I have this transmission in 85 W123 300D. It makes a loud clunk in drivetrain when shifted into reverse. Otherwise shifts fine.

I am currently replacing 2 yr old axles because they have wear and do clunk. Diff has wear after 460k km, but otherwise seems OK. Rpms normal. Engine/tranny mounts new.

I feel I may be treating a symptom, rather than cause

Given that shifts are otherwise smooth, does anyone here know if there could be a possible transmission issue that would cause just Reverse to have hard shift and cause rear end clunk and lift?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Subframe bushing? Control arm bushing? Have someone in the car apply the brake firmly and apply throttle in F and then R whilst you stand outside and watch the rear wheels for excess forward/aft movement/shifting.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

We have done that. Metallic clunk comes from inner cv joint. With wheels on ground and brakes on, the axles rotate about 1 bolt diameter (8mm). Car can't move, so transmission lifts car. Just like it squats going into Drive when brakes are on.

Doing exactly same on my 107, same things happen, but no alarming clunk. Shift into Reverse on 107 is actually delayed a second or so and not harsh.

I have checked entire drive train, and only lash I found, is from normal wear in diff itself and the CV axle joints (which I am replacing at moment).

I am interested in input on what could cause a harsh shift from transmission, just in Reverse. This to prepare me for still having clunk after axles are changed

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Since you are in the process of replacing the axles, you should likely wait until they are replaced.

There is a very old thread on this but if I remember from it correctly there is no way to adjust say the reverse band on your trans.
If there is something in the valve body that can cause you symptoms, I never read that.

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84 300D, 82 Volvo 244Gl Diesel

I am really mainly researching possible causes, but will wait until axles are back in. Maybe I can at least check out vacuum.

In the trouble shooting section of the transmission manual, there are trouble shooting tips. These two may be relevant:

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

^^^^Excellent find ^^^^ Great info for anyone with a W123 w/automatic. Thanks for the detective work!

Before the axles arrived, I did a few vacuum checks.

Vacuum at source - 20"Hg.
Vacuum in line to modulator at idle - 17" Hg
Revving engine (without knowing rpms), vacuum dropped to 12" Hg.

On this version (1985), the vacuum at modulator is apparently normally in 12-17" range at idle and then drops to 5" as speed is increased. After that boost kicks in and vacuum drops to zero.

My problem only occurs when shifting to Reverse, so modulator vacuum pressure at idle would be only factor. If issue continues with new axles, I may check modulator pressure, or maybe first just dial it back a bit.

Should have axle job complete tomorrow.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Are you certain it's not a bad rag joint on the drive shaft? Those were neglected on every 123/126 that I've owned.

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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.

Drive train has been checked. Flex joints are good. Engine & tranny mounts relatively new.

Now, diff mount & Axles are new.
Latest additions to be tested once I fill the diff.

Suspect harsh reverse may be tranny related even although it is otherwise good.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

2 thumbs up and best wishes.

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84 300D, 82 Volvo 244Gl Diesel

Thanks.

Today, I first ran drive with rear wheels off ground, just to make sure there were no issues. Then I lowered car and very carefully moved shifter from park to N, then N to D, Then N-R. No clunk. Just a gentle engagement like it used to do.

Took car for a ride to warm up transmission. Did a few fwd/reverses along way. Then got home and backed into garage. No clunks!

To be honest, I was surprised. Only real changes were the new axles and diff mount. And diff mount didn't show any signs of movement when I checked it out early on (it did need changing due to corrosion).

I was planning on tweaking the vacuum to modulator, but now will leave that alone!

I will change the fluid and filter. Another awkward job for an old guy. Wonder what a Mr. Transmission would charge for that? I will probably end up doing it!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Decided to do the fluid/filter change myself to day. My records showed that the fluid hadn't been changed for about 80k miles. However, when draining the pan, the fluid came out red and looked like fresh ATF! Made me wonder why I was doing this. And if I really needed to drain the converter and install new filter. But going to do those anyway!

I came up with a way of lining up the torque converter drain plug single handed. Took me about 5min

This was how this old guy got the converter lined up

I happened to have one of these:



Fed camera down through engine bay and tie-wrapped it in place:


Connected to phone in engine bay:


Rotated engine using PS pulley nut. (Belts didn't slip but if they do, just pull up on lower part of belt while turning). And Voilą - there is the drain plug

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Graham,
Congrats on getting your problem fixed and thanks for sharing that great gadget for the phone.
Who says you can't teach an old dog new tricks!

I'm going to get that scope. I'm 66 and find I'm putting off jobs more and more on the car
and that scope will get me off my rear end to tackle some tranny issues of my own.


Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

After changing ATF and Filter, I had to check the level. Went for a good drive (about 25 minutes) on roads that I could do 60mph. Outside temperature was 22C. When I got home, the level was at lower mark. I checked temperature of pan and it was 67C.

I think I am probably close to proper level, but apparently the temperature for measurement is supposed to be 80C. Based on following, I will check it cold in morning.

Did some checking, and I found in several places that the level can and probably should be done cold (20-30C) - which is a lot easier to do in a shop or wherever. For my 722.315 transmission, 10mm below the minimum mark when cold, is apparently equivalent to the upper mark when at 80C.

For later transmissions this excerpt from an MB manual is helpful:

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanks for the info! Appreciate the MB shop manual reference. The correct fluid level check, using the ATF dipstick, has always seemed a bit mysterious with a variety of opinions as to the correct procedure. Always best to refer to mfg. documentation when available, imho.