Brake help after nbs master cylinder upgrade (1994 chevy fullsize blazer)

[94FSblazer]

1994 Chevy full-size blazer (5.7 tbi OBD1).
Recently did the nbs master cylinder upgrade. Grabbed a mc out of 2001 Tahoe with vacuum booster.
After installing, bled the brakes and it is terribly squishy, worse than before. Dangerous lack of brake power. Was going to bleed again. But thought I’d ask some questions first.

What abs system is this? I don’t see this in anyone’s pics or videos of the upgrade. And can I bleed it?

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Do I need to switch the brake lines (front to back, back to front) since the new mc has the larger reservoir in the front instead of the back like the stock mc? If I do, how do I go about making new lines?

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Im so frustrated with this and worried I screwed it up. I don’t mess with abs usually so I am clueless with messing with that system. Also hated bending those very short brake lines to fit to the new mc - I know I’ll need new ones if I need to switch the position of the two lines. How do I do that?
Please help if you can! Thank you!!

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[Schurkey]

Perhaps a moderator will move this thread out of "Engines" and into Axles + Brakes.

1994 Chevy full-size blazer (5.7 tbi OBD1).
Recently did the nbs master cylinder upgrade. Grabbed a mc out of 2001 Tahoe with vacuum booster.

Unless you changed the front calipers to ones that DON'T have the low-drag feature, this was a huge mistake.

If you've got stock "1500" calipers, the best thing you can do is get a stock master cylinder for JN/JB/JD5 or 6 brakes having the 1 1/8" bore, and GET RID OF THAT "NBS" MASTER CYLINDER.

It takes way more effort than most folks realize to properly bench-bleed a master cylinder. Good chance that's jpartly why your pedal is worse than before. Did you adjust the rear brakes? ESPECIALLY if you've got the 254mm (10") leading-trailing drums, rear brake adjustment is crucial. If you've got the 11.x Duo-Servo drums, rear brake adjustment is more-likely to be correct already--but worth a look.

You MUST have a scan tool to properly bleed the ABS. Some folks bleed the system as best they can, then go out on a gravel or icy/snowy road, nail the brakes a few times to activate the ABS, then drive back to the shop and bleed the brakes again. I guess this can work. In real life, I have no faith in it. You'd have to assure that ALL channels of the ABS were chattering; and then you'd have to assume that the air bled out of the ABS doesn't go back into the ABS on the drive back to the shop.

See attached .pdf for bleeding brakes.

What abs system is this? I don’t see this in anyone’s pics or videos of the upgrade. And can I bleed it?

You must be registered for see images attach

I don't recognize that unit. I suppose it's a Kelsey-Hayes EBC4 based on your model-year of '94. Whether you can bleed it or not depends on whether you've got a scan tool that will chatter the valves (ABS Auto-Bleed).

Again, see the attached .pdf.

Do I need to switch the brake lines (front to back, back to front) since the new mc has the larger reservoir in the front instead of the back like the stock mc?

You need to get rid of that master cylinder.

Im so frustrated with this and worried I screwed it up.

If you've still got the low-drag "1500" calipers, you did. Sorry. I wish that they'd remove that big thread about "NBS" master cylinders, or at least warn folks early in the thread that it's a disaster if they still have the Low-Drag front calipers.

 

[Orpedcrow]

Did you bench bleed the master cylinder before installing it?

 

[94FSblazer]

Unless you changed the front calipers to ones that DON'T have the low-drag feature, this was a huge mistake.

If you've got stock "1500" calipers, the best thing you can do is get a stock master cylinder for JN/JB/JD5 or 6 brakes having the 1 1/8" bore, and GET RID OF THAT "NBS" MASTER CYLINDER.

Got it. I guess feeling how much better the brakes felt in a 93 and 94 I drove after this mod made me feel confident in it. I did bench bleed the MC before install. Even tilted it like you said should be done.

Yesterday went out and made sure the rear drums were adjusted properly. rear drum upgrade to duo servo was on the list for down the road as well. I guess I should go get 2500 calipers too if I want to keep this MC.
It is dumb that most of the info out there about the upgrade doesn't talk about the calipers in the rigs before install. Most of the how-to's and videos are definitely with jb5's unless they just didn't mention it.

Anyway, I found that there was a leak at the front driver bleeder, so I fixed that. I am taking it to a shop tomorrow to have the ABS bled since I am sure it hasn't ever been bled and since it has never really worked properly.
I have no problem going back to a stock MC, I just saw so many people doing this mod, praising it, and I had one to use & it is an easy install. Was hoping to get some better info or help with what I had. I will work to remedy this and ask further questions about it. Just want my brakes to work better and came for some help.

 

[Burdom13]

1994 Chevy full-size blazer (5.7 tbi OBD1).
Recently did the nbs master cylinder upgrade. Grabbed a mc out of 2001 Tahoe with vacuum booster.
After installing, bled the brakes and it is terribly squishy, worse than before. Dangerous lack of brake power. Was going to bleed again. But thought I’d ask some questions first.

What abs system is this? I don’t see this in anyone’s pics or videos of the upgrade. And can I bleed it?

You must be registered for see images attach

Do I need to switch the brake lines (front to back, back to front) since the new mc has the larger reservoir in the front instead of the back like the stock mc? If I do, how do I go about making new lines?

You must be registered for see images attach

Im so frustrated with this and worried I screwed it up. I don’t mess with abs usually so I am clueless with messing with that system. Also hated bending those very short brake lines to fit to the new mc - I know I’ll need new ones if I need to switch the position of the two lines. How do I do that?
Please help if you can! Thank you!!

You must be registered for see images attach

You must be registered for see images attach

So!!! Not saying to do this, but this is what I did cuz I just recently stepped up to the gmt800 front calipers and also did the ms swap. I completely deleted my abs, one line splits off for front, larger line goes to rear. Brakes are nice and tight now. Might be going to a proportioning valve tho, feels like I need more front braking than what its currently doing. Hope that helps!

 

[Erik the Awful]

If your truck still has drum rear brakes, your master cylinder likely isn't sized correctly. Disc brakes require more pressure and fluid to stop a vehicle. There is a ratio difference between the two. Your rear brakes will be more likely to lock up, which can result in a spin instead of a straight stop.

Basically, if you go GMT800, you should go all the way with a rear brake swap.

 

[scott2093]

If you've got stock "1500" calipers, the best thing you can do is get a stock master cylinder for JN/JB/JD5 or 6 brakes having the 1 1/8" bore, and GET RID OF THAT "NBS" MASTER CYLINDER.

Are there any upgrades recommended for master cylinder of JB5?

I wish that they'd remove that big thread about "NBS" master cylinders, or at least warn folks early in the thread that it's a disaster if they still have the Low-Drag front calipers.

Youtube pretty good at addressing other issues when they want. Apparently, possible brake disasters isn't one of them.

 

[Schurkey]

Are there any upgrades recommended for master cylinder of JB5?

Stock, or stock replacement in good condition

Youtube pretty good at addressing other issues when they want. Apparently, possible brake disasters isn't one of them.

I was thinking about the various threads on this site.