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post #16 of 31 Old 10-15-2020, 01:47 PM Thread Starter
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Quote:
Originally Posted by bgredjeep View Post
So currently that valve is the only thing between the master cylinder and the calipers? That should be fine, and that valve should let you put full pressure to the rear. The adjustable valve is intended to dial down the pressure so the rear doesn't lock up before the front.

If that's the case, all I can think of is air in the system somewhere. When you've bled it various times, are you seeing any air in the system, or only fluid?

If fluid only, I normally wouldn't suggest this but, maybe adjust the rod in the booster out to press into the master just slightly at rest and see what happens. Also, double check for any indication of brake fluid getting through the back of the mc into the booster. Could possibly be a bad mc introducing air into the system.

Just spit balling at this point. There's only so much to the brakes, and you seem to have the parts needed to avoid the soft pedal.
If I bleed it multiple times even if it's weeks apart, the only air that comes out is the first split second to clear the bleeder. I'll get maybe 2 bubbles that will track down the tube and the rest will be solid fluid.

There is no fluid dribbling into the booster. Maybe I'll jack up both axles and put them on jackstands. Then I could see if preloading the MC would cause any drag. I'm more concerned about dragging the brakes on the road and overheating them so I really need to verify the preload before going for it.



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post #17 of 31 Old 10-15-2020, 01:52 PM Thread Starter
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Originally Posted by 4Low2G0 View Post
OK so rear drum M/C will not move enough fluid for a rear disc, you need to find a MC for 4 wheel disc and go from there
Maybe that's it then... I know drums run a lower pressure typically so if the drum side of the MC isn't supplying the higher pressures that disc brakes run, maybe the only method to fix what I've got is to gut an old prop valve so the disc side can aid the rears. I know several people make this MC work.


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post #18 of 31 Old 10-15-2020, 02:03 PM
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Quote:
Originally Posted by Waternut View Post
Maybe that's it then... I know drums run a lower pressure typically so if the drum side of the MC isn't supplying the higher pressures that disc brakes run, maybe the only method to fix what I've got is to gut an old prop valve so the disc side can aid the rears. I know several people make this MC work.

If you do this you loose the dual circuit brake system, tear a line and all braking
goes away like on a 50's car. I'd find a 4 wheel disc MC

It's the volume of fluid that is needed to move the piston, the proportioning valve regulates
pressure so the system can be balanced front to rear.

also IIRC a larger MC will move more fluid for X amount of travel
but require more pedal pressure for the same amount of force at the pad.

A smaller MC will require a longer stroke to move the same amount of fluid but
will have more force at the pad.

also what fluid are you running?

Whats over that next ridge?
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post #19 of 31 Old 10-15-2020, 02:36 PM Thread Starter
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Quote:
Originally Posted by 4Low2G0 View Post
If you do this you loose the dual circuit brake system, tear a line and all braking
goes away like on a 50's car. I'd find a 4 wheel disc MC

It's the volume of fluid that is needed to move the piston, the proportioning valve regulates
pressure so the system can be balanced front to rear.

also IIRC a larger MC will move more fluid for X amount of travel
but require more pedal pressure for the same amount of force at the pad.

A smaller MC will require a longer stroke to move the same amount of fluid but
will have more force at the pad.

also what fluid are you running?
I did a lot of math and pressure calculations to find the MC size that I've got now so I'm familiar with the whole pressure vs volume thing. Finding that 4 wheel disc MC that's the right bore size, has an o-ring built in, and fits the WJ booster with even minor modifications is a lot harder than just swiping the credit card....

I just run regular DOT 3 fluid.


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post #20 of 31 Old 10-15-2020, 04:02 PM
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So, it's basic but, the bleeders are on the top of the calipers so any air can escape right?

I think you're bleeding is done right, there could be a bubble trapped in the line above the rear axle,
you could crack that line with pressure applied to be sure, but pressure bleeding should have got that.

To me it almost sounds like a caliper is flexing as pressure is applied. are the calipers lined up on the rotors?

Have you compared the distance on the pedal from the pivot to the hole for the rod is attached
on the WJ VS the YJ as that will alter MC travel and pedal feel. but doesn't change proportioning
so that will not address the rear brake issue.
.............................

Whats over that next ridge?
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post #21 of 31 Old 10-15-2020, 04:42 PM
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Do all your hubs roll true? If a hub or rotor has a lot of runout it will back a caliper piston way in and cause a low pedal.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #22 of 31 Old 10-15-2020, 06:16 PM Thread Starter
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Quote:
Originally Posted by 4Low2G0 View Post
So, it's basic but, the bleeders are on the top of the calipers so any air can escape right?

I think you're bleeding is done right, there could be a bubble trapped in the line above the rear axle,
you could crack that line with pressure applied to be sure, but pressure bleeding should have got that.

To me it almost sounds like a caliper is flexing as pressure is applied. are the calipers lined up on the rotors?

Have you compared the distance on the pedal from the pivot to the hole for the rod is attached
on the WJ VS the YJ as that will alter MC travel and pedal feel. but doesn't change proportioning
so that will not address the rear brake issue.
.............................
Yes the bleeders are on top. I thought about caliper flex which is why I replaced the rear calipers back when I initially had the problem. Pretty sure all 4 calipers are self centering but even if they aren't, I just tried to push a 0.005" shim (smallest I could find) between every pad and rotor and couldn't even ram it between the two so there isn't a lot wiggle room anywhere.

I have not compared the actual pedal ratio between a YJ and WJ since I don't have a WJ to measure.

