2500 Master Cylinder on 1500?

[Boots97]

Hi Everyone,

I fully rebuilt my front and rear brakes on my 1997 Chevrolet K1500 Z71. I installed 2500 calipers with Raybestos Element 3 pads and installed 3500 dually wheel cylinders with Raybestos 473PG shoes and Brake Best hardware kit. I bled the brakes all around 3 times and overall am happy with the swap. However, I feel like there is more sponge with the brake pedal than I remember and was wondering of upgrading to a 2500 master cylinder would help?

 

[termite]

I'm sure others here will chime in with more experience and expertise, but i believe it will be recommended to swap to the corresponding master to match the slave cylinders. Was recently discussed to some extent in a recent thread with links to others regarding brakes and swapping parts from other rigs. See if i can find it again.

Post in thread 'JB5 Rear to JB6 Drums 6 Lug - Help with Models to pick' https://www.gmt400.com/threads/jb5-...g-help-with-models-to-pick.59172/post-1362902

 

[movietvet]

Yes, the bigger cylinder bore should make for a better feel.

 

[Boots97]

I'm sure others here will chime in with more experience and expertise, but i believe it will be recommended to swap to the corresponding master to match the slave cylinders. Was recently discussed to some extent in a recent thread with links to others regarding brakes and swapping parts from other rigs. See if i can find it again.

Post in thread 'JB5 Rear to JB6 Drums 6 Lug - Help with Models to pick' https://www.gmt400.com/threads/jb5-...g-help-with-models-to-pick.59172/post-1362902

Wow! What a convenient time! @1998_K1500_Sub If I'm reading this right, it would be best for me to upgrade to a JB7 MC and possibly the booster as well? or would you recommend something else like a JB8 MC?

 

[1998_K1500_Sub]

If I'm reading this right, it would be best for me to upgrade to a JB7 MC and possibly the booster as well? or would you recommend something else like a JB8 MC?

I assume you have / had JB6 brakes (11" drums).

As for your spongy feel, there might be a concern with air in your ABS. But first, you need a new MC, then if the brakes don't feel right you can focus on the ABS. Read on...

So, upgrade the MC, yes, esp. because it will match the calipers you've installed; your OE quick-take-up MC isn't IMHO going to work well with the "regular" calipers you have (i.e., they aren't "low drag" and hence aren't designed to work well with a quick-take-up MC).

As for the booster, I can't suggest. I retained the vacuum MC on my Suburban and I feel it's adequate. A lot of guys install hydroboost and love it.

You'll have to chose whether you install the 1.25" or 1.125" bore MC, as I think both are available to you. Considering you've already got the bigger slave cylinders, I would be inclined to use the 1.25" bore MC. AFAIK the JB7/JB8 MCs are the same, just different bore sizes depending on hydroboost (1.25") / vacuum boost (1.125"). Somebody else may know better; that's how I remember it.

You'll like the MC upgrade, definitely.

Putting SS brake hoses on will make a very nice improvement as well, just make sure you get them with the proper fittings as sometime around 1997/1998 GM switched from SAE to Metric fittings on the lines. Install them both front and rear; doing only the front doesn't yield the full benefit (@Schurkey and I both noticed this independently).

I'll be out of town for the next four days so my replies with be few and far between

 

[Boots97]

I assume you have / had JB6 brakes (11" drums).

As for your spongy feel, there might be a concern with air in your ABS. But first, you need a new MC, then if the brakes don't feel right you can focus on the ABS. Read on...

So, upgrade the MC, yes, esp. because it will match the calipers you've installed; your OE quick-take-up MC isn't IMHO going to work well with the "regular" calipers you have (i.e., they aren't "low drag" and hence aren't designed to work well with a quick-take-up MC).

As for the booster, I can't suggest. I retained the vacuum MC on my Suburban and I feel it's adequate. A lot of guys install hydroboost and love it.

You'll have to chose whether you install the 1.25" or 1.125" bore MC, as I think both are available to you. Considering you've already got the bigger slave cylinders, I would be inclined to use the 1.25" bore MC. AFAIK the JB7/JB8 MCs are the same, just different bore sizes depending on hydroboost / vacuum boost. Somebody else may know better; that's how I remember it.

You'll like the MC upgrade, definitely.

Putting SS brake hoses on will make a very nice improvement as well, just make sure you get them with the proper fittings as sometime around 1997/1998 GM switched from SAE to Metric fittings on the lines. Install them both front and rear; doing only the front doesn't yield the full benefit (@Schurkey and I both noticed this independently).

I'll be out of town for the next four days so my replies with be few and far between

Thanks for the quick response!

I considered it might be an ABS issue too. Wasn't totally sure so I wanted to ask about Master Cylinders on here before I made any assumptions. My truck came with JB5 brakes from the factory, but I currently have JB6 Brakes on my truck after getting a 14 bolt swap. From the other thread, it does seem that my original MC isn't going to work well with the new brakes I installed. I'm going to keep my original booster for now and if I have to swap it later, I will. Knowing that JB7/JB8 MC can have 1.125" or 1.25" bores, I'm inclined to use the latter as you stated above.

I already installed SS brake hoses recommended @df2x4 and @Schurkey after my hoses deteriorated during a brake fluid flush over the summer. Made the brakes much better and I would've never known about them unless I was on this forum.

 

[1998_K1500_Sub]

I considered it might be an ABS issue too. Wasn't totally sure so I wanted to ask about Master Cylinders on here before I made any assumptions. My truck came with JB5 brakes from the factory, but I currently have JB6 Brakes on my truck after getting a 14 bolt swap.

I think you'll be very pleased after an MC swap, given the changes you've already made. You literally need an MC swap, given the caliper design (non "low-drag") you've installed.

