2500 Master Cylinder on 1500?

[Boots97]

I've seen 4x4 Tahoes in the local yards with the 11" brakes(JB 6). Most of them have the JB5 10" though; the drums look different if you're familiar with both of them. Burb's got the JB 6 because they are about 1000# heavier than a half ton rclb pickup, with the extra metal, glass and interior. By the time you get to the triple extra large truck like a C/K 3500 crew cab long bed, though, the weight is closer to the Burb.
I think the "standard" 16" steel wheel on the 400s tire size is 245/75-16; and the Z71 got the 265s as an upgrade. Could be wrong, though...it does happen occasionally LoL.

Yes, Tahoes could get either JB5 or JB6 brakes. Suburbans got JB6 standard which makes sense given the weight.

According to this link here, you COULD get 225/75/R16s, although I've never seen one in my own experience.

Most 400s are 245/75/R16. Z71 and 265s are separate RPO codes. Z71 is the off road package, while the 265s are RPO Codes XGD (front tires), YGD (rear tires), and ZGD (spare tire). Again, in my experience, all Z71s came with 265s from the factory. Regular 4x4s could either get 245s or 265s

1997 Chevrolet K1500 - Wheel & Tire Sizes, PCD, Offset and Rims specs

Wheel size, PCD, offset, and other specifications such as bolt pattern, thread size (THD), center bore (CB), trim levels for 1997 Chevrolet K1500. Wheel and tire fitment data. Original equipment and alternative options.

www.wheel-size.com

 

[Boots97]

IIRC my Suburban came with 245/75 tires on 16" rims.

Yes, all GMT400 Suburbans should've gotten 245s on 16" rims. None came with 265s from the factory, as there was no Z71 Suburban or offering with oversized tires at the time.

 

[Boots97]

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UPDATE:

I got my new JB7 Master Cylinder last night. Looks pretty good, but HOLY F*** was the lid tight. I was using all the strength in my hands to pull this lid off which I don't have to do with my other MC. There's also a little bit of a vaseline type lube on the edge of the reservoir and it's not making the lid easier to put on either. I'm pounding down HARD on this lid to get it to close and it's sad that this has such poor fitment. Plan on reusing my old reservoir since it's still good.

 

[1998_K1500_Sub]

I got my new JB7 Master Cylinder last night.

That definitely is not a "stepped-bore" quick-take-up MC

I'm just not a fan of the low-drag caliper / quick-take-up stepped-bore MC design used on GMT400 JB5/JB6 (and some others).

I've got the L-D caliper / Q-T-U MC brakes on my '95 S10 and I've learned to live with the imperfect braking response to pedal input. It always felt "odd" and in a panic situation seemed slow-to-respond and unsafe.

The Suburban's system had the same imperfect response but to a much greater extent. I swapped out a lot parts (see my earlier post #7, this thread) years ago in desperation, without really knowing what I was doing, trying anything to make the Suburban's brakes better, and eventually landed on a combination that IMHO works quite well.

Earlier I had no knowledge of the L-D caliper / Q-T-U MC brake design; from today's vantage point, I consider it flawed on account of, at least,

1. the resistance present in the pedal travel during the period the large bore is still in play, during which time the brakes are hardly engaged (if at all) yet the pedal is firm, in combination with
2. the lost motion prior to actual brake engagement; then
3. the question of whether the rebuilders actually rebuild the L-D calipers properly (see attached .pdf) and the attendant possibility of introducing a new problem

Maybe in an ideal world the L-D caliper / Q-T-U MC brake design always works well. In my experience with the Suburban, it has not. My father's 1995 K1500 RCLB had JB5 brakes and they had much better pedal feel than the Suburban's, so perhaps there was more happening then met my eye. Regardless, I've settled-in on a configuration that I like very much on the Suburban.

More on the topic, here:

GM "low-drag" calipers - A discussion on JalopyJournal.com

I stumbled upon this discussion about the GM low-drag calipers on the JalopyJournal website. I know most on GMT400 understand the low-drag calipers and their corresponding quick-take-up master cylinders, but for everyone this may be interesting and possibly useful reading. The various posts...

www.gmt400.com

 

[1998_K1500_Sub]

Any update???

