Can't shift into 3rd

[mecharedneck]

So I finally got the M37 on the road, licensed and all that stuff. Brakes are still a little sketchy, but I'll be replacing the leaky line this weekend.

The problem I'm finding now that I can get up to speeds where I need to shift, is I can't get into 3rd! When the motor is off, i can move the stick into the spot for third, but if I'm moving, it's a no go. I've been reading about double clutching, but I don't know if I'm doing it right. I can get into 1st, 2nd and 4th no problem (it is a little touchy about downshifting though).

I watched a youtube vid, and the guy in that was double clutching really smoothly and with very little pause between gears. I wound it up to about 20 and just kept letting it decelerate as I tried to go into 3rd multiple times, and it was nothing but grind city.

Does anyone have any tips?
Thanks

 

[T. Highway]

You have to match your engine speed to the ground speed. It will take a little practice if you have never "speed shifted" a manual trans without using the clutch. Try increasing the RPMs slightly between the double clutch and it will work for you.

 

[armytruck63]

The M37 has syncromeshed gears, except for first gear (and reverse, of course). If you have to double clutch in order to switch gears, then the transmission might need to be rebuilt.

First, pull up the cab floor and pull off the transmission top. You could just have bent or misadjusted shift forks.

Resist the temptation to take that truck on the road until you get the brakes working properly.

 

[armytruck63]

Another possibillity, are you sure your clutch is releasing completely? A dragging clutch will cause the same symptoms.

 

[T. Highway]

Only 3rd and direct drive are syncro'd.

Another thing you may want to check but will require removal of the tranny.
You will need to remove the main shaft, then remove the 1st and 2nd sliding gear. Under those gears is a snap ring that holds the syncro gear in place. The slot/groove on the mainshaft that holds the snap ring tend to break off, if so you will need to replace the main shaft.

Hope this helps.