722.315 slow to engage forward when warm - PeachParts Mercedes-Benz Forum

KAdams4458 · #1 01-08-2013, 07:16 PM

When cold, the transmission from the '83 300D donor engages drive and reverse immediately. Once things warm up a bit from driving around, reverse still engages promptly without delay, but drive begins to stop engaging while at full stop, and the transmission just sits as if it is in neutral unless you goose the throttle for a few seconds, then when it does grab, it grabs hard as if drive had just been mysteriously selected.

Fluid levels are spot on. Bushings are all new and the rod is adjusted correctly per the FSM. I drained and filled the transmission when it was installed about 700 miles ago, and the fluid seems fine. I'm just wondering if I am sitting on a time bomb here, as the length of time that the throttle needs to be raised before drive engages is increasing noticeably. Can anyone here shed some light on this? I can't seem to find any references by searching the site to anything like this.

I forgot to add that there is a discernible whine directly effected by engine speed which comes from the transmission. The pitch changes slightly depending on temperature, as well as when the transmission is shifted from park to any other gear. That seems like a front pump issue, but I'm not sure if it is related to the delayed engagement problem.

Diesel911 · #2 01-08-2013, 08:20 PM

I am not sure what transmission you have. Does a 722.315 have a Rod instead of a Bodwen Cable?

Mine started doing that when cold. I changed the Fluid and Filter (also about that time the temp got a little warmer in the morinig) and it ran OK for less than 1 year and then the B2 Piston Broke.
I never tried putting it in Neutral.

Diesel911 · #3 01-08-2013, 08:35 PM

I am not sure what transmission you have. Does a 722.315 have a Rod instead of a Bodwen Cable?

Mine started doing that when cold. I changed the Fluid and Filter (also about that time the temp got a little warmer in the morinig) and it ran OK for less than 1 year and then the B2 Piston Broke.
I never tried putting it in Neutral.

Questions I ask about 1 year before the B2 Piston broke:
http://www.peachparts.com/shopforum/diesel-discussion/265356-b2-piston-problem-something-else.html

KAdams4458 · #4 01-08-2013, 09:38 PM

Bowden cable... and it is adjusted to spec. Shifts are right where they should be relative to throttle, rpm, and slope. Occasionally 3 to 4 is slow when tranny fluid is cold, but doesn't flare.

Also, any forward gear selector position results in the same behaviour once the transmission warms up. Gotta rev it up a few times before it grabs, and then all is normal again until the next time it goes in to park or reverse. Putting it in neutral and then back in to drive does not cause the lack of engagement.

Diesel911 · #5 01-08-2013, 11:37 PM

Still sounds like a B2 starting to Fail but a Filter and Fluid change is often the first step people take.
When I was troubleshooting I fundge a little and reused the ATF but changed the Filter.

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Govert · #6 01-09-2013, 05:50 AM

Did you check the vacuum?

It could be that if the oil is cold, it is more viscous, so that the oil pressure is higher, even when the oil pump is not performing to the max. Once the oil is hot, oil pressure drops, causing the problems of delayed engaging.

B2 piston as mentioned is also a possible cause.

You can check the oil pressures inside the transmission with a gauge.

KAdams4458 · #7 01-09-2013, 06:55 PM

Vacuum is fine, but in this case unrelated.

I can try another fluid swap in a few weeks, but I don't hold much hope that it will help. A sticky B2 might explain the issue, especially in conjunction with a weak or leaking pump. It's the whine that the pump seems to be making that really worries me.

Oh, what I wouldn't give for a manual transmission.

Diesel911 · #8 01-09-2013, 07:23 PM

Quote:

Originally Posted by KAdams4458

Vacuum is fine, but in this case unrelated.

I can try another fluid swap in a few weeks, but I don't hold much hope that it will help. A sticky B2 might explain the issue, especially in conjunction with a weak or leaking pump. It's the whine that the pump seems to be making that really worries me.

Oh, what I wouldn't give for a manual transmission.

In My case it was the Filter Change that helped as I reused the Fluid.

KAdams4458 · #9 01-09-2013, 08:37 PM

Well, the filter is already new, so I don't hold out much hope that changing it would do any good. The original transmission fluid was pretty dark, however. Maybe another fluid change will help.

Govert · #10 01-10-2013, 02:26 AM

Quote:

Originally Posted by KAdams4458

Vacuum is fine, but in this case unrelated.

No, it isn't.

KAdams4458 · #11 01-10-2013, 02:47 AM

That is not what I have gathered from the factory service manual. How does vacuum have anything to do with not engaging drive? Without vacuum, or too much vacuum effect shifting between gears, but the transmission should engage in drive regardless of vacuum condition. If that isn't the way it works, then there is some misinformation circulating... and my reading comprehension must be slipping. Lol.

KAdams4458 · #12 01-10-2013, 02:49 AM

How is vacuum related to a transmission not grabbing when drive is selected? I've been through the FSM, but never caught anything to suggest that.

Govert · #13 01-10-2013, 03:14 AM

Vacuum affects the oil pressure inside the transmission, so I would want to rule it out as a cause.

Dark transmission oil is not a good sign.

KAdams4458 · #14 01-10-2013, 03:29 AM

Quote:

Originally Posted by Govert

Vacuum affects the oil pressure inside the transmission, so I would want to rule it out as a cause.

Dark transmission oil is not a good sign.

Hmm. I still thought that only applied to shifts. Either way, the vacuum is perfect. And the old fluid was a little dark looking, but there was nothing worrisome in pan. The fluid just probably had not been changed for a long while.

Govert · #15 01-10-2013, 04:52 AM

In my experience, when you want to diagnose a problem, it is best to keep an open mind at first and start eliminating possibilities by testing and measuring. So if you say vacuum is fine I'm assuming you have used a vacuum gauge to test the workings of the VCV, tested the vacuum modulator whether it is air tight, and also checked if the plastic pin of the modulator was still in one piece.

How did the fluid smell?