 

[Boots97]

Update:

Been driving around a while and I really like these brakes. There's a bit of sponge, but then there's this really firm wall and all of a sudden, the brakes grab with all their might. Much better than what I originally had and it reminds me of the brakes I used to have, but more aggressive. I really like it over the JB5/JB6 brakes, and I think I can get them better after bleeding them again. These brakes are not like JB5/JB6 brakes where you "lean" into them. They prefer to be hit hard and that's when they really work. I wish these came this way from the factory. Oh well, that's what this forum is for.

 

[Boots97]

That definitely is not a "stepped-bore" quick-take-up MC

I'm just not a fan of the low-drag caliper / quick-take-up stepped-bore MC design used on GMT400 JB5/JB6 (and some others).

I've got the L-D caliper / Q-T-U MC brakes on my '95 S10 and I've learned to live with the imperfect braking response to pedal input. It always felt "odd" and in a panic situation seemed slow-to-respond and unsafe.

The Suburban's system had the same imperfect response but to a much greater extent. I swapped out a lot parts (see my earlier post #7, this thread) years ago in desperation, without really knowing what I was doing, trying anything to make the Suburban's brakes better, and eventually landed on a combination that IMHO works quite well.

Earlier I had no knowledge of the L-D caliper / Q-T-U MC brake design; from today's vantage point, I consider it flawed on account of, at least,

1. the resistance present in the pedal travel during the period the large bore is still in play, during which time the brakes are hardly engaged (if at all) yet the pedal is firm, in combination with
2. the lost motion prior to actual brake engagement; then
3. the question of whether the rebuilders actually rebuild the L-D calipers properly (see attached .pdf) and the attendant possibility of introducing a new problem

Maybe in an ideal world the L-D caliper / Q-T-U MC brake design always works well. In my experience with the Suburban, it has not. My father's 1995 K1500 RCLB had JB5 brakes and they had much better pedal feel than the Suburban's, so perhaps there was more happening then met my eye. Regardless, I've settled-in on a configuration that I like very much on the Suburban.

More on the topic, here:

GM "low-drag" calipers - A discussion on JalopyJournal.com

I stumbled upon this discussion about the GM low-drag calipers on the JalopyJournal website. I know most on GMT400 understand the low-drag calipers and their corresponding quick-take-up master cylinders, but for everyone this may be interesting and possibly useful reading. The various posts...

www.gmt400.com

From what you write here, and the link you sent me to the other thread with another link to a forum talking about this, I PERSONALLY believe that these are one of those 70s designs from the gas crisis era that engineers created to make vehicles as fuel efficient as possible and GM designers/engineers/bean counters said, "well this works well enough, so why change it".

Also, these calipers/master cylinder/wheel cylinder combos were originally put on GM A-G bodies. much of which were old school V8 sedans with small block chevy's like in our trucks. From my reading, I believe that GM designers/engineers/bean counters also thought that since this truck can come with a 5.0l/5.7l just like the GM A-G bodies did back in the 70s-80s-90s, then these brakes are perfectly fine for this application bc it's the same engine which means it's stopping the same power.

However, this isn't totally how it works. Vortecs got more power than 70s small block IIRC and also the weight of our vehicles was never accounted for. Our trucks (especially Suburbans) are taller and heavier than GM A-G bodies and it's no wonder that people have problems/complaints with the design. That, and being 1000 years old doesn't help (stole that quote)

The L-D caliper /Q-T-U master cylinder likely works well in old school V8 sedans (IDK, I've never driven one) but doesn't work all that well in these trucks bc of what I've stated above. Your father's stock JB5 brakes work well on his pickup bc he's got a lighter setup than you do with a Suburban and his were adjusted/broken in properly for ideal braking performance. I went the same route that you and @boy&hisdogs went bc I had JB6 brakes bc of my 14 bolt swap and I also had crumbling shoes inside which needed to be replaced anyways, so I may as well have upgraded to JB8 wheel cylinders and JB7 calipers and master cylinder while I'm at it.

 

[1998_K1500_Sub]

The whole Q-T-U MC / L-D braking system is an enigma.

