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

[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!

[El conquistador]

Originally Posted by CDR

You may be referring to the design change on the NBS brake circuits being flipped F/R?

With our trucks using the step bore master the front circuit had to use the forward portion of the cylinder to drill the stepped bore ( can't put a bigger bore bit thru a smaller bore hole)

Since the nbs uses the same bore size for both circuits, the engineers chose to reverse the layout, but they should operate identically.

So the "store bought" instructions just flip flop the lines to match the front and back of the NBS master cylinder, even though there is no difference in the performance in the front and back.

[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.

[speedygonzales]

It also appears that the original MC in the vehicle has twice the volume output from the rear port vs the front port According to the page posted by Keith. Which is usual for GM where the larger back reservoir feeds the front brakes when there are front disk and rear drums.

So what about the new style MC? Does it have a difference from the front and rear ports? If it does, I should switch the ports like the SSBC says to do. If it doesn't make a difference than switching won't do anything bad. It sounds as though I may try switching the ports. I'm about ready for a bleed anyway.

I'll let you know what happens.

[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

[dragginmetal]

What's the difference in a JB system and a JN? My 88 has a JN.

[Keith Seymore]

Originally Posted by dragginmetal

What's the difference in a JB system and a JN? My 88 has a JN.

Attachment 1338074

Just the RPO designation.

I suspect it was changed to avoid confusion with the the carryover C/K/R/V vehicle (ie, carryover got "JBx", new GMT400 got "JNx" for a comparable system).

K

[speedygonzales]

I know the most powerful is the hydro JB8.

The question I already asked was isn't the JB7 the most powerful vacuum booster? And are the pages you printed showing the "DA" is a JB7

The whole reason this discussion of boosters came up because someone changed from a single to a double. So my natural question is do I have a single or a double? It has "DA" on it and I already posted it's dimensions. Once I figure out what mine is, I can determine if a more powerful booster is available. Capish?

[speedygonzales]

OK my RPO label says "JB5
I have 11" rear brake pads (I know cause I just changed them).
The booster label is "DA"

There is this from earlier
Vacuum-boosted:
JB5 = Power Brakes, Disc/Drum, 6,400 lb
JB6 = Power Brakes, Disc/Drum, 7,200 lb
JB7 = Power Brakes, Disc/Drum, 8,400 lb

The page posted by Keith lists under the JB7 column the booster as
18024268/DA
Is that the sticker on it?

If a JB5 is supposed to be the lesser of the three as far as power, why would a JB5 system have a JB7 booster?

Who can help with the booster I have?

[Keith Seymore]

Originally Posted by speedygonzales

I know the most powerful is the hydro JB8.

The question I already asked was isn't the JB7 the most powerful vacuum booster? And are the pages you printed showing the "DA" is a JB7

Yes, and yes.

Originally Posted by speedygonzales

The whole reason this discussion of boosters came up because someone changed from a single to a double. So my natural question is do I have a single or a double?

240S = single
240T = "tandem" = dual
So you have a "double" already.

Originally Posted by speedygonzales

It has "DA" on it and I already posted it's dimensions. Once I figure out what mine is, I can determine if a more powerful booster is available. Capish?

Absolutely.

Originally Posted by speedygonzales

OK my RPO label says "JB5
I have 11" rear brake pads (I know cause I just changed them).
The booster label is "DA"

There is this from earlier
Vacuum-boosted:
JB5 = Power Brakes, Disc/Drum, 6,400 lb
JB6 = Power Brakes, Disc/Drum, 7,200 lb
JB7 = Power Brakes, Disc/Drum, 8,400 lb

The page posted by Keith lists under the JB7 column the booster as
18024268/DA
Is that the sticker on it?

Yes

Originally Posted by speedygonzales

If a JB5 is supposed to be the lesser of the three as far as power, why would a JB5 system have a JB7 booster?

Because aaaaaaaaaaaaaaaallllllllllllllll those other components listed on that chart make up the brake system; not just the booster.

Originally Posted by speedygonzales

Who can help with the booster I have?

I'm not sure...

K

[speedygonzales]

Originally Posted by speedygonzales

I know the most powerful is the hydro JB8.

The question I already asked was isn't the JB7 the most powerful vacuum booster? And are the pages you printed showing the "DA" is a JB7

Originally Posted by Keith Seymore

Yes, and yes.

So???????????? Doesn't this answer the question????????? The JB7 is the most powerful and you said yes the DA is a JB7.

Am I missing something?

[Keith Seymore]

Originally Posted by speedygonzales

So???????????? Doesn't this answer the question?????????

Yes

Originally Posted by speedygonzales

The JB7 is the most powerful and you said yes the DA is a JB7.

Yes

Originally Posted by speedygonzales

Am I missing something?

I'm beginning to wonder.

K

[speedygonzales]

Originally Posted by speedygonzales

Who can help with the booster I have?

Originally Posted by Keith Seymore

I'm not sure...

Originally Posted by Keith Seymore

I'm beginning to wonder.

Your original response was you weren't sure. Do you not understand my confusion?

DA=JB7 the most powerful vacuum booster there is on a 1998 So there is no need to look for a more powerful one. Any more gains will come from either boosting vacuum or something else.

[Keith Seymore]

Originally Posted by speedygonzales

Your original response was you weren't sure.

True - but I've reviewed the charts and now believe that the DA is the "biggest" vacuum booster.

Originally Posted by speedygonzales

Do you not understand my confusion?

I did at one time, but you seem kind of stuck.

Originally Posted by speedygonzales

DA=JB7 the most powerful vacuum booster there is on a 1998 So there is no need to look for a more powerful one. Any more gains will come from either boosting vacuum or something else.

Correct. Time to re-visit the master cylinder swap or look at the foundation brakes at the wheels (calipers, rotors, drums, etc).

Or look at hydroboost.

K

[JTWard]

I know I'm getting in on this subject a little late, But I got a hell of a problem with the brakes on my 1990 1/2 ton 2WD. I came home from visiting a Marine Buddy in a re-hab and on the way home I had to stop short and really put my right foot into it and I still wound up a part way into the cross road ?. I have replaced everything, new Husky Lite truck pads, new rotors, stainless steel brake lines , bleed the thing 3 times and still you can't get this thing to lock up the brakes, I know I have the ABS module for the back drum brakes. . . but that isn't even worth the effort to toss away as their useless. The brake pad is like stepping into soft new dug up dirt. your foot just keeps going down. It's a 1990 1500 Silverado with a 5600 weight capacity. It's got a 5.0 liter 305 V8 !


So fellows, I'm lost on this thing. I've got a 5600 pound weight rating but I'd be afraid to put a 1/4 ton or try to tow 10,700 tow capacity. I'd never be able to stop, I can't stop with an empty bed ! Please throw me some life saving info to help. I just got down a 3 year full body off restoration. I need help !

[El conquistador]

Brake fluid looks mighty dark in the photo. But it could be the pic. Did you change the master cylinder? If not, ditch it for the NBS master. Also, doid you replace the flexible lines?

[CDR]

JT, you have a step bore MC. The swap to the NBS MC will firm up the feel of the brakes. The knuckle swap and 14.5 inch rotors I did on my 4x4 were the problem solver for me, but won't work on your 2wd rig.

The mc swap is cake, I'd recommend it.