NBS master cylinder Swap

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SUBURBAN5

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Yes as far as I know, the hydroboost is designated by JD# and the vacuum booster system is designated by JB#.
I think the EVO system is working okay on our Burb. Easier to park, and power assistance proportioned as you need it. Admittedly sometimes on Houston area crappy roads it's hard to tell.
Did you get the master cylinder sorted out on your Burb? It sucks to get bad parts when the store is only across a small town; can't imagine how it feels when you have to wait for it to swim across the Atlantic....

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
 

Pinger

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Yes as far as I know, the hydroboost is designated by JD# and the vacuum booster system is designated by JB#.

Cheers! Another piece of the GMT400 jigsaw in place.


I think the EVO system is working okay on our Burb. Easier to park, and power assistance proportioned as you need it. Admittedly sometimes on Houston area crappy roads it's hard to tell.

And sweet when it works that way...

Did you get the master cylinder sorted out on your Burb? It sucks to get bad parts when the store is only across a small town; can't imagine how it feels when you have to wait for it to swim across the Atlantic....

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!
 

Schurkey

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Anyone got an answer on the JB vs JD designations?
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.
 

HotWheelsBurban

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

arrg

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

scott_williams2

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$120?

You can do it much cheaper than that.

Try $12.

I went to my local junkyard and got a used master cylinder for $8 (every wednesday is 1/2 off) and picked up the adapter fitting for around $3. I already had brake fluid so it was all good.

I also cut the lines when I removed the cylinder, so I was able to use them to bench bleed it in the truck.

It's a night and day difference, and everyone should do it.

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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
 

scott_williams2

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1. Why are you posting brake issues in "Engine Performance + Maintenance"?

2. "NBS" and "OBS" are vague and ambiguous terms.

3. JB3 and JB5 brakes have the ****** leading-trailing shoe rear brakes. It's uncommon to find them properly adjusted, and therefor they rarely work properly.

4. Replacing a Quick-Takeup master cylinder with a non-Quick-Takeup master is a FRIGGIN' DISASTER. You will LOSE hydraulic advantage, and you FAIL to supply the low-drag calipers with a "gush" of low-pressure fluid to push the pistons up to the rotor. GM put STEPPED-BORE master cylinders on these vehicles FOR A REASON.

Photo 1. Note HUGE rear piston, and stepped-casting. JB3 has a 1" nominal bore with 32 or 36 mm (I forget which) rear low-pressure piston. JB5 & (I think) 6 have a 1 1/8 nominal bore with 40 mm rear, low-pressure piston.
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Some doofus removes a correct-but-failed master cylinder, installs an incorrect but working master, and thinks he's accomplished something. Then he tells other folks who also don't comprehend the concept of low-drag calipers and high-volume (stepped) master cylinder bores, and they make the SAME MISTAKE.

The JB3, JB5, and (I think) JB6 (well, xx3, xx5, and xx6) brake systems use low-drag front calipers, and NEED the quick-takeup (step-bore) master cylinder.[/
1. I dint exactly know which category to post it too. Suspension???? If you are an admin feel free to move the post for me
2. If u spend even 5 minutes on at least one GM truck forum you will learn very quickly what a nbs and obs is. Seems to me you must live under a rock because your probably also the only person on this post who doesn’t understand these terms
3. Previous owner who I am friends with blew the rear end and replaced the whole rear axle with a BRAND NEW unit not junkyard/reman and the NEW rear brakes were properly adjusted bled etc by a certified mechanic I know personally with 20+ years experience.
4. I will not argue with you on the exact sciences on brakes bc quite frankly it’s not my strong suit. I’m an electrician not a brake expert. If this new MC is supposedly so bad and shouldn’t work blah blah blah then PLEASE TELL MY WHY IT WORKS A LOT BETTER FOR ME. All I know is the brakes work a lot better than factory brakes it had. If it works for me and helps me drive more safely for myself and others on the road then I’m all for it. When GM designed these brakes, we still used cassette tapes. This ain’t the 90s anymore get with the program. People used to also design paint with lead in it but them realized there was a better way. Same can be said for the nbs swap. I saw an opportunity to improve MY truck and figured I’d share to maybe help other OBS enthusiasts improve their old tired 20 year old trucks too. I can’t tell other folks how it will help them but it helped me TREMENDOUSLY. In the 2 weeks I’ve drove wit it I have had ZERO issues. My truck brakes a whole hell of a lot better and my other braking components are In good shape as well. I don’t get on this site but maybe once every other week or so but when I got on tonight and read your post I felt obligated to reply. If you have a difference in opinion you could haverespectfully replied to me instead of pretending to be a keyboard gangster. So have fun with your raggedy 20 year old squishy brakes and claim it’s supposed to be like that because “it was designed for it”. Me and the rest of the “doofuses” with“NBS” master cylinders are happy with our firm brakes. I’ll log back on in a week or two hopefullyyou have a more respectful response. Have fun trying stomping on thst marshmallow in themiddle of your floorboard when you have to startbraking 100 yards from a stop sign going 60
 

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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.
 

Pinger

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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.
 

thegawd

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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 **** 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 **** 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
 
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