[joes455]

Tried to send pics,but I've never seen a site where it's so tough to post pics

[joes455]

Here are pics

[joes455]

More pics

[HWYSTR455]

So on that MC, the rear reservoir feeds the front brakes? Sure you don't have those on backwards?




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[HWYSTR455]

Usually, the larger fitting feeds the rear brakes.



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[joes455]

You referring to the larger fitting or the larger line feeding the rear?The rear has the 5/8 nut with the 3/16 line

[HWYSTR455]

You put a T fitting at the MC for the rear lines? And have the prop valve on the front lines?


It looks like you have the rear line plumbed to the front MC fitting? And a T off the rear MC fitting?

You sure that MC front fitting is supposed to feed the rear lines?


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[JLMounce]

I'm not certain which master cylinder that is. Some MC's like you find on C6 corvettes have a reverse arrangement from the typical C3 corvette master that many people run. The front most port, nearest the bumper feeds the rear lines. This is something that should be checked, but I think his configuration is probably accurate.

If you haven't already backed out the adjust completely, do so and see where that puts you. If you're still locking up the rears too early, you need to compensate at the caliper. The Metric calipers you are using likely have a 2.375 or 2.5" single piston. They create a lot of clamping force, just like the front's. You may need to go to a caliper with a smaller piston area to reduce the clamping force.

[HWYSTR455]

The largest port size on the MC almost always goes to the rear, regardless of what size fitting or line you plug into it. That's how I've always been able to tell, but maybe that's not always the case?

Also, I have been told that the largest reservoir always feeds the front brakes.

Many 'universal' masters are the same front/rear, so those you can plumb either way.

Should be able to search the original service manual for an Astro/Safari, and find out for sure. But if it had drum rear, then most likely it would use whichever the smaller reservoir is.


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[JLMounce]

Originally Posted by HWYSTR455

The largest port size on the MC almost always goes to the rear, regardless of what size fitting or line you plug into it. That's how I've always been able to tell, but maybe that's not always the case?

Also, I have been told that the largest reservoir always feeds the front brakes.

Many 'universal' masters are the same front/rear, so those you can plumb either way.

Should be able to search the original service manual for an Astro/Safari, and find out for sure. But if it had drum rear, then most likely it would use whichever the smaller reservoir is.


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That thought crossed my mind as well. The master cylinder if it's setup specifically for a disc/drum configuration my be part of the problem. Pressure and fluid volume requirements are much different with a drum brake than a disc brake. Typically the drum requires more volume, which is why you see the larger lines. If you're sending a wall of fluid to a disc caliper, especially under the types of pressure a hydroboost creates, that may cause the issue that the OP is seeing.

[joes455]

The MC pn is 18012985 build date is 95 .The front feeds press to the prop valve in side,the output side feeds the rear stock size 1/4 line that goes to the rear brakes.The rear of MC feeds the 3 way block then out to the front brakes.The reservoirs hold about the same volume of fluid so I guess I could swap lines just for troubleshooting.Still waiting on new prop valve before I do any swaping around

[HWYSTR455]

The rear line should be 3/16, the fronts should be 1/4.

Still think you should dig on the MC to see which port feeds what, but like I said, pretty sure the larger port should be feeding the rear lines, and the adjustable prop valve should go on the rear line side.

If you use an adjustable prop valve, you should not be using a combo or another prop valve anywhere.

This is one reason I suggest to many to just buy a kit, the guess work is all figured out for you.

Then of course the hyroboost which adds another level of complexity, and just had this conversation on another thread.

What little you may have saved jig-sawing a kit together in an attempt to save money you are paying more for in the long run.

Take a look at hydratech, they have masters listed, and bet if you call them they would know exactly what any issue could be. Just to say, they show masters which front port feed front brakes and rear port feeds rear brakes:

https://www.hydratechbraking.com/mastercylinders.html

The #8123, #8129, & #8126 MCs are the opposite, front port feeds rear brakes. There's a few others too, maybe you can tell by the pics which you have. Looks like all the late model stuff is like that, but still you never know, have to check.



