Does anyone "float the gears" when shifting M39/M809?

[US6x4]

Not sure if I've asked this before but...

I'm curious if these Spicers can handle it or put up with it. I've never tried it myself - just always used the clutch to shift like a pickup truck.

How does everyone row the gears?

 

[txturbo]

Should work just fine. I’ve only driven mine about 20 miles so far but haven’t tried it yet. Plan to once my tire fiasco is dealt with.

 

[Brutacus]

I do, but only from 4th to 5th and from 5th to 4th. The lower gears can be hard because you have to control the throttle more precisely due the how big the gap is in between the gear ratios. The bigger gap allows the engine enough time to rev down. From 4th gear to 5th gear is much easier because it's only a 32% jump in between those gear ratios. The others are anywhere from 50% to 80%.

 

[M813rc]

Is there an advantage to shifting that way?
I've always driven my 813 the way the military taught me - clutch in, blip throttle, shift, clutch out

Cheers

 

[US6x4]

Is there an advantage to shifting that way?
I've always driven my 813 the way the military taught me - clutch in, blip throttle, shift, clutch out

Cheers

The advantage might be avoiding the fatigue on your left leg and the wear & tear on the clutch parts?

Or maybe there's no advantage and it simply moves the wear & tear from the clutch to the synchros instead...

 

[txturbo]

The advantage might be avoiding the fatigue on your left leg and the wear & tear on the clutch parts?

Or maybe there's no advantage and it simply moves the wear & tear from the clutch to the synchros instead...

Is this transmission synchronized? Most big trucks aren’t.

 

[Brutacus]

That's hard to say, all the transmissions I'd normally float through gear were not equipped with synchros, so it was never considered bad to do it. Just as long as you don't grind the gears. When you have 10 or more gears, it does save some wear and tear for the clutch and your leg too. Once again I only float inbetween the 4th and 5th gears. When done correctly, the shift can be much smoother on the drive line. It's easier on the trnsfer case, u-joints, and the differentials.

 

[US6x4]

Is this transmission synchronized? Most big trucks aren’t.

I'm pretty sure 2,3,4, & 5 are synchro'd

 

[txturbo]

The advantage might be avoiding the fatigue on your left leg and the wear & tear on the clutch parts?

Or maybe there's no advantage and it simply moves the wear & tear from the clutch to the synchros instead...

Synchronizers work with or without the clutch so I don’t think that’s an issue.

 

[98G]

30 years ago I learned to shift without a clutch.

More recently I've learned not to, unless there's explicit need to do so.

I've talked to big truck mechanics who have said they can visually tell by the wear patterns
when a transmission has lived its life without the clutch being used . @rustystud may have something to say on this topic.

if you lose a clutch, its a good skill to have. I lost a clutch in redtruck and made it from OK to CA shifting without it, except for taking off from stops.

But as a standard practice, even if you're good at it, you're just trading clutch wear for wear elsewhere.

 

[biscuitwhistler37]

I was curious about this as well, more so for the M35 but still, I'll have a 5 ton some day and it would be nice to know. Also if OP doesn't mind my asking here, what's your opinion on "free wheeling"? I was raised to always let the vehicle coast in neutral (with manual transmission) while slowing and only apply the brake if/when necessary, have always driven like that, never had an issue. I freewheeled my M35 last time I had it out, no issues, just curious as to why we're not supposed to and if it were the same for the M800 series trucks.

 

[Mullaney]

I was curious about this as well, more so for the M35 but still, I'll have a 5 ton some day and it would be nice to know. Also if OP doesn't mind my asking here, what's your opinion on "free wheeling"? I was raised to always let the vehicle coast in neutral while slowing and only apply the brake if/when necessary, have always driven like that, never had an issue. I freewheeled my M35 last time I had it out, no issues, just curious as to why we're not supposed to and if it were the same for the M800 series trucks.

.
I was taught to leave the vehicle in gear and allow it to help slow it down.

 

[US6x4]

Keeping it in gear while slowing is much safer in these trucks because you're giving yourself redundant braking capabilities (compression braking + parasitic drive train drag) which can help get you out of trouble if the hydraulic service brakes fail. If freewheeling then you're relying on single-circuit service brakes 100% to bring you to a stop and they can fail on occasion.

I always try to give myself room to coast but it's always in gear. Anymore, I use the jake brakes as often as is legally allowed.

 

[txturbo]

I was curious about this as well, more so for the M35 but still, I'll have a 5 ton some day and it would be nice to know. Also if OP doesn't mind my asking here, what's your opinion on "free wheeling"? I was raised to always let the vehicle coast in neutral (with manual transmission) while slowing and only apply the brake if/when necessary, have always driven like that, never had an issue. I freewheeled my M35 last time I had it out, no issues, just curious as to why we're not supposed to and if it were the same for the M800 series trucks.

You shouldn’t free wheel in neutral for safety’s sake. Transmission should always be in a gear unless stopped.

 

[G744]

A clutch linkage is a lot easier to fix than a transmission...

 

[M813rc]

Check your state law, but free wheeling is illegal in many states, for precisely the reasons mentioned above.

Cheers

 

[kubotaman]

This has been a long debated topic, but I was always taught not to float synchronized transmissions which has been reinforced by every transmission rebuilder I've talked to. Sure you might save some clutch wear, but at the cost of premature syncro wear. Clutches are cheaper than transmissions.

Most large trucks are not synchronized and can be floated more easily with less wear, but Deuce and 5 ton transmissions are more like car and pickup transmissions being synchronized in every gear except first and reverse.

 

[m1010plowboy]

Had a hippie teach me how to float a 5 and 4 international back in 1981. Wasn't his truck so the lesson was free but I drove that truck for 17 summers without any clutch work. Wish I could open it up to have a look.

The training goal was to be able to slow the truck without brakes or clutch. The bonus education is learning to listen to RPM, feel road speed and allow the engine to slow the truck without brakes. We got real good at knowing when to burp the throttle out of a higher gear to feather the throttle up....controlled enough..... to grab a lower gear within the rpm range. Learning how to stop a truck without brakes was a skill we never needed but it sure is good to know.

My trainer was good. Stopping awareness and looking at traffic lights far in the distance meant we'd 'time' every light. Managing mass, speed and gravity, timing the stop lights was a great way to save brakes......and maybe clutch, but maybe not synchros.... good to know.

Driving the 5/4 was the first time I won a bet too. Had a buddy say that transmissions don't have 4 ranges in reverse. I slammed 4 gears across a 300ft. parking lot, in reverse, and won a case of Canadian beer.

Whether hard on mechanical parts or not, it's a handy skill that should be taught.......says the guy with automatics.