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Clutch brake usage


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I was browsing back through old posts and came upon one discussing proper use of the clutch brake. Most posters agreed that the only time the clutch brake is used is when engaging a gear to prevent grinding. That comment took me back many years........(flashback here).....

I was working for a sand and gravel company driving a White 2300 dump with the 555 Cummins. They bought two new DM-600 Maxidynes. They had the smaller cab w/green dash, six speed twin stick, but larger Mack letters on the front, which tells me they had to be at the very end run of the green dash versions, late 1973. Anyway, when I finished work on Friday afternoon I was told I'd be assigned one of the new Macks on Monday. I was so cranked up I could hardly sleep the entire weekend which actually crawled by cause I couldn't wait to drive the new Maxidyne. On a whim I grabbed the operator's manual and read it cover to cover over the weekend. And, I clearly remember reading about clutch brake usage, which of course described using it to ease gear engagement when stopped, but it also mentioned using it to shift the transmission faster between gears, i.e, you depress the clutch pedal fully to use the clutch brake between shifts, not double-clutching at all. Well, it worked. When I mentioned that to my boss, he said the clutch brake was only used to prevent rolling back on hills when stopped. I thought he hadn't a clue what he was talking about but kept that opinion to myself. :-) To this day, when describing the procedure I always mention that I learned it from a Mack operator's manual.

So, I got thinking that perhaps someone on this forum remembers the same thing, or better still, someone actually has an original Maxidyne operator's manual that describes this procedure. I didn't post on the original BMT post which would bump it up to the front because it was at least five years ago.

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The clutch brake is used to stop the trans gears from spinning to ease in shifting into gear but ONLY when the truck is at a full stop, engaging it while the truck is moving or even rolling very slow will brake it.

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Jeff,

I had heard about the old (optional) clutch brake that was not mounted on the main shaft but on the end of the lower countershaft on a 72 series trans. I don't have that type on my truck,but from what I've been told you could use it to shift gears faster than normal.You still double clutched it. On your second clutching,you depressed the pedal a little further to engage the clutch brake,and slow the countershaft to make the shift quicker.Took some timing on the drivers part. MACKS,you're right.You would not want to do with todays clutch brake being mounted on the main shaft. You will tear that thing up in no time! Not a fun job to replace.Although easier with the Babcock 2-piece replacement. Al

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IF YOU BOUGHT IT, A TRUCK BROUGHT IT..AND WHEN YOU'RE DONE WITH IT, A TRUCK WILL HAUL IT AWAY!!! Big John Trimble,WRVA

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I was browsing back through old posts and came upon one discussing proper use of the clutch brake. Most posters agreed that the only time the clutch brake is used is when engaging a gear to prevent grinding. That comment took me back many years........(flashback here).....

I was working for a sand and gravel company driving a White 2300 dump with the 555 Cummins. They bought two new DM-600 Maxidynes. They had the smaller cab w/green dash, six speed twin stick, but larger Mack letters on the front, which tells me they had to be at the very end run of the green dash versions, late 1973. Anyway, when I finished work on Friday afternoon I was told I'd be assigned one of the new Macks on Monday. I was so cranked up I could hardly sleep the entire weekend which actually crawled by cause I couldn't wait to drive the new Maxidyne. On a whim I grabbed the operator's manual and read it cover to cover over the weekend. And, I clearly remember reading about clutch brake usage, which of course described using it to ease gear engagement when stopped, but it also mentioned using it to shift the transmission faster between gears, i.e, you depress the clutch pedal fully to use the clutch brake between shifts, not double-clutching at all. Well, it worked. When I mentioned that to my boss, he said the clutch brake was only used to prevent rolling back on hills when stopped. I thought he hadn't a clue what he was talking about but kept that opinion to myself. :-) To this day, when describing the procedure I always mention that I learned it from a Mack operator's manual.

So, I got thinking that perhaps someone on this forum remembers the same thing, or better still, someone actually has an original Maxidyne operator's manual that describes this procedure. I didn't post on the original BMT post which would bump it up to the front because it was at least five years ago.

I remember exactly what you're talking about.

I remember reading the same thing.

I tried it a few times and it worked great but never got used to doing that way!

Ron

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I remember exactly what you're talking about.

I remember reading the same thing.

I tried it a few times and it worked great but never got used to doing that way!

Ron

Well, that's a relief--at least I didn't imagine it. I've used the technique over the years on many trucks, but not all that often--usually when skip-shifting between gears with a roadranger. I've had numerous assigned trucks over the years and haven't worn out the clutch brake prematurely.

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I recall on the early 1076 and 1078 5 speeds the clutch brake was spring loaded so you couldn't shear the ears off them.That was so they could be used for shifting.I'm sure the early 6 speeds had this also. Steve

The thing is if the wheels of the truck are turning then the transmission is turning and the clutch bake is not going to stop it unless your just rolling very slow and use the clutch brake to stop the truck witch you should not do.
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How far does one have to push in the clutch for the brake to work?

If everything is adjusted correctly, it should engage the clutch brake in the last inch of travel.

My 1992 R model handbook says the clutch brake is NOT to be used going up or down on shifts.

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Jim

It doesn't cost anything to pay attention.

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Right! Not be used like that in today's trucks, for sure. As Jeff stated in his initial post, it was still an option in the early '70's for the countershaft mounted clutch brake. It was listed in the B,G,N,H model Operator's Manual that I have.

IF YOU BOUGHT IT, A TRUCK BROUGHT IT..AND WHEN YOU'RE DONE WITH IT, A TRUCK WILL HAUL IT AWAY!!! Big John Trimble,WRVA

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If everything is adjusted correctly, it should engage the clutch brake in the last inch of travel.

My 1992 R model handbook says the clutch brake is NOT to be used going up or down on shifts.

The MH handbook has similar verbage. I don't think I push it to the floor when I shift. Reason being, when I am sitting and want to put the tranny in gear I need to push the clutch in until it hits the floor stop. Thanks!

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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