Hydroboost Installation question

[jamesroney]

Can someone with a hydroboost that has "great braking" tell me how much pedal travel you get in your early bronco?

With the engine running, can I get a measurement from the pedal to the floor, before and after applying the brakes.

My new Hydroboost with an AstroVan HB, and a 1-1/8 Corvette MC is going from 6.5 to 3 inches from the floor. Pedal is solid, and brakes stop the Bronco. But an awful lot of travel?

Thanks.

 

[ksagis]

For whatever its worth, I have right at 3 inches of travel and hate it. Been chasing making it better with 1.25” MC (I also had a 1 1/8 Vette MC prior), making sure the hydro rod was within 0.010” of MC piston, dorking around with my Caddy brakes parking mechanism, and also clocking of caliper to be sure Caddy bleeder is at TDC.

@toddz69 (aka as Brake Meister) gave me some measurements some time ago, think his was 1.5” total which felt like what I wanted mine to be.

 

[ksagis]

Oh, one more thing I haven’t done yet but saving for hail mary is changing my pedal ratio to 5:1. Down selected to 5:1 since that only results in minor misalignment to hydro axis and bought me a direct 20% redux in pedal travel. (Most power brakes setups are 4:1 to 5:1)

Seems to me that hydro brake feel would be better with less mechanical advantage at pedal.

 

[toddz69]

For whatever its worth, I have right at 3 inches of travel and hate it. Been chasing making it better with 1.25” MC (I also had a 1 1/8 Vette MC prior), making sure the hydro rod was within 0.010” of MC piston, dorking around with my Caddy brakes parking mechanism, and also clocking of caliper to be sure Caddy bleeder is at TDC.

@toddz69 (aka as Brake Meister) gave me some measurements some time ago, think his was 1.5” total which felt like what I wanted mine to be.

That sounds about right - I'm not able to measure mine right now, otherwise I'd go check. 3" sounds like a lot more than I had even with my 1.125" master cylinder.

Todd Z.

 

[jamesroney]

That sounds about right - I'm not able to measure mine right now, otherwise I'd go check. 3" sounds like a lot more than I had even with my 1.125" master cylinder.

Todd Z.

@ksagis and @toddz69 Can you please tell me your configuration? I purchased the offset bracket from ebay, and it was built with a bell crank ratio of 2.5 to 1.8 which is .72 the wrong way! So at 6 inch pedal travel, the actuator pin moves about 7/8 inch. Then the hydroboost input moves about .63 inches. The first 1/8 inch of HB stroke is taken up in the valve. So at full pedal travel, I’m only getting 1/2 inch at the master cylinder piston. And that’s not enough.

The other solutions that I see use a 1:1 bellcrank ratio (or straight thru) but even that would not optimize the master cylinder stroke. So I’m baffled.

 

[jamesroney]

I called the seller, and he recommended that I search the Classic Broncos site for technical expertise. In the meanwhile, I ordered an additional unit to modify.

I removed the arm from the bellcrank, and took 1/2 inch out of the pedal side, and added 0.4 inches to the HB side to give me a ratio of 2 to 2.2 = 1.1 the right way. So now with 7/8 inch of pedal pin travel, I get .965 at the booster. Obviously this causes problems at the firewall.

 

[jamesroney]

I can’t live without a boot at the firewall, so I decided to clean up the lever alignment. I put 4.5 degrees of angle into the bellcrank support stand. This aligned the pedal lever with the firewall hole. I had to bend the levers to match. Also cleaned up the levers. It looks decent now.

 

[phred]

My cobbled together astrovan/corvette master set up is fantastic. Almost too good. Pedal moves about 1.5-2”. Can hold the truck at a stop light with just toe pressure.
I put an f250 h-boost unit and master on my 78 bronco with t-bird calipers and the pedal moves about 3”.

 

[jamesroney]

My cobbled together astrovan/corvette master set up is fantastic. Almost too good. Pedal moves about 1.5-2”. Can hold the truck at a stop light with just toe pressure.
I put an f250 h-boost unit and master on my 78 bronco with t-bird calipers and the pedal moves about 3”.

