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Old 04-27-2015, 07:32 PM   #1 (permalink)
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friends Rockwelled YJ brakes waaayy too touchy

Hey everybody,

Going to help a friend with sorting out his braking issue this weekend. Hes got a Yj on 42s that he has been playing with for a while and just starting to get it all dialed in. one of his last issues is that braking at any real speed starts to get a little sketchy. he hardly has to hit the brakes and all 4 tires lock up. its rare that I'm trying to help folks solve brakes being too good, and I am not well versed in rockwell/pinion brake set ups.

He had mentioned reading of people doing away with the booster and going with just the master cylinder. I have never heard of this...opinions?
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Old 04-27-2015, 07:52 PM   #2 (permalink)
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Yup.

And a smaller master. Master is designed for 2 calipers an end (or 2 calipers and 2 wheel cylinders)
Its now pushing close to double what it needs to. Maybe more depending on what caliper is on his pinion brake.
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Old 04-27-2015, 09:33 PM   #3 (permalink)
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Yup.

And a smaller master. Master is designed for 2 calipers an end (or 2 calipers and 2 wheel cylinders)
Its now pushing close to double what it needs to. Maybe more depending on what caliper is on his pinion brake.
Can you explain more on going smaller? Because of booster delete?

Smaller master cylinder will push more pressure.
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Old 04-27-2015, 09:53 PM   #4 (permalink)
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Most OEM boosted MC's have a front and a rear reservoir with two separate pistons in the same bore. That way if there is a failure on one axle you still have the other axle working as a separate system. Its like 2 master cylinders built into one. Some OEM master cylinders will share a reservoir but still have two pistons in the same bore. Therefore each piston is designed to fill 2 calipers from one port. This is what spidr is referring to.

Boosting pinion brakes is going to make everything super-touchy because with pinion brakes on rockwells you have a 6.72:1 gearing advantage over wheel brakes. The first thing he needs to do is get rid of the booster.

If he figures out some way to use his stock MC without the booster it is worth a try. (Keeping in mind that I have no clue what MC he is using.) He could plumb the front axle from one port and the rear from the other to achieve the same safety redundancy that the OEM's intend. This is what I have done on my rig. I use a MC out of a 1999 Acura CL and it works great. But it is obviously meant for a small car so if you are using a truck MC you are going to be moving more fluid volume than I am which may make for a very short travel pedal. If that was the case you could re-plumb both axles to operate off of one port to get more pedal travel with the same pressure. You would lose the safety of having redundant front and rear systems though and if you broke one line you would loose pressure / braking at both axles.

The smaller the MC bore the higher the line pressure will be but the longer the pedal travel will be. But adding boost adds hundreds if not thousands of lbs. of pressure (depending on if it is vacuum vs hydro) so you would have to go to a very small bore MC to match the pressures offered by boosting and chances are if you went that small you wouldn't have enough pedal travel to be effective. So there's no way that any realistic un-boosted setup is going to offer as much pressure (which is what you have too much of) as you currently have.

Being that most OEM boosted MC's don't lend themselves very well to being actuated without the booster behind them, I suspect your friend will find it easier to get a Wilwood pedal and MC setup. Their small 3/4" - 1" bore single piston MC's combined with relatively low pedal ratios are perfect for pinion brakes and you can get a dual MC pedal to run each caliper off of its own MC like an OEM MC is essentially doing.



I'll just add that I've never heard of anyone actually running pinion brakes on rockwells with boosted brakes. A lot of the beauty of pinion brakes is that they are so simple and don't need the boosters.
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Old 04-28-2015, 05:24 AM   #5 (permalink)
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He should be able to use an adjustable proportioning valve to dial down the pressure. Usually they are added to the rear for bias. But I don't see why they couldn't be used on both ends.
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Old 04-28-2015, 01:23 PM   #6 (permalink)
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Quote:
Originally Posted by iwishihad1 View Post
Hey everybody,

Going to help a friend with sorting out his braking issue this weekend. Hes got a Yj on 42s that he has been playing with for a while and just starting to get it all dialed in. one of his last issues is that braking at any real speed starts to get a little sketchy. he hardly has to hit the brakes and all 4 tires lock up. its rare that I'm trying to help folks solve brakes being too good, and I am not well versed in rockwell/pinion brake set ups.

He had mentioned reading of people doing away with the booster and going with just the master cylinder. I have never heard of this...opinions?

They will remain touchy even with out the booster. Nature of them, from my experience they all are jumpy.
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Old 04-28-2015, 02:46 PM   #7 (permalink)
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thanks for the follow ups here....it sounds like we still start with removing the booster and seeing how that works and go from there.
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Old 04-28-2015, 05:52 PM   #8 (permalink)
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Quote:
Originally Posted by iwishihad1 View Post
Hey everybody,

Going to help a friend with sorting out his braking issue this weekend. Hes got a Yj on 42s that he has been playing with for a while and just starting to get it all dialed in. one of his last issues is that braking at any real speed starts to get a little sketchy. he hardly has to hit the brakes and all 4 tires lock up. its rare that I'm trying to help folks solve brakes being too good, and I am not well versed in rockwell/pinion brake set ups.

He had mentioned reading of people doing away with the booster and going with just the master cylinder. I have never heard of this...opinions?

They will remain touchy even with out the booster. Nature of them, from my experience they all are jumpy.
Hm. I've had 2 rigs with pinion brakes and neither was touchy at all. My current rig feels about like any normal DD. It's just all about pressure and volume. With a 6.72 mechanical advantage using the same hardware that rigs with wheel brakes do is going to not work great. But if you plan the system right it can work great.
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