are you high dude? Every diesel ford now has hydroboost, chevy vans have had hydroboost since the 80's and every chevy gas and diesel has hydroboost. You can't tell me the chevy can't produce vacuum well enough to brake. And with rodney, my peddle effort has increased but firm feeling feedback.

 

Pedal feel aside, as it's a very subjective matter - the brake booster is a force amplifier, it takes the force applied to the pedal and multiplies it by whatever, say x5, and transfer that to the master cylinder piston. The different boosters have different amplification capabilities - say a single diaphragm F150 booster is capable of x3 or x4, the dual diaphragm factory F350 booster is x5, and the hydro is x6. Assuming a constant pedal force, about 175 lbs in my case (my weight is about 150 lbs, so you can see I definitely do not suffer from weak leg syndrom), this will result in 875 lbs applied to the master with the vac booster, and 1050 lbs with the hydro. These two different forces act on the same piston surface area, so the resulting line pressures will be different - again higher force equals higher line pressure. Line pressure gets transferred to the calipers, where it gets converter back into force - again since we're using the same calipers the pistons surface area is identical, so the higher line pressure directly results in higher clamping force at the calipers. This is all simple physics and you cannot argue with it.

Now let's look at caliper flex - a caliper is designed to withstand a certain force trying to spread it apart (which is actually the clamping force from its pistons acting on the rotor through the pads), if said force is increased significantly this will yield more flex in the caliper. And what does a hydroboost do - oh wait, that's right, it increases the clamping force per fixed pedal force input. So yes, if the line pressure is increased the caliper will flex more, thus "wasting" some of the newfound hydroboosted clamping force. Most people will not notice this, but if you actually put gauges on the caliper you will see this happening, and I know this from experience with hydroboosted F450 Superduty brake calipers that we had to redesign for that very reason (the bean-counters wanted them cheap, but found out cheap don't hold up well to the line pressure the hydro was putting out with a big heavy-foot guy on the pedal).

Brake hose expansion also changes, however this is for the most part negligible if the hoses are of decent quality.

Front/rear bias does not change, you're correct on that, however I did mention I'm leaving the rear brakes out of this because they lock up so easy regardless of the booster used.

You do have a point that all this matters none if the factory brake booster is capable of locking up the front wheels. However, you must have one helluva booster if yours allows you do that, as I've worked on many older trucks and I'm yet to see one with a vacuum booster that can lock up the fronts on a 10k lbs truck with good tires on clean high-friction pavement (read asphalt). And Oreo is correct on the GM part of things, their 454-powered 1-ton trucks have had hydro boosters for like forever, and those (especially the TBI ones) tend to pull more vacuum than I ever saw out of a 460...

 

yea same here bro

 

Again, if you can lock your brakes, a stronger booster does not increase your braking force. Whether it's done by leg power or booster power, a given fluid pressure at a caliper or wheel cylinder will do the same no matter what booster you run. I think many might think their modified system works so much better because they're doing it after the stock one is going bad. My motorhome has a stock vac. booster and I can lock the brakes, tho I avoid it. I've driven and serviced many heavy trucks with vac. assist and none had stopping issues. I can see where putting monster tires on stock brakes would create a need for more assist, but I'd recommend the appropriate braking system, not just more pressure to force them to work outside their designed parameters. Anyway, this all started with someone wanting to make the change--if you do it right you should be safe. If you repair the stock system to work as designed you should be safe, so it's up to your preference or 'need'. Make sure the lever/pushrod is good through its entire travel, rod to master clearance is right, ect. Test, measure, and assure! Some people are saying the brake pedal gets easier to push, some say it's firmer...whatever. Just make absolutely sure it's all done right.
Since I'm the only one here that knows that the booster just supplies assist toward pushing the master cylinder and does nothing for the brakes' mechanical capabilities I'll just bow out of this thread.

Happy braking to all!

 

Absolutely correct, hence why I focused on front brakes only in my posts - therein lies the problem tho, not many people seem to be able to lock up their front wheels with the vacuum booster. For what it's worth my brakes worked great with the vac booster, they weren't quite able to lock the front wheels but I never felt them lacking stopping power - the hydro for me was mostly a result of several factors acting together, in other words my vacuum pump went out, couldn't find a decent one for cheap, and I already had the hydroboost plus my PS pressure line needed replacement anyways. That, and I never quite liked the pedal feel with the vac booster, but this goes into the highly subjective field again.

That could very well be. However, how would you explain GM installing hydroboost on their 454-powered DRW trucks, while those exact same trucks if equipped with a smaller engine would instead get a vacuum booster? It's not cause the 454 don't pull as good vacuum as the 350, that I am certain of as I do actually use the manifold vacuum readings as a diagnostics tool... Same with their diesels as well, they all got the hydroboost, even tho they use the exact same vacuum pump that Ford used on our trucks to operate the vacuum brakes as well... And the fun part is that in many cases the brakes used by both Ford and Chevy are nearly identical in design and performance, why then would GM go through the extra expense to power these same brakes through a hydroboost unit?

Well that's a pretty damn ignorant thing to say, don't you think? Especially coming from someone with medium-duty truck maintenance background and directed at someone who has hands-on experience with the development and testing of braking systems for those same trucks... A bit more professional courtesy here won't hurt, ya know

 

throw a set of 42" tires on your truck, tell me if your vacuum system will lock the tires up still..... then when it doesnt, install a hydroboost and try again. and when it does lock them up come back and tell me theres no difference between the two.

 

This. My '89 Jeep YJ on 37's has a brake booster setup. Another guy in town has hydroboost on his YJ. FAR SUPERIOR. And yes, my entire braking system is new.