BLF-26C leaks! Wrong line size? [NBS MC SWAP]

[boy&hisdogs]

BLF-26C leaks! Wrong line size? NBS m/c swap [FIXED but still more problems]

So yesterday I attempted to do a master cylinder swap on my 98' 1500 vac brakes to a 99-02 (Delco part #18M1159) master cylinder. I got the BLF-26C fitting like everyone said except... it leaks! It's a small leak, about one drip per stomp on the pedal. The flare inside the female end is smaller than the flare on my brake line! What gives??? Has anyone had this happen before? Does anyone know the brake line sizes for the 99-02 trucks? I believe mine is 1/4" for the larger one (closer to the radiator) and 3/16" for the smaller one (closer to the booster).

Does the BLF 26 or 26B fit? They list them all as the same thread sizes but make no mention of line diameter. What about the Edelman #285306? Or Weatherhead #7912? I'd prefer the Edelman since it's steel. I'm going to try and track down as many of these as I can, if not all of them today, but I thought I'd make this thread to see if I could gets some input.

I'm about ready to juts lop the end of that line off and put on the right fitting myself. I'm getting really sick of things not working.

 

[boy&hisdogs]

Well, today I found an Edelman, and it has a slightly bigger flare on it than the AGS. It worked. No more leaks.

The pedal is still squishy and makes the woosh sound in the first little bit of travel though, then it seems stiffer than I remember. I'm not sure if the stiffness is from the new M/C or if it's from a bad booster. The old master cylinder puked a good amount of fluid on the booster over the years and it's pretty nasty around and below the master.

 

[Tommy1234]

Well, today I found an Edelman, and it has a slightly bigger flare on it than the AGS. It worked. No more leaks.

The pedal is still squishy and makes the woosh sound in the first little bit of travel though, then it seems stiffer than I remember. I'm not sure if the stiffness is from the new M/C or if it's from a bad booster. The old master cylinder puked a good amount of fluid on the booster over the years and it's pretty nasty around and below the master.

Taking notes

 

[Schurkey]

So yesterday I attempted to do a master cylinder swap on my 98' 1500 vac brakes to a 99-02 (Delco part #18M1159) master cylinder.

There is a huge-long thread about that "NBS Master cylinder" swap on this very web site. Far as I'm concerned, that thread should be removed as a potential liability issue.

Various people who DID NOT KNOW WHAT THEY WERE DOING proposed and completed that swap, without any understanding of the engineering of the front calipers used on the 1500 trucks.

All, or virtually all of the 1500 trucks have low-drag front calipers. The newer master cylinder is not compatible with low-drag calipers.

The swap is a disaster, actually unsafe if the power booster fails.

GET RID OF THAT NEW-STYLE MASTER CYLINDER, then you don't need the leaky adapter fittings. You need a three-chamber (step-bore) master cylinder, where the gigantic third (rear) chamber supplies a gush of low-pressure (high-volume) fluid to the calipers to get the pistons/pads up to the rotor, then the normal high-pressure, low-volume chamber takes over to actually stop the vehicle.

Note size of rear piston compared to the ones in front:

You must be registered for see images attach

 

[Schurkey]

The pedal is still squishy and makes the woosh sound in the first little bit of travel though,

Did you use a scan tool to bleed the ABS unit? You've probably got air trapped in the ABS, maybe in the rest of the system depending on how thoroughly you've bled the master before installing it (bench-bleeding takes more effort than most folks provide) and how thoroughly you bled the rest of the system.

The new, correct 3-chamber master cylinder will need to be COMPLETELY bled, before being installed, and then bleed the ABS and the rest of the system according to the instructions linked.

See attached .pdf.

then it seems stiffer than I remember.

Because you've got (improperly) big pistons in the "NBS"-style master cylinder. If the booster fails, you'll need both feet and lots of adrenaline to stop the truck. If your wife or daughter is driving, I hope you have good insurance. That master cylinder needs to be REMOVED, so that you can reinstall a correct master cylinder.




