How to: NBS master cylinder swap for firm brake pedal

Half Assed

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How to swap out the squishy brake pedal for a firm brake pedal. The OBS trucks are known for a horrible squishy brake pedal.

-NBS 1500 series master cylinder (buy the corresponding master cylinder for your truck, 1/2 ton=1/2ton, 3/4ton= 3/4ton)
-AGS BLF 26C brake line adapter (I got mine at autozone)
-DOT 3 brake fluid
-master cylinder bench bleeding kit

The OBS master cylinder has different sized ports. One is 9/16-18, the other is 1/2-20. The NBS master cylinder is 1/2-20 on both ports. This is why you need a 9/16-18 female to 1/2-20 male adapter. AGS makes an adapter #BLF 26C that I got at autozone. It was behind the counter, so ask for help. The bench bleeding kit was also behind the counter.



I first attached the adapter.

Then I bench bled the master cylinder. There are plenty of videos on youtube showing you how. In my case I used the kit and cycled the piston with a 3/8" socket extension against a tire stop. :lol:

You must be registered for see images attach


Then I removed the 2 brake lines and removed the 2 nuts holding the old master cylinder on the brake booster.

picture of old master cylinder:
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Bolt the new cylinder cylinder on with the 2 nuts. Then gently bend the brake lines to reach the holes. The NBS master cylinder is shorter than the OBS master cylinder.

Only thread the nuts back on just a little, enough to let brake fluid and air leak past.

Inside the truck use an object to press down on the brake pedal and hold it down. This may get brake fluid spray on the surrounding area, cover with a rag to catch any spray.

If the lines haven't leaked, loosen up the nuts just a tad on the brake lines to let out any air and let some fluid drip out. Then tighten all the way up.

Release the brake pedal after both lines are tight.

Very little air should be in the system. If you think there still may be air, go ahead and bleed the brake lines.

Finished product:
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Enjoy the firm pedal your truck should have had. :D
 

sewlow

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Excellent! I think...!
Another mod on my list!
This forum keeps adding to that & lightening my wallet! Lol!
Thanks for this. I'll do the Hydro-boost on my '98 & this ^^^ on the '97!
 

1997chevydriver

OBS MAGIC!!
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Don't you have to swap out the push rod due to different length?

Sent from somewhere in MN
 

Half Assed

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Excellent! I think...!
Another mod on my list!
This forum keeps adding to that & lightening my wallet! Lol!
Thanks for this. I'll do the Hydro-boost on my '98 & this ^^^ on the '97!
hydroboost and NBS master cylinder is a little more complicated. Check here:
http://www.fullsizechevy.com/forum/...brakes-obs-hydroboost-nbs-master-project.html

Don't you have to swap out the push rod due to different length?

Sent from somewhere in MN

I don't think so.
 

bluex

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Yes the NBS 1/2 ton MC will not work with obs hydroboost, I have tried.

Looks easy enough to make work though. Glad I found this before buying my new master for my hydroboost swap. Have you tried a 3/4-1 ton gmt800 master?
 
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