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

[z71se]

Hey guys I just got done with the GMT800 MC swap and I also took the opportunity to install 02 knuckles and rotors/ calipers (to fit under my stock 16" Alcoa wheels). New drums, shoes, and stock replacement wheel cylinders out back. The dead spot does seem reduced, but I'm not 100% sure the braking significantly improved. As others have stated, the GMT800 MC has a smaller bore size so you have to push harder on the pedal even though the pedal is firmer. Anyways, I'm still not satisfied with the brakes even after all this work (reaming the GMT800 knuckles was kinda a pita). Am I correct that converting to hydroboost is my last option? I wish there was a GMT800 master cylinder that had a slightly larger bore size. My truck is a 2000 Z71 Tahoe (old body style).

[Chris95GT]

I've done this swap on my GMT400 99 3/4 ton, it was simple and I noticed an improved pedal feel and quite a bit better panic stop feeling. Houston traffic sucks. Before, during a panic stop I felt like the pedal was darn near bottomed out and I wasn't going to stop in time, the few panic stops I've done since the swap felt much much safer. I'm very happy with the GMT800 Master so far, my only regret is not doing it sooner. (I had it sitting around for 2+ years before finally doing it)

Next step for me is GMT800 Front and rear disk swap with stock GMT800 calipers, disks, and pads, but I still need to get and modify GMT800 knuckles to fit my truck, and get new tires for my 6 lug wheels (I'll be going from 8 lug to 6 lug)

[z71se]

Originally Posted by Chris95GT

I've done this swap on my GMT400 99 3/4 ton, it was simple and I noticed an improved pedal feel and quite a bit better panic stop feeling. Houston traffic sucks. Before, during a panic stop I felt like the pedal was darn near bottomed out and I wasn't going to stop in time, the few panic stops I've done since the swap felt much much safer. I'm very happy with the GMT800 Master so far, my only regret is not doing it sooner. (I had it sitting around for 2+ years before finally doing it)

Next step for me is GMT800 Front and rear disk swap with stock GMT800 calipers, disks, and pads, but I still need to get and modify GMT800 knuckles to fit my truck, and get new tires for my 6 lug wheels (I'll be going from 8 lug to 6 lug)

You'll want to convert to hydroboost at that point... I would not have converted to the GMT800 fronts had I known they would feel this way (I installed the GMT800 mc at the same time). Yes, the dead spot is gone but the pedal effort required to stop the truck is 25% greater (due to the larger bore size of the GMT800 master) so braking confidence is not significantly improved, if at all. I will be converting to GMT400 hydroboost shortly.

[z71se]

Also - reaming out the GMT800 knuckles is a huge PITA! If you would like to use my tool (I only used once), let me know and you can borrow it! I also have some tips on how to make the reaming easiest... you'll want to use an air ratchet with the knuckle mounted in a vice. Get an old or new GMT400 upper and lower balljoint handy to test fit as you go along. Both the upper and lower balljoint holes will need reaming. The reaming tool in a socket in conjunction with the air ratchet was definitely the best method I found...

[Brandon_Lutz]

Sorry to drag this thread back up, so please forgive me. I've searched many threads on many forums about this swap and I'm still getting kind of confused on which MC I should be looking at.

I have a 95 K2500 with the 5.7. I'd like to do this swap on my truck but I'm not sure with NBS Master Cylinder should I be looking at to to replace it. I'm not looking to go to hydro-boost and I plan on keeping the setup as it currently is, vacuum assisted.

I've found conflicting issues in various places on whether I should get a 1500 4x4 Master Cylinder from an NBS as the 3/4 ton trucks and up were hydro boost on some models. Or I should look into a 2500 master cylinder. Can anyone tell me definitively which one I should look into getting?

[Chris95GT]

Originally Posted by Brandon_Lutz

Sorry to drag this thread back up, so please forgive me. I've searched many threads on many forums about this swap and I'm still getting kind of confused on which MC I should be looking at.

