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Mr. Bill

5 Speed Clutch Brake Cannot Shift

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I have a 69 R685T that grinds and won't shift into 4th and 5th. Transmission is a 5 speed not synchronized. Downshift is impossible. Heres the history.

Installed new clutch plates, pressure plate, bearing and had flywheel machined. Put together and adjusted to what the book says with 1/8 inch clearance on the throw out bearing and the clutch brake at about 1 to 2 inches from the floor.

It shifted when I drove it home but after repairs it will not downshift or shift into 4th or 5th. The clutch brake I can feel presssure through the pedal so it is engagine. The plate also has about 1/8 inch lining on it.

Any ideas ???

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Why are you trying to use the clutch brake for shifting? That's not what it's meant for.

All you have to do for an upshift is let the RPM's drop to where they would be if you were already in the next higher gear, and slide the stick into that gear at that point

Downshifting is just the opposite, pull the stick out of gear, raise the engine RPM's to where they would be if you already were in the next lower gear, and slide the stick into gear at that point.

The clutch brake is designed to stop the transmission gears from turning when you are at a stop in order to get the trans into gear without grinding or having to wait a long time for the gears to stop turning. Using it for anything else is improper and will ruin the clutch brake quickly.

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What HK said,you just have to remember,engine speed must match trans speed,try lightly scratching the gears while raising or lowering the rpm you will be able tell by sound and feel when its just right to slide into gear.

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Well, that sounds better than what I got out of the book. I will try it today and see what happens. I read where the clutch brake was used to stop the gears from turning. Didn't connect that that was for setting still.

Thanks HK and Macks. This helps me out. I like my Mack but don't know to much about it yet. Sure glad to find fellas like you to that know.

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Well, that sounds better than what I got out of the book. I will try it today and see what happens. I read where the clutch brake was used to stop the gears from turning. Didn't connect that that was for setting still.

Thanks HK and Macks. This helps me out. I like my Mack but don't know to much about it yet. Sure glad to find fellas like you to that know.

With experience and familiarization with the characteristics of your truck, you won't "scratch" gears very long till they will slide right in without noise.

Don't never shove the clutch pedal to the floor unless you are dead still wanting to go into gear from neutral.

Rob

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all the above is true, and also you can't downshift a 5 speed Mack until the rpms come WAY down anyway. The one I drove ( 300,5 spd.) would turn 2400 rpms but I didn't downshift until it got down to about 11-1200 rpms. Neat thing about a 5 spd. Mack with the high torque rise engine- you can be driving down the road loaded, let off it 'til the rpms drop to 11 or 1200,mash on it and it picks it right back up, with no downshifting.

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