Transmission shifting hard at low speeds?

[nehuge]

Hi there, have a '95.

The transmission shifts hard sometimes in 2 scenarios: (note, this happens when trans is cold in the morning (I know about the cat warmup module that delays shifts) and it also happens after hours of driving and everything is hot.

1) When upshifting at low speeds with barely little throttle only on the 1-2 shift. Think of going around the parking lot at the store from a stop, and if I give it enough throttle to creep and it eventually winds up to shift into second, sometimes it snaps your heck and feels like a kick in the back when it hits second.

2) What makes it do it most of the time is when you've been doing like 50mph, and slow down to turn at a light or turn down a street and then get back into the throttle not just barely, but a little more spirited than that that would justify it to kick down one gear, that kick down is just as snappy and kicks in the back with the same clunk as in #1 above.

So basically it does it at slow speeds with little throttle upshift 1-2, and then does it when you're already at speed, and slowing down to take a turn and a little more throttle for it to kick down.

The other shifts are all fine, no matter the throttle input or speed or kickdown. Even the kickdown on the freeway (both kick down levels) don't bang like #1 above.

It has done this like three years and I'm finally getting around to resolving it. It also did it before I did new diff bushings and new carrier bushings and new trans bushings and has done it after.

If I tune down the vacuum modulator then I get the 2-3 flare and the #1 and #2 above weren't really improved.
I even tuned it using a gauge in the side port to the psi on the specs. Filter and fluid are also brand new. Turning down the modulator a lot doesn't really change that "bang" much, maybe 30% less?

150k miles on this trans that I know of.

Vacuum modulator holds vacuum and doesn't really leak down, if it does it is over minutes to do so.

Ideas?

 

[gerryvz]

Replace the vacuum line going from the intake manifold down to the vacuum modulator.

 

[gsxr]

First confirm that you are getting correct vacuum signal at the modulator. You can test-drive with a vacuum gauge "teed" in at the modulator.

If the vac signal is normal and the pressures are set correctly, I'd replace the modulator next, if it's original.

 

[Benzy Boy]

I have this too 722.6 – R129
Maybe not as bad
Same procedure for me?

Sometimes I'm creeping at a light to make a left turn from stop and it just jerks me forward (shifts gears)

 

[gsxr]

722.6 is *completely* different, and is fully electronic... there is no vacuum signal, no vacuum modulator. If you changed the ATF on a 722.6 and didn't reset adaptation afterwards, I'd try that next... might help. Need a digital scanner that can talk to the TCU... I'm not sure if there's a keypad shortcut to reset without a scanner (@LWB250 ? @sixto?)

 

[nehuge]

First confirm that you are getting correct vacuum signal at the modulator. You can test-drive with a vacuum gauge "teed" in at the modulator.

If the vac signal is normal and the pressures are set correctly, I'd replace the modulator next, if it's original.

What hg of vacuum should I expect on this tee?

 

[gsxr]

What hg of vacuum should I expect on this tee?

It should vary with load... high vacuum at idle, low vacuum at WOT, and vary proportionally in between. I can't recall exact numbers offhand.

 

[nehuge]

acuum line going from

First confirm that you are getting correct vacuum signal at the modulator. You can test-drive with a vacuum gauge "teed" in at the modulator.

If the vac signal is normal and the pressures are set correctly, I'd replace the modulator next, if it's original.

One thing I did try with ignition off is to disconnect the vacuum line from the intake and put my mity vac on it. This way I put vacuum into the long vacuum line on the engine side all the way to the modulator. Pumped it up to like 25 or 30 or so, and it held it strong for like 5 minutes with no drop. Would I still have to tee in with it running as well?

 

[gsxr]

Your vac test confirms no leaks downstream, which is good. It would still be useful to verify vacuum readings are "normal" at the modulator. Based on what you describe, I'd be tempted to replace the modulator assuming it's original... but replacing the modulator is not a fun job, even with a lift. Very little space to work, and difficult to keep the bore clean once the modulator is out.

 

[nehuge]

Your vac test confirms no leaks downstream, which is good. It would still be useful to verify vacuum readings are "normal" at the modulator. Based on what you describe, I'd be tempted to replace the modulator assuming it's original... but replacing the modulator is not a fun job, even with a lift. Very little space to work, and difficult to keep the bore clean once the modulator is out.

Ya I've done one on another car. Hmm, wonder if maybe another vacuum leak anywhere on the motor can do this. I wonder if I should measure manifold vacuum of the port it is hooked to? What vacuum reading should that be?

