Ford 9" Disc Brake Options - Advice?

[Stan the Man]

I'm doing preliminary research on building a 35 spline semi-float 9". I'm currently running through the disc brake options and there's so many to choose from. The initial 4 that fit the budget are:

RuffStuff weld on kit - uses bronco front rotors and Chevy calipers
Explorer kits 11" Bolt on
Jeep JK kit 12"
Wilwood 11" or 12"

- Is there any benefit going from 11" to 12" discs?
- The Wilwoods are 4 piston, while the others are 1 piston. Is there any real advantage to going 4 piston in the rear once brakes are proportioned properly with stock front brakes? Seems like it might be wasted beed?

[biggiek]

I have the explorer kit on my 8.8 and am not impressed regarding additional stopping power.

[Stan the Man]

Well, seeing as how only 30% of braking power comes from the rear, I’m not expecting much gains. I did some research on Wilwoods website and learned a few things:

1. Caliper bore size applies the force (more force does not mean better brakes).
2. Larger brake pad area can lead to better braking.
3. Larger diameter rotors lead to more leverage and lead to better braking.
4. It’s possible to have too much rear braking so big brakes on the rear can be overkill.

[arse_sidewards]

These are 5000lb-7000lb vehicles depending on how kitted out you are with extra steel throughout the vehicle. Even with 35-37" tires the rear braking needs aren't that exceptional. Slap some '99+ E-250/350 drum in hat calipers on it with a rotor that matches your bolt pattern and be done with it. No need to get super fancy. The brake flange doesn't directly bolt to a 9" but I presume you own some sort of drill press and have enough money to buy a hole saw.

[ChaseTruck754]

A main piece of this puzzle many often don't think about is the E brake and if you want/need to maintain this or not. If not slide on rotors and chevy calipers with cheap brackets are super cheap and easy. If you want to maintain the e brake stuff gets a bit more tricky/spendy.

Also, one thing to think about with your 12" rotor question is if your wheels will fit over that. The stock 15" wheels probably don't even fit over the 11" rotor and caliper combo.

[Stan the Man]

A main piece of this puzzle many often don't think about is the E brake and if you want/need to maintain this or not. If not slide on rotors and chevy calipers with cheap brackets are super cheap and easy. If you want to maintain the e brake stuff gets a bit more tricky/spendy.

Also, one thing to think about with your 12" rotor question is if your wheels will fit over that. The stock 15" wheels probably don't even fit over the 11" rotor and caliper combo.

Thanks, all options I provided in the first post have e-brakes. I’d like to keep that. Also running 17s so no worries on fitment.

[ChaseTruck754]

Does the RuffStuff kit for the Chevy calipers use their redo of the El Dorado caliper then? If so read some reviews on that if you can. I don''t have any first hand experience with the El Dorado calipers but have talked with a few guys on the Old Fords forum I'm on who have used them and they had some pretty big adjustment issues. I think Dan (RuffStuff) claims to have addressed some of these issues in their version of the caliper, but it's definitely something to look into.

For the 4 piston thing on the Wilwoods - I missed that part earlier. On that, piston diameter has to do with the surface area in contact with the pad. It would seem the more surface area the better. I would think the "cool" part of the 4 or 6 piston calipers everyone is always bragging about is the piston area can be spread wider across a larger pad area. That is vs. a larger dia. single or dual piston which may have the same overall surface area as a smaller 4 piston, but that 4 piston spreads the piston area out more on the pad.
As has been mentioned the front does the bulk of the braking, but these things are heavy enough in the back that better rear braking may help more so than on a truck with not much weight on the back end.

[PaulW]

Stan, about the ebrake. Do you want drums or mechanical calipers.
Both have advantages and disadvantages. For off road use the non drum e brake has the advantage of no rocks caught in the drum area. The big disadvantage of the no drum is of much less stopping power. The brake will hold the rig on slopes that at are not to steep.
My Bronco had Varga sold by Ford and did not have the drum feature. Sold by Ford on the turbo 4 cyl Mustang of the day. IMO Varga makes good stuff. Yes I had the Wilwood Explorer with drums for a while. Now I have the Cadillac version with no drum on my 72 Bronco. Unlike the big Bronco that setup required a classical Corvette master.
Let the comments continue on my post.
Paul

[Tchajagos]

Just adding my 2 cents. Don’t forget to use the correct master cylinder. Disk pistons need more fluid flow than their drum counter parts and they don’t need the residual valves that drums need. Iirc we were upgrading to expedition master cylinders.

