Transmission Failure from Tracking

[3002 tii]

Just wrapped up a long weekend at Watkins, and by day 2, I was having difficulty getting into 4th and 5th. Oddly enough, downshifting is fine but I get resistance whenever I try to up shift to 4th or 5th. Gets caught in neutral and then I have to hold in clutch forever and gingerly navigate to next gear.

With the car off, I’m able to get into any gear easily. And during normal driving, up shifting is generally fine; it’s only when I have the revs above 5000 where I get resistance. But all signs point to worn synchros

I have to think there’s plenty of drivers with more seat time (in cars putting down more power), yet I do recall ever reading about a failed gearbox.

[Michael9218]

Yep, sounds like worn syncros.
I had my Diffsonline 5 speed box fail last year. Wasn’t the syncros, though. I started to get a howling in 4th gear. Helicut gears broke.

[3002 tii]

Originally Posted by Michael9218

Yep, sounds like worn syncros.
I had my Diffsonline 5 speed box fail last year. Wasn’t the syncros, though. I started to get a howling in 4th gear. Helicut gears broke.

What sucks (as you know) is the ZF’s are not rebuildable. I’m going to drain and fill and add some additive to see if I can finish out the season. I just don’t know what to replace it with, no point in buying another Z4 gearbox just for it to fail again. 5 speed is appealing but I drive to/from so it’s not ideal for street. Meh…

Re your diff did they warranty it?

[Michael9218]

These gearboxes can be rebuilt. I’ve heard of a shop down here that can rebuild it. Diffsonline can as well and they’re near you (outside Boston).

Since it’s a “race part” there is no warranty, but we did agree on a reduced price.

[Steeler]

My GS6-37BZ is making noises, but I think it's the bearing in the flywheel and or the input shaft bearing. Not the innards.

When I had the transmission out in the winter, I did notice that the input shaft had some lateral play, up/down and side to side, so I have sourced a damaged synchro's GS6 that I plan on pulling apart to see if the input shaft bearing is accessible to be replaced.
If it is I will pull the trans in the car and replace the bearing.

I found this online.

https://hobby.farit.ru/e30-325i-manu...peed-gs6-37dz/

[3002 tii]

Originally Posted by Michael9218

These gearboxes can be rebuilt. I’ve heard of a shop down here that can rebuild it. Diffsonline can as well and they’re near you (outside Boston).

Since it’s a “race part” there is no warranty, but we did agree on a reduced price.

I reached out to Diffsonline earlier this year and he said parts are so hard to come by he doesn’t work on them anymore.

[GuidoK]

Originally Posted by 3002 tii

I just don’t know what to replace it with, no point in buying another Z4 gearbox just for it to fail again.

Why not replace it with another z4/e46 (6spd) gearbox?
Afaik they're the same as the z4m gearbox (they have a different suffix, TJEE vs THEA, THEG or TJES), but that's I think maybe different output flange or maybe bell housing etc that you'll build over anyways.

Z4 and e46 gearboxes are plentyful at the car graveyard and made by the millions. Should be easy to source and for cheap (I see them here for €300), basically a maintenance part for tracking.
If your exhaust etc comes off easily, a swap should be 1 day work max if you have a carlift and transmission jack.

I don't know how much you've tracked your car (or what the previous owner(s) did), but the z4m is already a 15+ year old car. If your next gearbox will last that long again...

I assume you have grinding when trying to get in in gears? (that is the symptom for worn synchro's). You could try double clutching for the time being.

If you want to replace the box with something motorsport grade, it'll get really expensive. Brands like Quaife (UK) and Drenth (NL) do BMW motorsport gearboxes, but expect to pay $10+ for a Quaife and probably $25k+ for a Drenth. But you'll get really cool stuff (straight cut dogbox and sequential clutchless shifting with a shiftdrum become a possibility)

[Michael9218]

Originally Posted by Steeler

My GS6-37BZ is making noises, but I think it's the bearing in the flywheel and or the input shaft bearing. Not the innards.

