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Discussion Starter #1
This got buried in the pissing match over at: http://www.pirate4x4.com/forum/showthread.php?s=&threadid=32493

Let's assume that:
* you are fully locked
* your locker stays engaged
* your driveshafts and transfer case hold
(don't get me started on whether a Detroits is the same as a spool without power to the pinion :D )

I can throw out a bunch of information about effective gear ratio, brake ratio, and rotor speed, but I don't know firsthand how this works with two pinion-mounted brakes. I do know how this works with wheel-mounted disk brakes, and I understand how increasing brake swept area helps on an exponential scale...

But I am wondering whether pinion-brake systems can be very functional in the real world, especially on the street.

At first glance, with the rotational mass of everything 'outboard' of the pinion (that's the diff, the axle shafts, the 20" steel wheels, and the 53" billion-ply military tires), I can't see how a teeny 4-bolt rotor and two-pot caliper could even start to hold back 2 tons worth of trail rig, not even if there were two of 'em, one on each pinion.

Randii (who likes a brake on each wheel, thankyouverymuch!)
 

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Discussion Starter #2
In that other thread....

Pete (pcorssmit) posted:
I've asked how overheating could NOT be a problem on a few posts, and this is the first one I've seen where someone actually said something about it. Yes, the brakes will have plenty of power due to the gear reduction, but you still have to dissipate the same amount of energy. You're trying to stop the same or more weight (as the rig w/one ton axles) with 1/4 the brake area. I don't see how they could keep from overheating.

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Then CJ Lagos posted
I'm bothered by the fact that people are having their pinion discs get really hot. Think about it, your giving your brakes roughly a 7x multiplication. There should be a whole lot less force needed to stop the axle with that one caliper and the reduction than two calipers at the wheels. What I think might be happening is people are generally using smaller components. I'm shooting for 1/2ton chevy stuff, I don't think that will get over worked. g
 

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Discussion Starter #3
I see pretty small components in use, maybe that is part of the problem, but I dunno.

Brakes are pretty simple things, really -- they disippate kinetic energy as heat. The differential gears offer mechanical advantage, but that energy still has to turn into heat!

Food for thought....

Randii
 

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heh, we're actually discussing things close to this on anther board @ the moment. I have a friend that ran a pinion brake on the rear of the truck for a while. Stopped fine, but ate pads up quick. He was using a F150 caliper & rotor.
 

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Well then, why not two calipers per rotor? Or, why not run twin rotors with one caliper per rotor?
 

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Randii,

I think you're right on. There's a great book from HP books (The Brake handbook) that has all the info and formulae to prove it. But your instincts are correct.

Brakes convert energy, gearing has NOTHING to do with it. Consider the places where braking is the most critical, like F1 cars and Rally cars...thay have HUGE rotors at the wheel with multiple calipers on each. Shoot, those little lightweight Rally cars have 15 inch rotors!!!

I would think a pinion only brake would be pretty damn useless / scary on the street.

Of course, that's just based on theory. Any of the big boys wan't to prove me wrong, please post a clip of you doing 70mph than locking them up under a full panic stop.

Now - if you never do anything but back of a trailer and crawl at <10mmoh, that makes a HUGE difference.
 

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food for thought
on the downside:
not as much brake to dissipate the heat

require a proper locker to equilize braking

unlocking hubs are a nono

if the shafts break you lose brakes

may not be legal where you live anyways.

on the upside
you have a gearing advatage on the tires that increases
braking power compensating for large tires

the disk is spinning faster so it can move more cooling
air thru the vents, also it is mounted in an area that
sees more airflow than inside a rim and tire

I plan to try this out on my d70's when I set em up, seems cheaper than putting the disks on the hubs.
 

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Discussion Starter #8
Well then, why not two calipers per rotor?
That does not increase the disk's ability to shed heat. It increases the amount of friction material applied, but IMHO 4-pot calipers or the like from a high-performance car would get you there more easily.

Or, why not run twin rotors with one caliper per rotor?
This could work, but remember, the area of a circle goes up on a squared relationship relative to radius, so fitting a larger disk makes good sense, and using a vented (mebbe even drilled) rotor makes even more sense.

Trimming the radiator shroud to duct air could really help the front disk on the trail, but these are all band-aids to serious on-road heat. As BV pointed out, this may not matter for trails, but I have yet to see a production pinion service brake on the highway.

