94 Suburban C1500 MC upgrade and 4WAL bleeding

ShannonTxBurb said:

My vehicle

94 Suburban C1500 5.7L-350 Silverado trim 365,000 miles

Stock braking system at the start.

I let the burb sit for a few months and then got in it to get it back on the road. The brake pedal when to the floor and about the last two inches before hitting the stop, it managed to apply enough brakes to stop.

The brakes had been spongy for a while, a little more spongy than when new. They always had too much pedal travel for my taste but about half travel would engage the brakes and they worked. After renting a few new trucks and SUVs, the pedal on the bueb is not acceptable.

I bought Russell braided steel flex lines but hadn't put them on yet. I made a run to Summit and got the Power Stop Z36 kit, new rotors, calipers, pads. I figured replace it all at once.

I also read on here about the NBS MC upgrade. So I got a MC for a 2002 Tahoe with a 1.46" bore. I got it bled and installed. (Only part changed so far.)

I still have about 75% of pedal travel before I get brakes, but it does engage the brakes. I am not losing fluid anywhere. So I read that this is probably the 4WAL module.

Two questions:

1 Is the MC I chose OK for the basically stock brakes? NMC11122 at O'Reilly

2 What is the most reliable way to bleed that 4WAL KH module?

Other options?

Click to expand...

I got rid of my rwal, proportioning valve, installed all new everything; calipers, wheel cylinders, the works. Could not get the air out of my system until; I installed a 10lb Wildwood residual value to the rear line. Problem solved. Brakes now are better than ever.

thegawd said:

using an air compressor to fill that air tank to power bleed the brakes could actually put moisture in the brake fluid if the compressor dosent have an air drier. Iv always bleed brakes the 2 person method and with a hose on the bleeder running into a jar, through a lid, with only brand new brake fluid in it. bubbles out clean fluid in instead of air. glad My wife is patient!

I'm a firm believer in replacing brake parts by RPO and not mismatching brake systems. There is one system that isn't very good and could be upgraded, but it's more than just a MC swap. you need the entire system for it to work right.

Al

Click to expand...

Good point for @Pinger A drier may be a good idea for that setup.

For my little HF kit no air is pushed into the system it uses a venturi to create a vacuum which pulls air out from the caliper so it's a non issue in that case.

I was wondering if there could be a "bladder" to separate the air from the fluid. but most of the kits or homemade converted weed sprayers are more or less an air fitting plumbed straight into the tank. and for me growing up with an air compressor and knowing what some of those parts wire for on that giant antique crazy ass air compressor that my dad had. he always made it a point to drain the water from the drier. so I never made one of those auto bleeders based on those facts. I live smack dab in the middle of most of the Great Lakes, maybe humidity isn't as big of a deal everywhere like it is here.

TheAutumnWind said:

Good point for @Pinger A drier may be a good idea for that setup.

.

Click to expand...

A drier is only needed for tanked air.
The air I'm pressurising is the same air the fluid comes into contact with the reservoir lid open for fluid replenishment.

thegawd said:

I was wondering if there could be a "bladder" to separate the air from the fluid. .

Click to expand...

I had that option when I made mine. If I hadn't chosen to break through the rubber then there would have been physical separation between fluid and air.

mwyson said:

I got rid of my rwal, proportioning valve, installed all new everything; calipers, wheel cylinders, the works. Could not get the air out of my system until; I installed a 10lb Wildwood residual value to the rear line. Problem solved. Brakes now are better than ever.

Click to expand...

With air in the system, did the pedal feel springy or spongy?
The residual valve never lets the pressure in the rear line drop below 10psi and prevents air being drawn in past the slave cylinder seals when the brakes are released - yes?

Pinger said:

I bought a Schrader valve stem and bolted it into an old MC reservoir lid.
Pressurise it with the tyre compressor that plugs into the ciggy lighter socket. Leaks at the seal but that's OK - saves over-pressurising - but still provides enough pressure to push fluid.

Click to expand...

TheAutumnWind said:

That's a great idea

Click to expand...

No, it isn't.

The reservoir on these trucks isn't designed to accept pressure. Too much pressure can blow the reservoir off the master cylinder--it's only held on with a pair of rubber seals. The reservoir itself isn't all that sturdy.

