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+--- Thread: Rugged Downshifts in '84 300SD (/showthread.php?tid=3292)
Rugged Downshifts in '84 300SD - Serial Crusher - 01-22-2012
I had a recent disaster with my '83 300SD that made it a total loss. It wasn't in the best of shape and was starting to have a few serious problems emerging so it wasn't the worst that could happen. No property damage and no injuries, so all's well.
I checked craigslist for a couple of days looking for replacements in my price range, and found a gentleman selling his '84 300SD and managed to get it for $1150. Initially it would only reluctantly start, and wouldn't shut off. I changed the glowplugs and repaired some vacuum fittings and now it seems strong. The man had put a ton of effort into this car, but some of the simpler, common problems he didn't fix, like the door latch, dome light, seat belt, bad potentiometer, standard stuff that I've fixed. He has the paperwork and receipts that he gave me to show that he rebuilt pretty much everything I wanted to fix on my old one.
Anyway, after going through everything (basic diagnosis, it's cold as hell here) the car is still shifting goofy. It has the normal soggy shifts and flaring of a poorly adjusted vacuum system. It seems to flare the worst when shifting into fourth. The most alarming thing is when it downshifts into first. If you allow it to downshift to first normally it slams into first, sometimes with enough force to break traction on snow or ice. However, if you manually downshift into 3 while you're slowing down the downshift seems smooth and normal. The bowden cable seems normal, and there aren't any leaks I can detect topside, but because of the weather and my limited access to a shop I haven't had a look at the transmission connections yet.
So do these seem like normal adjustment problems? Or should I start looking for another transmission?
RE: Rugged Downshifts in '84 300SD - Silberpfeil - 01-24-2012
(01-22-2012, 04:54 PM)Serial Crusher I had a recent disaster with my '83 300SD that made it a total loss. It wasn't in the best of shape and was starting to have a few serious problems emerging so it wasn't the worst that could happen. No property damage and no injuries, so all's well.
I checked craigslist for a couple of days looking for replacements in my price range, and found a gentleman selling his '84 300SD and managed to get it for $1150. Initially it would only reluctantly start, and wouldn't shut off. I changed the glowplugs and repaired some vacuum fittings and now it seems strong. The man had put a ton of effort into this car, but some of the simpler, common problems he didn't fix, like the door latch, dome light, seat belt, bad potentiometer, standard stuff that I've fixed. He has the paperwork and receipts that he gave me to show that he rebuilt pretty much everything I wanted to fix on my old one.
Anyway, after going through everything (basic diagnosis, it's cold as hell here) the car is still shifting goofy. It has the normal soggy shifts and flaring of a poorly adjusted vacuum system. It seems to flare the worst when shifting into fourth. The most alarming thing is when it downshifts into first. If you allow it to downshift to first normally it slams into first, sometimes with enough force to break traction on snow or ice. However, if you manually downshift into 3 while you're slowing down the downshift seems smooth and normal. The bowden cable seems normal, and there aren't any leaks I can detect topside, but because of the weather and my limited access to a shop I haven't had a look at the transmission connections yet.
So do these seem like normal adjustment problems? Or should I start looking for another transmission?
It might be worth doing a fluid / filter swap and seeing where that gets you??? I know when I did this and changed to synthetic fluid it made a world of difference but I wasn't experiencing the level of problems you are....
Is the rest of the vacuum system functioning properly?
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 01-24-2012
The vacuum system on this '84 is remarkably different from my '83. On the passenger fender in front of the coolant overflow there is a junction block or distributor with about 6 vacuum lines coming out of it I've never seen before. I can't tell from pictures I've found whether it's stock or a previous owner did it. It has a consistent hiss when idling. I did try diagnosing it yesterday morning, with the vacuum line to the transmission disconnected there is no change in shifting. Adjusting the modulator on the IP had no effect either. Completely unscientific, but roughly, in the '83, the modulator on its IP would adjust shift rpm and the one on the transmission would adjust shift firmness.
In all the other threads I've read, rough downshifts were accompanied by rough shifts, if I can find a dry spot somewhere I'll do some adjustments to the transmission modulator. Also, I'll upload a pic of the suspect vacuum junction.
Nice, my local Napa has the filter/gasket set in stock. They've been pretty good through this, and have had most of the more common parts in stock. I looked over the options and I think I'm going to go with ATF +4 instead of the synthetic. My local stores want double or more for quality synthetic.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 01-24-2012
Another update: I did a couple spins around the block to check various things. With the bowden cable completely disconnected, the problem is the same. Of course the adjustment on mine is broken, so i tightened it with some .25" zip ties. Two gave very firm shifts, and only a reluctant shift into fourth. With just one the shifts are firm, but not harsh, and much faster, zero flaring. The shift into fourth is so smooth I had to watch the tach to see it. Still clunks down into first if I don't manually downshift. I'm keeping my fingers crossed that a fluid and filter change will remedy that.
