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Discussion Starter #1
Recently I changed my brake setup on my truck so it has a pinion brake in the front and drums in the rear. When I get on the brakes the front makes a rattle noise and I can't seem to figure it out. The truck stops fine, it just makes this noise. I checked the pinion bearings and they are fine. Anybody have an idea as to what it could be?
 

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drive shaft angles on the front? With leaf springs it could also be caused by axle wrap, it could be causing enough load that your getting a vibration just like having improper angles on a rear shaft when accelerating.
 

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Discussion Starter #3 (Edited)
Definitely not front driveshaft. I took it out thinking that might be it and nothing changed. I guess I'll get to work on a traction bar for the front and see if that helps. I was thinking maybe it was the rotor slipping within the caliper when stopping, but that's just a wild guess.
 

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Discussion Starter #4
Anybody else have an idea what it could be?
 

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i used to have two pinion brakes on my two front rockwells(i have rear steering), and for sometime i had what you described.
after all kinds of trial & error attempts to solve this very disturbing fenomenon, i found out that my front axle had too much axle movement(wrap) due to too long distance between the upper and lower links.
it did indeed prevent axle wrap while throtteling, but caused the complete opposite action when stopping.
eventually, i got to the conclusion that i need only one pinion brake in the rear and eliminated the one in the front. later on i changed the front suspension, but immidiately after removing the front pinion brake, all my troubles were history.
i do'nt know what front suspension you have, but whatever you run, just get rid of the front pinion brake and the drums and go for one rear pinion brake.
my vehicle weighs 6000lb and it stops very very well with only one rear pinion brake. moreover, you do not need those drum brakes - they are HEAVY and you would cut some100-150lb off just your rig's weight, by geting rid of them.
let us know what you find out - it's interesting.
 

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Discussion Starter #6
I run 12" leafs up front since it's mainly a mud truck and I'm not worried about ride or travel. I used to run a single pinion in the rear but moved it to the front after cracking a rotor due to a panic stop. It stopped pretty well before with that setup, so what do you think about moving the pinion brake back to the rear axle and hooking up the drums as well? I don't think removing the drums would make enough of a difference as far as weight is concerned on my rig since it's probably over 8000 lbs. I could very well be wrong, but I think even a limited amount of additional braking provided by the rear drums would be more advantageous than ditching them all together.
 

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the pinion brake is working on the input shaft of the axle, before the 6.72:1 gearing.
this means that a single pinion brake is worth almost 7 times a usual brake. i guess it would be even more than this when it comes to a usual drum brake as opposed to a usual disk brake.
this is why the drums are totally insignificant in this case.
moreover - since it's a mud truck, i do'nt have to tell you what the mud does to drums and what a nightmare they become after a good mudding.....
i'd say put a stout dual piston caliper as a rear pinion brake and throw those lousy drums away.
 

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Ok I'm sorry for digging this post up, but after much searching it's the closest to troubleshooting I could find. On my rig I run front wheel brakes and a rear pinion brake. My rear diff is clocked so it's more to the center, and my pinion brake is hanging off the back (on the larger pinion bearing side). I to have this rattle/clanking noise that seems speed dense (the slower I got the slower the noise got). However, the harder I press on the brakes the more the noise dampens. Being I had minor driveshaft vibes at cruise I figured that was the culprit. I tilted my rear end up to where it's about 2* below the t/case output and redid my trac-bars. The noise still persists. Hell sometimes the truck will shutter as if the driveshaft is binding up (which should be impossible in this case?). If the driveline angles ended up being the culprit I was gonna run 1410 CV joints on both ends from high angle driveline and turn the axle back down (for 4 wheel steer). This obviously isn't the case though. I've removed the drive hub flanges off the rear and set the truck in drive to see if I could hear anything in the diff, no such luck. Anybody heard or dealt with this before? :confused: I could just run my homebrew wheelbrakes out back but I love the stopping force and simplicity of my pinion brake. I've tuned the shims before so the yolks are still nice and tight.

Thanks,
Billy
 

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Its the backlash (I think thats the term) in the gear set. With the drivetrain in neutral, how much play do you have at the pinion. Meaning, can you rotate the pinion any with out trying to turn the tires? On mine, there is about a quarter turn (1/8th both ways) before the gears take hold. What is happening is this:
Apply brakes, driveshaft/pinion stops
Ring gear/axleshafts continue for that slight slack amount
Slack is taken up and the pinion is driven by the axleshafts - rotor breaks lose for a moment then the cycle continues.

At least thats what I think is happening.
 

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Hero said:
Its the backlash (I think thats the term) in the gear set. With the drivetrain in neutral, how much play do you have at the pinion. Meaning, can you rotate the pinion any with out trying to turn the tires? On mine, there is about a quarter turn (1/8th both ways) before the gears take hold. What is happening is this:
Apply brakes, driveshaft/pinion stops
Ring gear/axleshafts continue for that slight slack amount
Slack is taken up and the pinion is driven by the axleshafts - rotor breaks lose for a moment then the cycle continues.

At least thats what I think is happening.
Honestly, I partially figured that to. When the truck is cold, I believe the rotor is cold. The sound is very minimal to none. Once the brake warms up (doesn't take long). I believe either the vanes or deformity of the rotor itself causes vast pulsing. Making the gears knock around inside. What I didn't understand is how this can cause shuttering/violent vibrations inside the truck? I've tuned it once. Maybe it's time to tear the caps back off and tune it again.
 

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studlybilly said:
Honestly, I partially figured that to. When the truck is cold, I believe the rotor is cold. The sound is very minimal to none. Once the brake warms up (doesn't take long). I believe either the vanes or deformity of the rotor itself causes vast pulsing. Making the gears knock around inside. What I didn't understand is how this can cause shuttering/violent vibrations inside the truck? I've tuned it once. Maybe it's time to tear the caps back off and tune it again.
Maybe when its cold its not gripping as well allowing the axle to drive the rotor easier? Hell, I dunno. All I know is that when I lock em up the truck will rock back and forth in that slack for a bit before it settles down. I dont think the rotor is warping any, just that the friction changes enough to make a differenance.
 

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Hero said:
Maybe when its cold its not gripping as well allowing the axle to drive the rotor easier? Hell, I dunno. All I know is that when I lock em up the truck will rock back and forth in that slack for a bit before it settles down. I dont think the rotor is warping any, just that the friction changes enough to make a differenance.
I appreciate the help, gonna go reset backlash and check a few other doodads in hopes I can eliminate the problem.
 
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