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

[DZL1]

No pics of your mod installed?

DZL1.

[t_graham11]

Me? No I just ended up buying the two MC's the new body's type and te stick one for my truck. I'm putting the stock one in today and I'm going to buy a new hydro boost next month and get it machined out that way I'll have the parts on hand next time I need to do the brakes ill swap out the new mc and hydro boost.

**i don't know if in allowed to post outside links**

But here is the write up I found.... http://www.fullsizechevy.com/forum/g...r-project.html
Posted via Mobile Device

[Keith Seymore]

Originally Posted by t_graham11

I did some searching and the new cylinder is 1.8" and the original is 1.6" so you'll have to bore out the .2" on hydro boosted trucks. Some guys have said they did it them selfs but I'm going to buy a new hydro boost and get the machine ship to bore it out for me.

I'm not sure I'm following you -

Are you talking about boring out the center bore of the master cylinder (affecting line pressure)? or are you talking about the outside diameter of the hub that fits into the brake booster?

K

[t_graham11]

Yeah the outside diameter of the nbs master is .2" larger diameter so you need to bore out where is slips inside for the plunger to push.

It'll be a while but I'll take pictures of everything and give a good explanation
Posted via Mobile Device

[Keith Seymore]

Originally Posted by t_graham11

Yeah the outside diameter of the nbs master is .2" larger diameter so you need to bore out where is slips inside for the plunger to push.

It'll be a while but I'll take pictures of everything and give a good explanation
Posted via Mobile Device

Ok - thank you. Understood.

There were a couple different sizes used in that area; they also varied based on Quick Take up vs Non quick take up master cylinders.

K

[Mickeymotormount]

Finally did this swap myself on my '93 Extended Cab Long bed 1500 4X4. Pedal feel was definitely higher/harder. But I feel that it still takes a firm push to achieve any kind of decent stopping power. Even with new rotors, 1 ton calipers and pads, new rear wheel cylinders and flex lines. I might have to upgrade to hydro boost next.

[speedygonzales]

Mickey, why don't you try a manually adjustable proportioning valve before you do anything else?

[Mickeymotormount]

Thanks for the reply, Speedy. I must say, your "Pride and Joy" is beautiful. For me, someday........ in a dream.........


My truck already has the 14 bolt rear(light duty 3/4ton), which has larger brakes than the 10 bolt rear. This was standard on my vehicle which has RPO code F44(heavy duty chassis). I thought about changing to an adjustable proportioning valve, but since my truck needed new front hardware/rotors, I figured I would go this route. I have read much here about the upgrade to bigger calipers and the NBS master cylinder. It definitely seemed like the right approach. My rear brakes are about to the point of locking up before the fronts do with the NBS master cylinder so I figured I'm close with the proportioning aspect of the brakes.

[speedygonzales]

Well let's relate what I read about the rear disc conversion to your situation. The disc conversion needs more pressure than the drums. So the kits usually have a new MC.

Now let's look at your set up. You have larger, MUCH larger front calipers and larger rear wheel cylinders. I think you aren't getting enough pressure. You should get the gauge kit and check each location for it's pressure.

[t_graham11]

Mickey, I think your going through the same problem as I am. I have a SAS and the front brakes rotors and calipers were upgraded (I'll have to look at my records to know to what exactly) my rear end felt like it was doing all the stopping and it got so bad that the brake cylinders began to leak. I put in a proportioning valve and the front is doing most the work.

I'm getting the hydro boost bored out and will be switch to the new mc soon, I just replaced the original mc and I still get a spongy brake, happen to me a couple times where it's gone to the floor. Ill gravity bleed tonight to see if that helps
Posted via Mobile Device

[mountie]

Originally Posted by speedygonzales

Just wanted to clarify for those not sure what we are referring to.

If you have one of these:
crappy master cylinder
replace it with one listed above that looks like this
good replacement

I click on the link, and get a real nice black screen.....

[Mickeymotormount]

Thanks for the replies guys.

My original calipers were for somewhere around 6600 lb. gross vehicle weight. These were standard on the 1/2 ton with the heavy duty chassis option. The caliper piston was around 2-7/8" in diameter. The new 1 ton calipers have pistons around 3-3/16" pistons.

While pedal feel is much better, I feel the breaking could be better. Before I owned this truck, I owned an '86 1 ton pickup with hydro boost. That truck stopped extremely well. With a future upgrade to hydro boost, I'm hoping I can get similar braking to what I remember.

[speedygonzales]

Originally Posted by mountie

I click on the link, and get a real nice black screen.....

That's odd cause I can even pull up the links you copied. Better check your computer.

[Mickeymotormount]

Links come up for me as well.

[mountie]

Originally Posted by speedygonzales

That's odd cause I can even pull up the links you copied. Better check your computer.

Weird... still not opening up.... ...Huh.......

[speedygonzales]

Originally Posted by mountie

Weird... still not opening up.... ...Huh.......

What browser are you using?


How about now?
http://www.carid.com/1998-gmc-savana...m-8666437.html
crappy one

Amazon.com: ACDelco 174-1003 Brake Master...good one

[mountie]

Originally Posted by speedygonzales

What browser are you using?


How about now?
http://www.carid.com/1998-gmc-savana...m-8666437.html
crappy one

Amazon.com: ACDelco 174-1003 Brake Master Cylinder: Automotive
good one

Mozilla / Windows

Opps...... it opens now..... got it...... I'm getting it.......( AC Delco version) Thanks for your help....

[Tom]

Originally Posted by Mickeymotormount

Thanks for the replies guys.

My original calipers were for somewhere around 6600 lb. gross vehicle weight. These were standard on the 1/2 ton with the heavy duty chassis option. The caliper piston was around 2-7/8" in diameter. The new 1 ton calipers have pistons around 3-3/16" pistons.

1/2tons and light duty 3/4's used the same calipers, HD 3/4 and LD 1 tons shared a different caliper with larger piston bore and oh so slightly larger pad, and HD 1 tons used an entirely different setup that doesn't swap. Swapping the larger bore calipers on, if anything, would have made the pedal softer. I didn't notice a difference when I did mine.

[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?