Hey everyone, I got a problem on my dad's 85 300sd. My oldest brother drove the car and ran it low on fluid with a leaking front seal over 2 years ago since his pickup truck was broken and it took out 4th gear, he complained about it sounding like a jet engine under the car, what a moron. So the car sat for awhile and it got driven around my community since it was a 3 speed now, it would just slip horribly and not go anywhere in 4th gear. Me and my two buddies did a transmission swap and the donor transmission was given to us by a reputable form member and we were told it worked great on the car it came off of. Now this is where everyone is going to roll their eyes probably but, the transmission got water in it somehow, so there was an atf/water mix in the transmission and we drained all gunk out since it sat for "a while" and cleaned the inside of the trans with brake clean. We also used some wd40 to try and sop up any leftover moisture, but after we cleaned the pan and the exterior of the valve body we went after the front main seal and oil pump seal since the water probably ruined those. Water is heavier than transmission fluid and thus it all piled into the bottom of the pan and lower valve body, when we drained the torque converter it was perfectly clean with bright red fluid and with the front oil pump out it was almost spotless clean, so I am assuming the water never reached the clutch packs just the pan, filter, and valvebody. Anyways after our cleaning fiasco, the reinstallation of the transmission was pretty easy however the problem came along when we went on a road test today. After making sure the fluid level was perfect, we drove it around and found the transmission has no fourth gear, it will lurch forward trying to find fourth gear and will decelerate. I can drive around in 2nd and 3rd perfectly fine but it just wont shift into 4th gear. I spun the bowden cable all the way in to give the cable maximum slack just in case it was binding up, but to no avail. I drained out some of the fluid just to see what it looks like only to find it looks like pepto bismol, I added more fluid to make the fluid level at the maximum again in case I need to move the vehicle in my driveway but I am at a loss and am reading Kent Bergsma's manual on automatic transmissions. After a little research, I found that the pink color of the fluid is from moisture (water) in the trans that we didn't remove and it diluted the fluid. I also want to point out that the transmission is strong when its in gear and when its shifting into gear. It doesn't take more than 1 second to shift into reverse or drive and with my foot on the brake you can tell the car wants to move. My question is where do I start diagnosing? I would assume the vacuum to the transmission and the hydraulic pressure within the trans would be wise, I don't think the transmission fluid will affect the shift into 4th since I have 2nd and 3rd, I may be wrong but I do know it needs a fluid change until the fluid is bright red like its supposed to be. As a last resort, we have a spare valve body from a transmission out of a junkyard that had bright red and clean fluid, so if the valve body is clogged or something is rusted shut I can swap the valve body and use a new gasket from the complete gasket kit we have. I know this transmission will be a headache from the water that is in it, but I don't have a choice the car needs to run and drive correctly since it will be getting sold by the end of the month to a family friend who is in need of reliable transportation. Any thoughts appreciated

https://atracom.blob.core.windows.net/gears/2008/2008-07/2008_7_38.pdf

You could have ruined clutch packs with water.
Buy cheapest ATF and refill, run, drain a few times. Take out valve body, clean, make sure everything is lubed and movable. Then fill again with ATF to correct levels and try driving, for starters. Check the pdf.
Also, you need a new TV plunger for the valve body, per the manual - once coolant/water gets in there, it has to be replaced.
So if you have a valve body from the same transmission model, swap that in. Easy. Be mindful 3 of the bolts are shorter than other.

@filp Yes me and my father are going to get more fluid at Walmart tonight and run new fluid through multiple times to disperse the contaminated fluid. We do have a spare valve body to swap in that is in perfect working order so that will be next on the docket. I doubt the clutch packs are toast since every other gear works perfectly forward and reverse are very strong and the shift timing is less than a second, however that may be my own superstition. Could you please elaborate on how this "TV Plunger" in the valve body works and how to replace it if the need be?

This video helped me a lot: https://www.youtube.com/watch?v=h9thWDLR5yo

Take many pictures with your phone, and work slow. You'll need those.

See the last page here: http://www.w124performance.com/docs/mb/transmission/trans_722.3_TransTec.pdf

I strongly recommend you go to Index of /docs/mb/transmission

and learn the exploded diagrams of the valve body. Each is a little bit different, and element orientation is crucial for proper operation. Don't ask me how I know...

