Hydroboost vs Vacuum assist

[Jaybr]

In my intro thread it was mentioned that I should go hydroboost for brake upgrades. I was thinking aftermarket like a Wilwood setup.

It was stated that vacuum would be good up to 33" tires.

I understand the differences in how they work, what I don't understand is what are the technical limitations of the vacuum setup?

Is there not enough vacuum to give adequate boost? Not enough flow? Would larger disc or calipers help?

What do the resto-mod builders use?

 

[Scoop]

There's a mix of restomods that use vacuum or hydroboost. I have hydroboost on my crawler with 37's but may go with vacuum assist on my street restomod which currently has 31's - I may go to 33's but no bigger on this one.

Main advantages of hydroboost:

1. Much more stopping power for larger tires.
2. It does not depend on engine vacuum to work. This may sound stupidly obvious but any built engine with a larger cam will have low vacuum and this directly and adversely affects vacuum braking.
3. You still have power braking (for a short while) when the engine dies.

Disadvantage:

1. HB needs to be set up correctly or brakes can be too "touchy"!

 

[garberz]

The 8” diaphragm of a vacuum booster can never equal the power assist that the hydro boost can create, not in that given size. I had the factory vacuum assist and switched over to hydroboost, it’s a night and day difference.

Mark

 

[SteveL]

I was going thru vacuum boosters running 35s. Having much better results with hydro.

 

[Glass Pony]

I probably went through every combination on my disc front/drum rear brakes running 33's.
Manual MC, (master cylinder)
vacuum assist w/stock MC
vacuum assist w/stock MC and T-Bird calipers
vacuum assist w/1-1/8" piston/MC and T-Bird calipers
I ended up with Hydroboost w/1-1/8" piston/MC and stock calipers and it stops good now as the vacuum assist set ups had me wanting more.
One of the worst combos I thought next to manual MC, was the vacuum assist w/stock MC and T-Bird calipers.

 

[DirtDonk]

One of the worst combos I thought next to manual MC, was the vacuum assist w/stock MC and T-Bird calipers.

Interesting you say that Pony. You're not alone from what it sounds like.
In your case though, with all the others under your belt to compare to, what was it that you didn't like about that last combo? Was the pedal too soft, or did it just not have the power you wanted?

Thanks

Paul

 

[DirtDonk]

I understand the differences in how they work, what I don't understand is what are the technical limitations of the vacuum setup?
Is there not enough vacuum to give adequate boost? Not enough flow? Would larger disc or calipers help?

As was alluded to, it's the physical size of the boosters available to fit under the hood of a Bronco. If you could fit an F350-sized vacuum booster in the space available you could have extremely strong brakes even with big tires.
A hydro-boost might be on par with one of those, but there's just no comparison between a hydroboost even as used on a small-ish Astro Van and a tiny Pinto/Mustang II-sized vacuum booster.

And then there is new vs old. Just from limited comparisons, those that have had their old stock units rebuilt vs using new aftermarket have felt like the originals offered most assist.
There are several regular posters that are original owners of their '76 or '77 EB's with vacuum boosters, but not sure if they've had to replace them with new and have a direct comparison. But if they have it would be nice to hear from them as well

To your other questions, yes there are times when there is not enough vacuum. More and more people are installing high-performance engines with lower than stock vacuum. So that has an effect for sure.

And yes, a larger diameter disc rotor has a leverage advantage over a standard sized one. The downsize that stops most people is when they want to stay with 15" wheels. If up-sizing to 16" or 17" or larger wheels is in the cards though, then using larger diameter rotors is a viable option.

Larger calipers, whether through a larger diameter single piston, or multiple pistons equaling a larger surface area will provide more clamping force for a given amount of pedal pressure. So as long as the friction surfaces can handle the heat and force (usually not a big issue for truck-sized components I don't think) you can get more clamping force.
The trade-off is that the more piston area you have, the more pedal travel you have. A small change might not be a big deal, but a big change could literally have you pushing the pedal too near the floor for comfort.

So yeah, it's all doable. But a brake system is so critical that you literally have to think of every component as part of that "system" so that when you want to modify/change one of them, other things need to be taken into account too.
Probably knew that part, but since we're getting into some nitty gritty, figured it was worth mentioning.

Paul

 

[Glass Pony]

Interesting you say that Pony. You're not alone from what it sounds like.
In your case though, with all the others under your belt to compare to, what was it that you didn't like about that last combo? Was the pedal too soft, or did it just not have the power you wanted?