Great! Can you please tell me what your astrovan/corvette master cylinder is bolted to?

1. Direct to firewall with a modified pedal box.
2. In line with factory pedal with a custom astrovan plate delete but using the giant nut.
3. Offset on an angle bracket using a Bronco bracket.
4. Offset on an angle bracket using a custom bracket.
5. In line with factory pedal using an offset bracket.

 

[JB Fab]

After ordering the eBay bracket (unimpressed), I built a bell-crank assembly into the stock pedal cluster under the dash and moved the MC / booster away from the engine. I didn't like the MC sticking out into the engine compartment,

 

[jamesroney]

After ordering the eBay bracket (unimpressed), I built a bell-crank assembly into the stock pedal cluster under the dash and moved the MC / booster away from the engine. I didn't like the MC sticking out into the engine compartment,

Yes, and I have long admired your fabrication skills. (from afar...) It turns out that @ba123 created a similar configuration in his build thread.
But I'm running a clutch. (and yes, I could hang a clutch pedal on your pivot shaft, but I would lose the air vent box...)

He also used a 1:1 Bellcrank ratio. By that, I mean that his pivot rod to actuator pin length is exactly the same. Which means that you don't get any multiplication in the bellcrank. If that is true, the I suspect that you will see a nominal 3 inches of pedal travel on a 1.25 bore master cyl.

If you have those pillow blocks mounted in the factory location, I imagine that you are also 1:1 on the bell crank. Can you please confirm your pedal travel in inches? I'm guessing the answer will be about 3 inches of stroke.

 

[JB Fab]

Yes, you are correct ~3", but it will lock up the tires at 1".
It' a little touchy until you get used to it........

 

[jamesroney]

Yes, you are correct ~3", but it will lock up the tires at 1".
It' a little touchy until you get used to it........

I understand. And thanks! But it is confirming my hypothesis that many on the Hydroboost bandwagon are touting great results when in fact...they are seeing the compound effect of power assist, AND reduced pedal effort...at the expense of pedal travel.

I did a search, and it looks like @ksagis has been fighting this for a while on this thread. https://classicbroncos.com/forums/threads/mc-bore-mc-stroke-pedal-ratio.321155/#post-3508484 I can also see where @Madgyver has done some excellent empirical engineering to optimize his pedal travel vs effort vs master cylinder stroke issues. I think I now fully grasp the nuances of the design constraints. So a big "thank you" to everyone on this thread, and to the others that posted on the other thread, like @ntsqd

So in order to maintain the correct master cylinder piston travel, and the correct pedal effort, the factory put significant design and engineering into the conversions. The 67-70 Mustang, and Fairlane, and the 76-77 Bronco and the E-body Mopar all had different ways to solve the booster amplification problem. Some did it with linkage, and some with pedal ratio. Every time I have done a power brake "upgrade" I ended up having to "fix" the input side. Here's a picture of the two different pedals for the exact same car...one with power, and one with manual brakes. Both use the same master cylinder bore. Pedal ratio is defined as the mechanical advantage provided by the pedal lever...so in a 67-70 Mustang with manual brakes, the pivot to pin is 2 inches and the pivot to pedal is 12 inches. 12/2 = 6:1. With power brakes, the pivot to pin is FIVE (5) inches, and pivot to pedal is 15 inches. 15/5=3:1

I've also attached a pic of the booster linkage from my 70 'Cuda, which also has an amplification of about 2:1 which yields a pedal ratio of about 3:1.

 

[JB Fab]

NOTE: part of my touchy brake issue is the D60 outers (front/rear) allow me to run sizable brake hardware.

 

[jamesroney]

NOTE: part of my touchy brake issue is the D60 outers (front/rear) allow me to run sizable brake hardware.

Maybe, but forgive me if I'm skeptical. With 17 inch wheels, my 06 Megacab Cummins has bigger brake hardware than most D60's. It takes significant effort to achieve lockup. (and the tires are nominally 33 inch.)

