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+--- Thread: 1985 300SD Transmission issues. Help please?? (/showthread.php?tid=4573)
1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 05-12-2013
Well I found a really nice 300SD on craigslist for the right price but it's an hour away and the trany doesn't shift above 2nd gear... The redeeming factor is that it comes with a spare transmission that was with it when the seller bought it.
The problem is getting it home to fix it. I'd have to either get a tow dolly and beg a friend to tow it for me (not preferred), or I drive through the longggg way in second gear, or it somehow miraculously happens to be something stupid like a loose vacuum line, or I find a lot to jack it up in and swap the transmission right there in like a day (assuming the transmission really is bad).
The facts:
The car was beautifully maintained. 101,000-ish miles on it. Near squeaky clean everywhere. The fluids all look good. The seller said the main booster hose was off when he got it so therefore someone messed with the vacuum lines. And the central locking system doesn't work. And yes I did check the kick-down switch.
When I test drove it, it seemed to shift seamlessly from 1st to 2nd but anything after it would slip like crazy. I don't think it even got to 3rd. So this leads me to believe that it's a vacuum issue.
What I need from you amazingly knowledgeable people is ideas as to what could be wrong with it besides the actual trany being bad. Like who knows it could be a single line that popped off. If that's it, then I'll bypass everything non essential.
Is there any common problems or things I should check for? So please let me know what you guys are thinking. Thanks!
RE: 1985 300SD Transmission issues. Help please?? - aaa - 05-12-2013
You mentioned the common problem, the kickdown switch. Be ready to swap in the spare.
RE: 1985 300SD Transmission issues. Help please?? - SurfRodder - 05-13-2013
I would see if the seller is adverse to you bringing some tools, a jack and a jackstand to swap it in their driveway after the purchase... Even if you havent done it before it should only take 5 or 6 hours to swap out... worst case you start on a sat morning and have to come back on sunday...
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 05-13-2013
Ok thanks. I doubt he'd care. He's probly one of the friendliest pot-heads I've met. lol I should be able to do it with the tools I have idk. I'll have to check On-Demand for the actual process too. I never cease to be impressed by MB engineering. I looked at the transmission and it's barely bigger than a GM T5 manual, and yet it's tough little auto. I'm also impressed by the tow-start feature. Pretty sweet!
Anyway after I get it I'll probly start a build/restoration thread so keep on the lookout.
RE: 1985 300SD Transmission issues. Help please?? - SurfRodder - 05-15-2013
Cool, man I look forward to it.
The R/R is pretty straightforward... only "weird" tool is a 10mm (IIRC) allen socket bit for the starter attachment bolts. Youll need plenty of extensions to get at those as well as to get at the top bellhousing bolts... althought thats on a w123, so with the slightly larger w125, it should be a little easier to get to...
I have used about 36" or so total extension and a universal drive to get at those... if you have good quality extensions, you wont have excessive twist on the extensions... If you have HF extensions, I would use the 1/2" extensions/universal and an adapter to step down to whatever socket youre using (or use a larger socket as well)...
RE: 1985 300SD Transmission issues. Help please?? - willbhere4u - 05-15-2013
w126 not w125
RE: 1985 300SD Transmission issues. Help please?? - SurfRodder - 05-20-2013
(05-15-2013, 04:43 PM)willbhere4u w126 not w125
yeah, typo...nice catch!
(I had to do a Ctrl+F to see it...or actually was too lazy to find it w/o)
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 11-13-2013
Well guys this is an old thread by now but I figured I'd just not make clutter by making a new one. I ended up buying this thing and a friend of mine with a beastly V6 Dodge van with a bad valve offered his services and we got it home just fine on a tow dolly with it facing backwards. Didn't help that the idiot I bought it from wasted like $120 moving it an hour north from where it already was... Took at least 3 hours to get it home... On top of that we didn't have a key to steer it onto the tow dolly. That was a nightmare... I got a new key for it so it's all good.
So I got to play around with it recently. I fixed a vacuum leak or two that were obvious. Can't test it further unless I cap off the body lines. No change. I've been doing research and according to all that info the most likely issues could be a stuck kick-down switch, stuck shift switch (next to L on the shifter), stuck solenoid, or maybe a bad governor. Not sure if a tranny this old had the plastic helical drive gears for the governor (if it's even the same type) or not. Those were prone to breaking.
I have the spare tranny in the trunk but it's mad cold in the state of NY as of the last week so I'd like to avoid that swap... I'm about to go outside and mess around with the kick-down switch etc and look for issues with that. I did notice something odd yesterday. I was underneath the car inspecting everything and I saw that the solenoid wire was kinda hangin out and was weaved through those mounting ear things on the back-bottom of the tranny and in to the solenoid. And there's a wire-nut splice in the middle of the wire. Odd to say the least. Hopefully gonna do some extensive tweakage on it tomorrow. I'm really hoping to get it on the road on Friday.
Any thoughts?
RE: 1985 300SD Transmission issues. Help please?? - larsalan - 11-13-2013
I had one trans cooler line bust a hole. Once they get too low on fluid they stay in 1st and 2nd. And the fluid pump starts to suck air and froth up the mix. Pretty amateur problem, low fluid. But maybe that's it. No matter what it's going to be too cold to work outdoors much now.
RE: 1985 300SD Transmission issues. Help please?? - Jooseppi Luna - 11-14-2013
The governor gears are metal.
RE: 1985 300SD Transmission issues. Help please?? - willbhere4u - 11-14-2013
The kick down switch is under the gas pedal
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 01-01-2014
The governor gears on this one may be metal. But later on they were made of plastic. I'm just saying screw it, I'm taking it to the transmission shop tomorrow to be diagnosed. I can't do anything myself in this cold.
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 12-15-2014
Well I thought I'd just finish this thread up, after many hours of tweaking, fiddling with modulator pressures, and adjusting random things, I've pretty much determined that the transmission was badly abused and the bands are probly burnt up. So a buddy of mine came over and replaced the 722.315 that was in the car with the spare 722.303 that came with the car. Seems to be shifting perfectly. So I'm happy. But now I'm having a couple minor electrical issues... Reverse lights aren't working. I checked the switch, all good there. Checked the harness, all good. Checked the bulbs and fuses, they seem to be all good... So Idk, I'll figure it out.
RE: 1985 300SD Transmission issues. Help please?? - sassparilla_kid - 12-15-2014
If nothing else you could do like me and put in a toggle switch to control the reverse lights, just don't achievable l accidentally leave them on lol
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 12-15-2014
I may have to do that. I'm gonna look and make sure the connectors are all good in the trunk.
RE: 1985 300SD Transmission issues. Help please?? - dieselsmoke300d - 12-19-2014
Turns out someone went and disconnected the lead to the reverse lights in the fusebox. It was supposed to be connected to fuse 10 with another lead that goes to a bunch of things. AND, the one lead that was disconnected also goes to the kickdown solenoid... I think we found out what killed the original transmission...