NBS master cylinder Swap

Discussion in 'Engine Performance + Maintenance' started by scott_williams2, Jan 16, 2021.

  1. SUBURBAN5

    SUBURBAN5 I'm Awesome

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    I agree hard to tell. Biggest difference is on the high way. When mine was working I enjoyed it. When I went to the bypass setup it just has full powersteering feeling which I've gotten use to
     
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  2. Pinger

    Pinger I'm Awesome

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    Cheers! Another piece of the GMT400 jigsaw in place.


    And sweet when it works that way...

    I've had to order another (due 27th) then return the current one for a refund - which will be a bit of a PITA but that's how it is. Hopefully this one cures what's been bugging me since March.
    And I'll take you back to something you said back then. ''Our trucks, they're like metal kids the attention they need''. Out of everything written on this forum in 2020 I nominate that for the Most Truthful Comment Of The Year Award. It wins hands down!
     
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  3. Schurkey

    Schurkey I'm Awesome

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    It's a rule-of-thumb, not a definitive distinction. From my '97 C-K service manual:

    JB 5, 6, 7 are vacuum assist.

    JD 5, 6, 7 are hydroboost.

    But JB8 and JF9 are hydroboost, too

    And I need to dig around my '88 service manual for the xx3 designation. Seems to me it may be another screwy one. But they were all vacuum, no hydroboost available on xx3 systems.
     
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  4. HotWheelsBurban

    HotWheelsBurban Burbs are great!

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    JB3 is the really bad tiny brakes on the half ton pickups, right? The leading/trailing shoe one?
     
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  5. arrg

    arrg I'm Awesome

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    Yes, they are the really tiny brakes on the half tons, but they only came on 88-91 single cab trucks. The JB5 is still leading/trailing shoe drums in the rear, but the front calipers are bigger than JB3, and the rotors are thicker but the same diameter. JB3 also has a single diaphragm vacuum booster, so half the power assist.
     
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  6. scott_williams2

    scott_williams2 I'm Awesome

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    Yea I figured I could hit the junkyard but it was just more convenient to buy a new one. My local yard gets hit FAST. Most 99-06 are stripped by the first week. If u could do the same thing I did and it works for u for $12 I say hell yea
     
  7. scott_williams2

    scott_williams2 I'm Awesome

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  8. Schurkey

    Schurkey I'm Awesome

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    1. You need to type your reply AFTER the "[/QUOTE]"

    2. Your mistake in logic is assuming that the trucks were designed with "marshmallow" brakes. They weren't. They get that way over time, because parts fail, and/or the brake system is improperly serviced.

    3. My whole point was that it's best to fix the RIGHT thing, instead of covering-up one problem by stuffing an incorrect master cylinder in place and causing a different problem. I've explained to you how the system is supposed to work. I've explained to you what the incorrect master cylinder accomplishes; and why it cannot work properly in this application. The fact that it works better than your previous master cylinder tells me the previous one was defective. So...you replaced a failed master cylinder with an incorrect, but functional master cylinder, and things improved. Imagine how good they'd be if you had the proper master cylinder in place, that worked like it was supposed to.
     
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  9. Pinger

    Pinger I'm Awesome

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    One thought that comes to mind thinking about MCs that lead to higher pedal pressures - what happens if booster assistance is lost? Kind of spooks me anyway that a broken serp belt on a Hydroboost truck means steering and brakes are going to get heavy. Maybe not immediately in the case of the brakes but not many applications before residual boost is gone and without Hydroboost I could hardly hold back my truck just idling in drive.
     
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  10. thegawd

    thegawd I'm More Awesome!

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    (edit cuz it wrong info... )

    when my booster blew unexpectedly coming up to a stop sign, there was a loud hiss and no breaking power, I smashed the pedal and it went to the floor, I shit my pants, but the truck did slowly stop. However out of fear when I smashed the brakes I blew a line at the same time and went through the stop sign of a major road, with 4 ways on, no one coming, phew. clean the shit out of my pants. discover an empty master for the front brakes. pinch the line with vice grips, fill the master up, test and proceed. I had my entire family in the truck. after every stop I pulled over and topped the MC back up because vice grips wont actually close the line off completely.

    Iv been over the brake lines many times but for some reason I never traced the front passanger line and it was rotten sitting on top of the front frame hidden above the plastic splash guard shroud. this spot is terrible for a visual inspection but that plate comes off very easily. I re-routed this line slightly so it didnt sit right on that frame and took a slightly different route to the caliper.

    so with a failed booster you will still have brakes but it seems to come at the end of the peddle travel.

    I was lucky that I'm not the kind of person to fly up on a stop sign or lights and smash the brakes at the last second. I'm more of the annoying kind who let's of the gas way before and let's the engine brake slow the truck down before activating the brakes.

    Al
     
    Last edited: Jan 26, 2021
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