RE: Rugged Downshifts in '84 300SD - serverman777 - 01-24-2012
What part of Indiana Do you live in? I live in bloomington...
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 01-24-2012
Way up north, I'm about a mile from Michigan Between South Bend and LaPorte.
I picked up the trans filter and gasket from Napa today and was shocked to see they have a shelf full of LubroMoly stuff. They have all of their products in stock. The salesman said it was for the Euro stuff. They had one quart of some German trans fluid on the shelf they were asking $17.99 a liter for... They also didn't have trans fluid in gallon jugs, so I didn't buy. I won't have time to do the service until this weekend anyway.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 01-28-2012
Well the gasket Napa gave me was wrong, Thankfully the filter wasn't. I did an oil change, trans fluid and filter and valve lash yesterday. Old gasket was in good shape and the filter it had was a Meyle. Trans fluid was a little milky, but not burned and no metal in the pan. Initial test drive showed no change in the downshift problem. I made some adjustments to the IP modulator and the trans modulator and did a few additional test runs. The downshift is now far less pronounced, but still noticeable. It no longer sounds like it's bashing the piss out of my diff and CVs, so I guess I'll have to live with that for now. It definitely seems like there is a vacuum leak I'm not finding now. It was reluctant to idle cold before I set the valves. A few of the valves were off by as much as a hundredth. Now it idles much more smoothly and I don't have to stay on the throttle to keep it from dying with the initial cold start. Now that the low end is nice and smooth, I've found that accelerating with the heater on makes it hesitate.
I fixed the antenna mast and the totally 80's bass cannon in the trunk, so all the squeaks and rattles magically went away
Like I promised before I'll post some pictures of the vacuum system particulars just as soon as I get some AA batteries for my dinosaur camera.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 02-04-2012
Still no pictures, but another update. I changed the gear lube in the differential today because I read it mentioned on another thread today. It looked like it had never been done before, there was still undercoating on both plugs. The oil was nasty and obviously ruined, but there weren't any big pieces in it. I replaced it with Lucas 85w140. I've only driven it a few miles since then, but there hasn't been any change in the downshift. With as nasty as it was I might drain it again in a few hundred miles.
PS. I had a seriously hard time finding anything that would drive a 14mm allen. I wound up going all over and eventually finding one at Harbor Freight.
RE: Rugged Downshifts in '84 300SD - larsalan - 02-04-2012
Those plugs can get stuck in there pretty good. Maybe add a little trans fluid to wash out those gears for a while. Run that some miles before you drain it again. Or, pull that back cover off and really get at it with some brake cleaner. There's certainly a layer of sludge over the whole inside.
Or whatever, just my 2c
RE: Rugged Downshifts in '84 300SD - Hercules - 02-05-2012
High modulator pressures( adjusted by someone) will cause a hard down shift into first gear. Also A old stiff modulator reacts to slowly to vacuum changes,can cause poor shifts and cannot be set properly.Mbz also up dated the push rod under modulator to improve shifting quality. Proper Trans. adjusting procedures must be followed,accounting for wear.
IMO,you changed the diff.oil once,that's enough.Repaired Mbz for a dealership for many years,the only diff.that ever went bad was the one"s that were serviced. This happened so often that servicing was never again done. If no metal flakes are found in oil than oil change will be helpful. If metal flakes found, re-install old oil,drive intill diff. gives(noise). The metal flakes take up the wear between the gears,flushing the metal out ,diff. will become noisie. Good luck.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 02-05-2012
(02-04-2012, 09:57 PM)larsalan Those plugs can get stuck in there pretty good. Maybe add a little trans fluid to wash out those gears for a while. Run that some miles before you drain it again. Or, pull that back cover off and really get at it with some brake cleaner. There's certainly a layer of sludge over the whole inside.
Or whatever, just my 2c
This one was seriously stuck. I had a 2' breaker bar on it and I was still grunting. Judging by the inside of the plugs there was some some serious gack built up. I had to hose them with brake clean and a brush. It looked like there was rust on the inside of the drain plug. With as nasty as it was the trans fluid might not be a bad idea, I'm not too wild about pulling the cover, although it would be nice to have a look at it. Does it take a gasket or just RTV?