Well update everyone I found a big problem today, after doing some vacuum system troubleshooting I found there is no vacuum going to either the VCV or the modulator on the transmission. So there is a gross vacuum leak I need to find and fix and then go after the shifting problem again. Knowing this I now know that the transmission actually only had first and second gear and would not shift into third or fourth because there was no vacuum. Also just finished running fresh atf through the transmission after letting the contaminated fluid drain all night, so the fluid on the dipstick should be bright red soon after I test drive it again once this vacuum leak is fixed. I'm used to the 722.1 transmission where it starts out in 2nd gear unless there is a load behind it. So that makes sense that the internal governor in the transmission was manually upshifting the car to 2nd gear during the test drive. (Note the governor will only upshift from first to second and vice versa, it will not upshift to third or fourth.)

Vacuum affects only the quality of shifts.

Just use a plastic golf tee to plug the lines going into the cabin. If that doesn't get at least 18" of vacuum, disconnect the line at the vacuum pump and measure there. Then add lines until you find one or more that have large leaks.

You can also drive it and shift manually to confirm that the transmission is basically good and only needs adjusting.

Please break up your posts. Many here have old eyes and won't even bother to read the details of your post because the points run together.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Ok another update for everyone so we found some vacuum leaks, one of the lines going into the cabin had such a bad leak there was no vacuum going to the transmission. Plugged that cabin line off and bypassed a leaking control box on the emission system, also found a very small leak in the ignition cutout circuit, but will resolve that later because now the car will shut off under its own vacuum system and does not need to be manually shutoff.

However upon further investigation I found the vacuum modulator on the side of the transmission is leaking and it is hissing and losing vacuum, I have a spare to replace it but hopefully that will take care of the shifting issue. The Vaccum at the modulator was around 8-9HG of mercury and the VCV was bleeding it off when the engine was accelerated so the VCV is fine. The vacuum at the brake booster was 22HG of mercury, so that was fine as well. Will report back with more results later!

You are on the right track. Good going.

https://manualzz.com/doc/6307340/722.3-and-722.4-transmission-adjustment-guide

Another update, ok after replacing the leaking vacuum modulator the vacuum in the whole system is now very stable. Off the mainline I'm pulling 22.5 Hg of mercury and at the inlet of the vacuum amplifier I'm pulling 16 HG of mercury and at the outlet to the trans modulator, I'm pulling 6 HG of mercury. I don't know what the optimum vacuum to the modulator should be at idle, but at full throttle, it should be 0 for maximum hydraulic pressure.

After fixing the modulator and test driving the car I found I have third gear back however third gear does not pull very strong like second gear, it will engage but I can rev the engine up a lot and it will barely accelerate. I also tried unplugging the kick switch and that did not help, My next step is to hook up vacuum gauges and look at the vacuum while driving down the road, if vacuum checks out then I need to check hydraulic pressure in the trans before I rule out there is something clogged in the valve body.

Also, something interesting to note is that while driving today and yesterday my antilock brake light came on for thirty seconds and then turned off and the ABS has never worked on this car since the wheel speed sensors are bad supposedly. To sum up the new shifting issue, the car will shift into third and will not lurch anymore, but it will only lightly pull in third gear at 20mph, I can floor the car and it will barely accelerate, more diagnosis is required. I also need to flush the fluid in the trans again to get more of the pinkish transmission fluid out.

Could someone send me the vacuum diagram for a 1985 300sd with federalized emissions? (Not the California model) I need to trace out some more vacuum leaks and I also need to make sure the vacuum lines are routed properly in the system. I'm trying to make sure the vacuum system is working properly and providing the correct vacuum to the modulator and VCV before I do any transmission adjustments.

The transmission should shift fine without any vacuum connected to the modulator, it'll just shift hard. You're barking up the wrong tree with chasing vacuum issues to correct your shifting issues.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

@Diseasel300 ok what should I try next then? even if vacuum is not the problem I still want to verify its correct

Failure to go into gears is a mechanical issue. Could be a fluid pressure problem, could be a clutch/brake problem, or could be a valve body problem. Find yourself a copy of the ASTG service manual for the 722.3/4 (it's available online if you Google for it) and check pressures to make sure you don't have pressure problems. You have confirmed that you have adequate fluid in the system? Engine running, ran through gears pausing in each one, then checked level with the engine still running in park? Won't be as accurate as checking at operating temp, but you should at least be between the marks on the dipstick.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)