Black Fiber Synchros on all 5 gears?

[John Coffey]

Of course there's always this option - John Jeffries brought it to my attention.

http://www.eliteracingtransmissions.com/products/datsun-240z-dog-gear-kit/

 

[Zed Head]

Thanks for adding.  Hope I'm not blowing up biodi's thread.  It looks like the servo synchro problem has been confusing people for many years.  Found another old thread that suggests improper fluid can cause problems.  SWEPCO raises its head again, JMortensen's favorite from his Porsche days.

Maybe the Redline MT90 isn't the best for this transmission?  Who knows.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=508611

 

p.s. I think that baulk essentially means "stop", which is what the rings do in a relative way.  So both servo and borg warner style should both be baulk rings.  People seem to be using "baulk" to differentiate.  Anther confusion.

Edited January 12, 2016 by Zed Head

[John Coffey]

Swepco 201 is the gold juice in the Porsche world for the 901 and 915 transmissions.  In short order it ruined the synchros in my Nissan 4 speed after a day of racing at PIR.

Edited January 12, 2016 by John Coffey

[Chickenman]

Just to clarify John , would that would have been Brass synchros in your 4 speed that the Swepco ruined? Not Porsche type steel synchros?

[blodi]

Any info on the fluid is good. I think the Redline MT-90 is what may have caused my steel 2nd gear synchro to fail so quickly. 

Mine are definitely the servo style synchro as shown here on the right vs the warner style on the left...

 

Ok, so the trans guy counted the teeth on the gears....this is super confusing.....

1st- 33 Main 19 Counter=2.357

2nd- 28 Main 19 Counter=1.473

3rd- 26 Main 28 Counter=.928

4th- 22 Main 31 Counter=.710

5th- 19 Main 31 Counter=.613

This makes for really odd ratios that don't match up to anything I see listed. What am I missing? Cause this would mean 4th and 5th are both overdrive. I know that isn't right. The car wasn't that "long legged" when driving it.  At 70 it was turning 3.5k in 5th on the highway. 

 

Edited January 12, 2016 by blodi

[blodi]

Ok, if I assume 4th is 1:1 and divide 1 by .710....then multiply the other ratios by that 1.4xxxx figure....the ratios fall into place and it's a wide ratio....

32010-N3030   3.321    2.077    1.308    1.000    0.864  (wide ratio)

[Zed Head]

Weird.  Plain old 77-78 ratios but with steel servo type synchros.  What do you do with that?

[blodi]

Yeah...I mean, that looks like it was one of the options with the comp boxes....

http://www.zhome.com/ZCMnL/tech/GearRatios.html

I think I'm just gonna keep this trans and save myself the headache of trying to sell it and find another, rebuild that one...etc...

I doubt with the wide ratios it's too valuable to vintage racers. 

But, I still need to find a synchro ring that works. 

Edited January 12, 2016 by blodi

[Chickenman]

 

I don't think your Mechanic counted the constant mesh gearing ( Main drive gear) from the Input shaft to the Countershaft. Count those gears and you will probably find that the ratio works out to be 1.408xxx. Countershaft will always be rotating at 1.408 ( or whatever the ratio works out to be ) times the speed of the Input shaft. So that figure has to be multiplied across all the gear Teeth count for 1st through 5th.

I'd double check all his teeth count and go from there.

Edited January 12, 2016 by Chickenman

[Chickenman]

This picture of a FS5W71 should make it a bit clearer. Gear on Input shaft #15 drives Constant mesh gear #45  on counter-shaft.  Countershaft can be at 1 to 1 ratio of mainshaft, under-driven or over driven, depending on design criteria.

On most transmissions, the Countershaft is over driven so that mainshaft gears are smaller in diameter. That means less weight and less inertia to spin them up when Synchro's are engaged by sliding coupler.

 

[blodi]

Gotcha, yeah, that makes sense now. 

So for the Porsche synchro rings...sounds like there are two possible sizes...I'll have him measure mine today...

http://forums.pelicanparts.com/4279865-post6.html

The Porsche patent syncros are VERY sensitive to the installed size you are looking for. Additionally they must be used with the Porsche sliding sleeve and the Porsche engagement dog ring splined onto the free gear. These are sufficiently sensitive that in some cases, simply turning over a slightly worn syncro can prevent proper shifting. Needless to say you must use the Porsche stops and bands Even the side clearance from the circlip is important.

There are two basic sizes: the 87.1 and 88.1 mm ones used on the 1st and 2nd gears of a 915 and the 78.0 mm ones used on the 3-4-5 gears of a 915 and all 901/911/914 gears. These are “free” dimensions with the syncro ring not installed on the gear.

Acceptable diameters for installed syncros are in the range of 86.20- 86.25 mm for the large 915 1-2 syncros. This is with the syncro ring bottomed under the engagement dogs and the side clearance between the syncro ring and the circlip. Porsche specifies 86.20 mm to 86.54 mm. Normal diameters are about 76.25-76.35 mm for all the others with Porsche specification 76.12 mm to 76.48 mm.


How is this Alfa retrofit accomplished? Does it use the Porsche hub for the sliding sleeve? How is it splined onto the shaft? How is the engagement dog ring attached to the free gear? Does the shift fork properly fit the sliding sleeve (side clearance spec is ? How much of the shift fork engages the circumference of the sliding sleeve? Porsche uses about 180º while some other manufacturers only use 30º or so.

Best,
Grady

 

[Zed Head]

Worst case, use the front case to make a more modern transmission.  Sell the servo synchro parts to the racers out there that are also in your boat.

http://zhome.com/ZCMnL/tech/240SX5spd/transmission.htm