From the factory I had JB6 brakes on my Suburban and they worked, but not well.

I changed the front calipers first, to 3.15" bore cylinders, which didn't make a lot of difference.

Adding SS hoses up front (only) made a bit more improvement.

I then changed to a non-"quick take up MC", the NBS MC in my case, which has a ~1.34" (34mm) bore. That made a huge improvement (a GMT400 JB7 1.25" bore would work as-well or better, with more hydraulic advantage over the slave cylinders b/c of its smaller bore).

Finally, I made the change to 1.1875" cylinders and SS hose (rear), which made another marked improvement.

This on my '98 L31 K1500 Suburban which across-the-scale is almost 6200#, practically evenly split front/rear.

I've also got 10% larger tires on it than OE.

Other combinations of parts would work well too, depending on the vehicle.

I think what is MOST beneficial:

- replace the JB5/JB6 "quick-take-up MC" and "low-drag calipers" with those for JB7/JB8; this mandates at least the 3.15" / 80mm front calipers (or optionally the 86mm calipers) as replacements for the JB6 3" / 76mm calipers, and an MC for JB7/JB8 brakes or for the NBS brakes.

- replace the hoses with SS

- on JB6 11" drums, change the rear slave cylinder, but on a case-by-case basis, e.g., depending on how much weight is or might be on the rear of the vehicle. In my case, the Suburban is relatively a$$-heavy.

My $0.02

 

[Boots97]

I think you'll be very pleased after an MC swap, given the changes you've already made. You literally need an MC swap, given the caliper design (non "low-drag") you've installed.

From the factory I had JB6 brakes on my Suburban and they worked, but not well.

I changed the front calipers first, to 3.15" bore cylinders, which didn't make a lot of difference.

Adding SS hoses up front (only) made a bit more improvement.

I then changed to a non-"quick take up MC", the NBS MC in my case, which has a ~1.34" bore. That made a huge improvement (a GMT400 JB7 1.25" bore would work as-well or better, with more hydraulic advantage over the slave cylinders b/c of its smaller bore).

Finally, I made the change to 1.1875" cylinders and SS hose (rear), which made another marked improvement.

This on my '98 L31 K1500 Suburban which across-the-scale is almost 6200#, practically evenly split front/rear.

I've also got 10% larger tires on it than OE.

Other combinations of parts would work well too, depending on the vehicle.

I think what is MOST noteworthy is:

- one should replace the quick-take-up MC / low-drag calipers; this requires at least the 3.15" / 80mm front calipers (or optionally the 86mm calipers) as replacements for the JB6 3" / 76mm calipers

- one should replace the hoses with SS

- changing the rear slave cylinder should perhaps be considered on a case-by-case basis, e.g., depending on how much weight is or might be on the rear of the vehicle. In my case, the Suburban is relatively a$$-heavy.

My $0.02

Thank You so much! So far the brakes aren't bad, but I'm ordering a new MC rn for the reasons you stated above.

JB6 did wonders to mu truck and made it much more pleasant to drive. IDK why JB6 didn't come standard on pickups as it did with SUVs?

I am also running calipers with a 3.15" bore. I've noticed some improvement.

Adding the new non "quick take up" calipers and wheel cylinders with the stock JB5/JB6 MC gave the pedal some sponge, but it feels like what my truck felt like when I originally bought it before I did any bleeding/line/hose replacement.

I currently am running SS hoses in the front. My SS back hose threads partially stripped out causing a leak, but I had a new AC Delco rubber hose sitting in my tool box drawer and I replaced it with that and had no issues since. Still a lot better than my original front and rear rubber hoses which were deteriorating from the inside.

I plan on ordering a JB7 MC as I'm writing this out. I figured this would probably be necessary given the mods I've done, but wanted to check.

I too, am running 1.1875 cylinders with a new AC Delco rubber hose. Originally had SS, but the threads were damaged which is why I have what I have now. Definitely an improvement from what my truck originally had on it.

My truck is a '97 L31 ECSB Z71 1500 Pickup. Don't know the GVWR, but it's medium sized in the world of GMT400s.

I currently have 265/75/R16 tires, which are factory oversized from the standard 245/75/R16 tires. My truck came from the factory with 265s.

You've hit a lot of main points that I agree with and I've already done. I'm very grateful that you've responded as soon as you have and I appreciate it.

I'll definitely be getting that JB7 MC ordered up ASAP.

IDK if 1.1875 Wheel Cylinders were as necessary, but I figured that if I'm doing all this work, I may as well go all out. Probably not as needed as you bc my pickup is a lot less a** heavy than your Suburban.

 

[1998_K1500_Sub]

IDK why JB6 didn't come standard on pickups as it did with SUVs?

I'm pretty sure I've seen 4-door Tahoes with the JB5 brakes in the junkyard, which contrasts with my Suburban. I assume the Suburban got JB6 on account of its heavier stature relative to the Tahoe and pickup.

I currently have 265/75/R16 tires, which are factory oversized from the standard 245/75/R16 tires.

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

Now it's got 265/75 tires on 18" rims; they're approximately 10% larger than the OE, so I re-geared the rear end from 3.42 to 3.73 accordingly. The larger tires put the brakes at a disadvantage and more worthy of improvement.

 

[HotWheelsBurban]

I'm pretty sure I've seen 4-door Tahoes with the JB5 brakes in the junkyard, which contrasts with my Suburban. I assume the Suburban got JB6 on account of its heavier stature relative to the Tahoe and pickup.


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

Now it's got 265/75 tires on 18" rims; they're approximately 10% larger than the OE, so I re-geared the rear end from 3.42 to 3.73 accordingly. The larger tires put the brakes at a disadvantage and more worthy of improvement.

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.