The big problem is that the reservoir is small, pressurizing it can blow the fluid out the bleeder screw so fast that the master cylinder goes empty.

thegawd said:

I was wondering if there could be a "bladder" to separate the air from the fluid.

Click to expand...

ALL real pressure bleeders have a rubber diaphragm exactly for that reason. If you look in the service manual, GM specifies a pressure bleeder having a diaphragm. They specifically warn against using a "garden sprayer"-style bleeder.

Garden-sprayer bleeders are not "real" pressure bleeders.

Pressure bleeder attachment for my Trailblazer, or for GMT800-style reservoirs. The GMT400-style adapter is COMPLETELY different because the reservoir is less-sturdy. I'll get a proper photo tomorrow.


Patent application for one style of pressure bleeder attachment for the GMT400-style reservoirs. This bleeder style puts no pressure on the top or sides of the reservoir--only on the part that's well-supported by the sealing bushings where the reservoir contacts the master cylinder.

I have one of these, but it's in poor condition and missing one small piece.

Proper pressure bleeder having diaphragm to separate fluid from air. I pressure bleed at about 10--15 psi.

Pinger said:

A drier is only needed for tanked air.
The air I'm pressurising is the same air the fluid comes into contact with the reservoir lid open for fluid replenishment.

Click to expand...

True. But you're allowing the fluid to come into contact with MORE ambient air. More air = more humidity = more contamination.

Schurkey said:

No, it isn't.

The reservoir on these trucks isn't designed to accept pressure. Too much pressure can blow the reservoir off the master cylinder--it's only held on with a pair of rubber seals. The reservoir itself isn't all that sturdy.

The big problem is that the reservoir is small, pressurizing it can blow the fluid out the bleeder screw so fast that the master cylinder goes empty.

Click to expand...

If I had anything resembling a seal between the lid and the reservoir what you say would undoubtedly be true. As it is, it leaks so copiously that the gauge on the (small) electric compressor barely comes of its stop. Before connecting (considering even) I tested it with a hand bicycle tyre pump. The wheezing from the leaking lid seal told me what I intended was fine.

Schurkey said:

True. But you're allowing the fluid to come into contact with MORE ambient air. More air = more humidity = more contamination.

Click to expand...

True, but humidity in NE Scotland isn't a feature. I pierced the membrane only to prevent it being pushed down into the fluid and dripping fluid everywhere on removal. I might do it differently if doing it again in light of what's been said.

Schurkey said:

No, it isn't.

The reservoir on these trucks isn't designed to accept pressure. Too much pressure can blow the reservoir off the master cylinder--it's only held on with a pair of rubber seals. The reservoir itself isn't all that sturdy.

The big problem is that the reservoir is small, pressurizing it can blow the fluid out the bleeder screw so fast that the master cylinder goes empty.


ALL real pressure bleeders have a rubber diaphragm exactly for that reason. If you look in the service manual, GM specifies a pressure bleeder having a diaphragm. They specifically warn against using a "garden sprayer"-style bleeder.

Garden-sprayer bleeders are not "real" pressure bleeders.

Pressure bleeder attachment for my Trailblazer, or for GMT800-style reservoirs. The GMT400-style adapter is COMPLETELY different because the reservoir is less-sturdy. I'll get a proper photo tomorrow.

You must be registered for see images attach

Patent application for one style of pressure bleeder attachment for the GMT400-style reservoirs. This bleeder style puts no pressure on the top or sides of the reservoir--only on the part that's well-supported by the sealing bushings where the reservoir contacts the master cylinder.

You must be registered for see images attach

I have one of these, but it's in poor condition and missing one small piece.

Proper pressure bleeder having diaphragm to separate fluid from air. I pressure bleed at about 10--15 psi.

You must be registered for see images attach

True. But you're allowing the fluid to come into contact with MORE ambient air. More air = more humidity = more contamination.

Click to expand...

Lol thanks Schurkey

I use Earl's solo bleeds

https://www.summitracing.com/search...ortOrder=Ascending&keyword=earl's solo bleeds

and flush a quart of brake fluid through everything on the driveway once a year.

I have one of the HF Vacuum bleeders and it's o.k. but the threads of the bleed screws have to
seal for it to work well. I own a pressure bleeder but I have never even put fluid in it. I use the HF vacuum bleeder as a catch can for the solo bleeds.