MC upgrade question

[xAFNYx]

Hello everyone. I recently got my first truck (98 silverado k1500) and I've been slowly working on it. I had learned from here that you can upgrade the master cylinder to a NBS MC for better braking. I read through a few threads and guess im just bad at searching this forum, but i couldnt really find a part list. I purchased a new MC (dorman M630031) and the AGS BLF-26C brass fitting. My question i guess is if i got the correct MC? I dont want to do the upgrade and end up making my brakes worse.

Any help is greatly appreciated and i apologize in advance if this is a dumb question. I'm new to trucks in general.

 

[Schurkey]

Do you have JB5 brakes (common on 1500s) or JB6 brakes (rare on 1500s)? If so, you have low-drag front calipers. Those are not compatible with the so-called "NBS" master cylinder.

Low-drag calipers require a three-chamber master cylinder, with a huge bore at the back end. The third chamber provides a huge volume of fluid at low pressure, to push the caliper pistons up to the rotor face. Then the high-pressure part of the master cylinder actually applies the brakes to stop/slow the vehicle.

Three-chamber master cylinders have a step in the casting like the one below. Note the large-diameter piston and seal at the rear of the primary piston:

You must be registered for see images attach

If the original master cylinder you removed from the vehicle had a step in the casting, you bought the WRONG master cylinder. The "NBS" master has a large bore all the way through, which throws away hydraulic advantage--if the booster fails you'll need both feet on the brake pedal. If your wife is driving, I hope you have good insurance.

Stop trying to re-engineer the brake system, and fix what's wrong--as I said in your other thread, you've got failed brake parts, you've got air in the system, or you've got brakes that are way out of adjustment. Maybe a combination of problems.

Have you ever bled the ABS using a scan tool?
Have you ever popped the drums off and adjusted the horrible leading-trailing shoe rear brakes? If you have JB5/ leading-trailing rear drum brakes, and you don't use the park brake frequently, the brakes aren't going to self-adjust.

 

[Gibson]

Schurkey is right, the NBS masters are used on 4 wheel disc applications.
But their is more to it, their are lots of "Step bore" MCs that are used with "Normal drag" disc/drum systems, and they do have a larger rear bore, and can appear to look just like a step bore MC that is used for "Low drag" calipers.
Swapping brake systems is a popular thing, but the MC needs to be paired with the rest of the system.
JB5 brakes=JB5 master, JB6 brakes=JB6 master,, and so on.
Each of the different systems require the matching master to operate properly, as they all have different pressure/volume curves.
And, you need to use the combination valve that matches the system.

 

[Schurkey]

But their is more to it, their are lots of "Step bore" MCs that are used with "Normal drag" disc/drum systems, and they do have a larger rear bore, and can appear to look just like a step bore MC that is used for "Low drag" calipers.

I'm not aware of step-bore masters used on non-low-drag calipers. Can you give me an example of an application?

 

[Gibson]

I'm not aware of step-bore masters used on non-low-drag calipers. Can you give me an example of an application?

Sure, both of the old Square body rigs that I had, the '76 and '80, and my '97 Sub all had/have MCs that have 2 different dia. pistons in them.
The big piston runs the rear drums and the small piston runs the front discs.
The '76 and'80 had JB8, the Sub is JB7.

 

[Endo]

Do you have JB5 brakes (common on 1500s) or JB6 brakes (rare on 1500s)? If so, you have low-drag front calipers. Those are not compatible with the so-called "NBS" master cylinder.

Low-drag calipers require a three-chamber master cylinder, with a huge bore at the back end. The third chamber provides a huge volume of fluid at low pressure, to push the caliper pistons up to the rotor face. Then the high-pressure part of the master cylinder actually applies the brakes to stop/slow the vehicle.

Three-chamber master cylinders have a step in the casting like the one below. Note the large-diameter piston and seal at the rear of the primary piston:

You must be registered for see images attach

If the original master cylinder you removed from the vehicle had a step in the casting, you bought the WRONG master cylinder. The "NBS" master has a large bore all the way through, which throws away hydraulic advantage--if the booster fails you'll need both feet on the brake pedal. If your wife is driving, I hope you have good insurance.

Stop trying to re-engineer the brake system, and fix what's wrong--as I said in your other thread, you've got failed brake parts, you've got air in the system, or you've got brakes that are way out of adjustment. Maybe a combination of problems.

Have you ever bled the ABS using a scan tool?
Have you ever popped the drums off and adjusted the horrible leading-trailing shoe rear brakes? If you have JB5/ leading-trailing rear drum brakes, and you don't use the park brake frequently, the brakes aren't going to self-adjust.

The JB5, JB6 uses the same Master Cylinder and front calipers. Part numbers are the same from GM dealership.
Please see attached image.

You must be registered for see images attach

 

[xAFNYx]

Alright, So i returned the MC and when i have the shop replace my shocks and tires I'll ask them to adjust the shoes and do a full system bleed.

the only 2 things i really dislike about the truck is the super spongey brakes and the incredibly loose steering

 

[thegawd]

loose steering could be an old worn out rag joint. its made of rubber and has a life span. you can replace the joint or do an upgrade that changes the rubber rag joint into a universal joint.

it could also be the EVO sensor since your truck is a 98 it has EVO.... I dont have a clue what E V O stands for but it is a sensor on the steering shaft right under the dash that reads how fast your turning the steering wheel and it boosts power steering pressure for when your driving slow like in a parking lot. when these fail it just randomly sends the full boost signal and it feels like the truck just slipped on ice.... some unplug the sensor and forget about it. others rebuild the power steering pump so it dosent have this ability or just swap it outright with one from a truck that dosent have EVO.

 

[xAFNYx]

loose steering could be an old worn out rag joint. its made of rubber and has a life span. you can replace the joint or do an upgrade that changes the rubber rag joint into a universal joint.

it could also be the EVO sensor since your truck is a 98 it has EVO.... I dont have a clue what E V O stands for but it is a sensor on the steering shaft right under the dash that reads how fast your turning the steering wheel and it boosts power steering pressure for when your driving slow like in a parking lot. when these fail it just randomly sends the full boost signal and it feels like the truck just slipped on ice.... some unplug the sensor and forget about it. others rebuild the power steering pump so it dosent have this ability or just swap it outright with one from a truck that dosent have EVO.

wow. replacing that sensor looks like a HUGE pita.

 

[xAFNYx]

the rag joint also doesnt look too fun to replace.