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[HWYSTR455]

You need to check your pushrod to cup clearance too, and make sure the rod isn't depressing the plunger at all at pedal rest.


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[HWYSTR455]

Everyone should have one of these in their tool box:

https://www.amazon.com/Upgraded-Adju...&tag=hyprod-20

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[joes455]

Here you go

[FrankieT/A]

Compression fittings on hydraulic brake lines are a no no.
You must use a master cylinder for disc/disc. If you want to use a m/c from a disc/drum then you must take the check valve out.

[Skip Fix]

"If you use an adjustable prop valve, you should not be using a combo or another prop valve anywhere."

I used one autocrossing my 78 TA when it was disc/drum. An old C2 Vette one then replaced with a Mopar direct connection one when it started leaking. Then when went 81 TA 4WD set up just T'd the fronts and adjustable prop valve in the rear

Did the same with the '79 Camaro when it was a disc/drum C/P autocross car. Now a manual 4WD drag car T's from the Line Lok and an adjustable prop valve in rear. The 81 TA now also has just a T and and adjustanle as I think the factory 4WD prop valve was not working correctly.

[joes455]

Good catch Frankie on the compression fitting,it's just temp.In the pics there are no other valves being used except for the adjustable prop valve.The reservoir I'm using is not like pictured above mine has a big reservoir liked pictured in post 42.I took a side picture of one for a astro van because there were hard headed non believers whom thought I had lines attached wrong ,even one who thought is was a "jig saw"set up.Anyways I have an update ,installed new adjustable prop valve and system works great I have knob almost all the way out,I could probably go in another turn to get more rear braking.The rear brakes are now tunable.Thanks for everyones help besides the critics who should be more open minded and professional

[HWYSTR455]

https://mpbrakes.com/how-to-series-w...ination-valve/

"As fluid enters the combination valve, the metering valve comes into play with a front disc/rear drum brake setup. The metering valve holds off pressure on the front brakes ever so slightly to allow the rear drum brakes to engage first. Once that predetermined pressure point is reached, fluid is allowed to pass through the valve and then reach the front brakes."

" The only time that the proportioning valve works is in a panic-stop situation. When this happens, line pressure within the valve spikes. This spike causes the proportioning valve to then regulate line pressure going to the rear brakes. If this didn’t happen, the excessive line pressure reaching the rear brakes would cause the rear brakes (either disc brakes or drum brakes) to lock up and in most situations cause the driver to lose control of the vehicle."

https://mpbrakes.com/drum-to-disc-brakes-conversion/

"In most instances, people are using a combination valve of some sort if the car already has front disc brakes. If a factory valve is present, it is probably best to replace the valve with a disc/disc combination valve because of the unknown."

"If the car already has a universal combination valve, it may be able to be converted to a disc/disc. In both instances, what we are trying to do is remove the metering valve from the system."

In many opinions, it's easiest to just remove the combo/prop valve and use only an adjustable. It prevents a lot of guess work.

As for being a hard-headed non-believer, all I was saying is that you need to verify the MC in use, to be sure the lines are correctly connected. In some cases, it actually may not matter, but it still would most likely not be optimum if reversed. If people looked at the links, you would see there are MCs that are each way, and even some where it doesn't matter. Simply posting a pic for an MC proved nothing. And actually, you probably could have used the MC that was on there to begin with. (and, as with many newer MCs, not have to change to metric lines.)

I wasn't taking a shot at anyone with my comments, and sorry if some got butt-hurt. When someone takes the time to help, usually people are grateful, regardless if the advice was used or not, right or wrong.


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[joes455]

There was no stock prop valve ,metering valve being used just the adjustable prop valve that was at faulty. MC that you was convinced the lines were backwards after I stated they weren't. So explain to the viewers why you called my set up a "jigsaw"setup ?My brakes work great now.That was an ignorant statement and you coming back with your stupid nonsense with the above post furthers that theory of such.I took the pic of MC as requested.Everyone else understood it .Why it didn't prove anything to you is beyond me.