High RPM shifting dynamics

[duragg]

Today:  Pulled the C/G Main drive gear which allows removal of the input stub, 4th gear and access to the synchro ring, springs and keys.

Indeed I could do surgery on just these parts without having to strip the entire main shaft.

 

If you have read the article referenced above by Jacks's Transmission then the pictures below will be self-explanatory.

2nd gear looks perfect

 

3rd gear looks like it is too far.  Jack calls this "Teeth preloaded too early".

 

Same with 4th, to a lesser degree:

 

I believe the gears and hub are all assembled properly.  There is a note in the FSM about making sure this 3/4 hub is installed correctly, but it could be vague on the exact direction of installation.  Assuming "Front" means Front of car?  Or does it mean something else in metric?  I can assemble my spare shaft (as if) and test easily enough.

 

I believe if I could case 3/4 to look like 1/2 I would be home free.

Still mentally determining if springs tension would even alter this, or if it involves machining.

 

[duragg]

Trans gear-set is back together and sure looks to be in better shape for fast shifting.

 

Regarding 3&4 grinding, all the parts looked perfect except for a few anomolies.

The 3&4 Synchro hub was a little narrow.  Of the two I had one was .030" wider so I used that one.

I analyzed and measured my 9 spare keys and picked the best and sharpest.

 

Installed about .060" shim under the key springs and installed the widest and cleanest slider i had. I used two #2 stainless washers which are each about .030" under the spring keys.  Anymore and you just can't get the keys in there before exhaustion sets in.  I also noted some unusual wear and metal transfer on the 3&4 shift fork, and so I switched to my spare fork.  And also one of the sliders was wider than the others so I ran that one.   After doing this when I begin to engage 3rd gear, simulating the gears in action, the dog keys all line up just right.  So I am hoping for a "good kill" this time.

 

When I pulled the tranny Saturday there was some leakage from the shifter area so I ordered new o-ring and lip seal for the shifter mechanism which has to come Overnight from LA.

 

Lastly... A few times while beating on the car and reaching for 3rd gear I got 5th instead.

To preclude this I put a shim under the 5/R thing to increase the force required to get into 5th.  This should give me a better gate to 3rd.

 

Should be back on the road late this week and finally done with tranny mods with no leaks and a whole lot more knowledge on what to look for when rebuilding a tranny.

[Leon]

Great thread, TJ! It should be sticky'd. Awesome links, nice photos of the process, and clear explanations of the logic behind it. That's going to be one sweet-shifting tranny!

 

Car sounds great, BTW.

[duragg]

Waiting on the seals for the shifter body and striker rod.

 

By reference to this ancient writings:http://forums.hybridz.org/topic/31661-280zx-short-throw-shifter/?hl=msa%20short%20throw%20shifter

and this:  http://forums.hybridz.org/topic/101175-raised-shift-lever-and-linkage/?hl=short+throw+shifter&do=findComment&comment=949101

 

I think I will machine a 2nd hole 20mm higher in the ears for a shorter shifter should I want it down the road.

I have a spare lever I will modify too.

[duragg]

They day or reckoning is upon my great adventure.

 

I had some oil leak from the shifter so ordered new seals and while I was at it I drilled the 2nd hole for a future short-shifter.

Or... perhaps just a lightening hole if nothing else.

 

Tranny reassembled, installed and tomorrow I will finish hooking everything else up and give it a whirl.

 

Installing a tranny alone is a PITA.

Somewhere between "Can you help me move" and "Can I borrow a thousand bucks"    is "Can you help me put my tranny in?"

 

 

[JMortensen]

Just put it on your floor jack next time. I have a bunch of friends who like to prove their manliness by rolling the trans onto their chest and then benching it in, but you can set it on the jack and get it done pretty easy. Good luck!

[duragg]

I use the floor jack, inserted from below the diffy and that works fine.

Still a process.  I can leave the exhaust in place with my current setup which saves a little time I suppose.

[Xnke]

I've always used the he-man method, just because I have an easier time getting the splines lined up that way. The floor jack works good too.

[duragg]

I've always used the he-man method, just because I have an easier time getting the splines lined up that way. The floor jack works good too.

I am feeling like a girly-man now!  I've got the car jacked as high as it will go on the big floor jacks, no way I have the muscles to do that.

[Sam280Z]

Get a couple of old head bolts and cut off the heads. Screw them into the block and use them to guide the trans on.

 

[Six_Shooter]

Get a couple of old head bolts and cut off the heads. Screw them into the block and use them to guide the trans on.

 

This is what I do, though I just bought the longest bolts I could an cut the heads off of them. Usually just a pair of guides, one of either side of the bellhousing mating surface is enough.

[duragg]

Fail. 3rd gear at 7000+ shift Improved but not gone. I can still push past the keys and get a crunch. Not F-ing with this box anymore (for a while) except perhaps to play with sauces. Learned a LOT. Tj

 

Edit:  2 hours hence, beer is setting in, cooler head prevailing.

Among the things I did NOT do on this round was to "lap" the synchro rings into the gear cone.

I had sound reasons, but I question them now.

 

The good news is that after 500 or 1000 miles of driving and shifting those synchros will bed-in more with their mating surface and the braking action may improve.

Edited February 23, 2013 by duragg

[duragg]

HI.  I'm back... I have more to discuss.  You can tune out now.

 

A little recap:

Fault 1)  2nd gear grinding - Worn Synchro:  FIXED.

Fault 2)  2nd gear popping out- Worn shift fork:  FIXED

Fault 3)  3rd gear grinding only under spirited driving:  NOT FIXED.

