First hand experience with changing to the NBS master cylinder WOW!

[CDR]

Speedy,

Thanks for the top-notch write up, I did the MC on my 99 burb last weekend and everything went to plan. I think I want to try the larger calipers now!

[speedygonzales]

Originally Posted by CDR

Speedy,

Thanks for the top-notch write up, I did the MC on my 99 burb last weekend and everything went to plan. I think I want to try the larger calipers now!

Before you do that, why not try different pads and slotted rotors? I love EBC green stuff pads. I'm going to swap out the crappy pads that came with my SSBC calipers. See my previous post with the calipers in it. They suck. The EBC's are chamfered and slotted.

http://www.summitracing.com/parts/ebc-usr7013/overview/

http://www.summitracing.com/parts/ebc-dp61273/overview

[CDR]

Speedy,

Well, great minds… I went to slotted rotors and green pads a while back. I remember when my rotors were regularly warped at 12k! The slotted rotors were definitely an improvement, as were the SS lines, regular bleeding and keeping the rear drums adjusted.

After a trip out west through the mountains the EBC pads (mind you they had 40k on them) melted down and had sort of disintegrated a bit from the metal pad bases. I showed them to a couple of mechanic buddies and they hadn't seen anything quite like it. I think they were just toasted from the mountain roads. BTW, my rear drums are still original, I feel that's just too much of a load to put on just the front brakes.

At that point I replaced the slotted rotors and green pads with the same, added the new proportioning valve (from the TSB), and was getting on with life. Small improvements overall but still a spongy pedal and some omg moments during hard braking events.

I had talked with a guy years ago about some upgrades-he explained the limitations of the six-bolt options and why big brake kits sometimes disappoint owners. He was a big advocate of the bosch hydroboost- as well as the larger HD brake calipers, a straight bore MC, different proportioning valve, thicker rotors and also going up a size on the rear cylinders. I was then re-deployed and lost momentum on the project.

Later, I talked with a mechanic friend about his hydroboost and although he did have better brakes, the system was prone to some leaks and his pedal was still plenty mushy. He wasn't a big fan of the expense of the project I described and that took some wind out of my sails. Talking with another GM mechanic he thought the straight bore MC idea was definitely worth a try.

...So! That's my story so far. I hope your new rotors and pads treat you well! Hopefully one day we'll get these things all dialed in...

[83GMCK2500]

I have been seeing this topic/procedure popping up more and more, I am very grateful that someone has figured this out and it is good to see a write-up here on it. The only thing I would change is the vague and irritating forum slang that is obs/nbs. GMT-400/GMT-800, far more accurate than some acronym that came from a forum years ago which gets edited everytime a new truck/suv platform comes out.

There is another brake upgrade that I will be performing soon on my DD, GMT-800 dual piston front calipers...

[speedygonzales]

Originally Posted by 83GMCK2500

The only thing I would change is the vague and irritating forum slang that is obs/nbs. GMT-400/GMT-800, far more accurate than some acronym that came from a forum years ago which gets edited everytime a new truck/suv platform comes out.

There is another brake upgrade that I will be performing soon on my DD, GMT-800 dual piston front calipers...

I did spell out the acronym on my very first post for those not familiar with it. People use it because they can see with their eyes a new body style to an old body style. They don't usually know 400 Vs 800.

With regard to your 2 piston caliper change. I did that after I changed the master cylinder and it made NO difference. Complete waste of time.

[Tom]

A guy on FSC.com just posted up how to put NBS 13" rotors+dual piston calipers both front and back on OBS trucks. So friggin simple its blowing my mind.
t_graham11- the slang doesn't ever change. OBS will always be 88-98. OOBS is 73-87. NBS 99-whatever and so on.

People use it because they can see with their eyes a new body style to an old body style

That would make sence if the terms changed with updated designs, but they don't. Nobody would think OBS means 88-98 unless the NBS was the only style out. We've marched on, so the meanings aren't so clear anymore.

As for the dual vs single piston debate, they only help if the single piston caliper doesn't have the power to clamp. They also spread the force more evenly across the pad.

[burkey05]

Originally Posted by Tom

A guy on FSC.com just posted up how to put NBS 13" rotors+dual piston calipers both front and back on OBS trucks. So friggin simple its blowing my mind.

do you have a link to this thread?

[Tom]

Originally Posted by burkey05

do you have a link to this thread?

http://www.fullsizechevy.com/forum/g...i-install.html

[tismy55]

will this MC set up work on my 89 C2500 Silverado

[speedygonzales]

No bleed like normal. Use the bottle method I mentioned.