For the record, "most" 1500 pickups have the craptastic 254mm leading/trailing shoe rear drums. They're just about guaranteed to be out-of-adjustment. You'll need to pop the drums, adjust the shoes, and then make sure the park brake works properly, because frequent use of the park brake is what keeps the shoes in adjustment, and nobody uses the park brake any more.

 

[L31MaxExpress]

The answer for better braking on a 2wd is the 8-lug (single rear wheel not dually) front calipers that are not low drag and 370 series front pads combined with the matching 1.34" bore master cylinder. Get parts for a 98 Police Tahoe. The same calipers fit a 4x4 but use the 369 pads to clear the 4x4 rotor hat. Make sure it all states Police. When my van was 5-lug it had all those parts, save for I converted to hydroboost and used the hydroboost version of the same master cylinder. Then convert to the JB6 rear drums that were on a Suburban or Van. You need the backing plates and drums for the swap in addition to the larger wheel cylinders, matching larger shoes and hardware set. The weak smaller setup is just that, weak and prone to coming out of adjustment, especially if the parking brake is not used at the end of every trip.

Also replace your brake hoses and flush the system, even if the hoses look ok, change then anyway. I use Dot 4 in all my vehicles.

A good swap for the 4x4 is the 03-05 Astro AWD knuckle. Then you can use the NBS dual piston front calipers.

 

[Hipster]

There is a huge-long thread about that "NBS Master cylinder" swap on this very web site. Far as I'm concerned, that thread should be removed as a potential liability issue.

Various people who DID NOT KNOW WHAT THEY WERE DOING proposed and completed that swap, without any understanding of the engineering of the front calipers the 1500 trucks.

All, or virtually all of the 1500 trucks have low-drag front calipers. The newer master cylinder is not compatible with low-drag calipers.

The swap is a disaster, actually unsafe if the power booster fails.

I would say something but it would be this pretty much verbatim. With the amount of info on this, I don't why the next guy comes along thinking he's got it figured out. Your dealing with differences in bore sizes , displacements, pedal travel, etc. Every body thinks their an enginneer , OR doesn't even consider the math involved with what's needed for an existing system. It is a disaster and a train wreck waiting to happen without getting deeper into it.

 

[boy&hisdogs]

Did you use a scan tool to bleed the ABS unit? You've probably got air trapped in the ABS, maybe in the rest of the system depending on how thoroughly you've bled the master before installing it (bench-bleeding takes more effort than most folks provide) and how thoroughly you bled the rest of the system.

The new, correct 3-chamber master cylinder will need to be COMPLETELY bled, before being installed, and then bleed the ABS and the rest of the system according to the instructions linked.

See attached .pdf.


Because you've got (improperly) big pistons in the "NBS"-style master cylinder. If the booster fails, you'll need both feet and lots of adrenaline to stop the truck. If your wife or daughter is driving, I hope you have good insurance. That master cylinder needs to be REMOVED, so that you can reinstall a correct master cylinder.




For the record, "most" 1500 pickups have the craptastic 254mm leading/trailing shoe rear drums. They're just about guaranteed to be out-of-adjustment. You'll need to pop the drums, adjust the shoes, and then make sure the park brake works properly, because frequent use of the park brake is what keeps the shoes in adjustment, and nobody uses the park brake any more.

At the time no, but I've since used a scan tool the bleed the ABS unit, I tried it a few times and it never made any difference. And yes I bench bled the crap out of it when I initially put it in and have not run it dry or taken it off since then.

I don't have stock brakes anymore front or rear, I swapped to the bigger 2500/3500 calipers in the front and a 14bSF 6 lug rear end. Braking is much better but I have been thinking about going back to the correct OBS master cylinder for a long time. That m/c swap was 8 years ago and it hasn't given me any issues but I still wonder about it a lot. I just need to figure out which one I need, perhaps from the heavy half or light (six lug) 2500.

 

[boy&hisdogs]

Taking notes

It's not worth it, don't do it. No actual performance gain it just feels a little different.