Quote:
Originally Posted by Boojo35 View Post
Do all your hubs roll true? If a hub or rotor has a lot of runout it will back a caliper piston way in and cause a low pedal.
Wouldn't I feel a horrendous vibration under braking if that was true? Also, wouldn't the problem go away if the rotors weren't turning?


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post #23 of 31 Old 10-15-2020, 07:21 PM
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Quote:
Originally Posted by Waternut View Post

Wouldn't I feel a horrendous vibration under braking if that was true? Also, wouldn't the problem go away if the rotors weren't turning?
Yes, that is correct.

so the problem was the same with the WJ master and calipers I think is what you posted.

how was it with the stock set up?

Whats over that next ridge?
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post #24 of 31 Old 10-15-2020, 07:36 PM
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I don't think my pedal moves quite as far as yours and I don't really mind my stopping ability with 35 inch tires. I like you just feel like there is something that can make rear braking better. You say you are running the Durango MC and it might be a rear drum MC. I am running a 1978 Mercury Marquis 4 wheel disc MC with 1.125 piston. Bolted up nice to the 95 YJ DD booster. But still not enough rear braking.
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post #25 of 31 Old 10-15-2020, 08:29 PM Thread Starter
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Quote:
Originally Posted by 4Low2G0 View Post
Yes, that is correct.

so the problem was the same with the WJ master and calipers I think is what you posted.

how was it with the stock set up?
I never really had a stock setup. Someone had put an odd MC on this Jeep before I got it and the whole setup was junk. It was adequate when I had a manual trans. When I swapped to the V8 and auto, I had to push the Jeep into neutral to keep it stopped at a light.

Quote:
Originally Posted by wizekrakr View Post
I don't think my pedal moves quite as far as yours and I don't really mind my stopping ability with 35 inch tires. I like you just feel like there is something that can make rear braking better. You say you are running the Durango MC and it might be a rear drum MC. I am running a 1978 Mercury Marquis 4 wheel disc MC with 1.125 piston. Bolted up nice to the 95 YJ DD booster. But still not enough rear braking.
Funny, I was looking at other MC options and came across that. I also came across a ton of people on pirate4x4 and irate4x4 that say they can lock up 4 wheel disc brakes with 40" tires using the Dodge 2500 MC that I have. Going to try a few things tomorrow or this weekend and see if I can find the magic bullet. If I can't figure it out, it may just be a bad MC unit.


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post #26 of 31 Old 10-16-2020, 06:49 AM
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The grand marquis master will not help the soft pedal issue. I ran that mc when I was on d44s and it was great. Stepped up to 1tons and the bigger brakes made the pedal soft again so I stepped up to the dodge master.

Snap a picture is your master cylinder and proportioning valve setup. I just want to make sure I'm not overlooking something.


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post #27 of 31 Old 10-16-2020, 07:31 AM
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Late to the party but my observation is your bigger master should have MORE peddle feel than the smaller master...

My thought is to make a temporary sleeve for the brake pedal that “preloads” the master cylinder pushrod 5-10% of total available travel of the master. This will take creativity and it’s a bit of a sketchy safety thing but you are only testing it...

Provided the master isn’t bad- assuming it isn’t- it is possible that the pushrod retracts far enough to not provide pressure until it strokes into the bore which makes what should be like 1-1/2” of peddle travel into 3-4”... I’d eliminate that possibility.

The other thought was the booster but your symptom is 180* opposite of poor booster assist so?

Do you have measurements of your pushrod VS the previous pushrod sticker from the mounting flange?

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #28 of 31 Old 10-16-2020, 07:31 AM Thread Starter
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Quote:
Originally Posted by bgredjeep View Post
The grand marquis master will not help the soft pedal issue. I ran that mc when I was on d44s and it was great. Stepped up to 1tons and the bigger brakes made the pedal soft again so I stepped up to the dodge master.

Snap a picture is your master cylinder and proportioning valve setup. I just want to make sure I'm not overlooking something.
Pulled the ECU back down to get a clean shot. Here you go. The front line coming out of the MC has gotten twisted over the various changes and I may change it along with the front passenger side and rear line going across the axle just to ensure everything is new and clean but haven't gotten there yet.

Here is the full size image since you probably can't read the labels I wrote on the lines.
Attached Thumbnails
PXL_20201016_132313891.jpg  


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post #29 of 31 Old 10-16-2020, 09:10 AM
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Yeah, looks like I'd expect (I like that valve setup).

So currently you have the valve turned all the way in (max pressure) right? The line for the rear looks fine. A kinked or crushed line somewhere in the system crossed my mind but I doubt that twist in the front has anything to do with the issue.

I read through your setup again and on paper the dodge mc should be on the large size for your braking system. I ran the 1-1/8" grand marquis master with a similar axle setup and it worked great. If you can't find any damaged line on the way to the rear brakes, I'd be thinking a bad mc. Nothing else makes sense.

If you try something different than the current dodge mc, just make sure you get one with an o-ring or gasket to seal to the mc or you'll have a vacuum leak (at least that's how the tj dual diaphragm booster works).


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post #30 of 31 Old 10-16-2020, 10:24 AM Thread Starter
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I've tried the adjustment maxed in both directions and can't really tell a difference. Then again maybe I'm not getting enough fluid to activate the proportioning valve. From what I can gather, fully in is wide open. The dial says "increase and decrease" but it's a little confusing as to whether that means increase fluid flow or increase proportioning (aka restriction). The instructions say turn counter clockwise (out) and adjust clockwise in to get what you want and even that isn't real clear but I suspect they want everyone to setup on the conservative side first to prevent locking up the rears.

I'm going to adjust the rod out of the brake booster a little more and see how it does this weekend on the trail.


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