Twin sticking a syncro np205

[SpeedlabDan]

Ok so I'm thinkin I'm gonna dive right in...

So here's the story, I'm twin sticking my np205 and it's a syncro. @sweetk30 was a sweet guy and shipped out a standard front output shaft l, shift fork and covers etc. So once I got the shift rail in the mail from him I'm laying my rail next to it and they are indexed identical and share the same length.
So the shaft can be modified just the same.
The front output shaft is similar with a spring loaded shift collar. (see picture)

So why couldn't the shift rail be independent? I don't forsee this causing an issue to grenade as a result of a high /low conflict between front and rear bc it operates the same way.

Now one draw back I do see is the possible strength of the front output being weaker as a result of spaller diameter rear cover bearing and the smaller diameter of the coupling gears.

Correct me if I'm wrong but this being a tow rig it would be nice to shift on the fly and I'm not turning 40s so?

 

[Hogback Fabrication]

The synchro front output doesn't change the NP205 shifting on the fly unless you have auto hubs.

I can double check things tomorrow to see why I thought the front output rail was different on the synchro 205's.

 

[SpeedlabDan]

The synchro front output doesn't change the NP205 shifting on the fly unless you have auto hubs.

I can double check things tomorrow to see why I thought the front output rail was different on the synchro 205's.

But technically if the manual hubs are locked in would it work the same way?

 

[Hogback Fabrication]

But technically if the manual hubs are locked in would it work the same way?

If the hubs are locked in, you can shift any NP205 (synchro or not) from 2HI to 4HI.

You can't shift any NP205 from high to low (or vice versa) at any speed.

The only purpose of the synchro front output is to spin the front driveshaft to convince the auto front hubs to lock in. The synchro front output serves no purpose with manual lockout hubs.

 

[SpeedlabDan]

If the hubs are locked in, you can shift any NP205 (synchro or not) from 2HI to 4HI.

You can't shift any NP205 from high to low (or vice versa) at any speed.

The only purpose of the synchro front output is to spin the front driveshaft to convince the auto front hubs to lock in. The synchro front output serves no purpose with manual lockout hubs.

I understand, but does the syncro shift selector allow easier shifting from 2hi to 4 hi while moving?

 

[Hogback Fabrication]

I understand, but does the syncro shift selector allow easier shifting from 2hi to 4 hi while moving?

Not at all. If the front driveshaft is spinning the same speed as the rear (i.e. hubs locked in), the 205 will go from 2HI to 4HI (or vice versa) like butter. Syncho 205 or not.

Some of the 80's 205's had synchro front outputs, as do all GM 208's and 241's (in the square bodies anyway). The reason is completely for auto hubs. When you pull on the transfer case shifter to engage 4HI, a synchronized case will start to spin the front output just a bit. With auto hubs, when the front shaft starts to spin it makes the hubs lock in. Once the hubs lock in, the t-case will shift the rest of the way into 4HI.

 

[TreeFarm]

The shift rails are the same, the shift forks and front sliders are different. mine has twin stick rails in it(my first failed attempt at modifying rails) When I had mine apart and together it never seemed to want to shift the front rail the same as my non syncro unit, but that could be all the extra junk in there. There is also different gear spacing and mesh between the syncro and non syncro units.

 

[SpeedlabDan]

Looks like fat shaft it is! Now to the milling machine.

 

[454Sub]

I have never seen one of these in real life opened up before. And I refuse to Google it.

 

[SpeedlabDan]

Correction: the shaft being modified is the rear/short shaft not the front as I previously mentioned. It's probably easier to just use a fresh flapper wheel and use a deft grinder hand.

 

[nvrenuf]

Show off.

 

[sweetk30]

Show off.

ya real men doit with a hand grinder and like it .

 

[TreeFarm]

Correction: the shaft being modified is the rear/short shaft not the front as I previously mentioned. It's probably easier to just use a fresh flapper wheel and use a deft grinder hand.

View attachment 280484

Flapper is how I did mine. That’s why I messed up my first rail haha

 

[SpeedlabDan]

I finished with a fresh 120 grit flapper and tested for high/low lock out. Came out nice