How to: NBS master cylinder swap for firm brake pedal

[Nak]

I'm not totally familiar with your year. I know the Combi valve bolts to the ABS unit. I'm assuming it's a combi unit anyways... You'll need to do a little research. Looking at the NBS with 4 wheel disc, it looks like they don't use a proportioning valve. That makes sense, since usually 4 wheel disc setups don't, at least that's my understanding.

What I'd try and do is run a complete setup out of a NBS. Get the whole ABS unit and replace yours with it, if that is possible. Will your ECM run the later ABS? I have no idea. If it does, I think that would be the way to go. If not, then you need to find a way to run your ABS without the disc/drum combi valve. Again, I have no idea how possible or hard that will be to do.

What I do know is that running 4 wheel discs with a disc/drum combi valve is going to give you problems. Way too much braking will be done by the front brakes, increasing wear and limiting braking effectiveness.

 

[hawgnutts]

I'm not totally familiar with your year. I know the Combi valve bolts to the ABS unit. I'm assuming it's a combi unit anyways... You'll need to do a little research. Looking at the NBS with 4 wheel disc, it looks like they don't use a proportioning valve. That makes sense, since usually 4 wheel disc setups don't, at least that's my understanding.

What I'd try and do is run a complete setup out of a NBS. Get the whole ABS unit and replace yours with it, if that is possible. Will your ECM run the later ABS? I have no idea. If it does, I think that would be the way to go. If not, then you need to find a way to run your ABS without the disc/drum combi valve. Again, I have no idea how possible or hard that will be to do.

What I do know is that running 4 wheel discs with a disc/drum combi valve is going to give you problems. Way too much braking will be done by the front brakes, increasing wear and limiting braking effectiveness.

Thanks for the info. My '95 runs OBD 1 so I'm bettin it may not run the latest ABS system. The idea that my setup won't require a prop valve makes sense. It'll probly just need the NBS M/C & combi valve from a disc/disc ABS unit. I don't think the hydravac needs changed unless I get an unusual issue like that one fella had.

 

[SunlitComet]

abs system to obd type is irrelevant in the case of whether it will run or not. in this case any way. the ecm/pcm never runs an abs system. it defeats the purpose of sole autonomy for it to do its job correctly. it does however share data like speedoa nd such. for reference the disc conversion kits sold out there use the nbs mc because of bore displacements differences in the read disc calipers so it is best to start your rear disc conversion with one. iirc they also alter the proportioning valve as well. look at the summit racing kit page for an instructions link. No matter what you choose to change in the conversion Hydroboosting will improve any aspect of it.

 

[Nak]

Good info Sunlit. I didn't think his year ABS talked to the ECM, but I didn't know for sure. They do both get speed data from the buffer, so ABS and the ECM don't talk to each other at all. I know some later years the ABS talks to the ECM and won't function without it, but I didn't know what year that started.

 

[TexasMaq]

Now questioning if it was worth it

I tested the Vacuum assist unit this morning and it is working as it should. It really bothers me about the 40mm bore size of the old MC. I was expecting to see a really small piston. This really makes me wonder if perhaps the Z71 used a larger MC then the standard one. If this is the case I doubt the NBS MC will ever work correctly.

As far as the 4w ABS unit is concerned it is not giving any ABS error lights on the instrument panel and I did verify the unit was active by jacking all 4 wheels of the ground, placing the trans in drive and activating the brakes.

Later today I am going to hook up the GM Tech 2 tool to the Tahoe cycle and diagnose the ABS unit . Maybe there is some air in the unit but I would think that would give me a mushy pedal instead of one that is hard but has limited braking.

If I get no where with that I am going to re-bleed the system and drive it for a week or so to allow the new front pads to wear in before trying some agressive braking.

Other then that if all else fails I plan on putting the old MC back in place and looking at a Hydroboost setup down the road which from my estimates will cost me about $400. for all new or rebuilt parts.

I read on a forum somewhere you can disable the pesky ABS with that GM Tech 2 tool.