540i 6-speed sometimes difficult to shift

[JuzWerkz]

Greetings all,

I have a strange problem with the 6-speed manual transmission (and/or shifter) in my 2001 540i. I have searched this & other forums and have found a few similar threads, but none where an actual solution was discussed. If anyone can point me to a thread where this was resolved, I would greatly appreciate it.

For about a year, my daily driver 540i occasionally becomes very difficult to shift, as though something has physically moved in the path of the shifter or rails, and it feels as though the lever or something in the linkage hits a hard stop before the synchro lock ring can fully engage. When this phenomenon occurs, multiple gears are affected, and not always the same ones. The car remains in this state for a few days, and then, as suddenly as these symptoms occur, they disappear, and the car drives as normal again, sometimes for a month at a time. Then the cycle repeats.

When I first experienced this, I had already noticed my clutch was slipping in 6th gear, and I wondered if maybe the self-adjuster mechanism may be causing this as it stepped over the last ramp & started the cycle again. I just got the car back together about a month ago after changing the clutch, pressure plate, TO Bearing, flywheel & Pilot bearing, as well as doing the full VANOS/Timing Chain Guide replacement. When I first drove it, I thought this problem had also gone away, but last week, it came back. This morning, it went away again.

This time around, it was difficult to engage R, 1, 2 and 4, with 4 being the worst. Even when double clutching, it was difficult not to grind going into 4th.

I noticed that I could push the shifter forward into 1st until I hit the stop. Then as I let out the clutch to the point where the input shaft would start spinning, I could hear an audible clunk as the synchro would "suck" the locking ring the rest of the way into position to engage the gear. Having worked for a transmission company (not ZF), I know that this is NOT good for the life of the synchros, but I'm struggling with the idea that wear on the synchros themselves is what is causing this. I don't see an explanation for why this would come & go.

What would make sense to me would be wear on the detent pins similar to the issue seen on some of the 5-speed cars. If the pins were worn on one side, and rotate in their bores so that sometimes they operate as intended, and sometimes they catch & act as a stop. But that's pure supposition on my part.

Has anyone else experienced this, and more importantly, has anyone found an effective solution?


Thank you very much,

cj

[edjack]

When did you last replace the clutch master and slave cylinders? Or even flush the circuit?

The 6-speed has a fix for detents, but it's strictly for the situation where one cannot shift out of 3rd.

Make sure there is no play in the shift linkage.

[JuzWerkz]

I did replace the external bushings in the shifter as well as the transmission mounts while it was out. There does not appear to be appreciable play in the shifter.

The hydraulics were not flushed with the clutch swap, but I did not have any significant evidence that it was an issue. This feels much more like a mechanical blockage. Even when the blockage is happening, the clutch is still definitely slipping (open), so there isn't a complete hydraulic blockage.

I agree that some debris in the hydraulic system could cause intermittent functionality of the hydraulics, but I do struggle with the idea of it leading to this behavior. Next time it happens, I'll see if I can figure out a way to measure a difference in clutch pushrod travel...

cj

[geargrinder]

A clutch that drags and only partially disengages can act like that, refusing to go into gear and feeling "locked out". If your clutch is slipping also, maybe your PP is indeed jammed up and neither opening nor closing fully? Just spitballing.

[waters17]

I had a somewhat similar issue but only with 2nd gear. I wasn't able to quickly shift from first to second. It was like the shifter hit a stop. I'd try and try, but It wouldn't engage. It was never consistent, so I would never be prepared for it either.

This was very scary since it usually happened when I was trying to turn out onto a busy road. Double clutching was ineffective and the only remedy was to shift to third, which bogged down the engine and caused me to go incredibly slow, causing traffic to slow, which made me look like a jerk/idiot. Gradually, the problem became more frequent.

My theory was that it was some sort of hydraulic issue. I removed the CDV and bled the system about 4k miles ago and haven't had any issues since.

[geargrinder]

2nd is always the balkiest in these trannies for sure. Generally they hate to go into 2nd when weather gets cold as most people will notice. In winter I often do the 1st-to-3rd routine, which isn't bad if you're planning for it, but sucks if you get jammed up and aren't ready, as you say Waters...

[ND4SPDLSC]

The difficulty in shifting indicates some damage to the 2nd gear syncro and is exacerbated by old fluid. Frequent fluid changes with MTF LT 2 which is the BMW spec fluid is the best recourse. Royal Purple has also seemed to work but I stuck with factory fill based on their more sxhaustive testing. Obviously, not forcing the shift is key. I sometimes just skip second when cold. New fluid will help a lot.

[JuzWerkz]

I was just going through some old posts and I see that I never closed out this thread. I did ultimately solve this issue. The main shifter detent shaft in the transmission was broken. When I pulled the plug out, I was able to withdraw the spring and most of the detent plunger. The plunger is a hollow shaft with a fork on the end that pins a bearing which must ride on the shift shaft. When I pulled the shaft out, the fork was broken and the bearing was gone. When it would stick, this shaft must have rotated into place to block it. Then it would rotate to another position where the shaft would move freely. I replaced this part shortly after the last time I posted to this thread and never had another problem with it since. The engine running correctly is another story...

[edjack]

Where did you get these parts? Getrag does not provide internal parts.

Mine is always difficult when cold. I shift gingerly until it warms up. I run Redline MTL.

Don't force it; I understand the shifting forks are aluminum, and can be bent.

This is a brawny gearbox.

[JuzWerkz]

I don't believe the issue I had was the same as the "difficult when cold" issue everyone else experiences. But the detent plungers and springs are (or were) still available as shown here:

https://www.realoem.com/bmw/enUS/sho...21#23311282539

I replaced items 8, 9, and 15. It was item 8 that was broken on mine. I bought the replacement from the BMW Mini parts store.

cj