How to: NBS master cylinder swap for firm brake pedal

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Not sure exactly what year the master is. I got it brand new off a guy who had planned to swap it onto a truck he had years ago and wound up selling the truck before the swap so he held into it for like 3 years for me until I finally decided to do the swap and bought it from him lol.

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Oh ok. Well I got one the other day at junk yard off 2001 tahoe, waiting on braided lines to show up to do the swap
 

Sampuppy1

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Oh ok. Well I got one the other day at junk yard off 2001 tahoe, waiting on braided lines to show up to do the swap
I did everything on the truck. Master, prop valve, hard lines, flex hoses, and the wheel cylinders are newer, plus a new caliper and one newer one that didn't need replaced.

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Well I finally got mine done and works good. After hours of research on these truck and everyone has a opinion on it. Lol. Now just got to have new pads
 

KevinF

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For gmt 400 with Hydroboost you either run a stock 88-98 Hydro. M.C., or you can bore out the inside of the hydro unit to accept the NBS Hydroboost M.C. I have done both, I have the NBS Hydro. M.C. on my personal truck, I used a M.C. from an 04 tahoe with hydroboost, then I bored out my hydroboost unit with an air rotary file and lots of wd 40 to keep it cool as I was doing it, as I did mine on the truck, you could also use cutting fluid or something similar.


On my 98 I ran an 05 Tahoe HB and master because I had already swapped in a 03 5.3L so I knew the HB lines would match. It was easy to make the brake pedal rods mate up, you run a 3/8 NC die over each rod and connect them with an allthread coupling nut.



I have a question that I don't think has been answered here though. Are the hydro lines and fittings the same between GMT400 and GMT800 hydroboost? The options I am looking at right now are run the 400 HB and bore it out or run the 800 HB and master as a pair and adapt at the brake pedal rod. I have SD axles in the truck so I want to run a disc disc MC.
 

Ben Burrage

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Can anyone confirm if I should use the AC Delco 19295627 Master Cylinder from a 2005 with rear drums to do this upgrade?
 

laxman21

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Looks like the front line on the OBS master was for the front brakes and the NBS the front works the rears brakes. That's the way the OP installed them and other how to's on other forums. Mine is that was now and I will be looking to swap them. A mechanic told me it felt like my rears were doing most of the braking when he fixed a broken brake line.

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https://static.nhtsa.gov/odi/tsbs/2014/SB-10054261-7817.pdf

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kennythewelder

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Can a nbs master cylinder bolt up to the obs vacuum booster?
Yes. Its a direct fit. Thats how mine is. Another thing, People are over thinking this swap. Its a direct swap except for the brake line adepter. I installed the front line in the front hole, the back line in the back hole. The kelsy Haney is the proportioning valve. Thats where the pressure is regulated. Not in the master cylinder. Mine has been in my truck about 4 years. I never had any issues with the swap.
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Schurkey

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I read through this thread--five pages worth.

I understand very little of it.

I do recognize there's some mistakes, flawed logic, and outright bad information here 'n' there.

What I HAVE NOT seen is WHY the "NBS" master cylinder makes an improvement. What is different in the design?

Here's what I know: There's a one-inch bore master cylinder, and a one-and-an-eighth-nch bore master cylinder, in Quick Take-Up and standard varieties. There's at least three sizes of caliper pistons, and at least three sizes of rear wheel cylinders (drum brake style.)

Using a larger master cylinder bore on the smaller pistons will reduce pressure, increase volume, and raise the brake pedal. Smaller master cylinder with larger pistons will increase pressure, decrease volume, and drop the pedal. Basic hydraulic theory. It's equivalent to gear ratios and torque/speed exchange. In this case we're exchanging fluid pressure for fluid volume by changing master and slave piston sizes.

There's at least two sizes of vacuum power booster, a single-diaphragm and a larger, dual-diaphragm. The bigger booster provides more assist, which makes for lower pedal effort--or allows a larger-bore master cylinder to equal the pressure of the smaller-bore with approximately the same pedal effort.

And making things even more complex is the addition of ABS and low-drag calipers.

Low-drag calipers need a huge influx of fluid at low pressure from a "Quick Take-Up" master cylinder to move the caliper pistons to the rotor, then the high-pressure section of the master cylinder applies the braking pressure that forces the pads into the rotor. If the low-pressure section of the master is faulty, the pedal will be low. If some idiot installed a non-quick-takeup master cylinder on an application with low-drag calipers, the pedal will be low. If the calipers are sticking but not yet frozen, the pedal will be low.

Quick Take-Up master cylinder has a stepped casting, and a huge rear seal/piston--36 mm or 40 mm depending on whether the main part is 1" or 1 1/8".
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If the ABS unit is faulty, the accumulator absorbs fluid volume, and the brake pedal will be low.

Far as I can tell, none of the improvement you guys are finding is due to "NBS" master cylinders, Maybe it's just due to you finally getting all the air out of the hydraulic system, maybe it's due to replacing faulty masters, or faulty calipers or faulty ABS units with parts that actually function properly. .And whatever doesn't directly bolt up just creates more work for you.

But what the hell do I know? I may be old, but I'm not done learning stuff.

For the record, I really despise "NBS" and "OBS" and "NNBS". As soon as GM releases the next in the series, "NBS" changes. At least "Squarebody", "GMT400" and "GMT800" retain their meaning over time.
 
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