(02-05-2012, 02:05 AM)Hercules High modulator pressures( adjusted by someone) will cause a hard down shift into first gear. Also A old stiff modulator reacts to slowly to vacuum changes,can cause poor shifts and cannot be set properly.Mbz also up dated the push rod under modulator to improve shifting quality. Proper Trans. adjusting procedures must be followed,accounting for wear.
It may be a stiff modulator, but I was thinking a weak or broken spring in the valve body. I've read quite a few threads on similar problems, and it doesn't seem like anyone ever got resolution. It drives me nuts that it works fine if I manually downshift from D to 3. When in D it will only hammer the final downshift if it gets into fourth. It also does not seem to be a brake band because it happens regardless of engine rpm or vehicle speed and only into first.The adjustments I've made have changed the shifting characteristics, so I'm certain they're still working, but having a stiff diaphragm might explain it. The modulator on my trans is the older style (I think) it is the one that has the "T" key that is only retained by the rubber dust cap. On the other hand, upshifts are perfect. I made 4 or so adjustments to fine tune them, and now they're fast, no flare and very smooth. Maybe with the manual downshift it can't stack the 2nd and first downshifts....
RE: Rugged Downshifts in '84 300SD - larsalan - 02-05-2012
Just rtv.
Make sure and support the bottom of the diff if you are taking it off the body. I say that because if it lowers your brake lines may be at their max length. Or I guess it depends if you have the wheels off the ground too.
Or could just take that back support off there.
I had just been messing with mine a lot lately. Swapped in a 2.88 from a 3.07. Then later lowered it all down to trim the rear suspension springs.
Like Hercules said, it may not be a big deal with all the scuzz in there. Just that the 2 I was dealing with weren't all shinny and stuff.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 02-16-2012
Well as the new gear lube has worked its magic the downshift issue has subsided. It's still easily noticeable, but it isn't going to split a ring gear. As that problem has become something I can ignore, now another one is emerging. This thing makes no low end power whatsoever. It has gotten drastically worse over the last 500 miles or so. When cold, it hesitates so much at low rpm it's dangerous, it is still sluggish once it gets up to temp. It has new fuel filters, but fueling is definitely not an issue, it leaves cloud of raw fuel followed by a column of black smoke until it gets up to speed. I just changed the air filter about 100 miles ago, so it should be breathing well enough. When the turbo finally spools up it seems normal. It isn't using coolant or oil...
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 02-17-2012
Problem solved. I removed the EGR and my panzer is running like a champ again. Apparently it was stuck wide open and had a massive vacuum leak to boot. Now it has power off the line, and doesn't hesitate with the heat on.
RE: Rugged Downshifts in '84 300SD - larsalan - 02-18-2012
You put a block off plate in? Glad to hear that you're reversing the work the EPA put into these fantastic machines
RE: Rugged Downshifts in '84 300SD - sassparilla_kid - 02-18-2012
Congrats! EGR is one of the dumbest concepts I have ever heard of
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 02-18-2012
Thank you, and no doubt, a smog control that guards my retreat with a smokescreen... The only pain of it is that it takes it a few more minutes to reach temp, which can be a long time with as cold as it gets around here. We've been really lucky this winter though.
Intake side is a standard block. For the exhaust manifold side I drove a socket into a pipe with a piece of thin stainless between, it came out perfect. It hugs the manifold outlet and the old clamp holds it in place.
RE: Rugged Downshifts in '84 300SD - Serial Crusher - 03-04-2012
Got the odometer working the other day, gears were stripped, so I replaced it with the speedo/odo out of my old one. I got a good monovalve when I was at the yard too. Now the only problems left on the beast are the passenger side window regulators. I never did check to see if the A/C has been converted to R-134A or not, the last one had been, but the compressor was shot. I would be nice to have that working, especially if I can only get half the windows to roll down...
RE: Rugged Downshifts in '84 300SD - lpumb3 - 10-02-2012
have you have any problems with your tach ? ive been getting my tranny shifting properly , and one black line coming off the injection pump ,t 'ed to the firewall was attached to nothing . i plugged it got my tach back and then when replacing some old fittings near the 2/3 valves i lost the tach again , does the monovalve control rpm/tach reference to the cluster ?
any idea where that black line is supposed to end up under the dash ?
RE: Rugged Downshifts in '84 300SD - lpumb3 - 10-05-2012
just talked with a merc trans shop , the black line i was wondering about , is a bleed off for the vac system .
i guess my description wasn't very good either yeah monovavle dur . anyhoo with my shifts improving after that, ive got something else to deal with .