I have a 95 K2500 with the 5.7. I'd like to do this swap on my truck but I'm not sure with NBS Master Cylinder should I be looking at to to replace it. I'm not looking to go to hydro-boost and I plan on keeping the setup as it currently is, vacuum assisted.

I've found conflicting issues in various places on whether I should get a 1500 4x4 Master Cylinder from an NBS as the 3/4 ton trucks and up were hydro boost on some models. Or I should look into a 2500 master cylinder. Can anyone tell me definitively which one I should look into getting?

My truck is a true 3/4 ton 8600GVW 99 GMT400 truck. I went with the MC from a 2003 K1500 Avalanche (Just because it's what I had from another project). It's worked great for me so far. I don't know if there was a difference between the 1/2 ton and 3/4 ton vacuum master cylinders in the GMT800 platform, but I'm using a half ton unit on my 3/4 ton and love it.

[z71se]

Originally Posted by Brandon_Lutz

Sorry to drag this thread back up, so please forgive me. I've searched many threads on many forums about this swap and I'm still getting kind of confused on which MC I should be looking at.

I have a 95 K2500 with the 5.7. I'd like to do this swap on my truck but I'm not sure with NBS Master Cylinder should I be looking at to to replace it. I'm not looking to go to hydro-boost and I plan on keeping the setup as it currently is, vacuum assisted.

I've found conflicting issues in various places on whether I should get a 1500 4x4 Master Cylinder from an NBS as the 3/4 ton trucks and up were hydro boost on some models. Or I should look into a 2500 master cylinder. Can anyone tell me definitively which one I should look into getting?

You want the NBS 1500 master cylinder from a 1999-2002 Silverado. Dorman part # M630031.

[speedygonzales]

Originally Posted by Brandon_Lutz

Sorry to drag this thread back up, so please forgive me. I've searched many threads on many forums about this swap and I'm still getting kind of confused on which MC I should be looking at.

I have a 95 K2500 with the 5.7. I'd like to do this swap on my truck but I'm not sure with NBS Master Cylinder should I be looking at to to replace it. I'm not looking to go to hydro-boost and I plan on keeping the setup as it currently is, vacuum assisted.

I've found conflicting issues in various places on whether I should get a 1500 4x4 Master Cylinder from an NBS as the 3/4 ton trucks and up were hydro boost on some models. Or I should look into a 2500 master cylinder. Can anyone tell me definitively which one I should look into getting?

See this

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

Originally Posted by speedygonzales

NBS Master Cylinder numbers:
GM 19209249
Durastop 18M1159 made by AC Delco
AC Delco 174-1003
NAPA NMC M3432
Cardone 13-2881
Dorman M630031
Fenco NM3089

Go back to the first page for instructions because the lines are different sizes

[Brandon_Lutz]

Thank you all who responded. You guys rock

[jcramsey]

Gotta put this on the to-do list!

[54 jimmy]

I used a 2500 nbc on my 97 1500. no issues. I think the 2500 mc is the better option. I have better pedal feel in normal driving and panic stops. as far as the pressure feel of the pedal it is not hard to get it to stop. my wife loves how the brakes feel because they use to scare her before but now she feels much safer driving the truck. not good for me because now she wants to drive the truck. gotta take the good with the bad .

[Geomarq123]

Found this thread as I was swapping the rear discs on my 97 k1500. Then did the master cylinder, and figured I'd change to the right combination valve. Now I'm stuck, can someone help?

How can I plumb the new combination valve into the abs unit? The diagram shows what I have..the combination valve bolts and directly takes fluid in and the abs unit has three valves out...two valves for the front, one rear. The correct disc/disc combination valve has two ports in three out. The old is two in, two out. I've never liked the abs on this truck..should I discard? What's the proper way to disable the Abs?

[speedygonzales]

This issue should have it's own thread. People are going to come here looking for changing the master cylinder information.

Repost it as a new post.

[satisfied]

I have a 96 C1500 Burb. Will the switch out using the MC 2002 Siverado with rear disc brakes be compatible with my truck with rear drum brakes?

