Brake Master Cylinder ??

[cuervo]

My 91 3/4 suburban has a master cylinder(MC) that is all cast iron.

I read an upgrade about using a 1999 P30 van that has 4wheel disc on it that looks like.

I've also read a thread that said you could not convert to a plastic resevoir from a cast iron type. Anyone know why that is?

I know ORU has the http://www.offroadunlimited.com/orustore/pc/viewPrd.asp?idcategory=0&idproduct=8344 MC that is used for upgrade hydro system as well.

Can someone tell me what is different about a hydro MC?

And the money question is, does anyone have part number for an all cast iron 4wheel disc brake MC that will fit on a 91?

 

[dremu]

The hydroboost masters are made for different bore and/or travel than those for vacuum boost.

I've said it once, I'll say it again: My experience is that, even for disc conversions, a stock style master cylinder will function perfectly well.

-- A

 

[cuervo]

The hydroboost masters are made for different bore and/or travel than those for vacuum boost.

I've said it once, I'll say it again: My experience is that, even for disc conversions, a stock style master cylinder will function perfectly well.

-- A

Well, on my 91 it's not working so well. The peddle is very squishy. The ebrake works very, very well. I have no issues with that. In gear facing down hill in drive it holds great. I have to give it some gas for it to move.

For some reason, even after a good bleed it the peddle is weak. The truck stops fine but the peddle goes down pretty far.

Does anyone know what the deal is with changing out to a plastic resevior from a cast iron is?

 

[dremu]

Well, on my 91 it's not working so well. The peddle is very squishy. The ebrake works very, very well. I have no issues with that. In gear facing down hill in drive it holds great. I have to give it some gas for it to move.

For some reason, even after a good bleed it the peddle is weak. The truck stops fine but the peddle goes down pretty far.

Does anyone know what the deal is with changing out to a plastic resevior from a cast iron is?

Different brands or types may have one reservoir or the other; this doesn't mean one works better than the other.

If the pedal is soft, you have air in the system. If you're convinced you've bled it properly, then you have a leak somewhere. Check the calipers and wheel cylinders, and then, IMO, replace the master with a stock type, whatever that happens to be. Be sure to bench bleed it first.

BTW, the parking brake is cable operated, not hydraulic, so yeah, it had better work regardless of the hydraulic system.

-- A

 

[cuervo]

Different brands or types may have one reservoir or the other; this doesn't mean one works better than the other.


BTW, the parking brake is cable operated, not hydraulic, so yeah, it had better work regardless of the hydraulic system.

-- A

Well, I just mentioned the parking brake was working because I had seen so many threads about it not working for so many other people.

The peddle was going kind of spongy before the conversion, I guess I should try a stock MC first.

 

[cuervo]

And, if it's not leaking fluid anywhere could this be caused by the brake booster? What are the signs for a booster going bad?

 

[bot0611]

Yes check it as well, my dad's 80 truck had a torn grommet where the hose that goes to the carb goes, si the brakes were soft, till i changed the grommet, correct me if im wrong but they can go bad, they work with an inner diafram, mine did i replaced it.

 

[dyeager535]

I personally like the later plastic masters, as the metal style are more hassle to get the cover off of. I know, like you need to deal with it often. Not having them back to back, it seems from memory that the plastic ones have much larger capacity as well. Does your ebrake warning light from the combination (proportioning) valve work? I lost my master (slowly) never could get a firm pedal, when it started getting really bad, the light tripped telling me the master was leaking internally.

 

[cuervo]

I personally like the later plastic masters, as the metal style are more hassle to get the cover off of. I know, like you need to deal with it often. Not having them back to back, it seems from memory that the plastic ones have much larger capacity as well. Does your ebrake warning light from the combination (proportioning) valve work? I lost my master (slowly) never could get a firm pedal, when it started getting really bad, the light tripped telling me the master was leaking internally.

I was getting the light before the conversion, but I thought it was from really worn out front pads. I changed them before I did the conversion and I know what everyone is going to say, it only seem to get a little better.

I figured if I was going to change the MC I might as well go with something for 4wheel disc. Giving the former issues, I'll try a new stock disc/drum for $46 bucks first.

I read, in one thread only, that you could not changed to a plastic if you had cast iron. No real reason was given for this issue so I ask here. As of yet no one has said anything about the coversion issue with cast going to plastic. I wasn't sure if there were issues with pressure in the resevoir because of a design or what.

 

[dremu]

And, if it's not leaking fluid anywhere could this be caused by the brake booster? What are the signs for a booster going bad?

When the booster stops boosting the pedal gets really hard to push, like when the engine is off. Assuming it's a vacuum booster, you can test it for leakdown easily enough.

Run the engine, and without putting your foot on the brake, turn the motor off. Wait, say, ten minutes, then come out and with the engine still off, press the brakes. You should get two or three good presses before the pedal gets hard to press; this means the vacuum in the booster is used up.

If you get NO good presses in, i.e. it's hard from the get-go, then check the vacuum line for leaks or listen for hissing around the booster.

-- A

 

[dyeager535]

As long as they are similar apps I don't think there is a difference.

 

[dyeager535]

Light will NOT trigger unless the system has a leak. That means fluid is leaking externally (wheel cylinders, brake lines, etc., which you would see with a quick visual) or internally, and the ONLY internal leak point that the proportioning valve will sense is the master cylinder, as the master cylinder uses the same bore to pressurize the front and rear brake lines. If the seal between the front and rear piston in the master fails, fluid leaks between the two, which means that the pressure in one line drops, and the light trips.

 

[cuervo]

Well, I went to NAPA but had to order a new MC. I figure I'm better off with a new one. It'll be in tomorrow around 9 so I'll get it done then.

Thanks everyone.

 

[dyeager535]

Hopefully it's the problem and not bleeding though too...many people have had to take a LONG time to bleed their brakes before they got a firm pedal. I spent hours on mine and finally "settled" on spongy brakes, which lasted a few months before the MC finally failed.

 

[Hogback Fabrication]

The hydroboost masters are made for different bore and/or travel than those for vacuum boost.

I've said it once, I'll say it again: My experience is that, even for disc conversions, a stock style master cylinder will function perfectly well.

-- A

My truck is and always has been vacuum boost, its worked flawlessly.

When it was my DD (5200 lbs, 37's, 4 wheel disc) it had WAY more stopping capability than the tires could keep up with. Front and rear brake balance always seemed good, on dry pavement the front and rear tires would lock up at the same time, OUTSTANDING brakes (1 ton brakes on a 1/2 ton I guess ).

I hear about people changing to 1 ton master cylinders, switching to hydro-boost, etc to get better brakes but mine work so well I'll never switch. Maybe I'm the lucky one with good vacuum booster brakes or maybe I'm the one with the whole system in good shape, who knows.

 

[cuervo]

All I can say is































































MONEY!

The stock MC works pretty well on my 91. It has that first gen anti-lock brake stuff so it wont lock the tires to much, but that puppy stops pretty damn fast.

Thanks to all!