When I had the transmission out in the winter, I did notice that the input shaft had some lateral play, up/down and side to side, so I have sourced a damaged synchro's GS6 that I plan on pulling apart to see if the input shaft bearing is accessible to be replaced.
If it is I will pull the trans in the car and replace the bearing.

I found this online.

https://hobby.farit.ru/e30-325i-manu...peed-gs6-37dz/

Lateral play on the input shaft is normal on these gearboxes.

[Michael9218]

Originally Posted by GuidoK

Why not replace it with another z4/e46 (6spd) gearbox?
Afaik they're the same as the z4m gearbox (they have a different suffix, TJEE vs THEA, THEG or TJES), but that's I think maybe different output flange or maybe bell housing etc that you'll build over anyways.

Z4 and e46 gearboxes are plentyful at the car graveyard and made by the millions. Should be easy to source and for cheap (I see them here for €300), basically a maintenance part for tracking.
If your exhaust etc comes off easily, a swap should be 1 day work max if you have a carlift and transmission jack.

I don't know how much you've tracked your car (or what the previous owner(s) did), but the z4m is already a 15+ year old car. If your next gearbox will last that long again...

I assume you have grinding when trying to get in in gears? (that is the symptom for worn synchro's). You could try double clutching for the time being.

If you want to replace the box with something motorsport grade, it'll get really expensive. Brands like Quaife (UK) and Drenth (NL) do BMW motorsport gearboxes, but expect to pay $10+ for a Quaife and probably $25k+ for a Drenth. But you'll get really cool stuff (straight cut dogbox and sequential clutchless shifting with a shiftdrum become a possibility)

IIRC, internet lore suggests the Z4M gearbox is stronger than the E46M gearbox. No idea if this is true. You could use one, but will need a E46M clutch as the input spline count is different.

I’ve evaluated all the available aftermarket gearboxes one can bolt behind an S54. For a street driven car, you do not want straight cut gears or dog ring engagement. Very noisey and clunky. Proper sequential shifting requires a closed loop set up, which means aftermarket ecu. Gets expensive very fast.

Finding a replacement Z4M gearbox will take time and patience. I had one sitting in my shop for years before I finally sold it. Very little supply, but also very little demand.

[GuidoK]

Originally Posted by Michael9218

IIRC, internet lore suggests the Z4M gearbox is stronger than the E46M gearbox. No idea if this is true. You could use one, but will need a E46M clutch as the input spline count is different.

Not E46M but normal E46!
e46M has a stronger gearbox: 420Nm vs 370Nm. Normal E46 and 6spd Z4's also have the GS6-37BZ.

The spline issue is only relevant if you go from 5spd to 6spd.
All 6 speeds have a 22spline prise axle afaik.

I’ve evaluated all the available aftermarket gearboxes one can bolt behind an S54. For a street driven car, you do not want straight cut gears or dog ring engagement. Very noisey and clunky. Proper sequential shifting requires a closed loop set up, which means aftermarket ecu. Gets expensive very fast.

Yes. Expensive. noisy. clunky. but stronger
If stronger is needed, it's the way to go. However I doubt it's the case with a fairly stock engine.

Finding a replacement Z4M gearbox will take time and patience. I had one sitting in my shop for years before I finally sold it. Very little supply, but also very little demand.

Not z4M. Normal Z4! (or normal e46 6spd)
They are available by the thousands. And cheap.

[Steeler]

Originally Posted by Michael9218

Lateral play on the input shaft is normal on these gearboxes.

Good to know. I will see how much play I have on mine should my experiment work.

[dre99gsx]

I'll also confirm - lateral play on input shaft normal. The pilot bearing is there to keep the shaft centered when you are pressing in the clutch to change gears.

I'm on my 3rd transmission, I blow them up often due to heavy track use. Yes, Z4 nonM (22spine input). Z4M is same every which way other than changes in the input shaft.

