OBS to NBS Master Cylinder Upgrade REPORT

[kennythewelder]

Sorry, it's just that I'm an idiot.

I actually ordered the the brass conversion fitting with the m/c. But the two line fittings looked the exact same(My eyes aren't what they used to be). I was just looking at the size of the line.

This thread explains it:

https://www.gmt400.com/threads/how-to-nbs-master-cylinder-swap-for-firm-brake-pedal.17998/

Thanks!

No problem. The thread link you posted, is the thread I used when I did my swap. Grate info in this thread. The brake peddle is firmer with the NBS cylinder than with the OE cylinder. My last truck was a 93 WT LWB C1500 with a 4.3L. That truck would stop on a dime. My 97, not so much, but the MC swap does help some what. As for not seeing that grate, well Im 60 so I understand. I can see worth a damn without my glasses. I did need glasses untill I was about 45.

 

[95k150050]

will this work on a 95 k1500?

 

[kennythewelder]

will this work on a 95 k1500?

Yes.

 

[95k150050]

Giggity

 

[David89gmc]

Upgraded from the original master cylinder to a heavy duty master cylinder, with a larger diameter piston. Very nice pedal feel and braking action. The rear wheel cylinders are heavy duty 1 3/16" but the front caliper pistons are standard diameter.

This 1989 K1500 Sierra has an interesting mix of standard and heavy duty parts, but doesn't have the F44 or F60 option. Not sure it came from the factory with the heavy duty parts.

 

[laxman21]

Looks like the front line on the OBS master was for the front brakes and the NBS the front works the rear brakes. That's the way the OP installed them and other how to's on other forums. Mine is that way 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. Look and decide for yourself.

NBS

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

OBS

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[Tony Biddle]

I did the swap of my OBS master cylinder to a NBS master cylinder. 1999 2 door Tahoe 4x4. 3.42 gears, 35in KM2's

Part of my 4 month Tahoe Overhaul where my goal was to turn the Tahoe into a reliable DD, mechanical-wise, as if it were a new Tahoe. Example: Be able to go 80mph on the highway and sit in stop and go traffic at 110* and not have any mechanical or drivetrain problems.

Parts:
-2001 Chevrolet Silverado 5.3L 4X4 Master Cylinder; Vacuum Boost. Brand:AC Delco. Part Number: 18M1159 . $101 at O'Reilly
-Brass Adaptor. Autozone. Brand: AGS. Part Number: BLF 26C . $3.00

The adaptor connects the MC fluid outlet (furthest from the steering) wheel to the stock OEM hard brake line. Get the one from Autozone because its Brass and overall stronger than the equivalent adapter from O'reillys, which looked very maleable. The metal and precision of the small part looked inferior and weighed less. Not something I skimped out on when it comes to brakes.

The Results:
Wow! The pedal feels firmer than any truck ive ever driven. The stopping power is a night and day difference. I run 35/12.5/17in tires on my 2 door. I also had the mechanic install an extended rear SS brake line I bought 6 years ago (Skyjacker brand) and that might have helped helped too. My front lines are not SS. The rear SS was primarily so the line wouldn't break at full extension. Especially when on a mechanics lift, the rear stock rubber line was at maxxxxxx. You could touch it and it wouldn't move side to side due to all the tension. I'm lucky I didn't blow it before.

One thing to note. You can hear the rear drums squeak when you come to a stop from about 2mph to 0. I was told its just the increased pressure they are under and that it's okay. A bit annoying but not too loud like worn or warped front brake pads on a normal car.

I also replaced the front pads and rotors during my 4 month long Tahoe rebuild.

— hello I am new to the gmt400 forum, I tried to do the master cylinder swap on my 1999 k2500HD , 7.4 vortec. But I have factory hydro boost and the nbs master cylinder did not fit, the bore was too large to fit into my booster. Any ideas?
Thanks in advance!

 

[Supercharged111]

Yeah, hog it out. Better yet, with HB why did you even bother with an NBS master?

 

[Tony Biddle]

Yeah, hog it out. Better yet, with HB why did you even bother with an NBS master?

— I like the screw on cap, for bleeding purposes. And I have a VERY low/soft pedal. The truck will come to a stop and the brakes will lock at low speed, but I’d like more pedal height , also thank you for the response!!

 

[TheAutumnWind]

— hello I am new to the gmt400 forum, I tried to do the master cylinder swap on my 1999 k2500HD , 7.4 vortec. But I have factory hydro boost and the nbs master cylinder did not fit, the bore was too large to fit into my booster. Any ideas?
Thanks in advance!

Yeah you cannot install any NBS master cylinder with an OBS hydro boost. If you are having trouble with a hydroboost setup I would look at other solutions. Generally speaking properly functioning OBS hydroboost setups are more than fine. Have you tried maintenance items already?