First hand experience with changing to the NBS master cylinder WOW!

[ScoobyJD]

Originally Posted by Red88

I am following everything you said in this post, however I have a question. Can I just run the lines in a 90 degree bend to ports closest to each other? Only reason I ask is I couldnt get my lines to stretch without messing them up. The only thing I dont know is if the front and rear port of the master put out the same pressure and volume.

[speedygonzales]

Hey Red, what's involved in changing it and how do we identify which a vehicle has?

[Red88]

Sure.

Unbolt the master cylinder assemply from the booster, pull it away from the booster and leave it hanging by the steel lines.

Disconnect the vacuum line that runs from the intake to the booster. It's a pre-bent steel line coupled to a 1/2 rubber vacuum hose near the booster. In my case I couldn't get the hose off the steel line so I slit the hose along its length and pryed it off the steel line.

The booster has 4 studs in a square pattern that extend thru the firewall and are held on by 13mm (if memory serves) nuts inside the cab up and behind the brake pedal. 3 out of 4 nuts were pretty easy to get to, just pull back your carpet/vinyl a bit to expose them. The 4th required a u-joint socket adaptor and took awhile to get out. The booster "push rod" slips over a stud on the brake pedal assemply and a retaining clip holds it in place. A pair of pliers or screwdriver will remove the retaining clip, slip the booster push rod off the stud, remove the nuts from the mounting and the booster is free.

Note: there is a short steel machined cylinder stuck in the master cylinder side of the booster. Your new booster will come with it's own. Make sure it stays inside the booster or your brakes won't work!

I can't vouch for the 9" dual diaphram booster, but both the 10.75" single diaphram and the 10.5" dual diaphram booster have the same bolt pattern and push rod so the new booster will bolt right into place, connect up to the brake pedal assembly. Was a little nervous moving the master cylinder around to allow enough room the put the larger booster into place but I got away with it

Oreilly's didn't have 1/2 vacuum hose so I used 1/2 fuel injection hose which has worked fine so far for the replacment booster vacuum line. That with a hose clamp and I was back in business.

As far as how to identify here are some pics that make the visual difference pretty obvious, at least when it's off the truck. The booster have stamp id's on them, as I recall about 1/2" letters. The 10.75" single is stamped "AB" and both the dual diaphram boosters are stamped "HR". You could see the "AB" stamp on mine while in the truck. Just take a flashlight and take a close look at the master cylinder side of the booster body.

For the purposes of this mod I wouldn't bother with the 9" booster, cost is about the same as the 10.5". This is all about increasing the area of diaphram and thereby increasing the force applied thru the booster to the master cylinder and reducing the amount of pedal force needed to stop the truck.

From my research the standard brake system came with either no power booster or the 10.75" single diaphram booster. The heavy duty brake system variations came with the dual diaphram boosters at higher cost.

10.75" single diaphram:



10.5" dual diaphram:



9" dual diaphram:



Hope this helps!

[CDR]

Red, how much thicker was the dual diaphragm booster? I was wondering how much I'd have to move the brake lines where they attach to the MC...

[Red88]

I didn't have the presence of mind to measure but if memory serves about 2". There was plenty of slack in the brake lines coming up from the frame to make the connections. I imagine factory used same lines irregardless of the booster option.

[speedygonzales]

So is the JB7 really 13" and if so, how do I find it?

Or should I just try making a slightly longer intermediate rod?

[LEEVON]

Did the MC upgrade, and bled the whole system. Pedal feels great, although overall braking effectiveness is pretty much the same. I would like to add the dual-diaphram booster, 3/4 ton calipers and Powerstop drilled and slotted rotors.

[CDR]

Originally Posted by speedygonzales

So is the JB7 really 13" and if so, how do I find it?

Or should I just try making a slightly longer intermediate rod?

Hey Speedy-

Did you make any new findings on the JB7 booster?

[speedygonzales]

Originally Posted by CDR

Hey Speedy-

Did you make any new findings on the JB7 booster?

Nope never found anything

[Keith Seymore]

Originally Posted by speedygonzales

Nope never found anything

I apologize for not thinking of this sooner: I have the brake system release charts from the brake engineer for the '74 and '87 trucks C/K/R/V squarebody versions.

While not totally germaine (I do not have the corresponding GMT400 versions) it will give you an idea of the proliferation and the way the components are structured and named (by part number and broadcast code).

I don't see the "DA" coded booster on here but you can imagine where it would go. One of the ways you would find the corresponding part number for the "DA" booster would be finding a chart like this and working backwards.

