High RPM shifting dynamics

[JMortensen]

I only have experience with Porsches, but their tubes are not the driveshaft. They have a large tube with a thin shaft like an axle inside.

[HowlerMonkey]

Yes, and it's mass is substantially more than a 8 inch input shaft.

 

This beats up the synchros.

Edited January 25, 2013 by HowlerMonkey

[johnc]

Uuuhhhh, the driveshaft MOI is insignificant compared to the MOI of the wheels and tires and the tire's grip on the pavement.  They are diecrtly connencted to the output shaft in the transmisison - via the halfshaft, diff, and driveshaft.  The synchros slow down the inout shaft, not the output shaft.  In the context of synchro life its input shaft speed, not output shaft speed.

[JMortensen]

He's talking about 944s and 928s. What's weird is that I only saw one 944 synchro replacement when I worked for a Porsche shop for a couple years and no 928s, but I saw probably 20 911 replacements (although part of that was that the 911's used the steel synchros and the 944s brass).

Edited January 26, 2013 by JMortensen

[HowlerMonkey]

Edit function is a bit screwey.

 

 

Edited January 26, 2013 by HowlerMonkey

[HowlerMonkey]

Uuuhhhh, the driveshaft MOI is insignificant compared to the MOI of the wheels and tires and the tire's grip on the pavement.  They are diecrtly connencted to the output shaft in the transmisison - via the halfshaft, diff, and driveshaft.  The synchros slow down the inout shaft, not the output shaft.  In the context of synchro life its input shaft speed, not output shaft speed.

 

I'm discussing input shaft mass and it's affect on synchros.

[duragg]

Well I can't live with it anymore. Track day yesterday and it tends to pop out of second and grind. Hopefully I haven't damaged it more than necessary.

 

Choices are:

1) rebuild another which doesn't allow me to learn what went wrong on this one.

2) open up this one and try to learn what I screwed up, but which wont show me if I somehow assembled it wrong.

3) get another unmolested one and do them both side-by-side to compare & contrast with the FSM.

[JMortensen]

Popping out of 2nd is not uncommon. One simple bandaid is to put a stiffer detent spring in on the shift rail. Mine was doing this pretty bad when I stopped driving it, and the detent spring fix was no longer working. A friend who has rebuilt a bunch of transmissions thought the issue was the mainshaft nut backing off. My plan was to either cut two nuts and double nut it or tack weld the nut to the shaft to prevent the issue.

[duragg]

I do wonder about the nut. But the later models are even reverse threaded.

 

This is making me want to go pull the tranny right this very minute... and I am supposed to be cleaning the house today...

Edited January 27, 2013 by duragg

[duragg]

I used the Arizona Zcar Organic clutch, but just a stock 240mm flywheel that was leightened some.

If I pull the tranny I will probably go to the lighter flywheel while I am there and gives me a chance to fix the oil leak too.

 

I guess its easier to pull tranny from below rather than pulling engine and tranny together?

[NewZed]

It's easy to pull from below but make sure you first get the car high enough to slide it out once it's on the ground.  It's a pain to raise the car when the back of the engine is sitting on blocks.

 

This book is a good read if you wanted some other views on things to look for.  Has about a page on grinding and another on jumping out of gear.

 

http://www.amazon.com/Rebuild-Modify-Transmission-Motorbooks-Workshop/dp/0760320470/ref=sr_1_1?ie=UTF8&qid=1359313881&sr=8-1&keywords=bowen+transmission

[duragg]

Sometimes I wish I had taken up golf.

Edited January 27, 2013 by duragg

[duragg]

Boy am I in trouble. ...

 

I'll be reporting to TonyD's office for this screw up...

[duragg]

Pulled tranny and disassembled.

The synchro-balk clearance is supposed to be 1.2mm to 1.6mm but none of that was there.  All were way under.

1st was 1mm

2nd was .5mm

3rd was 1.1mm

4th was 1.31

5th I forgot to write down.

So whatever clearance I measured, or thought I measured, or wanted to exist when I put it together last is now AFU.

All gear clearances were in spec and the gears themselves looked perfect, so the grinding must just sound worse than it actually is.

 

A bunch of pictures below, along with the flywheel and clutch which have odd wear? 

Good news is the RMS I thought was leaking is NOT leaking.  Guess it is the VCG afterall.

 

I think this is the right measurment place.  Basically it measures how deep the brass ring goes into the gear.  This is too far in and hence doesn't work.

Supposed to be 1.2mm to 1.6mm and this one is maybe .5mm

  -> uploaded wrong picture.  I don't have a pic of the proper measurement place.

 

the 1/2 shift fork is different than 3/4.  it is not as rigid and has the plastic dowels.  Never quite got this, related to popping out?

 

This is the 3/4 fork and 5/R looks the same.

 

Rear main seal not leaking afterall?

 

240mm flywheel I will probably chuck and get a lighter one while I am here.

 

Arizona Zcar pressure plate.  Funky wear? Only probably has 500 miles.

Edited January 28, 2013 by duragg

[duragg]

Will try to order GENUINE Nissan rebuild parts tomorrow.

On the list in this picture should be:

 

* All 5 synchro rings (1-4 same, 5th different).

* Superceded reverse check assembly (just in case a newer version is better..?)

* New 1/2 shift fork (is superceded P/N).

* New components on the lock ball assembly for 1/2 with superceded p/n

* gaskets and some other little stuff.

* Shifter end bushing

 

Edited January 28, 2013 by duragg

[tooquick260]

Shifting above 7000 rpm is a common problem for these cars. You can go the route of removing every other tooth on the synchronizer. This is what they call pro shifted gears. It opens up the window for the gear selector to change the gears. 

 

There is a draw back on these, you can not granny shift if you do this. It will grind on every shift that you try to gently put into gear. Like trying to shift without the clutch pedal. We seem to sacrifice when we want to go fast.

 

The other thing you could look at is that the chassis and the driveline may be in a bind under this extreme acceleration. What are you using for motor mounts, tranny mounts and diff mounts? You could go solid mounts or some other type of stiffer mounts. My drag racing experience has a lot of the later issue with missing a shift or not able to shift to 2nd gear. The torque you are putting through the driveline with your HP and propably sticky tires.

 

Good luck, as I said we sacrifice a lot for what we want and you may have to go some of these routes.

[duragg]

I read about deleting some synchro teeth on another forum and might consider that.  Need to read more on that.

I have come to realize this is a track car, not a drag car.   (Drags require windows up, NASA events are windows down... its the little things that make me happy).

 

However after seeing that my synchros are all WAY under spec, perhaps I will just rebuild to proper spec and see how that goes.

But faster bang-shifting does sound fun... 

 

This will be my 3rd FS5w71B teardown / reassemble and so far-so good actually.

Glad to be able to learn exactly how things work and tweak them to my needs.

[duragg]

Experimental Mods with unknown results....

1)  Deleting every other synchro engage tooth.

2)  Shimming up the springs under the 3 keys that push the synchro ring into the gear.

3)  Heavier spring on the 1/2 ball that holds the fork in gear.

[tooquick260]

I ran this type of a pro shifted gear setup on another type of car and hated it. It would fix your problem but a pain to drive. It was a 1958 VW Beetle with a 1966 transaxle. Strip street car running nitrous, ran mid 10's at 123. Killer 1.39 60 foot times on DOT drag radials. Was a killer street killer. That cars demise was the big Bang effect of nitrous.

[RebekahsZ]

Your pressure plate looks just like mine did when the clutch wasn't TOTALLY disengaging. I still think that might be the root of your trouble.