Pinion brakes seem to me to make sense in the same fashion that t-case brakes make sense -- as emergency brakes, but not as service brakes.

Mebbe you Rockwell boyz should be running drag strip drogue chutes. :flipoff2:

Randii
 

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mytzlflick said:
the disk is spinning faster so it can move more cooling
air thru the vents, also it is mounted in an area that
sees more airflow than inside a rim and tire

Maybe it eats more pads because the rotor is spinning 6x faster than one on the wheel would be. It might be eaiser to stop with all that gear multiplication if it wasn't spinning that fast. Just thinking.
 

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The guys I've talked to running the pinion brakes say they stop really well. Im wondering about using two calipers per rotor, I might do that, that's a good idea.

CJ
 

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probably eats pads becuase twice the overall force is required on a single disk. if you run one ton disks I would imagine more sucess as they are disigned to stop a lot more weight in the first place. and yeah i imagine that kind of surface speed would be a problem. if you run highway speeds with 7.17 gears your disk would think it was running 350mph, probably a little outside the average design parameters of a brake pad.
 

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I would never use a pinion brake setup on the highway for the simple reason that there is no mechanical ebrake. I would want at least one braking system at the last possible point of failure-the wheel. However, my rig is trail-only, so I feel that pinion brakes, coupled with a t-case e-brake will be more than satisfactory.
 

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what about 2 roters per driveshaft. one on the tcase output and one on the pinion (assuming rockwell).

i have thought about trying to rig something like this under my motorhome for supplemantal braking to the rear wheels for thoes long down grades...totally separate system with its own pedal etc..
 

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Seems like the guys running Rockwells and the need for pinion brakes are not real worried about heat buildup...


I mean seriously - for normal trail use, just how hot are your brakes gonna get? :confused:
 

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Yea - it seems the deciding factor is whether the rig would ever be street driven. Imagine, you panic stop, and the tires grab and lock, but the U-joint you hadn't noticed was wearing lets go under the stress, now your "brakes" are firmly holding the shaftt while the wheels spin merrily out of control.



The guys I've talked to running the pinion brakes say they stop really well
CJ - did they quantify "stop really well" at all. As in, stop really well when I'm rock crawling at 5 mph, or stop really well as in a panic brake and swerve manouver at 70 mph in the rain?
 

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DRM said:
Seems like the guys running Rockwells and the need for pinion brakes are not real worried about heat buildup...


I mean seriously - for normal trail use, just how hot are your brakes gonna get? :confused:

Yup.
 

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Discussion Starter #17
However, my rig is trail-only, so I feel that pinion brakes, coupled with a t-case e-brake will be more than satisfactory.
Excellent -- I appreciate the redundancy in that setup. Kudos for planning well... I'd park behind you on the trail any day. :D

There are WAY too many folks relying only on their service brakes, without a functioning emergency brake... and far too few of them park nosed up against something when they stop. Thinking back to that Toyota that swimming in Spider Lake, wouldn't a functioning e-brake have been a good thing?

Randii
 

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Discussion Starter #18
I cant post pics until monday
Those will be FUN pictures! I'm imagining a 6-by locked up and sideways. :D

...know that I can lock up 6 tires at any speed the real problem is the brakes work too good...
Yeah, that's proof of part of the issue, but how does the truck handle lengthy braking sessions, like when you are descending a mountain, working turn-by-turn. Engine braking only gets you so far...

I'm not meaning to attack you -- I am honestly curious. :cool: This is great tech!

Randii
 

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I run pinion brakes with my bronco, one on the rear pinion and one on the front of the t. case. It's trailered
The reasons I use them are:
Drum brakes and related hardware weighed 180 lbs. (unimog)
With my axles pinion is 27'' high (unimog, flipped 9'')
Pinion brakes work great at slow speeds.

Using 9'' rotors, 3/8'' thick the rotors would quickly become RED HOT so I'm having Coleman make 1-1/4'' vented rotors.
The pads also wear down fast. (200 mi.)
Using detroits, there is a " clunk" as all the slop is taken out when the brakes are used and they're somewhat jerky
I would never consider pinion brakes for street use.
 

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I'm woundering in street use as a detroit sometimes decided to change lanes under power would this create the same effect under braking with pinion brakes? I'm still gonna try it on my t-case. hey jr do you have to run a flange on the case to mount those or can they go on a normal yoke somehow?
 
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