NBS Master Cylinder Upgrade

Reega

Newbie
Joined
Jan 23, 2016
Messages
37
Reaction score
24
Location
Knoxville
Personally I would not use the NBS master cylinder. You lose emergency stopping power. With the larger piston you cannot get as much hydraulic pressure as the stock system Had one on my Express van for about a week and it felt down right dangerous. Hydroboost is the best improvement.
I totally agree-firm pedal, but not braking force I needed-I went back to the old MC
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
1,725
Reaction score
1,102
Location
DFW, TX
I totally agree-firm pedal, but not braking force I needed-I went back to the old MC
I have a NBS van (03+) master cylinder in my van now, but it is paired with the larger NBS van hydroboost. Pedal is firm and I had more stopping power than ever. Wonder if one could use a NBS vacuum booster in a GMT400 and get back the pressure lost from the larger piston. Although a GMT400 hydroboost and pedal swap would work too. Hydroboost is an instant massive increase in braking pressure.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
1,725
Reaction score
1,102
Location
DFW, TX
Same experience here. Felt like there was too little “bite” in the brakes.

I wanted to like it.

Exactly, not enough WHOOAA when you really needed it. I swapped mine back out after noticing how much longer the stopping distances were after having to stand on the pedal with both feet to keep from rear-ending an idiot that shot over in front of me on the highway into the fast lane doing about 40 mph while I was rolling 75 mph. I was 300 lbs at the time too.
 

east302

I'm Awesome
Joined
Oct 4, 2013
Messages
2,812
Reaction score
2,113
Location
Jackson, MS
Yep, that sounds about right.

It was almost like having a bad brake booster but not quite. The best I could describe it, it was like having smooth glass for brake pads. No grip, perhaps. It just wasn’t quite right and I wasn’t confident that it could handle an emergency braking situation.

I’m sure there’s some hydraulics to it and think that @Schurkey (hope I spelled his name right) delved into it a while back.
 

Schurkey

I'm Awesome
Joined
Jan 14, 2018
Messages
3,372
Reaction score
2,824
Location
The Seasonally Frozen Wastelands
I have a 96 GMC Yukon... ...I’m now looking into the master cylinder upgrade and found this one (Dorman M630031 Brake Master Cylinder for Select Cadillac / Chevrolet / GMC Models https://www.amazon.com/dp/B001PYTM7C/ref=cm_sw_r_cp_api_i_LR8yFbDAG48CV) and was wondering if that’s the correct one for my truck along with the BLF-26C adapter from AutoZone. Any help is appreciated.
1. Why are you posting about brake issues in the "Engine Performance" section???

2. You've probably got JB5 brakes currently. A look at the glove-box sticker would confirm. The "5" brakes, like the JB3 brakes, use low-drag calipers which need Quick-Takeup master cylinders for proper brake action. It's not an upgrade to install a non-quick-takeup master when you need the high volume of fluid to move the caliper pistons at the beginning of braking.

BUY THE CORRECT MASTER CYLINDER FOR YOUR VEHICLE, not some internet-rumor "upgrade" that has been "engineered" by people who DON'T UNDERSTAND HOW THE SYSTEM IS SUPPOSED TO WORK.
 

thegawd

I'm More Awesome!
Joined
Feb 29, 2020
Messages
853
Reaction score
1,656
Location
Southern Ontario, Canada
I almost did the master cylinder upgrade a month or so ago. I have the adapter and a Tahoe to steal it from. I was replacing the vacume booster after it failed so I had a good opportunity. This is something I have wanted to do for a long time.

I really wanted some damn good advice as to why not to do it. I was researching the rpo codes for my burb, i realized that my brakes were one of the best available on the 1500's and i just didnt think i had the engineering understanding to actually mess with it properly. Remember, gm put these trucks in a wind tunnel and actually made them aerodynamic.... that front valance ect.... they had the best engineers build these trucks, I just couldn't believe they would put shitty brakes on them and something else must be happening.... 20 year old system that needs to be rebuilt properly was my thinking. I didnt think I had a problem whatsoever with my master cylinder and couldn't bring myself to mess with it. My brakes worked absolutely fine before the vacume booster blew. I wanted some understanding as to why some people swear by the upgrade and some people change it back to the original. Well I reached out to Shurkey and his explanation lined right up with my thinking soooooo I didnt swap it.

I still have the adapter in the glove box.

Al
 

SUBURBAN5

I'm Awesome
Joined
Jul 18, 2020
Messages
3,423
Reaction score
5,637
Location
Houston
1. Why are you posting about brake issues in the "Engine Performance" section???

2. You've probably got JB5 brakes currently. A look at the glove-box sticker would confirm. The "5" brakes, like the JB3 brakes, use low-drag calipers which need Quick-Takeup master cylinders for proper brake action. It's not an upgrade to install a non-quick-takeup master when you need the high volume of fluid to move the caliper pistons at the beginning of braking.

BUY THE CORRECT MASTER CYLINDER FOR YOUR VEHICLE, not some internet-rumor "upgrade" that has been "engineered" by people who DON'T UNDERSTAND HOW THE SYSTEM IS SUPPOSED TO WORK.

What if its JB6? What does that mean?
 

thegawd

I'm More Awesome!
Joined
Feb 29, 2020
Messages
853
Reaction score
1,656
Location
Southern Ontario, Canada
From here.....
https://www.gmt400.com/threads/jb5-jb6-jb7-jb8-size-thread.39647/

Hello,

After hours of looking around i can't find a thread that list all the sizes of the various brake components of JB style brakes. Please let me know if what i have so far is correct. I'm sure i have things wrong as all info is coming from other threads.

JB5(6400lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 11.86x1.29
Rear Drum- 10x2.25
Vacuum- Double Diaphram
1 3/16" wheel cylinder

JB6(7200lbs):
1.574" Bore MC
Low Drag Calipers 2.935" Piston
Front Disc- 12.50x1.28
Rear Drum- 11.15x 2.75
Vacuum- Double Diaphram(same as JB7)
1" rear wheel cylinder. 11' drum has self activating shoes, therefore does not require as much pressure as the 10"

JB7(8400lbs)Single rear wheel:
1.25" Bore MC(used in JB5 and JB6 Hydro Units)
Conventional Calipers 3.15" Piston
Front Disc- 12.50x1.54
Rear Drum- 13.00x2.50
Vacuum- Double Diaphram(same as JB6)
1 1/16 rear wheel cylinder

JB8(10000lbs)
1.312" Bore MC
Conventional Calipers 3.4" piston
Front Disc- 12.50x1.54
Read Drum- 13.00x3.50
Hydraulic Hydro Boost
1 3/16 rear wheel cylinder
 

Latest posts

Forum statistics

Threads
52,633
Messages
1,166,661
Members
30,874
Latest member
beatlebob32
Top