 

[Alphasud40]

Do you have a 400E throttle body installed? if the shift selector is in D then you are starting in second gear right? So your harsh shift point is from 2nd to 3rd and 3rd to 4th is normal? If that is the case B1 is coming off and K1 is coming on. Most likely going to be in the valve body. I am going to be taking one apart soon and resealing the unit and cleaning the valve body. I bought a shift improvement kit that includes springs to alter the shift quality. Maybe placing a call to Sun Valley transmission to ask them. If it’s a valve body issue you might be able to buy one that has been reconditioned.

 

[nehuge]

Your vac test confirms no leaks downstream, which is good. It would still be useful to verify vacuum readings are "normal" at the modulator. Based on what you describe, I'd be tempted to replace the modulator assuming it's original... but replacing the modulator is not a fun job, even with a lift. Very little space to work, and difficult to keep the bore clean once the modulator is out.

Still going to replace modulator this week like you said since I have no history of it.

Nevertheless, here is the behavior the car has had since I got it, and just addressing it now that I have time.
I usually don't put freeway miles on the car as I am just in town but here is what happens:

While going freeway speed, when I push the throttle down a little bit it does the little what I call the "mini" downshift and that kicks down fine one notch and accelerates and upshifts when needs to.
However, when I really wanna hit it, when I push the throttle down hard to click the little kickdown switch under the gas pedal, it will downshift and kickdown fine, but instead of upshifting when the time is right, it kind of does a "rev limiter" behavior and won't upshift. I have to let off the throttle slightly for it to upshift.

I know I may be jumping the gun as I'm asking this prior to having the modulator replaced this week, but I guess I'm just adding to the story for the record.
Anything like springs in the valve body, or bowden cable or any other cables that could cause this short of the modulator? My bowden seems to be adjusted correctly with the car shift points being ok.

Here is the behavior I put on a video:

Anything to do with my severed VSS wire at my rear diff that I too will have replaced this week?

 

[gsxr]

Oh wow. Never seen that before (at 0:36 in the video, lol). That is not the transmission, that is engine management (HFM computer) limiting the revs.

What fault codes are present on the HFM (pin #8)?

 

[luckymike]

My '95 E420 does this exact same thing so I'll be following this with interest.

 

[gsxr]

My '95 E420 does this exact same thing so I'll be following this with interest.

Mike, the E420 computer system is very different... likely related to the EZL. Do you have fault codes, and is there a thread discussing your E420 issue? I vaugely recall something but my memory is swiss Cheesed these days.

 

[luckymike]

Mike, the E420 computer system is very different... likely related to the EZL. Do you have fault codes, and is there a thread discussing your E420 issue? I vaugely recall something but my memory is swiss Cheesed these days.

No to all. I'll just be a passive observer for now. It's a low priority at the moment...

 

[Alphasud40]

Other thing that comes to mind is a clogged catalyst if no fault codes are present. I agree with gsxr the transmission is working correctly. If your engine is down on power and as long as your pedal is depressed to activate the kick down solenoid it will stay in the lower gear until you reach the max RPM or lift off the throttle.

 

[nehuge]

I'll see what codes and what-not the shop brings up and what pins they found them on in the next couple weeks. I just like getting opinions here whether I'm taking it to a shop or not so I can be fully armed with information.
I have a couple of separate posts here with a myriad of issues with this car currently and whether they are inter-related or not.

Basically everything going on with my vehicle from my other posts where I have them in separate topics is this:

1) The vehicle speed sensor (VSS) on my rear diff had been replaced last year but the wire wasn't secured, and it ended up rubbing on the flex disc and rubbing through the wire sheath. That could maybe explain my sudden lack of cruise control and also this rev-limiting "won't upshift during kickdown gear behavior"...?
2) Also, if the ECU under the passenger floor is talking to this badly wired VSS sensor, that may reinforce #1?
3) The hard-shifting at random times could be vacuum modulator or a mixture of it and #1 or #2 above?
4) The other post I have where my ETA (electronic throttle actuator) is making a squealing sound, and my idle is kinda rough even after plugs/coils/wires, etc. Could it also be related to #1, #2, #3 above?

So a whole lot of stuff to look at that all may be separate or inter-related, I really don't know.
Worst case I do a new VSS at rear diff, new vacuum modulator, and new/rebuilt ETA?

I'm worried about this and any expenses regarding it. I am at a certain point now where I don't have time to wrench like I usually do.

 

[gsxr]

If you don't have a blink code reader yet... BUY ONE! They are cheap, click here. Get one with 4mm pins. No need to pay a shop to do this, although a good shop will be able to pull digital codes from HFM, which are far more specific than the blink codes.

