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Looking to upgrade the front brakes on the 79 J20. Bigger tyres (33's) and modern driving combined with 70's brakes makes for some interesting moments.
The current discs are in very good condition and I have new "ceramic" pads ready to fit.
The main problem, however, looks like the single piston calipers up front.
I've seen wilwood do a twin piston caliper, but is there any other bolt on twin/four piston calipers?
P.s tried a search and seen a mention of gm calipers that might fit, but I want to be sure before ordering, as the shipping gets expensive to the UK
Cheers

I have to say in my J10, I have never had an issue with stopping power. And I have certainly had to do some emergency stops before. Before going and doing upgrades, have you verified both the brake fluid is in good condition, and that the lines have no air bubbles?

Upgrading the rears to disc can certainly help. For the front, if cooling is the issue you can go with slotted rotors. The J20 already has larger rotors and calipers than a J10/Wagoneer. I am sure you can find some lager diameter brakes with calipers that will work. It will require going with larger wheels most likely.

Are you doing a lot of towing or hauling?

A popular upgrade is using the Chevy JB7 caliper and pads. The piston is approx' 30% larger ad the pads are much bigger. Search JB7 here on the site and many people have done it.

Brakes are in good condition, po fitted new hoses with the lift kit.
They just don't work that great. I've done the drilled and grooved rotors on other vehicles but better calipers make the biggest difference for the price.
I recommend watching this video regarding braking distances and larger tires, certainly opened my eyes.
https://youtu.be/jO6QYM59ANw

You should really check the system for air. 33's aren't a large tire, and with the J20 already having bigger brakes, it really should stop well when empty. Hauling/towing changes things.

What are the diameters of the two pistons on the calipers you're looking at?

Willwood state the piston area is 6" on their calipers, but they only do up to '78.
I think the 79 has metric fittings but I'll be checking that out later as the clutch is first priority.

I find that your calipers have a 2.9 dia piston which has 6.6 sq in area. Obviously Willwood's would be worse whether you can make it work or not.

Two pistons isn't necessarily better. Trying to fit two with a total area greater than a single in the same space probably won't work. Now if it comes with a custom mount too...

Looks like each piston is 2"
https://www.wilwood.com/BrakeKits/Brake ... option=All

Ive never understood how they list the piston area of Two 2" pistons as 6.24 when 6.24 is the area of one piston. Shouldnt it be 12.48 for the two 2" pistons? Im certain that each piston isnt 1".

rocklaurence wrote: ↑Tue Jul 28, 2020 6:18 am Ive never understood how they list the piston area of Two 2" pistons as 6.24 when 6.24 is the area of one piston. Shouldnt it be 12.48 for the two 2" pistons? Im certain that each piston isnt 1".

The area of each piston is 3.142 sq in. So when they are both added together you end up with 6.284 sq in.

Still less than the stock 6.6 but again I was looking at '79 diameter and those are for '78.

But my point is that two pistons don't guarantee more braking "power" than one. Fix what you have first. Is the booster operating properly? Is the master the correct part? A bigger bore there will give you less power.

Stuka wrote: ↑Tue Jul 28, 2020 7:07 am

rocklaurence wrote: ↑Tue Jul 28, 2020 6:18 am Ive never understood how they list the piston area of Two 2" pistons as 6.24 when 6.24 is the area of one piston. Shouldnt it be 12.48 for the two 2" pistons? Im certain that each piston isnt 1".

The area of each piston is 3.142 sq in. So when they are both added together you end up with 6.284 sq in.

So, your saying that each piston diameter is 1"=3.142 PI? Arent they 2" in diameter?

rocklaurence wrote: ↑Tue Jul 28, 2020 7:25 am

Stuka wrote: ↑Tue Jul 28, 2020 7:07 am

rocklaurence wrote: ↑Tue Jul 28, 2020 6:18 am Ive never understood how they list the piston area of Two 2" pistons as 6.24 when 6.24 is the area of one piston. Shouldnt it be 12.48 for the two 2" pistons? Im certain that each piston isnt 1".

The area of each piston is 3.142 sq in. So when they are both added together you end up with 6.284 sq in.

So, your saying that each piston diameter is 1"=3.142 PI? Arent they 2" in diameter?

To find the area of a circle you use A=πr2. If the diameter is 2", the radius would be 1".

Please excuse the hijack, to put JB7 calipers and pads on a J10 is there a problem with the flex line connection? If so can I use the Chevy flex line?

jeepman6 wrote: ↑Tue Jul 28, 2020 5:26 pm Please excuse the hijack, to put JB7 calipers and pads on a J10 is there a problem with the flex line connection? If so can I use the Chevy flex line?

Yes you can or you can grind off the key on the caliper and use the Jeep line. I install the bango bolt when grinding off the key because if you nick the seat it will leak.

My flex hoses are old, does the chevy hose fit the jeep end as well as the jb7? If so what part do I ask FLAPS for '85 chevy 3/4 ton?

Lower GVRW J20 WILL HAVE jb6 . Higher GVRW J20 WITH 13 INCH REAR Drums will have jb7 . All j20s are not the same

Hey Artif,

Did you ever figure out the problem? Did you go down the road of brake upgrade?

Not yet, I only get home at weekends and I've just replaced the clutch. I did order a set of ceramic brake pads with the new clutch, so I'll try them first. Maybe this weekend. I'll update as I find out more