Intermittently Not Going into R or P from D

[emerydc8]

I am not able to get the gear shift lever into R or P when parking. I thought it might be the Neutral Safety Switch so I replaced it with my last NOS and adjusted it as per the factory manual, using an Allen wrench to pin the two holes in the switch (pic). The reverse lights illuminate when shifting to R. I also changed the shift bushings and, while I was there, changed the transmission fluid with Valvoline Dexron III along with a new filter. I tore the old filter apart and there were no broken pieces inside. It looked spotless. The pan looked fairly clean--nothing but the expected friction material after 30,000 miles (pic). This transmission has 106,000 since it was rebuilt and has given me zero problems since buying the car in 2013. Reverse has very little delay (1/2 sec.). The fluid level is just below the 180 F mark when hot and on level ground.

The intermittent problem of not being able to get into R (and then P) from D has occurred so far only after coming to a stop from fourth gear. I can eventually get it to work by shifting back into D and trying again.

My driveway is at the bottom of a hill and as I coast down the hill towards the driveway, which transitions to an up-slope, I noticed it shifts into fourth at speeds as low as 10-15 MPH. I don't recall it doing this in the past. Usually I could feel the transmission acting as a brake while coasting downhill but I noticed lately that I have to use the brakes to keep the speed under control. I usually have enough momentum to coast into the parking spot without having to give it any throttle. I'm not sure how this works, but if it actually is downshifting to first when this problem happens I'm not able to feel it. But I'm also not able to feel it downshift to first when the problem isn't occurring and it must be because it starts out in first after a stop light (this is a 124.034 by the way).

I checked the connecting rod as per the manual and the tips at the crank are exactly opposite of each other. The up-shift points feel normal and commensurate for the throttle input. Since my driveway slopes up hill I always put the car in N and set the parking brake before going into P, so the parking brake--not the transmission--keeps the car from rolling backwards.

The only significant event I can think of that occurred a few weeks before this problem started is a one-time inadvertent "crash engagement" of the transmission while transitioning from N to D. With 110-degree ambient summer temperatures in Tucson, I have a habit of shifting into N while sitting at long stop lights to minimize heat generated by a slipping torque converter. I was distracted at one light and was late shifting to D as the car in front of me started to pull away. As I started to increase throttle I felt the bump just above idle as the transmission finally shifted to D--the same as you would expect when shifting to D normally but at 1000 RPM it is much more notable and I'm sure it wasn't good for the transmission. Whether it caused the problem I'm having now I do not know.

In summation, I've done the following:
Replace NSS
Replace shift bushings
Changed fluid & filter
Verified connecting rod and tips at crank are aligned
No apparent obstructions to the shift linkage

I'm not sure where to go next on this one. Any input would be appreciated.

 

[nocfn]

Have you ever removed the valve body to clean it out?

 

[emerydc8]

Never. Is that a routine maintenance job? It looks complicated—like I could really screw it up. But I’m willing to try if a clog could be the culprit.

 

[gsxr]

The intermittent problem of not being able to get into R (and then P) from D has occurred so far only after coming to a stop from fourth gear. I can eventually get it to work by shifting back into D and trying again.

Jon, I have a "sticky" shifter in one of my 400E's and I haven't yet solved it. The trans is a low-mile rebuild and otherwise has no significant issues. Linkage bushings are good. I suspect it's something wonky inside the shifter mechanism itself (the black rectangle that sits atop the tunnel) but so far, moving the lever back & forth gets it into the desired gear location. Since it's very intermittent I've not been able to dive deeper into it.

The only significant event I can think of that occurred a few weeks before this problem started is a one-time inadvertent "crash engagement" of the transmission while transitioning from N to D. ... Whether it caused the problem I'm having now I do not know.

I really doubt that caused any problems.

In summation, I've done the following:
Replace NSS
Replace shift bushings
Changed fluid & filter
Verified connecting rod and tips at crank are aligned
No apparent obstructions to the shift linkage

I'm curious if the obstruction might be in the shifter assembly itself, not the transmission. This would be tough to verify without having the transmission not want to go into P/R and then disconnecting the linkage, and seeing if the transmission lever moves normally.

I'm not sure where to go next on this one. Any input would be appreciated.