@Alphasud40 has a good point about the plugged cats, but they would have to be severely clogged to cause that kind of rev limit - and, would still allow higher RPM if you had the shifter in 1 or 2 and more slowly approached redline (this would be a good test to try anyway). Clogged cats would likey have other symptoms as well.

What ECU is under the passenger floor? I thought only the Becker alarm box was in that location on M104 cars.

Hard shifting would be related to the transmission, likely vacuum or modulator.

VSS is unlikely to cause issues, but ETA could... contact Victor about a repair/rebuild.

 

[TerryA]

@gsxr,
I have never used a blink coder. I have used the blink code button provided by MB in the past. Referring to the chart the was posted here years ago which I haven’t seen in years.

Clicking on your “click here” reference in post #19 above it appears that the first two coders have different pins. You mention get the one with 4mm pins.

1. Of the 1st two up one appears to have RCA plugs and the 2nd has another type of plug. Are either of these 4mm?

2. Not having ever used this device. I understand where to plug the black and red pins in the 38 pin MB receptor. Where do you plug the yellow test wire?

Again I must mention that I have had only one (1) “check engine” light in my 19 years of ownership and it was 19 years ago. It turned out to be the air intake sensor behind the DS headlight. It was replaced with w/ an MB/OE part that cost about $10 at the time BUT I paid MB of Long Beach $120 for the diagnosis.

Anyway, Will this $35 coder help to avoid this the next time?

 

[gsxr]

The built-in blink code button+LED only shows fault codes for the Diagnostic Module (DM), which will only have codes if the CEL is on. There can be fault codes on other systems, but the DM/CEL only turns on when there are emissions-related faults.

You need the separate, hand-held blinker box to check other fault codes on other modules, including HFM. Use this document for M104-HFM cars.

The code readers with larger (4mm) plugs are for 8- and 16-pin diagnostic ports, including your W124 E320's. The yellow test wire plugs into the numbered port on the diagnostic connector. Read the document linked above for more info on which port number is for which system (i.e., HFM, ABS, etc).

 

[nocfn]

I remember when I first got the car when that Rev limiter kicked on...... I thought I blew the engine. DOH!

 

[nehuge]

If you don't have a blink code reader yet... BUY ONE! They are cheap, click here. Get one with 4mm pins. No need to pay a shop to do this, although a good shop will be able to pull digital codes from HFM, which are far more specific than the blink codes.

@Alphasud40 has a good point about the plugged cats, but they would have to be severely clogged to cause that kind of rev limit - and, would still allow higher RPM if you had the shifter in 1 or 2 and more slowly approached redline (this would be a good test to try anyway). Clogged cats would likey have other symptoms as well.

What ECU is under the passenger floor? I thought only the Becker alarm box was in that location on M104 cars.

Hard shifting would be related to the transmission, likely vacuum or modulator.

VSS is unlikely to cause issues, but ETA could... contact Victor about a repair/rebuild.

I do have a code reader, a little 3 wire thing and it was pointing to the VSS at the time (can't remember which code), and that is when I didn't know that was pointing to the sensor at the back of the cluster or the sensor at the differential.

I'll see what codes the shop pulls this week.
Their update to me today was that they replaced the diff's VSS under warranty (lucky for them, as a wagon, I have a very strategic razor blade slit in the carpet under the butt part of the folding rear seats, to where the pivot points of the backrest of those seats hide the slit in the carpet. It is VERY convenient to have, as you can just peel that part back, get to the vacuum pump, the diff's VSS's connector, etc and then plop the carpet back into place like a little access trap door and you can't see that it is cut or where the two seams meet) Otherwise they would have to have taken the door sill plate off, and some of the felt around the door opening, and get under the carpet from the side, etc. and they took it for a drive and now it has cruise! And no related CEL either. So that's a good step. Perhaps that takes the ETA being related to the cruise inop out of the equation. I'll still have them look at the ETA's "squeal" however.

Shop did mention cats as one thing to consider but he'd have to verify. Wouldn't heavily plugged cats though make my car gutless? I think it pulls as it should, very healthy power.

The ECU under the passenger floor is like this one (just found a pic of it randomly online): and I have a couple spares just in case (even though at the time trying each spare didn't make a change with my cruise and CEL, neither did trying a spare sensor at the speedometer but now those two things are out of the picture since the replaced diff VSS shows no CEL's and cruise works.