 

[JB Fab]

Just comparing it to one of our other Broncos that has D44/9" disc, same tire size. I would guess there is a bit of difference in the weight of your 06 Megacab Cummins from a topless Bronco...

 

[ksagis]

I can’t live without a boot at the firewall, so I decided to clean up the lever alignment. I put 4.5 degrees of angle into the bellcrank support stand. This aligned the pedal lever with the firewall hole. I had to bend the levers to match. Also cleaned up the levers. It looks decent now.

My setup is Hydratech bolted to firewall, direct linkage, 1.25 GM truck booster. 72 rig originally had manual brakes so is pedal ratio of 6:1.

One thing to note on hydro boosters, I’ve read a few places that they want the pushrod inline with the hydro bore to reduce internal wear, which makes sense to me. But for smaller angles, the side force is fairly small (roughly 20 lbs for a fairly aggressive stop). Couple that with lower miles driven vehicle so not too worried about it. (Looks like you have a few degeess yourself so thought I’d point it out).

Another note, I don’t think I’d size for 1” of MC piston travel at nominal pedal travel, particularly if you have a lot of pedal height remaining at depressed position. i.e. if you “pump and hold” to bleed, that would result in maybe overdriving the MC piston and causing other issues with its internal seals. Similar concern if you lost one of the brake circuits and pedal travel increased, and subsequent internal MC damage killed the other circuit.

Lot’s to consider in brake system designs.

 

[jamesroney]

My setup is Hydratech bolted to firewall, direct linkage, 1.25 GM truck booster. 72 rig originally had manual brakes so is pedal ratio of 6:1.

One thing to note on hydro boosters, I’ve read a few places that they want the pushrod inline with the hydro bore to reduce internal wear, which makes sense to me. But for smaller angles, the side force is fairly small (roughly 20 lbs for a fairly aggressive stop). Couple that with lower miles driven vehicle so not too worried about it. (Looks like you have a few degeess yourself so thought I’d point it out).

Another note, I don’t think I’d size for 1” of MC at nominal pedal travel, particularly if you have a lot of pedal height remaining at depressed position. i.e. if you “pump and hold” to bleed, that would result in maybe overdriving the MC and causing other issues with its internal seals. Similar concern if you lost one of the brake circuits and pedal travel increased, and subsequent internal MC damage killed the other circuit.

Lot’s to consider in brake system designs.

OK, so you are using something like the Hydra-Tech bracket bolted to firewall with the slightly angled mount?

I don't think those can ever be right, without some kind off link bar in the middle.

 

[toddz69]

@ksagis and @toddz69 Can you please tell me your configuration?

My current configuration is a BC Broncos firewall plate with a modified 1st gen Super Duty booster (adjustable pushrod) with a '98 Dodge 1500 1.25" master cylinder. 6:1 pedal ratio. I think my pedal is 4.5-ish inches off the floor in its static location. I'm guessing my pedal, when applied, is maybe 2.5-3" off the floor.

I've run a variety of configurations and boosters in my rig over the years - all with 1.125" master cylinders until about 2 years ago.

I've owned an '01 SD PSD with hydro boost since '02 and I've always used that as my baseline for how hydroboosted brakes should feel and react. My measurements of the SD configuration many years ago showed it had a 6:1 pedal ratio too (or something very close to it).

Todd Z.

 

[toddz69]

OK, so you are using something like the Hydra-Tech bracket bolted to firewall with the slightly angled mount?

I don't think those can ever be right, without some kind off link bar in the middle.

I had 1-2 brackets that I had built many years ago that served as the genesis/basis for the initial Hydratech brackets (I befriended the Hydratech owner, introduced him to Broncos and helped develop his first Bronco systems 20+ years ago). One of those brackets is still in place on @lars truck. They work great as far as I'm concerned - maybe I'm missing something though? My current BC plate is similar - it just moves the booster closer to the firewall than my initial design.

Todd Z.