[speedygonzales]

If you put the hose you attached to the bleeder in a clear plastic bottle and immersed in brake fluid, you can pump away all you want. Just don't allow the fluid level in the reservoir to get too low before you refill it. This way you can get done fast and you don't need another person.

By keeping the end of the hose in fluid, you won't allow air to get back into the system before you tighten the bleeder.

Also, if your bleeding out old discolored fluid, when the clear fluid makes it to the bottle, you know you did the entire circuit from the reservoir to the bleeder.

[tismy55]

so I can immerse the hose into a jar with fluid in it and pump until new fluid comes through without bubbles, and I don't have to close the bleeder screw in between pumps? Is that correct

[speedygonzales]

Yep just don't let the reservoir get too low.

Oh and always buy new fluid and if there is any fluid left over in the bottle, toss it. Don't keep it laying around. It draws moisture right through the plastic container sides. Metal cans won't but try finding brake fluid in metal cans.

And I'm sure you know this but start with RR wheel then LR wheel then RF and last LF wheel in that order.

I forgot to mention, after you start the engine. Press the brake pedal a few times before even putting it in gear. After you do put it in gear, allow the vehicle to stop as soon as you can. Don't wait until you need to stop. Stop moving a few times long before you come to the need to stop. In other words, try them when you don't need them in case of a problem.

[tismy55]

Do i need to bleed the dump valve as well

[hatzie]

Originally Posted by speedygonzales

Yep just don't let the reservoir get too low.

Oh and always buy new fluid and if there is any fluid left over in the bottle, toss it. Don't keep it laying around. It draws moisture right through the plastic container sides.

Metal cans won't but try finding brake fluid in metal cans.

Metal cans is the only way I buy it. Who knows how long the plastic bottles have been hanging around at the warehouse... Just say no to brake fluid in plastic bottles. Plastic bottles with foil lined caps and vacuum deposition metallized insides would probably do the job but they are trying to wring the last 1/8th penny of profit from any sales.

Brake Fluid I can buy locally in metal cans...

Pentosin DOT4 I can get both Super DOT4 and low viscosity DOT4 LV locally at Bond Auto Parts. DOT4 LV is a 1-2 day turnaround to order it in Super DOT4 is on the shelf. I believe Pentosin is available on-the-shelf at AutoZone for you folks in the city.


ATE DOT4 Type 200 and SL-6 are not as common to find on the shelf but the local NAPA franchise can and will get me the low viscosity SL-6, that I run in my LS4 Impala and VW, in 2-3 days. I have no problem stocking several metal cans because it keeps. They have several local folks with MGB and other semi-antique British cars that use this stuff too.

[speedygonzales]

If you have a way to do it, sure but I never have.

[tismy55]

Mine has a bleeder valve on it

[speedygonzales]

You got me there. I just checked the shop manual and it does not mention anything other than the normal bleeding at each wheel. Nothing else. It only mentions the pressure modulator valve if it's been replaced or if you suspect is has air in it.

The antilock bleeding procedure never mentions to open anything other than the bleeders at each wheel. It mentions to use the GM scan tool to run the automated bleed procedure. Then go back and do each wheel by hand.

So it doesn't look like you're gona be able to do any ABS bleeding. Just do the normal method and you're done.

[Red88]

I've got an 88 w/RWAL and the dump valve with a bleeder port on it. You use the same bleed procedure with the dump valve as with the wheel cylinders/calipers. The order would be Right Rear, Left Rear, Right Front, Left Front, Dump Valve assuming you don't need to bleed the master cylinder.

BTW Speedy, great writeup! I've installed the fenco version from autozone this weekend, along with new drums/cylinders/shoes/hardware/brake hoses. Am finishing up the hose installations today along with the bleeding process. Already a much firmer pedal. I'll post up results once I'm done but wanted to take the opportunity to thank you!

[BigRed76]

So what is it about the NBS master cylinder that is so much greater than the OBS master cylinder? I see that the piston diameter is slightly bigger on the NBS MS, 34mm NBS vs. 28.5mm (1.125") OBS...so is it the difference is piston diameter? Or something I missed earlier in this thread?

[Tom]

Originally Posted by BigRed76

So what is it about the NBS master cylinder that is so much greater than the OBS master cylinder? I see that the piston diameter is slightly bigger on the NBS MS, 34mm NBS vs. 28.5mm (1.125") OBS...so is it the difference is piston diameter? Or something I missed earlier in this thread?