Thanks

Paul

It didn't seem to have enough clamping force at the end. I guess it couldn't fill the larger piston T- bird calipers fast enough. I knew it wasn't enough when the guy at the DMV on the brake test said "you almost made it, lets give it another shot!"
After that I went to the 1-1/8" MC and while that was a lot happier with the T-Bird calipers, but I wanted a little bit more.

 

[SteveL]

As was alluded to, it's the physical size of the boosters available to fit under the hood of a Bronco. If you could fit an F350-sized vacuum booster in the space available you could have extremely strong brakes even with big tires.
A hydro-boost might be on par with one of those, but there's just no comparison between a hydroboost even as used on a small-ish Astro Van and a tiny Pinto/Mustang II-sized vacuum booster.

Paul

^^^this is basically what I was told by the brake shop about me going thru boosters. He said the small boosters they use to make em fit on the eb just aren't up to the task of stopping the larger tires on a daily basis. My original power brake swap on the 66 was the oem style from Duffy and it lasted longer than the type they(all the vendors)sell now. When it died after about 3years running 33s. I swapped to the smaller set up from bc to save space. The bc kit was the later booster most use now not the mustang2 style. Then somewhere in the mix I went to 35s. With the later boosters and 35s on both broncos I was getting 12-18 months on a booster.

 

[jckkys]

The OE '77 set up worked very well on my new Bronco. But then to keep the warranty, I couldn't run stupidly over size tires. I don't like anything over 31" now. The .new vacuum booster is good but not as good as the original booster. My engine is "built" but not for high RPM. Low RPM torque is far more useful in an off road 4X4. So there's plenty of vacuum except at high altitude. Just now, I'm installing the large car calipers. How people started calling them T-Bird I don't understand. Vacuum work as long as the engine is running. Hydroboost is gone when you loose the belt.

 

[SteveL]

The large bore front calipers were common on the 70s t-birds.

 

[sykanr0ng]

Just now, I'm installing the large car calipers. How people started calling them T-Bird I don't understand.

The large bore front calipers were common on the 70s t-birds.

You walk in and tell the kid behind the parts store counter you want large car calipers and you get a dumb look.

You walk in and tell the kid behind the parts store counter you want '76 Thunderbird calipers and you get the parts you went there for.

 

[toddz69]

How people started calling them T-Bird I don't understand.

As Paul Harvey would say, here's "the rest of the story" on why people call them "T-Bird calipers".

I was the guy that discovered these calipers (at least for the Bronco community) about 20 years ago. I was walking around one of my favorite Phoenix junkyards one hot summer day and was probably messing around with one of the late 70s Lincoln Mark V cars as I used to pull rear disc parts from them for conversions. From either looking at the front calipers or reading about them in one of my Wagner brake books, I realized they were a larger diameter bore caliper than the stock Bronco caliper. I pulled a caliper off a car and walked over to a late '70s F-150 in another part of the yard (they were somewhat common in those days) and tried it. Voila! It fit! I realized the brake line attachment was different and would probably require some work, but they fit.

Next, I went to the library and dug around in their Hollander Interchange Manuals (old-timers will remember those) and figured out the list of cars that the calipers came on. I posted the info on the two Bronco internet mailing lists at the time (EBML and Broncofix) as info for people in case they were interested. Chuck from BCBroncos came up with a line that would work and started selling them.

As time passed, people would ask from time to time what cars the calipers came on and I would research/dig out the list again. After awhile, I decided if I could just remember one year/model, I would just quote that instead of the long list as people were generally buying them rebuilt from part stores and not digging in junkyards anymore anyway. So I decided that a '76 T-Bird was an application I could remember.

And that's how they became known as the "T-Bird calipers".

Now, as wise owl Apogee has noted, depending on the master cylinder being used, your braking power may not be increased much or at all over the stock calipers but they have proved to be an effective upgrade for many folks.

Todd Z.

 

[Scoop]

Oh I get it. They are really T(odd)-Bird Calipers!!!! ;D;D

 

[SteveL]

From here on out we'll call it the toddz swap.

 

[Bronco Maniac]

A friend of mine was building his Bronco. I told him to go HB. He said it was not needed unless you had like 35's. His Bronco does not stop very well. Not sure of his tire size, but they are not as big as my 33's. He was running uncut for a while. He wishes he had HB.

 

[nvrstuk]

Yeah, but if we started calling all the cool upgrades that Todd is responsible for then people would get mixed us as to WHICH ToddZ upgrade is it you want to do???