appreciated and it would be a pleasure to return the favor of your expertise.

John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]