The valvebody is not likely to be the cause of the P/R issue, the VB primarily controls shift quality and shift points. If you have a spare VB you could swap it for grins but I suspect there won't be much change.

 

[nocfn]

I do not believe that it is, I was just asking. When I had my Trans rebuilt, they put in the e420 valve body in for me. The shop said that both the OE and my FGS valve bodies had some residue that would continue to build if not cleaned.

 

[nocfn]

Good thought GSXR, come to think I had some issues where I thought there might be a sloppy shift experience on the c126 and there was a loose nut on the shifter itself and also the spring holding it tight was a bit sloppy. Removing the vanity surround and having a look in the shifter area may reveal something to be corrected and it is simple to rule out an issue there.

 

[gsxr]

Never. Is that a routine maintenance job? It looks complicated—like I could really screw it up. But I’m willing to try if a clog could be the culprit.

This isn't "routine maintenance" and it's a tedious task, that requires a very clean environment and lots of careful disassembly / reassembly. There should be some videos online showing what's involved. Take lots of photos so you get the little balls back where they belong. I've never done this personally, but have a couple of problematic VB's that I'd like to try cleaning someday...

 

[emerydc8]

Thanks Dave (and @nocfn). I didn’t know about the shift mechanism box. Maybe that’s the problem. It’s strange the it would be intermittent though. Is that accessible through the top?

The shifting into high-gear at such a low speed is something new and bothersome. Is the horizontal connecting rod the only way to adjust shift points? I presume adjusting downshift points would also affect upshift points.

 

[gsxr]

Thanks Dave (and @nocfn). I didn’t know about the shift mechanism box. Maybe that’s the problem. It’s strange the it would be intermittent though. Is that accessible through the top?

Accessing this is a PITA. The entire assembly must be removed from above, but I'm not sure if the console has to be removed first. And, I'm not sure if this is the problem... or if you'd be able to repair it?

The shifting into high-gear at such a low speed is something new and bothersome. Is the horizontal connecting rod the only way to adjust shift points? I presume adjusting downshift points would also affect upshift points.

This is definitely unusual. The horizontal connecting rod adjusts all part-throttle shift points. You can experiment with this but I don't think it will fix the "new" problem. The connecting rod is fairly sensitive, only change a few mm at a time for coarse adjustment, less for fine adjustment. This is free and pretty easy, so it's worth a try.

I'm not familar enough with the 722.3 to speculate what might be causing this issue, assuming the connecting rod adjustment doesn't help. @Klink might have some ideas though.

 

[doolar]

This isn't "routine maintenance" and it's a tedious task, that requires a very clean environment and lots of careful disassembly / reassembly. There should be some videos online showing what's involved. Take lots of photos so you get the little balls back where they belong. I've never done this personally, but have a couple of problematic VB's that I'd like to try cleaning someday...

It is not difficult at all, there’s lots of documentation too. But of course documenting yourself is a must imo.

I will disassemble the FGS VB I just bought, if I get time I can make a How-to on it.

 

[emerydc8]

Today when the problem occurred I left the gear selector in N and shut the engine down. Then moved the key to the run position. Sure enough this allowed the selector to go right into R and P. I'm wondering if this has something to do with the cable interlock between the ignition switch and the gear selector--the one you have to unscrew when changing the ignition switch.

 

[nocfn]

 

[emerydc8]

Last night I replaced the stop lamp switch but it did not help. I found that when I am unable to get the selector into R or P, I can turn the engine off while still depressing the brake pedal and it goes right in—no need to turn the key back to the run position.

I have looked in the EPC for the cable lockout between the gear selector unit and ignition switch but can’t find it. I’ll have to dive into this next although I haven’t decided which end to examine first. I’m trying to determine if the cable is still available in the event I need one.

 

[gsxr]

Jon, the shifter mech & cables are in EPC Group 26. Both the cables are NLA per the MBCC site, although I'm sure plenty are available used from junkyards.

Either or both of the interlocks (ignition switch & brake pedal) can be bypassed/eliminated if desired. Early 124's did not have these, the interlocks were added for MOPF1 (USA 1990 model year) IIRC.

 

[emerydc8]

Thanks Dave. I looked for an hour but didn’t see it. I didn’t realize that the brake lockout is mechanical (cable) too. This helps.

