Another day another brake petal on the floor

[hemichallenger]

This time it was on a a3.
I loaded about 10000 pounds of scrap iron and was on the way to dump it and the petal went to the floor. I have not had any doubt the the brakes were working at 100 percent till the petal met the floor. After I got stopped and opened the hood pulled the brake fluid caps off both sides were full but air was bubbling from both sides. I drained the air tanks but air had entered the system so I could not pump them up. I started it and built up the air and it started bubbling again so I drained the air tanks and pulled the air lines off both air packs and sprayed pb blaster in the lines and put them back on and started it up and it was not bubbling. I then had to bleed the brakes to get any type of petal. I went and got rid of the load and drove back to the shop in discust.

 

[G-Force]

Sounds like one of the air valves on one of the air packs has decided to let air bleed back into the brake line to the master cylinder.

 

[jaymcb]

This time it was on a a3.
I loaded about 10000 pounds of scrap iron and was on the way to dump it and the petal went to the floor. I have not had any doubt the the brakes were working at 100 percent till the petal met the floor. After I got stopped and opened the hood pulled the brake fluid caps off both sides were full but air was bubbling from both sides. I drained the air tanks but air had entered the system so I could not pump them up. I started it and built up the air and it started bubbling again so I drained the air tanks and pulled the air lines off both air packs and sprayed pb blaster in the lines and put them back on and started it up and it was not bubbling. I then had to bleed the brakes to get any type of petal. I went and got rid of the load and drove back to the shop in discust.

26,000 pounds and no brakes have to cause a 'pucker moment' like you just can't believe.

I'm sorry you're disgusted; I would just be thankful no one was hurt, no equipment was damaged, and everything is safe. Brakes can be fixed, injuries (or worse) take a lot longer.....

 

[Heath_h49008]

The emergency brakes are inadequate....

Pinion brakes aren't good enough for on-road use by themselves...

But how tough would a GM master cyl and small tertiary brake pedal be to rig up to 1-2-or3 pinion brakes? The bracket/rotor kits are $120ea, calipers are $30-$40 ea.

Just thinking of a way to take out the "Pucker factor"...

Glad to hear you're safe.

 

[glcaines]

Glad to hear you didn't get hurt or hurt anyone else! The icing on the cake is that your truck wasn't damaged. One problem with an A3 is the automatic transmission. On the A2 you can gear down and even shift into low range to get it slowed way down as long as you have room. Although you can shift down to lower gears in the A3, you cannot shift the transfer case into low range unless stopped. Or at least, I don't know how to do it. It's hard enough to get into low range when stopped and in neutral.

 

[hndrsonj]

The emergency brakes are inadequate....

Pinion brakes aren't good enough for on-road use by themselves...

But how tough would a GM master cyl and small tertiary brake pedal be to rig up to 1-2-or3 pinion brakes? The bracket/rotor kits are $120ea, calipers are $30-$40 ea.

The brake is a parking brake only. It wasn't designed as an emergency brake. A pinion brake is actually a good idea for a parking/emergency brake.

 

[dburd72]

wildtimefabraction.com has pinon brakes setup i was wonder if they could be used as a backup if installed on on both rears ?

 

[Heavysteven]

Split system total brake fail.......

 

[nk14zp]

I thought that was the plus of the split system not loosing all your brakes?

 

[bones1]

Heath, I like the way you think. An emergency emergency brake.

 

[Heath_h49008]

Heath, I like the way you think. An emergency emergency brake.

Thank you! My brain rarely functions as intended by it's creator, or so I've been told. We may have to check the temp in H E double hockey stix if this idea is a good one...

I'm wondering if it could be run on the common pedal arm and out the firewall, to operate WITH the standard brakes. (Better brakes and the rotors wouldn't get as pitted from lack of use.)

Or, just put a second brake pedal in on the far left like old e-brakes. (But it wouldn't be ratcheting, and you would want to use it once or twice a trip to knock the flash rust off the rotors.)

The common pedal idea might not work because it would require both systems to be timed pretty precisely. The drums would need to hit first, then the discs at a low level, ramping up to a high level over the last 50% of the brake pedal travel.

Wait, I'm dumb. Just weld a tab, slide, or saddle to the secondary pushrod that made contact at the 40% travel point far enough down to still have full stroke before the pedal hit the floor. At 50% you are using 5% disks, for every % increase in pedal after that you increase disc load at a roughly 2-1 rate.

That's would actually be pretty easy to build, maintain itself well, give added braking power even before a failure, and act as an insurance policy in case of total primary failure.

 

[jwaller]

pinion brakes have been discussed to death. It simply cannot be done. the pinion turns at 6-7times the tire speed and all that's going to do is turn the rotor into a glowing fireball.

pinion brakes are for off road use only.

 

[Heath_h49008]

Someone already built the system with pinion brakes as emergency/secondaries? Which method did they use, separate pedals or linked?

 

[mktopside]

Seriously, do the math, it's not going to work. At 50mph the single rotor on your pinion brake would be spinning at 336 mph, trying to stop a truck that weights 14,000lbs. If you can afford reinforced carbon carbon brake rotors and pads to take the heat, you need to expand your hobbies.