For your entertainment:

[CDR]

Upgrading from a single diaphragm booster to a DD should make a noticeable difference. The 3/4 ton calipers should take advantage of your new MC as well. Just remember the 3/4 ton pads will rub your rotor hat, so either use 1/2 ton pads or grind down the metal backing plate on the 3/4 on pads.

I liked my powerslot rotors (not drilled though), hope they treat you well!

[Tom]

Originally Posted by CDR

Just remember the 3/4 ton pads will rub your rotor hat, so either use 1/2 ton pads or grind down the metal backing plate on the 3/4 on pads.

I've had a couple sets of 3/4ton pads on my 98 that also has the larger piston 3/4ton calipers and 1/2ton rotors, never had a rubbing issue.

[CDR]

Hey Speedy,

Since we dusted off this thread I thought I'd mention that the nnbs trucks added an electric vacuum pump to the brake systems. I plumbed one up to see if i could feel any difference...

[CDR]

Thanks, that's pretty sweet. Wish we had them for the 400/800's !

[Keith Seymore]

Originally Posted by CDR

Thanks, that's pretty sweet. Wish we had them for the 400/800's !

Well - actually - based on this thread I sent an email earlier this morning to one of the old brake engineers.

He says he has the charts for GMT400 (hardcopy) so I am going to swing by his desk and grab them on Thursday. I hope to be able to scan and post them for future reference, similar to the squarebody charts.

K

[CDR]

Wow! I'll keep my fingers crossed!

Thanks!

[CDR]

Correct, no difference between the front and rear circuits on the NBS mc. The instructions you attached appeared to be the bench bleeding procedures so I couldn't find the reference to line flipping...

[El conquistador]

Originally Posted by CDR

Correct, no difference between the front and rear circuits on the NBS mc. The instructions you attached appeared to be the bench bleeding procedures so I couldn't find the reference to line flipping...

This is what I was referring to.

Install factory brake lines to master cylinder. The gold fitting must remain in the port
closest to the power booster. You will have to install the brake lines in the opposite
ports than they were from the factory. This will require re-bending the brake lines, be
careful not to kink the lines when bending them.

[CDR]

Ahhhhhhhh! That's horrible...no I would not try to stretch and bend the lines. They'd never line up and seat properly and you'd probably end up jacking the line.

That's surprising to me, thanks for sharing!

[speedygonzales]

I didn't know about the "crossed lines" since I bought a unit from Advance Auto.

What would be the purpose of switching the lines?

We need information regarding the NBS brake lines vs ours. See if they are reversed from the factory compared to ours. I have 2 friends with a NBS 99 I'll take a look at over the weekend and get back to us. If that is the case, I may try reversing them. The lines are very flexible and if SSBC says to do it, it won't be a problem.

[El conquistador]

I got mine at Advance Auto, I just ran accross the SSBC instructions on line. I was just wondering about the difference. If GM changed the location of the front vs rear lines from the 400 to the 800, then SSBC may just be covering their butt by keeping the factory "front" activating the front brakes when you switch. It's easier to keep the lines in the old position, but there is plenty of flexibility in the lines to switch then...if needed.

[Keith Seymore]

Whelp - I've got good news and I've got bad news.

The good news is I got the stuff.

The bad news is it is pictured below....

that's a 3" three ring binder full of various folded up pieces of parchment paper, starting from 1969 through about 2001. Both full size truck and S truck.

I'm not quite sure how to get that all converted to electronic media in my lifetime, but in the short term I'll post up a representative GMT400 chart and would be happy to answer any specific release/part number questions you might have.

I'll also see if I can get some detail on that "DA" booster you were asking about earlier.

K

[Keith Seymore]

Sample page showing the '97 K truck (which my Suburban is) and detail on the "DA" vacuum booster.

P/N 18024268; It was released for:

K10516 & JB5
K10703 & JB5
K10706 & JB6
K10903 & JB5
K10906 & JB6
K10753 & JB6
K10753 & JB6 & F44
K10953 & JB5
K10953 & JB6
K20753 & JB7


Welcome to Truck Engineering!

K

[speedygonzales]

So is what you are showing mean if the marking is "DA" we have a JB7 and if I understand it correctly the most powerful vacuum booster is the JB7 or do I have any of that incorrect?

The part number 18024268 does not come up as a good replacement part number.

[Keith Seymore]

Originally Posted by speedygonzales

So is what you are showing mean if the marking is "DA" we have a JB7 and if I understand it correctly the most powerful vacuum booster is the JB7 or do I have any of that incorrect?

The part number 18024268 does not come up as a good replacement part number.

I'm not sure we can comment about the "DA" being the most powerful booster (there is also a 18024269/XF released for JB7) but I will say that once you go to JB8 they are all hydroboost.

The part numbers shown are production part numbers; service numbers will likely be different.

K