95 M3 5spd manual shifting problem

[NoLastName]

Howdy. New 1995 M3 owner and this is my first post! Did some searching but was unable to find posts with the exact same symptoms I have. Before starting I'll say that I'm mechanically adept (though not a professional mechanic) and have done several clutch jobs previously (but this is my first BMW job).

So... the input shaft bearing on the ZF manual in my car was shot, so rather than rebuild I sourced a used transmission from a BMW recycler. The replacement tranny was the same ZF as what came out of my car. Did the install over the weekend (what a royal PITA). Since I had the engine/tranny apart I dropped in a UUC lightweight flywheel, new clutch and related internal components. Also replaced the shifter bushings & coupler, guibo, center driveshaft bearing, motor mounts and transmission mounts.

Now that it's all back together the clutch works fine and the shifter feels great, but the car refuses to stay in 2nd or 4th gear. Reverse, 1st, 3rd and 5th all work fine. In other words I can access gears where the shift knob is pushed forward.

However, if I select 2nd or 4th - where the shift knob has to be pulled back - the transmission will pop out of gear violently as the clutch is released. Going by feel it seems like the shift lever is bottoming against the carrier before the selector rod pushes the transmission fully into gear. Tonight when I get home I'm gonna pull the console shift boot and see if that's actually the case.

Now... I'm thinking because I only have difficulty selecting the two gears that require the shifter to be pulled back, this is a shift linkage issue and not synchros. The 2nd and 4th gear synchros aren't related, right? Am I on the right track here?

The stock shifter and selector rod worked before the install and those parts were not changed... only the bushings were freshened up and a new shift coupler installed. The funny thing is the shift lever appears to be laid back at a bit more of an angle than it was previously. Like, when I look at the shift knob I'd think the tranny is in 2nd gear but it's actually in neutral. How could the geometry change if the shift lever, selector rod and shift carrier were not changed? Are there different length shift couplers available? I'm kinda stumped.

[Jeron]

If you are positive the trannys are the same, the I would reinspect the assembly of the shift linkage. There are at least two shift couplers. I know what they look like (I was shipped the wrong one) but I never really examined the length.

[NoLastName]

Last night I pulled up the shift boot and sure enough the shift lever bottoms on the carrier when I pull back to engage 2nd and 4th. Something is off.

The new tranny is exactly the same as the one that was replaced. The selector rod, carrier and shift lever are the exact pieces I removed and then reinstalled. But the shift lever geometry is definitely not the same as it used to be. It's almost as though the selector rod lost 1/4-1/2" in length. The only linkage part I can think of that would change distance between shift lever and tranny is the one part that was replaced - the coupler. But that appeared to be exactly the same as the old one too. It's the correct M3 style and not the different looking 325 style coupler.

The only other thing I can think of that might be different is maybe the gear selector shaft on the tranny doesn't stick out of the housing quite as far as the old one. Is there an adjustment for this lengh on the ZF transmissions?

This weekend I'll go back under to inspect things. Still have the old coupler, so I'll measure it and compare to the new one. I'll also measure the transmission selector shaft extension.

[NoLastName]

Ok... 99.9% sure it's the shift coupler now. The one that came off the old tranny is the sort of t-shaped coupler that Pelican Parts says is for the 318. The new coupler I installed on the new tranny is what's supposed to be the M3 coupler but apparently isn't in my case. The new coupler I installed is shorter in length than the 318 style coupler, which should account for the change in shifter geometry.

This weekend I'll swap back to the old coupler and see if that gets me squared away.

[NoLastName]

Good news and bad news. The good news is it was the shift coupler that changed the shift geometry on me. The one I got, though it was supposed to be for 95-99 M3, was not the coupler my 95 M3 needed. So I put the old one back in and the shifting is back to normal.

The bad news is the input shaft bearing on the junkyard transmission I installed is in no better shape than the previous tranny. It makes a different kind of noise but it's still a jacked up input shaft bearing. All that work for nothing...

[Jeron]

Are you sure its not another issue? What are the odds of two trannys with the same issue.

[NoLastName]

Jeron - I'm positive it's the input shaft bearing. When I did the job I replaced the guibo and center diff bearing, transmission and engine mounts, clutch, pressure plate & throwout bearing all at the same time.

The transmission is perfectly quiet when the clutch pedal is held to the floor in neutral or any gear. However, with shifter in neutral and foot off the clutch there's a nasty whirring, grinding/popping sound. It goes away when I press the clutch pedal, at which point I can easily hear the input shaft spinning down. Then if I lift the clutch pedal slowly the whirring noise comes back right at the clutch engagement point. The noise is present only when the input shaft is spinning. It's really noticeable when the car is idling, but when driving I can also hear the bearing protesting if I accelerate or decelerate.

The recycler I bought the tranny from will send me another unit - I'm just not looking forward to doing the work again. At least this time I know exactly where all the bolts are and how to reach them.

[Jeron]

Did you also replace the pilot bearing?

I feel your pain. I had a problem with a new flywheel so I had to do the job 3 time. Old -> New then New-> Old (needed the car for a track day so I couldn't wait) then Old ->New again when the part came back.

[NoLastName]

Yep, pilot bearing is new too. I've done enough clutch jobs to know it's cheap insurance to replace everything inside the bellhousing.

The next sad chapter is that I got home last night to find the replacement transmission the recycler sent (so now I have 3)... and the splines on the input shaft have huge chunks gouged out of them! It looks like a clutch disc broke apart on it. I swear everyone who owns these cars must get their kicks by doing 5,000 RPM clutch drops. Guess I'm gonna have to return this one.

I had hoped to avoid the cost of a full transmission rebuild but at this point it looks like my best hope is to just suck it up. Before this car I drove Miatas and reliable used parts were easy to source for those. Evidently not the case with M3s.

Any idea if it's possible to replace the input shaft bearing without cracking the case open? The ZF spare parts diagram show it's held in place with a circlip, but I'm not sure if it's possible to get the bearing to fall out without a puller.

[Jeron]

I dont know, but I have been wondering what it will take to rebuild mine. My syncros are slow when it is cold. Nothing worth rebuilding yet though.

I am planning to rebuild my ZF HP-19 auto this summer. I replaced it last summer but I kept the core to attempt a rebuild on.