[toddz69]

I'm doing preliminary research on building a 35 spline semi-float 9". I'm currently running through the disc brake options and there's so many to choose from. The initial 4 that fit the budget are:

RuffStuff weld on kit - uses bronco front rotors and Chevy calipers
Explorer kits 11" Bolt on
Jeep JK kit 12"
Wilwood 11" or 12"

- Is there any benefit going from 11" to 12" discs?
- The Wilwoods are 4 piston, while the others are 1 piston. Is there any real advantage to going 4 piston in the rear once brakes are proportioned properly with stock front brakes? Seems like it might be wasted beed?

If you're using the RuffStuff weld-on kit, they specify to use the Chevy 1/2 truck/Blazer front calipers, which don't have parking brakes. If you want parking brakes, you'll need to use the 76-78 Caddy Eldorado calipers. Until recently, they were pretty hard to find but TSM now has them in stock. I haven't ever used the parking brake function on them but if it's similar to the 79-85 Eldorado metric calipers that many of the kits use, then they won't work well, as Chasetruck754 notes. Or if they work well, they won't work well for long . Frankly, I think they're too much caliper for the rearend of the Bronco.

The Explorer kit works well if you have the right ends on your housing and use the 2.5" brake spacing. It's economical and parts are cheap. If your truck is heavy or you have >35" tires, it may be on the edge of acceptability if you're doing a lot of heavy braking. I've had Explorer brakes on my Bronco for more than 15 years now and like them a lot. I previously ran Cadillac calipers and Lincoln Mark V calipers.

I'm not familiar with JK kits for 9" semi-floaters (Currie has a FF kit that uses them) but I would say similar things about them as the Explorer kit except that you have slightly larger brake torque capacity based on the larger brake rotor diameter.

I haven't personally used the Wilwoods on my vehicles but I'm fairly familiar with them. There are a wide variety of kits available for the 9". They use a similar parking brake setup to the Explorer system and unlike the Explorer setup, doesn't use a dust shield so dirt and rocks can get in the parking brake mechanism, as Paul notes. I'm not a huge fan of fixed calipers like the Wilwoods on semi-floating rear ends as the axles can 'walk' a little bit causing piston retraction in the calipers, which *may* require an extra pump of the brakes at times. I think the fixed calipers also put stress on the retaining plate area on the axle and can cause axle seals to leak prematurely. I've seen this with some early Broncos with Wilwood brakes in the past.

12" discs will give you greater brake torque in the rear - if your Bronco can handle that and not get squirrelly, bigger is always better, as with a lot of things in life . No real advantage, in my opinion, with going multi-piston vs. single piston for what we use our Broncos for.

And as noted, you may need to change your master cylinder depending on your brake choices as well.

Todd Z.

[PaulW]

Todd reminded me about my wilwood setup. The movement of the retaining plate on my axle resulted in bent retaining plate which is why I switched to Varga/Ford calipers. Those wilwood plates were not very strong due to thickness.

[ntsqd]

Along comes johnnie come lately, who designed brake stuff for a certain, common aftermarket brake mfg a very long time ago.

RoT for brake rotor OD is that the max that will fit inside a given wheel is 3" smaller OD than the wheel's nominal size. So for a 15" wheel you're limited to a 12" rotor. There's exceptions to everything of course, with some calipers you can stuff a 12.188" rotor inside a 15" wheel, but not with every caliper out there and I'd be surprised if you can make a GM sliding caliper work with that rotor.

About that things learned #2; it is internet legend, false. The only thing that a larger pad area does is provide for a longer wear life because there is more friction material volume. Look at the formula for calculating brake torque. There is no mention of pad area in it. With no mention of it in the formula that calculates this, how can it increase braking torque?
If you have a pad with a large rotor contact area and you trim it's edges such that you move the contact area's centroid further out on the rotor, THEN it will improve braking power. But that is a function of the pad area allowing this mod and not of the pad area itself.