High RPM shifting dynamics

[duragg]

Its all fun when the parts are in...

 

Museum of Baulk Rings (aka: Brass synchro rings:).

 

Reassembled per the FSM and picked the best of the parts along the way.

I didn't do anything tricky with the synchro key springs.  Maybe I should have.  I Collected all 18 and picked the biggest and the best.

Then measured and picked the best of the keys and put it back together.

 

All gear end plays are perfect in spec. 
All the baulk rings have great clearance, its kinda funky to measure. 

 

 

Tomorrow I will torque the big Mainshaft reverse thread nut. and then start focusing on the forks and selectors.

I am planning to double pin the forks and just run the best of what else I have.

 

Circling back to the very start of this thread.  I think a thinner juice along the lines of 50/50 MT90/ATF.

 

[HowlerMonkey]

Strange how posts on topic of "high rpm shifting dynamics" have disappeared from this thread.

 

If someone deletes my posts, please PM me and explain the reason.

Edited February 7, 2013 by HowlerMonkey

[duragg]

I certainly didn't (can't) do such a thing.

I see your last input around #40, #42, #45, #46

 

Shenanigans?

Call it if you see it.

[johnc]

HowlerMonkey's last post in this thread was about a week ago.  None of the admins are deleting posts from this thread.

[duragg]

Thought maybe I was in trouble again... 

 

Ok she's back together and now we are circling back to the start of this thread.  Desire for an FS5w71B that shifts real good.

I ordered all the new parts I could and canabalized a spare tranny to get the best of the best.

 

For now I left it all stock but with new synchros, good gears, new check balls and springs and just better assembly attention.

Due to cost and availability I will probably do 50/50 MT90 and ATF, but I need to read way back into the thread to see what those with more seat time said.

I also installed the 12lb flywheel.

 

So this is all coming down to the following machinations:

1) It works great and I love it, but always wonder if modifications would make it even better (Greedy B'tard)

2) It doesn't work and I lie about it to save face, or just not come here anymore... but I usuallly end up with a few beers crying in my keyboard so that probably won't happen.

3) Do it all over again,.. which is likely as I will probably have a Z of some sort forever and I enjoy the process.

Blah blah blah...   Pictures or it didn't happen, ya I know:  Behold!

 

[Trevor]

I'm voting for #1 !!!

 

 

[duragg]

Tranny is back in and bolted up, but I forgot to order a new tranny mount and so that will be in tomorow afternoon.

.

No Clutch Drag:

Reached in through the tunnel and turn the driveshaft with the car in gear and the Clutch pedal IN -> No drag.

I had to come out about 2-3 inches before the first hint of drag.  So the clutch drag issue is confirmed not a player.

 

Hopefully I can finish this friggan saga prior to honey-dos.

[duragg]

We're done.  Back on the road.  Leak tested and road test good.

 

The shifts?
About like all of these FS5 trannies with new synchros.  A big delta in speed requires a momentary delay prior to the lever just "Falling" into gear.  I haven't forced any of the gears yes as I only drove about 5 miles just to see how it felt.

 

I am running a fairly thin gravy.  The exact makeup will remain a secret (prevents the inevitble "I TOLD you...")

Will put a bunch of miles with easy shifts before hammering it,  5 more miles should do it.

 

Really about the only thing I could do different is heavier synchro key springs.  The only thing this would prevent is the engagement ring being forced past the brass ring before it is ready.  EXAMPLE: Pull hard, speed not equal yet, but the brass ring is bypassed early resulting in a grind.  If this isn't happening, then the system is doing its job and the syncros just need more time to equalize speed. 

 

THanks for all the help along this journey, I can only hope that future Z fans will find something useful in this thread. 

[duragg]

Racing a different track today.

2nd gear decent.

3rd gear sucks.

 

Pulling tranny to do the super-spring trick next week.

Or maybe build up the spare.

[duragg]

Tranny back on the bench-  1 hour to remove, a record for me.

 

3rd gear would grind unless I was super gentle and patient with the synchros.

Going to check the clearances tonight and then go drink...

 

Plan is to do the super-spring mod.

[NewZed]

Are you still shifting at 7,000 RPM?  And you never said what fluid you were running.

 

Bummer that it's not there yet.  I was hoping.  Maybe there is no good way to rebuild an old transmission to like-new performance.

[duragg]

Today saw a lot of 6500 to 7500 action trying to stay ahead of a fast group.

 

Tranny torn down (2 hours total). 

Gears and synchros all look perfect, no wear or damage from todays pounding.

 

We're gonna make a big increase to the key springs and see what that does.  There is remarkably little overall wear in the tranny.

It is all well within factory specs.

 

Failure not being an option... we'll make this work.

[Six_Shooter]

I had a similar issue of 1/2 shift grinding, popping out of second gear, especially on decel.

 

Eventually, after getting pissed at a stupid driver, I pulled away from a stop and yanked on the gear shift, which finally revealed my problem. I ended up not having first or second gear and was SUPPOSED to go to a lapping day the next day. I was actually on my way to a friend's house to load up the car on a trailer.

 

Anyway, after losing first and second gear, I went home, and left the car alone for a bit, it was fall after all.