Following your suggestion to swap out vacuum modulator no matter what, even if it holds vacuum for a long time, as does the vacuum line going from the intake to the vacuum modulator at the transmission doesn't meant that it isn't having trouble "modulating" varying vacuum. My W126 years back had the little plastic rod inside of it cracked and it made stuff act funny even though the modulator held a vacuum. Plus, on the floor at 50 years old with floor jacks, the modulator is something I did on my W126, but don't want to do again myself on this car so while the shop has it they're gonna do it.

Shop said that if the modulator replacement doesn't fix those certain hard shifts that they may make sure the valve body doesn't have any broken springs. I did do the K1 spring last year for 2-3 flare, which helped, but again with that 1-2 hard shift and 30 mph "mild" kickdown being so jolting, turning down the modulator pressure helped (and I even tested it with the side port with a gauge) but then it was too soft and the 2-3 flare would come back until I turned the modulator back up. We'll see what they find.

 

[gsxr]

Checking the VB for broken springs is a good idea, although messy and tedious. And, the only replacement parts available are for K1 and K2... anything else, you need to source a used VB to raid parts from.

That control module under the passenger floor is the T/LLR module, this is the CC/ISC (cruise control / idle speed control) unit for the ETA. I haven't owned an M104 car in years, I forgot that was located down there!

 

[nehuge]

Little update on this one...shop called and one of the bolts for the modulator was rounded or damaged or something so they had to put some time into extracting it, possibly drop trans a couple inches for ease, etc. They did say that the plastic pin/piston inside the modulator was indeed broken, so maybe that is the problem. (i.e.: holds vacuum, but can't keep up with varying vacuum with broken part inside), and that they'd drive it this weekend and set the modulator and see its behavior. Perhaps it fixes that weird passing gear redline thing as previously mentioned, so I anxiously await. It if does, maybe they'd not have to go looking for broken springs in valve body and not have to drop the pan, fluid, etc as a result (more $$).
So cruise working...check.
Modulator working?....check?
Last things are the ETA squealing (if it is even it, they seem to think it may be the blower motor squeaking but not sure if I had the blower on when I hear this squeaking). That still doesn't speak to rough idle so not sure. Additionally I am having them do a valve cover gasket, and especially the o rings on the cover itself that surround the spark plugs as #5 and #6 did have oil on the threads when I went to change my plugs out a few weeks ago. Maybe oil on the spark plug is making it fire badly?

 

[gsxr]

Is the squealing noise heard while driving? If so, that ain't the ETA. If you hear squealing while driving, turn the HVAC to "Off" and if the noise stops, it's the blower motor.

A small amount of oil on the spark plug threads is normal, as long as there's no oil in the spark plug wells. The electrode and insulator should be clean and dry though; if those are oil-soaked, something is wrong.

 

[nehuge]

Is the squealing noise heard while driving? If so, that ain't the ETA. If you hear squealing while driving, turn the HVAC to "Off" and if the noise stops, it's the blower motor.

A small amount of oil on the spark plug threads is normal, as long as there's no oil in the spark plug wells. The electrode and insulator should be clean and dry though; if those are oil-soaked, something is wrong.

The squeal happens with no throttle and as I give it throttle it stops.

The plug wells on #5 &6 had oil but not electrodes.

 

[gsxr]

The squeal happens with no throttle and as I give it throttle it stops.

Perform the test mentioned above. I still think this is extremely unlikely to be the ETA.

The plug wells on #5 &6 had oil but not electrodes.

Oil in the plug wells indicates a valve cover gasket leak that needs to be remedied. If the electrodes were clean, this probably wasn't affecting ignition, unless there was evidence of arcing on the upper plug insulator, where the rubber boot attaches.

 

[nehuge]

Other thing that comes to mind is a clogged catalyst if no fault codes are present. I agree with gsxr the transmission is working correctly. If your engine is down on power and as long as your pedal is depressed to activate the kick down solenoid it will stay in the lower gear until you reach the max RPM or lift off the throttle.

No codes present at this time. Shop seemed to think the B1 was going. Only solution from them was recommend me getting a remanufactured transmission. I'd like second opinions before doing this. Also, I think they're starting to have a year cut-off as a shop as they are running into NLA for these older models too and may just be telling me this because they don't want to mess with it. They never did look at the VB and its springs.

Good thing is the cruise now works, no more cruise or VSS codes. Even when the vaccum modulator had the broken plastic pin on the inside that didn't seem to remedy that "clunk" I'm having as indicated in my higher posts. Any ideas?

I still need to get the HFM pin 8 readout to see if any codes.