 

For lack of anything better to do tonight, I want to explain my theory of the 3rd gear grind when the lever is pushed hard.

There is a lot of different types of grinding and the exact circumstance is important.  In this case, hard lever push causes grinding I believe due to the Engage Ring being allowed to push past the brass ring before the speed is ready from the keys losing preload too early causing a grinding.

 

You pull the lever from neutral towards a gear, the shift rods act on the shift fork to move the Engage Ring towards the desired gear, the Engage Rings have a detent inside where the Engage Keys ride held by spring pressure.  The Engage Keys are moved toward the gear cone due to this detent and they push the Brass Ring onto the gear cone causing the brass ring to turn just slightly in the key groove and align with the Engage Ring Teeth.  I think we call this PreLoad and the brass ring is just riding on the gear cone, no big braking force is happening yet.  The real braking to sync the speeds happens as the shift lever is moved just a bit more and the "Engage Ring Dog Teeth" contact the "Brass Ring Dog Teeth" at the 45 degree angle and the vector created by the lever push vs the spinning gear Blocks and prevents and blocks the Engage Ring from moving more towards the gear until the speed is equalized, at which point the Engage Ring can slip the Brass Ring aside and mesh with its Gear.

 

You really need to read and try to understand what the guys at Jacks Transmission are talking about with "Synchro Blueprinting" for this to make sense.

I believe in my case and many other trannies, the keys are pushed forward by the Engage Ring but when they contact the gear cone the "Engage Ring Dog Teeth" and "Brass Ring Dog Teeth" are WAY too far apart.  I measured about .030" gap between the teeth which must be touching for heaving braking (synchro action) to result.  But the shifter continues moving forward until the Dog Teeth mesh, however to make this movement the synchro keys have had to "give" some as the Engage Ring pushes them inward, and some of the preload is lost, causing less braking force and the engage ring just slips on by - crashing into its gear.

 

A bunch of random theory which is really hard to verbalize, but here is what I did.

I took the Brass Ring Keyways and measure them and in all brass rings I have the key slot measure about .160"

 

So then I took a spare brass ring and machined the keyway slot .020" thinner which will allow the Engage Ring Dog Teeth to be that much closer to the Brass Ring Dog Teeth when the shifter is pushed so the keys don't have to give up their spring pre-load to make full braking happen.

 

If this modification can be performed on my tranny soon, I should be able to Slam 3rd gear and since the dog teeth will be fully engaged they will provide full braking and total blocking of the engage ring until sync occurs and then the gear will slide in without any grinding.

 

 

 

 

 

[Leon]

Nice, looking forward to see if it helps!

[duragg]

This research is on PAUSE for a week due to a business trip.

On return I have conscripted a helper and we will make another attack on 3rd gear with a slight modification to the brass ring.

 

My favorite part so far is the new shifter seals (2 of them: Big o-ring and little Lip seal) and finally not a single drop of leakage.

[duragg]

Update.

Ordered a new Nissan Engage Ring "Sleeve" from Nissan, along with a few other seals and parts for the next surgery.

Like last time I will open up, and pull the front C/S bearing to access the 3/4 gear pack.

Going to replace the sleeve and modify the brass ring as needed to make the timing match as Jack's discussed on his website.

Replacing the front C/S bearing since I've pushed it on and off a few more times than it deserves and FRIGGAN PRAY!

or drink, either way.

[duragg]

Last round of parts came in to make one last push for perfect shifting in ALL gears.

The goal this round is to perfectly match the synchro engage ring / brass ring contact per Jacks website.

 

I did purchase a BNIB Nissan Engage ring, but I must say it doesn't look a whole lot different from the old ones.  The grinding is more noise than damage it seems.

 

But we'll try this ring, and some trimming of the brass ring clearances to perfect the timing.  If I am STILL able to easily push past the dog teeth during the shifting then... I'm buying a toyota.

 

[duragg]

Sneaking up on the best solution for "High RPM shifting dynamics".

I finally have all my new parts in from Nissan and tonight did some research on my spare tranny setup.

 

I have a shaft configured for testing various configurations.  I can test keys, engange rings, synchros, and all sorts of stuff.

 

Tonight I experimented with shims under the key springs to see about how much pressure the Engage Ring can put on the Brass Ring before the keys give way and allow the Engage Ring to slide by.

1)  Stock springs with new keys and new Engage Ring about 12 pounds.

2)  Add a .030" spacer under the key spring the Engage will put about 14lbs on the Brass prior to giving up the dugout.

3)  Add a .060" spacer under the key spring the Engage will put about 17lbs on the Brass prior to giving up.

4)  Add a .090 spacer and the force goes to infinity as the key springs are coil bound.

 

If you can visualize the way the keys work, they put the most pressure just after contact with the ring, and before the keys have had a chance to begin to receed much, its all downhill from there.  This is only about .010" of "squish" on the keys before they give it up.  This is the reason Jacks wants to "tune" the Engage Ring, keys and slider to hit at just the right time.  You want the Engage ring to smack its keys into the brass ring and pound it onto the gear cone initially, then with just about .010" movement compress the keys slightly JUST as the Engage Ring teeth mesh perfectly with the Brass RIng Teeth which prevent any further movement untl synchronization is complete, at which point the brass ring moves aside and lets the engage ring make the gear.

 

... is my theory this time...

Edited March 19, 2013 by duragg

[duragg]

That's a BIG smile from duragg...

 

I believe success has been achieved.

 

Beer and a shower time. Huge thanks to 510 kid "Vanmansam" for helping with todays 5 hour push to remove, fix, replace and test.

[Leon]

Sweet!

 

You're making me want to rebuild one of my ZX trannies...