Need help with no brake pedal

[307edition]

Okay this is a long one. I’ve got a 98 k1500 4wd that locked up on me on my way home from work one night a couple of months ago. I could pump up the brakes but they would not release. The brakes have always been sketchy on that truck and I was planing on revamping the system soon anyways so it wasn’t a huge deal. I started by replacing the brake booster, master cylinder, rubber lines and the front calipers. Here I ran into what I thought was just a bleeding issue as the pedal had no bottom to it. The brakes would work, sort of, but never really anything more than just being able to hold it when I put it in gear. I ended up running nearly 4 gallons of fluid through it between traditional bleeding, scanner on the abs, and pressure bleeding. My locking up issue wasn’t resolved so I replaced the whole abs module with a refurbished one and it fixed that but I still have no pedal. I took it to a shop and they believed it was the rear drums so those are also all brand new now. They had it for over a month and it stumped every mechanic there. I got it back and tried some isolation tests with plugs. I have hard pedal at the master cylinder. I couldn’t totally isolate the abs since the front right is a different fitting of course. With just the front right I have brake pedal like it was originally, kinda squishy but still had a bottom. As soon as I add either the other front or the rear brake lines the pedal disappears. My current theory is that the valve body isn’t functioning properly but any insights would be greatly appreciated!

 

[Schurkey]

What brake option code is shown on the decal in the glovebox? JB5? JB6? Something else?

Wheel bearings/hubs up front in good condition? Rotors aren't flopping around on wiped-out bearings?

When you run the auto-bleed function of the scan tool, do the solenoids actually chatter? Does the pedal pump itself up like it's supposed to?

The parts you installed are correct for your vehicle? You didn't install a deep-recess master cylinder on a short-pushrod booster? Didn't install a 1" bore master on a truck that needs 1 1/8-bore master?

Are the dash warning lights for ABS or "BRAKE" lit up?

If you have rubber brake hoses, you can lightly clamp them with a vice-grip to isolate front from rear.

 

[307edition]

It’s a jb5.

Wheel bearings were replaced about 500 miles ago and wheels are tight.

Not 100% all of them are working but you can hear at least some going off. The pedal will not pump up, unless the vehicle is off and even then it takes a lot of work for a small outcome.

The lash is set to 1/16 of an inch on the pushrod and the bore is exactly the same as what came out of it.

There are no codes on the dash and I can’t find any stored ones in the abs either.
Thanks for the reply!

 

[SUBURBAN5]

Is the abs module from and exact same truck or is it from another model. Meaning tahoe, suburban, sierra ect?

 

[Schurkey]

It’s a jb5.

Rear brakes are suspect. The 254mm (10") leading-trailing drums are known for problems; compounded by seized park brake cables.

Not 100% all of them are working but you can hear at least some going off. The pedal will not pump up, unless the vehicle is off and even then it takes a lot of work for a small outcome.

If the pedal doesn't pump itself up during auto-bleed, the ABS is toast.

There are no codes on the dash

I don't care about "codes on the dash". I want to know if the ABS or BRAKE lights are lit up.

and I can’t find any stored ones in the abs either.

Is your scan tool capable of reading brake codes?

 

[307edition]

Is the abs module from and exact same truck or is it from another model. Meaning tahoe, suburban, sierra ect?

I’m not sure I got it online. I hadn’t considered that it mattered.

 

[307edition]

Rear brakes are suspect. The 254mm (10") leading-trailing drums are known for problems; compounded by seized park brake cables.

Yep I’ve had a couple of guys tell me to check them and the shop I took it too had the exact same suspicion but they replaced the whole assembly and it only improved slightly.

I don't care about "codes on the dash". I want to know if the ABS or BRAKE lights are lit up.

I’m not sure I understand what you mean. The brake lights work. The parking brake light comes on when applied and the abs light on the dash is not lit up.

Is your scan tool capable of reading brake codes?

I don’t have one personally so I’ve been borrowing a friends and his is a really fancy snap on one. I believe it’s a solus plus.

 

[SUBURBAN5]

Few things. 1 abs module matters. Specially for 1/2 to 1/2. 3/4 to 3/4 and so on. Model matters. Suburban has more weight then a c 1500 short cab as an example. May not be your issue but keep that in the back of your mind. As for your scanner it's good enough IMO. You want to communicate with the abs module and see if there's any brake codes. For example no communication or faulty solenoids. Normally the scanner will display what ever. Kind of like trans codes without a "fault light on" . Last I would definitely follow the fluid like you were doing. From mc to abs inlet to outlet to rr wheel cylinder and so on. Are your parts OEM or some cheap aftermarket? Duralast, brake best, ac delco?

 

[SUBURBAN5]

What this video to get more understanding on the module. May not help but will give you some insight

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[307edition]

Last I Are your parts OEM or some cheap aftermarket? Duralast, brake best, ac delco?

The front calipers and mc are ac delco not sure on the brake booster or the rear drums.