My Suburban's brakes were almost certainly "original"... Dad bought it with 30kmi on it and 6 months old (he bought it in mid-1998, and it's a 1998 model year truck). When I got it from him around 2007 w/ 146kmi on it, the brakes didn't work well in panic situations. I'm sure he never modified the brakes, at least intentionally; I'm sure he had them serviced a few times, but I know it took it to the Chevy dealer. By the time I got it, maybe it *did* need a proper bleed (scan tool for ABS) and I was ignorant of the procedure. A couple of times I took it to the dealer (same one as Dad) and asked them to look at the brakes, but they either didn't understand the issue or turned a blind eye; I got no satisfaction.

So I started swapping parts. I can say this: I'm very happy with the result. Of the six or seven vehicles that I have (all licensed and insured, but everyday kinds of vehicles... not Porsches or anything), its brakes are on par with the best of them in terms of responsiveness / pedal feel.

Now: Que my brother's 1998 K2500. It's brakes were / are MUCH better than the Suburban's, and it took me the longest time to figure out why... same year as my Sub, same GMT400 truck, WHY SO DIFFERENT? No, it wasn't because of their size, but because of their pedal feel, that's what made them so much better... the pedal wouldn't provide resistance until the brakes were engaged... unlike my Suburban, where the pedal would resist -- particularly in a panic situation -- before the brakes would engage, which I attribute to the Q-T-U phase of the brake's operation (see my comments in Post #14 above).

It was only after being on GMT400 for a while that I learned about the Q-T-U MC / L-D calipers that were stock on the JB5/JB6 brakes (e.g., my Suburban) and how they differed from the JB7 brakes on my brother's K2500, and that was an Ah-HA moment for me... but by then I had already landed on a combination of brake parts for my Sub that worked (using the time-tested method of trial-and-error).

So anyway, I've rambled enough here. I have to thank @Schurkey for his persistent efforts to keep people on GMT400 aware and educated about brakes... and he's not the only one, there are others here who are as-capable but perhaps not as persistent has he I've learned from all of them and am still learning more.

I'm glad your configuration is working much better and I hope I've facilitated the improvement

 

[Boots97]

The whole Q-T-U MC / L-D braking system is an enigma.

My Suburban's brakes were almost certainly "original"... Dad bought it with 30kmi on it and 6 months old (he bought it in mid-1998, and it's a 1998 model year truck). When I got it from him around 2007 w/ 146kmi on it, the brakes didn't work well in panic situations. I'm sure he never modified the brakes, at least intentionally; I'm sure he had them serviced a few times, but I know it took it to the Chevy dealer. By the time I got it, maybe it *did* need a proper bleed (scan tool for ABS) and I was ignorant of the procedure. A couple of times I took it to the dealer (same one as Dad) and asked them to look at the brakes, but they either didn't understand the issue or turned a blind eye; I got no satisfaction.

So I started swapping parts. I can say this: I'm very happy with the result. Of the six or seven vehicles that I have (all licensed and insured, but everyday kinds of vehicles... not Porsches or anything), its brakes are on par with the best of them in terms of responsiveness / pedal feel.

Now: Que my brother's 1998 K2500. It's brakes were / are MUCH better than the Suburban's, and it took me the longest time to figure out why... same year as my Sub, same GMT400 truck, WHY SO DIFFERENT? No, it wasn't because of their size, but because of their pedal feel, that's what made them so much better... the pedal wouldn't provide resistance until the brakes were engaged... unlike my Suburban, where the pedal would resist -- particularly in a panic situation -- before the brakes would engage, which I attribute to the Q-T-U phase of the brake's operation (see my comments in Post #14 above).

It was only after being on GMT400 for a while that I learned about the Q-T-U MC / L-D calipers that were stock on the JB5/JB6 brakes (e.g., my Suburban) and how they differed from the JB7 brakes on my brother's K2500, and that was an Ah-HA moment for me... but by then I had already landed on a combination of brake parts for my Sub that worked (using the time-tested method of trial-and-error).

So anyway, I've rambled enough here. I have to thank @Schurkey for his persistent efforts to keep people on GMT400 aware and educated about brakes... and he's not the only one, there are others here who are as-capable but perhaps not as persistent has he I've learned from all of them and am still learning more.

I'm glad your configuration is working much better and I hope I've facilitated the improvement

You absolutely have given me inspiration to improve my brakes. I love how firm these brakes are. They're so aggressive they make the truck skip if I floor the brakes while driving. I'm also glad to have @Schurkey on this forum educating young dudes like me and without him, I wouldn't have the 14 bolt rear axle that I have.