[Keith Seymore]

Originally Posted by satisfied

I have a 96 C1500 Burb. Will the switch out using the MC 2002 Siverado with rear disc brakes be compatible with my truck with rear drum brakes?

I would say no.

If you have disc/drum brakes then you need a disc/drum master cylinder. I wouldn't think a disc/disc master would have the right design considerations for your setup.

K

[satisfied]

Speedygonzales,

Is your NBS MS already shot? A 1999 would have drum brakes as well.

[speedygonzales]

If it looks like this:


Then yes

Incidentally mine is shot already

[speedygonzales]

fluid leaking past the seals. It's been suggested the lines have to be reversed, will try that this weekend with a replacement unit.

[68C15]

Originally Posted by speedygonzales

fluid leaking past the seals. It's been suggested the lines have to be reversed, will try that this weekend with a replacement unit.

I'll be watching for your update. I don't have a newer truck in the shop otherwise I'd follow the lines and see which is which

[speedygonzales]

I looked for any published indication that the ports were reversed on the GMT800 MC. Could not find any.

The reservoirs both old and new seem to have bigger portions on the front. Even if they don't it makes no difference. I did not reverse the lines.

Still crappy brakes compared to everything else on the road but better then it was when it had the original MC.

[Eman85]

I've read thru this thread as a fix for my Chevy truck. I was a GM tech from the 70's up until these trucks were new. They always had the soft pedal from day.
The original MC had a step bore so it did make a difference how the lines were attached, plus since you had frt. disc only the reservoir for the frt. is larger. the reason for this is that disc brakes are self adjusting in the the piston moves out as the pad wears and the space is taken up by fluid. On a straight bore MC the only difference in ports would be if you had a MC from a frt. disc vehicle. The NBS MC is for a disc/disc vehicle so it doesn't matter how you connect the lines.

[SquareOne]

I did the NBS upgrade this afternoon after the drum brake wheel cylinders failed and I had to replace those and bleed the system anyway.

WOW! Night and Day. If you're on the fence, you're wasting your time. This is one of the easiest and quickest upgrades you can do.

I got lucky and I got the MC from a friend who was doing a hydroboost conversion on his 2001 NBS, so it didn't cost me a thing. I know that there is a piece of mind that comes with buying one new but I never hear about stock MCs failing that often so I decided to err on the side of saving money and we with the used unit.

The pedal feel and response is significantly better than the original equipment. I feel it now brakes just as good if not better than the wife's 2015 sedan.

[SquareOne]

I did the NBS upgrade this afternoon after the drum brake wheel cylinders failed and I had to replace those and bleed the system anyway.

WOW! Night and Day. If you're on the fence, you're wasting your time. This is one of the easiest and quickest upgrades you can do.

I got lucky and I got the MC from a friend who was doing a hydroboost conversion on his 2001 NBS, so it didn't cost me a thing. I know that there is a piece of mind that comes with buying one new but I never hear about stock MCs failing that often so I decided to err on the side of saving money and we with the used unit.

The pedal feel and response is significantly better than the original equipment. I feel it now brakes just as good if not better than the wife's 2015 sedan.

[mountie]

Square One is a perfect example why us truck owners are here....

To make our cool trucks better!

I did the MC upgrade 2 years ago, because I learned it here.

[speedygonzales]

All of this is a waste of time.

Trust me I started this thread. In addition to changing the master cylinder I also changed my front calipers to 2 piston and rotors to slotted type.

None of this works as well as the way the brakes should be from the factory. But I'll tell you what does! I just came in from doing it.

It's called the "automated bleed procedure".

I was poking around a few threads mentioning that nothing works until people did this. Some even said most GM's are this way. Without it you're wasting your time.

But what the hell does bleeding the ABS have to do with the normal brake operation. I"m sure I'm not the only one that said that and did normal brake bleeding procedure. I don't know and was skeptical until I did it.

See my new post for a little more information.