You can however move to a 22spline clutch disc and swap out the transmission to a nonM Z4/E46. Look for 2002-2004 Z4 3.0i modols or 2005-2008? 3.0si. Some e46 N52 motor bmws also have same transmission.

--- taken from one of my other posts:

https://www.zpost.com/forums/showthread.php?t=1842540

GS6-37BZ-THEA (M54) from 3.0i 2003
- end of input shaft to end of bellhousing: 1 1/16"
- start of splines to end of bellhousing: 2 3/32"
- pilot bearing OD 15mm

GS6-37BZ-TJES (N52) from 3.0si 2007
- same thing as above
- two of my lower mounting bolt holes don't line up with the Collins plate, I have to drill them out on the bellhousing. Easy to do.
- missing a locating pin on the bellhousing (not machined in there). I can make do without it, Collins plate has two locator bushings that still recess into the bellhousing.

GS6-37BZ-TJEE (S54) from Z4M
- end of input shaft to end of bellhousing: ~3/16" (5mm)
- start of splines to end of bellhousing: ~ 1 3/8" (35mm)
- pilot bearing OD 15mm
(Courtesy of Michael9218)

GS6-37BZ-TJEP (N52) 330i E90
- no idea...

GS6-37BZ-THEG (M54) 520i
- no idea...

All my transmissions blow up 4th gear. I take them to 8500 rpm frequently - yes, 650-700whp. I run Motul 74-90 and now 2 oil coolers with a Susa pump.

I noticed my 2nd one would get to 240F. Added second cooler, will see how long the 3rd one lasts. I never had a cooler on the 1st one but who knows how hot it got.

You're not blowing gears, but killing your synchros, that seems like something else is going on. Do some research on your clutch disengagement. Is is possible you aren't fully disengaging the clutch when things get hot in there form track duty? Can you slowly rev to 8k while mostly cool and see if you can shift up/down? That may give you a clue...

You may have to move up to the GS6-53BZ. Will bolt up, but require custom driveshaft, and a few other things. It is 22lbs heavier (I have one, I measured) and uses the "larger" output shaft adapter than what the 37BZ uses. That is (was) my next step but had hard time getting someone to build me a new custom driveshaft, so found a 3rd GS6-37BZ and will see how long this one goes.

I really think you need to invest in transmission and diff coolers. You're in NJ.. come up to my house some day, I'll give you a tour of my set up and perhaps some ideas on what you can do. We;ll grab a beer, whatever works. (Wait, you're in CT.. never mind)

[3002 tii]

Originally Posted by GuidoK

Why not replace it with another z4/e46 (6spd) gearbox?
Afaik they're the same as the z4m gearbox (they have a different suffix, TJEE vs THEA, THEG or TJES), but that's I think maybe different output flange or maybe bell housing etc that you'll build over anyways.

Z4 and e46 gearboxes are plentyful at the car graveyard and made by the millions. Should be easy to source and for cheap (I see them here for €300), basically a maintenance part for tracking.
If your exhaust etc comes off easily, a swap should be 1 day work max if you have a carlift and transmission jack.

I don't know how much you've tracked your car (or what the previous owner(s) did), but the z4m is already a 15+ year old car. If your next gearbox will last that long again...

I assume you have grinding when trying to get in in gears? (that is the symptom for worn synchro's). You could try double clutching for the time being.

If you want to replace the box with something motorsport grade, it'll get really expensive. Brands like Quaife (UK) and Drenth (NL) do BMW motorsport gearboxes, but expect to pay $10+ for a Quaife and probably $25k+ for a Drenth. But you'll get really cool stuff (straight cut dogbox and sequential clutchless shifting with a shiftdrum become a possibility)

I’m not opposed to trying a different gearbox especially if cheaper. But before doing so, ideally I can first diagnose what the issue is. Is is truly a deficiency in the Z4 M trans, driver error, excess heat?