Having the rotor turn into a fireball would be a "best case" scenario. At that speed and with that much heat your are very likely to have the rotor come apart, and hurl 1500F multi pound chunks of steel in a radial pattern..... At 300+ mph.

Google "expanding rod warhead"...... Yea, like that.

Have fun with your claymore brakes, you'd be safer with a large parachute.

 

[Heath_h49008]

If you are going to do this, it would be on all 3 axles, and not used except as a single full application once the primary had failed.

Worst case scenario... you're hauling 10k lbs and towing another 10k.. down a mountain... your stock brakes fail do to line rupture.

If the system is split, you're asking for 2 or 4 drums to stop you... worst case 2. They will fail.

If the factory parking brake is applied... you know, that idiotic pinion brake the factory put on the other end of the driveshaft... it will also fail.

But...

If you are the average guy who uses these in a parade, or hauling 5tons or less of whatever at off-highway speeds and you have an "Oh ****e!" moment at 35mph... after you've downshifted when coming to a NORMAL stop... the 3 pinion mounted chevy truck calipers/rotors will get one good stop in when you combine them with letting the clutch out.

Can they be used as a primary brake for a loaded truck? Of course not. Are you going to want them engaging at highway speeds, when the driveshaft is spinning at 3000rpm and expect them to do anything but grenade? Nope.

I'm reading the "Hydraulic E Brake" thread between working on my calc homework, and watching movies... Bear with me while I come up to speed on all the issues you guys have fleshed out, and what everyone's concerns were. I think it's a problem with a solution.

 

[mktopside]

I understand what you are trying to do, and it's a good thing. But, even with 3 rotors on the driveshaft (there's nowhere to mount them on the axles) you still have mechanical advantage against you. I also don't believe that the driveshaft, u-joints, or bolts could handle the massive amount of torque that you would need out of them to slow the vehicle down, as quickly as a pinion brake will.

The speed at that point in the drive line is just too great. Upon application the truck will lurch for a second, then the brake pad material is going to instantly explode into gas. If get a pad that doesn't do that, the rotor is going to instantly turn white hot, then shatter. The same would happen if you apply the brake slowly. In magic land, if you solved the heat issue or put 20 rotors on the drive shaft, the tires will lock and you'll be sliding. Every time you touched the pinion brake the wheels would lock.

There is a reason there isn't a single vehicle made from the factory with a pinion brake used for anything other than parking.

 

[Heath_h49008]

If the driveline can take it on acceleration, and during engine braking, it can take what relatively small amount of force a couple sets of pinion bakes could apply. But I get your point.

We are trying to quickly bleed energy from 3-7 points on the driveline, that are spinning at rates from 0-3500 rpm. How many ways can we do it? Are any of them cheap enough to justify vs just swapping $2000 worth of Ford F450 brake components?

Friction brakes converting kinetic energy to heat... driving another mechanical load... compressing a spring... heating a fluid... compressing hydraulic fluid/gas in an accumulator...

We also have the small shaft in front of the transfer case... a larger brake may be mountable there. Perhaps a single rotor from something much larger... like a Bendix air disc set-up. Again, the RPMs may be an issue. But, with these setups at least we have a better load rating to start with, and more and more semis will be in the junkyard with these, ripe for the plucking. I only question if there is enough room to mount them. Either end of the transfer case? On each diff?

I'm going to keep looking...

 

[jtron79]

I don't agree, It has been proven that pinion brakes are effective on these axles, also they can be mounted directly to the axle, there are several guys on pirate 4x4 that have proven this point, and are using them as SERVICE not emergency brakes. they may use them in offroad situations only but that doesn't mean they dont use them at near highway speeds on a daily basis.

 

[Goose2448]

I'm glad you did not end up running over the Beer truck. I think what Heath is trying to get at is put one or three on the truck to use as a parking brake, extra insurance, so the truck dose not roll away. Now say you had done that, and then you loose your brakes. What would you do? Keep plowing towards that school bus full of kids, or yank on that parking brake as hard as you could? I would yank like there is no tomorrow. Now I can say from having a parking brake on my burb, that they are as strong as a pile of poop. And are thin as all heck. But, if left with no brakes, you better bet your ass I would be slamming them on. Now by that, I mean in a controlled way. I had my drums lock up on my PU once and about went sideways. Done the same thing in the burb with Discs in the rear. But I would take sliding sideways over killing a bunch of kids, and I hate sliding sideways, last time I did, I ended up on my head.....

 

[Heath_h49008]

Parking brake? Nope.. wouldn't work. Every hydraulic system bleeds down over time... no version of "line locks" is going to hold for very long.

As secondary/emergency brakes they should work. If these guys are running them at 3000+ RPM on offroad trucks with even half the load we have to stop, then they will hold for the one emergency stop we are talking about needing them for.

Thanks for the lead to the "Pirate" forum! I can expand my search to see what these guys are doing and at what speeds these are capable of running.