The Stovebolt Site Forums The Parking Lot Big Bolts Two speed rear proper shift?? 22.5" rim Question. '56 6100

Hello:

It's been a while for me. Hope everyone is doing well. Anyway, today I put my '56 6100 dump on the road and put about 20 miles on it around town and highway. Couple questions. What is the proper way to shift the rear? I know it may be needed to split all the gears when heavily loaded...etc, but the how should I run the clutch and throttle when shifting. It has been a while for me. From shifting from low to hi, I pull the knob as I ease off the throttle and she shifts in pretty quick, maybe a second or so. What about going from hi to low? Taboo, or OK with these trucks. It is a vaccuum shift axle.

Second question is why do some trucks have 22.5" rubber? Benifits or drawbacks? All the big trucks I have had had 20" ten lug split or 1 piece rims. This truck has 22.5" rubber on 1 piece rims. Six lug front and rear with huge 1.5" lug nuts. The stud in the middle has a square end also. An old timer told me there was a tool for these that held the stud while loosening the nut. Any help is appreciated. The truck is alot of fun. 265, 4 speed, 9' Perfection dump body...etc.

Thanks

-John

i always shift the axle wait a second then let off the gas and let it shift same going up or down, but mine are are electric shift axles

You can shift the 2-speed both ways, with approximately the same procedure. Shifting from low to Hi, select hi range before you release the throttle and let the springs in the shift assembly preload themselves. Then, either tap the clutch quickly, or just let off and get back on the gas. The upshift happens pretty quickly that way. One second is a very long time for the shift to complete itself.

On a hi to low downshift, begin the same way, by preselecting low range BEFORE you let off the gas. Then, quickly close the throttle, and jump right back into it. The shift will happen almost instantaneously.

Split shifting:
If you need to select a lower gear in the transmission and a different rear end ratio, do it this way- - - -From 4th. gear low range to 3rd. high, fort instance, just preselect high range before making the transmission downshift. As you're moving the shifter, the rear end will shift itself back to low range. Same way for upshifts- - -go from Hi range 3rd. to low range 4th., etc. by preselecting the rear end ratio before making the tranny shift. An experienced driver can make an SM420/2-speed rear combo sound like an 8-speed transmission!
Jerry

I agree with 47chevy6400 about shifting a 2-speed axle, both electric and vacuum shift the same way. I have both types. 22.5 rubber is just the tubeless version of the 20 inch tube type tires. Hope this helps,
James

Shifting just takes practice. Going up thru the gears is pretty simple, coming back down takes a bit more practice, I'm still working on it myself.

As for the lugs, the square part on the rears is for the inner wheel. the nut is for the outer and can be tightened/loosened without holding the square part. I've seen the lug tool at Napa or they can be had at a truck parts store.

you will want that tool as sometimes it will drive the stud into the drum instead of removing the outer nut. then you wind up with both wheels off but joined together with the inner and outer nuts which is a bear to deal with, not much fun even with the correct tool. there is a special square socket for the inner nut. The special tool for problems is a q shaped short wrench which slips over the offending nut and has a lug that catches on the center hole to hold the outer nut still while you drive the inner nut down thru. if you do drive the stud into the drum usually gentle probing with a slender magnet will draw it back out without having to remove the drum.

The tool the old timer is describing is used when the outer nut is so rusty that the inner nut comes off along with it. An inch and a half box end will do the same thing. It holds the outer nut while you turn the inner nut usually with an impact. Although Budd type wheels are almost obsolete, most truck tire shops still have one. We have used nothing but hub piloted the last 10 years, but we still have the tool laying around. If the inner or outer nut is rusted, we heat it a little and then pour on cold water. The biggest problem is breaking the stud. That is the threaded part, that you screw the inner nut onto. With the old inboard drums, you have to take the whole hub off to put in a new stud. As for the 22.5 tires, at least anyone will change the tubeless. Most people are afraid of 2 or 3 piece tube type wheels. Regarding the 2 speed, you can preselect and when you downshift, just let off the gas momentarily and it will shift. Upshifting requires a little more skill. You must let the rpm's fall down to where it can shift. If you give it the gas too soon, it can grab and tear up the planitary gear.

i was asked a couple of times how many gears does that thing have because of the split shifting and showing off with my engine. i say eight and i get a funny look with a reply of " i didnt know they made an eight speed". i go on to say its a modified fuller ten speed and they thru two away and the funniest look come to thier face and i leave it at that.

because of where i live, i had to learn to shift the rear. i asked here a couple of yrs ago and was told what jerry posted but not as a detailed explanation as his with pracatice. even though i use it all the time with both trucks i still on occassion blow a shift when going from hi to low mostly because im not paying attention during the shift. either the motor races and then jumps into gear or it goes cling, cling, cling and you slow down until it jumps in. i have found out going uphill the motor races and going down hill it goes clang clang.