You are correct, double clutching alleviates issue but not really conducive to time trial/attacks. And true race gearbox is out the budget and not practical considering I still drive to/from the track. But to answer your question, yes if I don’t let revs drop to 3k and take my sweet time, I will get some resistance or grinding.

Originally Posted by dre99gsx

You're not blowing gears, but killing your synchros, that seems like something else is going on. Do some research on your clutch disengagement. Is is possible you aren't fully disengaging the clutch when things get hot in there form track duty? Can you slowly rev to 8k while mostly cool and see if you can shift up/down? That may give you a clue...

You may have to move up to the GS6-53BZ. Will bolt up, but require custom driveshaft, and a few other things. It is 22lbs heavier (I have one, I measured) and uses the "larger" output shaft adapter than what the 37BZ uses. That is (was) my next step but had hard time getting someone to build me a new custom driveshaft, so found a 3rd GS6-37BZ and will see how long this one goes.

I really think you need to invest in transmission and diff coolers. You're in NJ.. come up to my house some day, I'll give you a tour of my set up and perhaps some ideas on what you can do. We;ll grab a beer, whatever works. (Wait, you're in CT.. never mind)

If you’re in or near Bergen, I can definitely swing by.

Re clutch disengagement, agreed it feels like a hydraulic issue. Funny thing is I’ve largely kept my driving style consistent over the years, yet my prior n52 coupe never had issues. Only thing I’m perhaps doing different is spending more time near or at redline but I didn’t think that would be an issue for the gearbox.

And FWIW the clutch on my car was replaced it last summer, using all OEM parts. Only thing I can think of is faulty slave cylinder but I don’t recall seeing leaks last time I was underneath.

[3002 tii]

Question for the knowledgeable folks here. I plan to use this opportunity to freshen up both the shifter and gearbox

1. For track use, what gear oil are you running? Do you use 50/50 mix with ATF?

2. What are thoughts on chassis mounted shifters? Is lockout really necessary (assume 2nd gear is frequently used)? Will I find this annoying during my long drives to/from track? Because NOT racecar

3. Does anyone know the length of the factory selector rod?

[Michael9218]

I’m using Redline D4 ATF per Diffsonline.

I use a chassis mounted AKG shifter. Very direct/precise feeling shifter. Aluminum engine/trans mounts. Not what you want on a street driven car.

With the Gearmotive dogbox I screwed around with for a couple years, I used a gated shifter. IMO, not necessary for a synchro box (a must for a dogbox!).

My selector rod and driveshaft are custom length since I moved the motor back 80mm and am using the 100mm shorter 5 speed gearbox.

[3002 tii]

Originally Posted by Michael9218

I’m using Redline D4 ATF per Diffsonline.

I use a chassis mounted AKG shifter. Very direct/precise feeling shifter. Aluminum engine/trans mounts. Not what you want on a street driven car.

With the Gearmotive dogbox I screwed around with for a couple years, I used a gated shifter. IMO, not necessary for a synchro box (a must for a dogbox!).

My selector rod and driveshaft are custom length since I moved the motor back 80mm and am using the 100mm shorter 5 speed gearbox.

I’ll be honest - the more I read up on chassis mounted shifters, the less convinced I am it’s right for me. But I plan to sit in my friends GTS3 e46 which has a CAE ultra shifter to make final decision.

Mind sharing who you used for custom driveshaft?

[Michael9218]

Originally Posted by 3002 tii

Mind sharing who you used for custom driveshaft?

Local driveshaft shop. I’m sure you can find one near you.

[3002 tii]

Mini update - I was able to secure used Z4 M gearbox for a very reasonable price, cheaper than what it would’ve cost to use a different model and ancillary parts for conversion. But the e46 330i six speed is probably the next best option for M owners.

In addition to gearbox, will use this time to upgrade to RE trans bushings, replace clutch slave cylinder, remove CDV and freshen up the shifter linkage. I decided against the chassis mounted shifter, but instead look for a used/new AS kit. Fluid wise, going to try out Redline MT-LV per Bimmerworld.