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High RPM shifting dynamics


duragg

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  • 2 weeks later...

Hi.

Update. Smaller Slave restored my throw and pedal position for heel / boot / smash shifting.

The grinding was reduced all except downshifts into 3rd. Due to more disengagement?

 

Beating on the old box pretty hard...

CVR is a lot of RPM for me on 23" tires with a 4.38.

 

It was better tho.

I kinda want a dog-ring box...

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  • 3 weeks later...

With the new clutch setup the shifting was a lot better this time.   I really only recall and crunching when downshifting into 3rd.

 

I have another tranny to build up which I intend to make a hybrid of gears:  Close Ratio from 1983 with shorter Overdrive from a 1977.

This will be welcome on track instead of the big jump to the long .745 OD

 

All seems happy enough for the time if I can keep myself from trying to get into reverse at 90 mph...

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  • 4 months later...

Guess I haven't updated in a while.

I think my shifting is basically perfect now.  Or at least I have not noticed any crunching in the last 2 races and I am flogging the old box pretty hard.

 

I bought a *smaller* clutch slave cylinder which give me a little more throw and have adjusted the pedal to maximize the release.

Actually I had it mis-adjusted and noticed the tranny shifted perfectly so I just left it that way.

Doesn't slip and throw out bearings are cheap. 

 

ANyways.. I'm a happy shifter for the time being.

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  • 4 months later...

Back into my tranny for a few items:

2nd still grindeded a little

Reverse got mangled in the heat of battle.

Want a shorter 5th.

 

On inspection also found the 4th gear brass ring cracked yet it shifted perfectly.

 

No about that 5th... By installing the earlier tranny I can get a .78 OD instead of .745 which will help.

But.... The earlier trannies use older style syncros.

I found that I could press off the gear and I think I can adapt the Warner syncro to the older gears.

So.. Wish me luck!

post-1894-0-25934700-1417569247_thumb.jpg

 

post-1894-0-71143400-1417569296_thumb.jpg

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You've discovered the way that most of the older Nissan FS5W71C dog-ring boxes were/are made. Nifty, eh?

Well, this is a 71b?

Dog ring is different. (And would change my classing!)

Just a simple synchro hybrid

Unless you know more that you want to share?

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  • 2 weeks later...

Update. 

The 2nd gear crunch.  Racing rarely sees 2nd gear but it was crunching on downshift.  If you recall way back I put shims under the syncro key springs for 3&4 which helped eliminate 3&4 crunch.  But I didn't do it for 1&2.  Last night I added the shim washers for the 1&2 shift slider which hopefully will allow more braking force on the cone before the slider releases.  I also deglazed the cones and rechecked all the clearance.

 

4th is getting a replacement for its cracked brass ring and will radius the corners of the slots where I remove the meat.

 

The .773 5th is a little more work because the .745 OD gear is beefier and the Warner syncro system is smaller so I have to do some shimming and grinding to get things lined up properly again.  Pics to follow.

 

Next race is January 10 & 11 at a track that needs 2nd so we'll know soon enough.

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71C is just as light, honestly, and has a double-cone 2nd gear synchro. Might help, but will be a slower shift, I think.

 

The dog-ring method works for all the 71x boxes, pull the engagement ring off and press-and-weld the dog ring on, then cut the engagement teeth in the old shift hub.

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It incurs a decent penalty in my race class so I need to evaluate that "risk / reward" scenario. Is shifting my limiting factor? Is reliability more important? Will the penalty pay off?

 

And ultimately can I get it done in time for next race... No. :(

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  • 2 months later...

Having BIG clutch throw is a big help in high RPM shifting.  I have my throwout collar pretty heavily preloaded now and I get zero crunches. 
I also rebuilt the tranny again and maxed out the springs under the syncro keys.  Who knows what fixed what.

Wish I could find a much bigger Clutch Master Cylinder to give more throw to the slave.  Might see about adapting something else.

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