Difficulty Getting Into Gear at Speed

[Feffman]

I've been dealing with an on/off (more on that off) again issue with the 4=>3 downshift in the race car at high speeds with the ZF 5-speed. Bled slave, already had stainless steel pivot pin, checked tranny mounts, etc. and have come to the conclusion it's time for a different route.

I've ordered a 5-speed dog box from GearMotive (https://gearmotive.com/en/product/bm...-speed-dogbox/) which should be the end of the issue. 🤞

Feff

[sapote]

First finding and possibly the root of the problem: the nylon clutch pivot pin had completely sheared

The plastic pin normal wear should be on its tip where the metal clutch fork pivoted on, and so I don't think shearing off the pin shaft at its base (installed into the bellhousing) is a normal wear and tear. This broken pin shape could have happened when you misaligned the slave cylinder, leading to the slave's pushrod pushing on the fork with a side way force instead of a straight rearward force, and broke the pin.

As about using a SS pin, since the fork is metal and so metal pin to metal fork will wear out faster than plastic pin or brass. Make sure to add some moly grease to the pin tip/fork dimple cave.

[dukeofchen]

Did you replace the plastic pivot pin for the clutch fork?

Winner winner. Based on what I've read it seems like these usually just wear down vs. completely breaking, so it looks like I experienced a less common failure mode here as it had sheared along the shaft.

[dukeofchen]

Holy hell I have to say getting the transmission off on jack stands is no joke. Particularly when one of the E14 bolts had been mangled by whoever last touched it and was impossible to get seated in the socket (after an embarrassing amount of time wasted we took the risk and broke it free with an E16 socket).

First finding and possibly the root of the problem: the nylon clutch pivot pin had completely sheared, so it seems the clutch fork was likely out of position. If that was the case then it makes sense why the full pedal throw w/o a clutch stop was not translating into the distance required to fully release the clutch. Would also explain why I was having these issues without any kind of slip or noises that would accompany failure of the other components.

The inside of the bell housing is absolutely filthy, so rear main seal is definitely getting done. Even though it seems like this was due to the pin my inclination is to replace the RMS, clutch / PP, TOB, fork, retainer spring and pilot bearing along with throwing in the stainless pin. Will take a look at the flywheel but honestly I'd rather not do this again so regardless of condition I might replace that too.

[dukeofchen]

I think he needs to get there to inspect things based on his original post

I'm going to try to fish the parts out with a magnet and see if it can be rebuilt, but at 180k miles and dealing with a potentially original part I'll probably replace it, AutohausAZ had the OE unit on sale and their warehouse is close by.

If I can get it properly bled I'll attempt the clutch drag test, but at this point all signs still seem to be pointing towards dropping the trans and scoping things out.

[jbfrancis3]

I think he needs to get there to inspect things based on his original post

[heinzboehmer]

I think with a magnet and times you can fish out the pieces and no need to drop the tranny.

+1, I'd try that first too

[sapote]

While putting things back together tonight I must not have seated the slave cylinder properly while reinstalling and it burst when I went to start the car.

Yea, the slave push-rod had no load because the rod mis-aligned with the clutch fork, and so the slave piston gut and rod fell out in the bellhousing when the clutch pedal was pushed down -- it has nothing to do with engine run or not.

I think with a magnet and times you can fish out the pieces and no need to drop the tranny.

[FBloggs]

Did you replace the plastic pivot pin for the clutch fork?

[dukeofchen]

While putting things back together tonight I must not have seated the slave cylinder properly while reinstalling and it burst when I went to start the car.

Looks like regardless of the diagnosis the tranny is definitely coming out now, because the rest of the parts are inside of the bellhousing 😂

When life gives you lemons...

[sapote]

"There should be at least 0.5 to 1" free travel from "start release" to stopper."
I should have said clearance should be between 0.5 to 1" and not more than this. IF pedal has more than 1" free travel after release point, the PP plate diaphragm could be over extended if pedal was pushed down to stopper, causing the PP to reverse and touch the clutch disc instead of total release.

[dukeofchen]

No. Brake the car to hold it on a slope surface, then engage 1st or R gear. Release clutch pedal up (clutch fully engaged). Release brake and car is held by the engaged gear and clutch. slowly push down clutch pedal until car starts to roll down hill. This is the clutch releasing position and make note of the pedal position relative to its bottom position (stopped by the floor stopper). There should be at least 0.5 to 1" free travel from "start release" to stopper.

Ah okay that makes sense, thank you! Will report back with findings.

[sapote]

Just to be sure, the test would be (1) clutch all the way down, put into 1st or R (2) release clutch until it reaches lowest engagement point (3) evaluating the distance between the lowest engagement point and fully down, and if that distance is very small that points to clutch drag?.

No. Brake the car to hold it on a slope surface, then engage 1st or R gear. Release clutch pedal up (clutch fully engaged). Release brake and car is held by the engaged gear and clutch. slowly push down clutch pedal until car starts to roll down hill. This is the clutch releasing position and make note of the pedal position relative to its bottom position (stopped by the floor stopper). There should be at least 0.5 to 1" free travel from "start release" to stopper.

[dukeofchen]

I re-read your posts and thinking about this: the shifting resistance is more defined at around 4000 rpm. Since this is your first MT, do you try double-clutch or rev matching (bleeping the gas pedal) when down shift? Too much gear speed differential could lead to fast synchro wear out then having the same symptom as you described.

Have you tried this suggestion -- in your other thread -- to see if the clutch is dragging "This can be checked easy on a slope driveway or road: engage 1st or R then press down clutch pedal slowly until car starts rolling, then notice how much more the pedal can go down before hitting stopper. It should have enough free travel" ?

During my time of ownership at least (the last 45k out of 180k miles) I've always rev matched on downshifts. Perhaps a little sloppily as I was learning at the beginning, but I rarely if ever fully allowed the transmission to pick up any speed differential. Can't attest to the previous 2 owners though – would be a huge bummer if this ended up being a synchro issue in the end. If it were a synchro issue, would it present across all gears, or be localized to specific gears / gear changes? Because at this point just about any shift above that RPM threshold will produce the issue.

I forgot to try that exact clutch drag test, might throw the exhaust / tranny brace back on tonight and give it a go. Just to be sure, the test would be (1) clutch all the way down, put into 1st or R (2) release clutch until it reaches lowest engagement point (3) evaluating the distance between the lowest engagement point and fully down, and if that distance is very small that points to clutch drag?

Just did some searching and it looks like another similar test would be to put the car in 1st with the clutch fully down, then give it some revs and see if the car moves at all. I'll try both when I have a chance.

[Mystic3]

Long shot, but are all the bolts tight, trans to engine, etc.