 

When I pulled the trans apart, I found the 1/2 shift fork to be broken, at the point it wrapped around the shift shaft (Sorry I don't recall the proper name right now). It broke in such a way that the roll pin was still able to push on the shift fork, but the split went right through this area. I believe that the fork was split for a long time, but not completely broken until that day. I could see an area on the shift fork where the roll pin rests against that was smoothed out from the roll pin rubbing against it, or an extended period of time. My fork was also aluminium. The trans was pulled from a 1981 280ZX.

 

I ended up getting a 4 speed trans to swap the cast iron (cast steel?) shift forks from. I did both the 1/2 and 3/4 forks. I had to drill the roll pin holes larger in the 4 speed forks, due to the larger roll pins used in the later transmissions.

 

The transmission had never shifted so smoothly, or so, I'll call it deliberately, like it WANTED to shift, not just doing what it's being told. I run Synchromesh. I don't shift at 7300, but I do shift 6200 to 6300 regularly.

 

If you have the trans out again, take a good look at the 1/2 shift fork and make sure it's not splitting, or even flexing on the shift.

[AZGhost623]

So would a 280ZX Borg/Warner T5 be better/stronger option than the standard 5speed found in most of the Z's? I would really be curious to hear others chime in as to how they are getting around these problems with that high RPM shifting. I always hear about the rear ends people are concerned about breaking, but little to nothing on the trans... It seems a common problem because we ran into Tage (?) with his 240 Rebello 3.1 and was having shifting problems too at high rpm.

 

So from what I have gathered going back and reading all this, its Genuine Nissan syncro's, shift fork and then the heavier spring option with the syncro's right? I have a sneaky suspiscion Im going to run into these problems too once my car gets on the road. After break in of course I have no idea what the gear shop used when they did the rebuild on my trans replacing the syncros and other things, guess i will know soon enough on how well they rebuilt it.

Edited February 17, 2013 by AZGhost623

[Six_Shooter]

So would a 280ZX Borg/Warner T5 be better/stronger option than the standard 5speed found in most of the Z's? I would really be curious to hear others chime in as to how they are getting around these problems with that high RPM shifting. I always hear about the rear ends people are concerned about breaking, but little to nothing on the trans... It seems a common problem because we ran into Tage (?) with his 240 Rebello 3.1 and was having shifting problems too at high rpm.

 

So from what I have gathered going back and reading all this, its Genuine Nissan syncro's, and then the heavier spring option with the syncro's right? I have a sneaky suspiscion Im going to run into these problems too once my car gets on the road. After break in of course I have no idea what the gear shop used when they did the rebuild on my trans replacing the syncros and other things...

 

While I haven't used the Nissan version of the T5 that came in the 280ZX, I have used the T5 from the GM S-series behind a couple engines, and also driven a number of fox body Mustangs and Camaros that were equipped with T5s. If I owned one of those other vehicles, I would swap a Nissan trans in there instead of the T5. The ones I drove, usually didn't like shifting above 6000 RPM, and they were weak. My ZX 5 speed has taken more abuse than my T5s ever did. I would imagine that the Nissan version of the T5 to be very similarly designed and built.

[duragg]

Stuart took a video of the crimes in action: 

I was trying to shift slowly and not out run the synchros.  Oil leak causing some smoke on over run and the friggan thing was WAY hot.

Edited February 17, 2013 by duragg

[duragg]

Unknown creator:

 

 

Thinking out loud:

If I were to tap out that counter-gear just a bit, and pull back the input shaft, I ALMOST think I could pull the 3/4 slider off enough to expose and tweak the keys and springs without disturbing the Main Shaft which is all setup real nice.

 

From Studying Jacks Website it seems I may need to look real close at how and where the slider and brass ring are making contact.

Based on what he describes, my teeth may be meeting too deep allowing the ring to pass before the job is done.

Edited February 17, 2013 by duragg

[duragg]

Going academic.

DANGER-  Math ahead which is 80% likely frought with errors.

 

I made a spreadsheet to think about what each gear is doing at the point of Shift (7000RPM, clutch in, pull lever).

What does the Synchro see now?

 

Some things to think about as I test this spreadsheet.

- Suppose a draggin clutch: Shift-in RPM would = Engine RPM and skew that number higher?

- THick fluid would cause the inter-gear drag to be higher and the input RPM would more cosely match the output shaft RPM?

- Ultra thin fluid might cause the input RPM to decay very rapidly compared to output RPM?

 

Does my spreadsheet work to describe the Delta in RPM seen by the Synchro?

Crap... cant upload XL spreadsheets.

Edited February 17, 2013 by duragg

[Xnke]

I'm very interested in what you're working with now...I've had poor luck with 7000RPM upshifts with my '71C box; but it does have 370+ thousand miles on it. Syncros still work for granny shifting but big delta-RPM's they don't handle well. Hopefully your experiments will reveal some tricks that'll help when I go to rebuild the 91 240SX transmission in my floor.

[letitsnow]

This is interesting, I've never owned a transmission that shifted as well as my 71B. I shift at a lower RPM(~6000), but, it will shift as fast as I can pull the lever and not grind. This is an unknown mileage box with a loud input bearing. My datalogs show I can do a full shift(throttle release to throttle application) in .100-.150 seconds.

 

I'm using this stuff, straight. I'd say it's worth a shot, for science! Edit: looks like you tried this already, interesting.

 

I actually sped my shifting up a bit from this later that night and dropped another .3 off my ET.

Edited February 17, 2013 by letitsnow