 

[JeffSpicoli]

@emerydc8 did you ever get to the bottom of this? I have the same issue and was about to replace the stop lamp switch (even though my brake lights work perfectly).

A shop looked at it and thought that the shifter mechanism was the culprit.

 

[emerydc8]

Not yet, but I am waiting for the brake stop lamp switch to arrive from Laredo. I unscrewed the cable that goes between the ignition assembly and the gear shift assembly thinking that if I removed the cable it would eliminate the problem, but I found that the key wouldn't come out of the tumbler without the cable inserted.

I had an old stop lamp switch which I installed a few days ago to troubleshoot. It didn't do anything to help the problem of not getting into R or P but I noticed I no longer have cruise control so that switch is definitely bad. The strange thing is that wrote on the bag for this used switch that I was unable to get the car into R or P. I didn't write whether it fixed the problem but it might have. I don't even remember this. I'll find out and report back when I install the new switch.

 

[gsxr]

Not yet, but I am waiting for the brake stop lamp switch to arrive from Laredo. I unscrewed the cable that goes between the ignition assembly and the gear shift assembly thinking that if I removed the cable it would eliminate the problem, but I found that the key wouldn't come out of the tumbler without the cable inserted.

Jon, if you'd like to disable either or both of the ignition interlocks, more info is here. I think the interlocks appeared in 1990 USA model year / MOPF1?

 

[JeffSpicoli]

I was about to do the same (replace the switch) until i saw your other thread while i was looking for the part number. I rarely drive this car and recently have started "exercising" it more. Might be imagination but I feel like it's getting better meaning easier to get it to go to park, less fiddling around with the stick.

 

[emerydc8]

Jon, if you'd like to disable either or both of the ignition interlocks, more info is here. I think the interlocks appeared in 1990 USA model year / MOPF1?

Hi Dave,

I cut both cables for the shift interlock as per your post and I continue to have the same problem: In situations where it would not go into D or P before, it will still not go into D or P now, unless I turn the key off like before. Are there any other interlocks? Maybe something inside in the transmission?

For those considering deactivating the interlocks, in what is probably an unintended consequence of cutting the cables, the brake pedal takes a disproportionate amount of initial force to break it free from the static position, but once past that the pedal pressure feels normal. I suspect that is due to the lack of spring pressure at the shift assembly. I can get used to it.

 

[gsxr]

I cut both cables for the shift interlock as per your post and I continue to have the same problem: In situations where it would not go into D or P before, it will still not go into D or P now, unless I turn the key off like before. Are there any other interlocks? Maybe something inside in the transmission?

Well shoot. At least we know the interlocks aren't at fault. There should not be anything inside the transmission preventing the shift lever movement, AFAIK. This is a really rare problem, or at least I've only heard a couple of people ask about it.

For those considering deactivating the interlocks, in what is probably an unintended consequence of cutting the cables, the brake pedal takes a disproportionate amount of initial force to break it free from the static position, but once past that the pedal pressure feels normal. I suspect that is due to the lack of spring pressure at the shift assembly. I can get used to it.

Oh that is WEIRD. I didn't experience this on any of the cars where I disabled the interlocks. I wonder what the cause is!

 

[emerydc8]

Both issues are mysteries. I thought I might have screwed up and cut something else like vacuum lines so I pulled the center console cover and rechecked. Both cables go right to the shift assembly. The only thing I can think of is that somewhere in the 722.3xx manual there is mention of a safety feature that won’t allow the transmission to go into R while moving forward but I don’t know if that means the lever itself or something internal. If the safety feature is getting a faulty signal maybe it won’t release it until the ignition is turned off or the TC stops rotating. I certainly don’t want to test this feature while moving forward though. I changed from Febi (AutohausAZ) shift lever bushings to dealer bushings this week because after only 9 months the Febi bushings developed some play. The new bushings are tighter and I noticed the Febi turned hard and are a yellowish color from the heat. No surprise there. New bushings had no effect on my problem though.

As I mentioned in the last few paragraphs of my OP, supra, this problem occurred after an inadvertent crash engagement from N to D as the RPM was around 1000. I could feel the bump—kind of like if you're in a hurry backing up and you've ever moved the shift lever to D before the car comes to a complete stop. I think it may have damaged something with the shift input mechanism.