• Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!
    If you have problems registering or can't log into your account, please contact Admin.

Hydroboost with big brakes

PhantomEB

Sr. Member
Joined
May 25, 2004
Messages
453
Loc.
Calgary, Alberta
Just curious has any one done this?

I am gonna be running 79 d60 front with rear 14 bolt and discs all around. 42” Iroks 17” beadlocks.

Would like to hear from others who may have done the same.
 

nvrstuk

Contributor
Just a Bronco driver for over 50 yrs!
Joined
Jul 31, 2001
Messages
8,604
...but what calipers?? JD6 or JD7 or something else that you will fab up to the housing?

Just need to know so the responses will be more accurate.

Here's what I have:

Front- D60 from a '78 F350 with Chev JD7 calipers (big)

Rear- Ford 9" housing with Chebby 14 bolt hubs with Chev JD7 calipers (big)

I fought a problem for days trying to bleed the brakes with the M/C and hydroboost I was using prior to this install. It ended up being a simple fix as the AstroVan step up type M/C could not move enough fluid to bleed the rear calipers...not by gravity, not by pumping the brake pedal, not by using vacuum, not by pressure bleeding. I used to do brake systems at a GM dealership and my friend helping me off and on for several days on this issue had his own repair shop for 20+ years...we weren't novices...

I ended up figuring out that the JD7 calipers required 4 times the volume than what the more than adequate calipers were that I had on before.

I ended up using (thanks Yeller) an '85 Chev 1 ton hydroboost designed M/C...bolted right up to my Astrovan hydroboost...works PERFECT. It is 1.385" bore (big). Great pedal, not hard but perfect...

My advice...go with JD6 calipers on all 4 corners and use a m/c that is slightly smaller (maybe 1.250") so you can use a plastic snap on NO LEAK lid and alum body for NO RUST...I have to use a hose clamp on mine to keep it from leaking...after 3 new gaskets and 2 new lids I gave up and just clamped it...no leaks now!

Good luck, hope this helps. You can check out my build thread which describes what I did.
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
5,881
Loc.
Rogers County Oklahoma
I have JD6 calipers with 12-1/2" rotors on the rear and 3.5" bore GM 1 ton calipers with 13" rotors on the front, wish I had hydroboost and even smaller rear calipers, I have a manual pressure reducing valve on the rear, its turned down as far as it will go and will still lock the rears but at least its close to where the front locks. It does stop well but needs a little more boost when you really need it to stop. To get the balance really right I need a caliper that has a piston surface area of 4.5-5 square inches. maybe one day I'll get to that.....
 

Apogee

Contributor
Bronco Guru
Joined
Nov 26, 2005
Messages
6,033
I have JD6 calipers with 12-1/2" rotors on the rear and 3.5" bore GM 1 ton calipers with 13" rotors on the front, wish I had hydroboost and even smaller rear calipers, I have a manual pressure reducing valve on the rear, its turned down as far as it will go and will still lock the rears but at least its close to where the front locks. It does stop well but needs a little more boost when you really need it to stop. To get the balance really right I need a caliper that has a piston surface area of 4.5-5 square inches. maybe one day I'll get to that.....

Why not convert over to the 1978+ small metric caliper, the D154 with the 5.47" [139mm] pin spacing? You can get the weld-on brackets from AFCO for super cheap, or make your own. These calipers have a Ø2.50 [Ø63.5mm] piston with a 4.9 in^2 piston area and should be compatible so long as your rotor isn't too thick.
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
5,881
Loc.
Rogers County Oklahoma
Why not convert over to the 1978+ small metric caliper, the D154 with the 5.47" [139mm] pin spacing? You can get the weld-on brackets from AFCO for super cheap, or make your own. These calipers have a Ø2.50 [Ø63.5mm] piston with a 4.9 in^2 piston area and should be compatible so long as your rotor isn't too thick.

Rotor thickness is the problem. I should be able to turn the rotor down to 1.25" or even belt sand pads down to fit (have done that before) just not something I want to deal with at the moment. The system works well as is but would like to have a little better rear braking at lower pressures and in theory the smaller caliper does that by allowing a higher pressure setting on the pressure reducing valve.

Just had the realization I should expand on the "belt sanded brake pads", they were on an off road only rig so no children or nuns were ever in danger. and the owner volunteered to do it so it was his lungs, not mine.....
 
Last edited:

nvrstuk

Contributor
Just a Bronco driver for over 50 yrs!
Joined
Jul 31, 2001
Messages
8,604
If I was redesigning my braking system again I'd go with what Apogee mentioned, the smaller metric calipers....

Three reasons:

1- a Bronco doesn't need 1 ton braking capacity sized calipers...just doesn't

2- allows you to pick and choose amongst dozens of M/C applilcations...ones that are alum bodied and plastic reservoirs...no rust, they seal perfectly and are lighter

3- not important to 99% of Bronco owners but the smaller bracket gives you more room around the axle when designing 4 link systems, coill over/ORI mounts, etc.

I did forget to mention PhantomEB that you will need a brake bias valve to reduce the amount of pressure to the rear calipers. I have run a brake bias valve in the rear since close to '96. I'd never built a rig without that valve which allows you to absolutely dial in the brake bias...so important on such a short wheelbased rig

I have hydroboost with my setup and they work perfect...I mean they really are perfect... great pedal, great pedal "feel", stops on a flipping dime, I have the rear pressure reduced so they will just grab on gravel before the fronts... I like everything about the setup...EXCEPT the miserable leaking M/C. (it's cast and leaks).

I have run close to 8 different brake systems on this same Bronco since '76. Different axles, different calipers, combination disc/drum, etc... this ones the best.
 
Top