Om617 revving up and down at the top of 2nd/3rd gear - PeachParts Mercedes-Benz Forum

qwerty333 · #1 03-18-2018, 02:33 PM

I've been experiencing this issue for a few months now and was hoping somebody could help me out

hopefully I won't need a new transmission

My 1983 300d turbo has about 300,000 miles on it, and since I got it with 277k miles on it, it always had this little flare/hesitation at the top of 2nd/3rd gear but it seemed to go away once the engine warmed up and i figured it's probably normal

Now, it has progressed into a slightly more worrisome issue

Instead of a little flare, the engine RPM will start revving up and down for 3-4 seconds quite fast, before shifting to the next gear. It's not a violent shake or anything but it's quite noticeable and definitely more pronounced than before. It's acting like somebody is pushing and release the gas pedal a little bit every half-second

This also seems to go away when the engine gets warm.

Would this be an issue with the engine? Or is the automatic transmission failing?

I would appreciate any advice you guys can throw my way

CDTurbo001 · #2 03-18-2018, 04:23 PM

If it does it on the 3-4 shift, can you put the shifter in "S" and, both accelerating gently and aggressively, let it pass the RPM point where it would usually start doing its thing and see if it still does it at said RPM but without the shift? It sounds like the trans. slipping and trying to hook up repeatedly, but that exercise could narrow down if it's the engine wavering or the transmission failing to shift like it should (shift flare).

Secondly, locate the vacuum line to the transmission modulator (black, comes off a T from the vacuum control valve on the injection pump and goes down behind the engine) and disconnect it, then test drive normally and see what it does. This will supply more pressure to the transmission functions and firm up the shifts, so if it's indeed lazy shifts that this improves you know which area to dive into.

Try those two things and let us know.

Diseasel300 · #3 03-19-2018, 10:17 AM

Craptacular shifting from 2-3 is a well documented issue involving the K1 accumulator spring in the transmission valve body. Depending on what failed and how it failed, you can have abrupt shifts, stacked shifts (shifting rapidly 2-3-4), flaring, hesitation, etc. What symptoms you have depends on where the spring broke and how many pieces it's in.

The first thing to do with transmission issues is drain the pan and Torque Converter and replace the filter. While you're in there, change that K1 accumulator spring, it's a DIY job and takes only a couple minutes. See where that gets you.

Old fluid, wrong fluid, clogged filter, valve body problems can all cause shifting issues. Replacing fluid and filter gets you fresh oil and a clean detergent additive. Sometimes that's all it needs to flush out any sort of gunk in the valve body.

Mxfrank · #4 03-19-2018, 01:26 PM

+1 K1 accumulator spring. I wouldn't bother checking, the kit is cheap enough to just replace. The function of the accumulator is to feather the shift like your foot on the pedal of a clutch car. If it's too quick, you get a harsh shift, too slow, you get a flare as you go into gear. When the spring and piston function correctly, you engage the gear smoothly.

qwerty333 · #5 03-21-2018, 01:21 AM

thank you, I will change the fluid and install a new spring kit and will let you guys know what happens! Thank you so much

qwerty333 · #6 03-31-2018, 11:12 PM

Ok....wow....so this is embarassing

Somehow it didn't come into my head to check the level of the transmission fluid. So I pulled out the stick while the engine was warm...completely dry

Went and bought 1 quart of ATF. I poured in half...still completely dry. Poured the rest...still dry.

Bought another bottle, poured half...just the tip of the stick was wet.

Ended up having to use almost the full two bottles of ATF before it was at the correct level on the dipstick.

Immediately the transmission started working perfectly.

Last week I ordered the K1 spring, along with the filter and transmission seal, so I'll do a transmission flush & replace the spring anyways when it all arrives

Hopefully I didn't damage the transmission

CDTurbo001 · #7 04-01-2018, 03:32 AM

Ha! Shame on all of us for failing to cover that base. Glad you figured it out - hopefully it keeps working well.

Diseasel300 · #8 04-01-2018, 11:05 AM

This is another good example of why you should keep an eye on your fluid levels. Old car or not, it's a good idea to run an eyeball over things at least once a month at a minimum. You can often catch a problem before it becomes a catastrophe or breakdown.

If the transmission is working normally after topping up the fluid, there's likely minimal damage done. Drip the fluid on a paper towel and look at it and smell of it. If it's still red and doesn't smell burnt, you're in good shape. If it's brown or smells burned, there may be some damage done to the clutch linings from slipping, but likely minimal if the transmission is working normally with adequate fluid. Change the fluid and filter and move on with life. They're pretty tough old transmissions all things considered.