OBS has stepped piston and is overall larger. Larger piston=less pedal effort. Thats all.

[Red88]

First of all, thanks to all the contributors here most especially speedygonzales. As others have noted the brakes on my '88 k1500 have always been a source of worry in any hard stopping situation and knew it could be better. Had already replaced front pads/rotors/calipers, rear shoes/cylinders/drums, flushed and bled system to little improvement in the braking ability of this truck. Did this mod about a month ago and wanted to report my experience.

I found the Fenco master cylinder locally at Autozone along with the AGS #BLF-26C adapter. Removed OBS master, bench bled and installed NBS master with line adaptor. Had to carefully bend lines and was afraid they might snap but there is enough "slack" to allow the realignment to the NBS master. Bled system and found firm pedal but less braking power. No good!

I suspected my booster might be bad, did the various tests which it passed. In the process I looked up a new one and found 3 different ones listed for my truck; a single diaphram 10.75" (standard brakes) stamped "AB", dual diaphram 9", and a dual diaphram 10.5" both stamped "HR". My truck had the single diaphram 10.75" "AB" booster from factory which I assume was standard equipment for the cheapest brake setup from factory. I looked up the 2002 Silverado that my NBS master cylinder was originally designed for and found that the booster from this truck was an 11" dual diaphram. I figured the new master was designed to require the additional boost from a dual diaphram booster so I went and bought the 10.75" dual diaphram booster that came on some versions of my truck. For my truck, that was the key to good brakes. Firm pedal and much much better stopping power.

Bottom line, for those of you with original equipment single diaphram brake boosters: install the dual diaphram 10.5" along with the rest of this mod. You won't regret it!

Parts list:

Fenco NM3089 Master Cylinder (Autozone) $85.99
AGS BLF-26c line adaptor (Autozone) $2.49
Brake Best 54-71046 brake booster (Oreillys) $104.99

[Tom]

Originally Posted by Red88

Bled system and found firm pedal but less braking power. No good!

Originally Posted by Red88

This is all about increasing the area of diaphram and thereby increasing the force applied thru the booster to the master cylinder and reducing the amount of pedal force needed to stop the truck.

I'm confused. You didn't have less braking power with the original booster and NBS master. You just needed more pedal effort, which is the entire point of the swap. You changed the master cylinder to get a firmer pedal, then changed the booster style to get a less firm pedal? Sounds like you just needed a correctly functioning OBS master and 10.75" booster to begin with... Your diaphram research and pictures are excellent btw!

[Red88]

Originally Posted by Tom

I'm confused. You didn't have less braking power with the original booster and NBS master. You just needed more pedal effort, which is the entire point of the swap. You changed the master cylinder to get a firmer pedal, then changed the booster style to get a less firm pedal? Sounds like you just needed a correctly functioning OBS master and 10.75" booster to begin with... Your diaphram research and pictures are excellent btw!

Sorry if my explanation wasn't straight forward enough. In my truck the old master had a spongy pedal which also means it didn't stop very well. The NBS master had a much firmer pedal but I really had to stomp on the brakes to stop. Adding the dual diaphram booster gave me both a firm pedal and the stopping power I was looking for.

I don't know for sure if I had a correctly functioning OBS master and booster. No leaks, tested ok. I do know that the truck didn't brake very well at all. From what I read that is a common complaint of owners of these trucks. I think it's a fair assumption that the standard brakes on these trucks were not adequate for alot of owners. There were 3 different brake options on 1/2 ton trucks. Good-better-best. Good wasn't very good IMHO.

[Tom]

Originally Posted by Red88

Sorry if my explanation wasn't straight forward enough. In my truck the old master had a spongy pedal which also means it didn't stop very well. The NBS master had a much firmer pedal but I really had to stomp on the brakes to stop. Adding the dual diaphram booster gave me both a firm pedal and the stopping power I was looking for.

I think I get what your saying now

There were 3 different brake options on 1/2 ton trucks. Good-better-best. Good wasn't very good IMHO.

So I've been researching this today as I'm bored at work. Going by rockauto's pictures, 98's came with JB5,6,7 and 8 brake systems. They all used either the 10.5" dual diaphram or they used hydroboost. I'm guessing the other styles might be earlier setups? I know a couple people who put NBS masters on vortec 1/2ton trucks and had no complaints about pedal effort so I'm assuming they all had the 10.5" from the factory....