Touchy brake pedal w/ Hydraboost

[70LS1NOVA]

So, I hooked up the hydraboost from an astro van to the nova and the brakes are real sensitive. Especially driving slow like backing into the driveway. Touch the brake pedal and it is Locked immediately. Driving down the road, using very little foot pressure, it stops real nice, probably too nice. Not sure what the bore size is on my master cylinder, but it's the same SSBC master that I had on there with the vacuum booster. Wilwood brakes up front, drums in the rear. Any ideas or suggestions would be appreciated.
Mark

[rsk68]

Bore is more then likely to small, I think you should run 1.125 bore for that setup.

[GetMore]

correction: you do need the larger bore.

[70LS1NOVA]

See, that's exactly what I was wondering. I can't remember if I need to go bigger or smaller bore. I thought the smaller bores were used on manual brakes, bigger on vacuum, even bigger on hydraboost, but can't remember. I did measure the master cylinder that came with the booster and it is 1.250. I don't want to use it cause it's ugly as hell. I'm thinking I need to go bigger. Can anyone comfirm this?

[Tito]

For the same pedal ratio, booster assist, etc a smaller bore means longer pedal travel and less pedal effort. So... for manual brakes, typically a smaller bore is used to get the brake effort more reasonable BUT this also results in longer pedal travel.

In your case it's a question of -- are the brakes actuating too early (really low pedal travel?) or with too little effort (no force feedback on your foot before lockup). My vague memories of human factors at university recall that the human body is better at detecting FORCE feedback than POSITION feedback. Sooo, I'm thinking you need a larger bore master cyl, which would make you have to press harder on the pedal to get the car to stop...

This is consistent with the setups I've seen on trucks, etc. where they have "optional" hydroboost -- the hydroboost setups have larger master cyls (like 1+1/4"). Not sure if "everything else" is the same on those optional systems though (rotors, calipers, etc.)

[GetMore]

Yeah, you guys are right. I got it confused.
Push on a large area to get an increase in force on a small area.

I'll erase my bad info above to keep it simple.

[70LS1NOVA]

So, is anyone actually running an astro van hydraboost unit on thier car? If so, what size bore master are you running?

[Rhino]

I have an astro van master at home. I'll measure it for you and post up what I find. It may not be exactly what you asked for, but at least it will get you a measurement the booster was designed to work with.

I'm planning on running the astro unit as well, I had plans on using an LS1 F-body master. Having never driven it, I can't tell you how it would work out.

[Rick Dorion]

ALso, it may be the nature of the beast. I had hydroboost on my 69 using a 1 1/8" bore MC. Even after retraining my foot, I could too easily lock the fronts when a deer jumped out, etc. I used a complete system from Hydroboost.

[Rhino]

I don't know the inside diameter of the bore, but it appears to be 1 1/4" measured from the rear of the MC.

[130fe]

ALso, it may be the nature of the beast. I had hydroboost on my 69 using a 1 1/8" bore MC. Even after retraining my foot, I could too easily lock the fronts when a deer jumped out, etc. I used a complete system from Hydroboost.

I am in the same boat on my 68, Paul from Hydratech recommended the 1 1/8 one when I got the full system from him. I just "trained" myself to avoid locking the fronts up (even though it tends to happen from time to time). The F-body one is a 1 inch bore if that helps. I am doing a rear disc conversion shortly and will be watching this post to see if there is a better solution.

[Rhino]

The F-body one is a 1 inch bore if that helps. I am doing a rear disc conversion shortly and will be watching this post to see if there is a better solution.

By F-body do you mean 4th gen F-body? If so, I have a feeling that will be a little too small for a good petal feel. Goes to show how much planning I've done for my brakes at this time. You could always use the smaller bore MC and move the brake rod mount point further down the petal. Unfortunately that would mean you're also changing the mounting angle of the Booster/MC as well.

[130fe]

By F-body do you mean 4th gen F-body? If so, I have a feeling that will be a little too small for a good petal feel. Goes to show how much planning I've done for my brakes at this time. You could always use the smaller bore MC and move the brake rod mount point further down the petal. Unfortunately that would mean you're also changing the mounting angle of the Booster/MC as well.

Yeah, sorry if I wasn't clear about that. I know the 98-02 are 1 inch bore, don't know about the 93-97 (probably the same since the 93-97 guys upgrade to ls series brakes and use the same master).

On my setup (1 1/8), if it is touchy would going to a 1 1/4 one give me a better fell (less touchy)? Any help would be appreciated.

[Rick Dorion]

A 1 1/4 would help. Also pads with less coefficient of friction. I was using Hawk HP plus. Performance Friction were less grabby.

[Apogee]

Rick makes a good point...pad choice with hydroboost is a whole different ball game than pad choice with vacuum boost or manual brakes. If you use a decent vacuum boosted application as your baseline, I would typically recommend running one level more aggressive pads with a manual setup and one level less aggressive with the hydroboost to try and regain some modulation prior to lockup.

Tobin
KORE3

[Rhino]

Tobin,
While I do absolutely understand the reasoning for the more or less aggressive pads, I'm beginning to wonder why I'm contemplating a hydroboost to begin with. Would there be any advantage of using a hydroboost with less aggressive pads? My engine combo should still pull a moderate amount of vacuum, so that's a non issue.

Correct me if I'm wrong, but I would imagine that it would wear faster in a hydraulic boosted application in comparison to a vacuum booster given the same pad. This decrease in pad life negates the only advantage I could think in running a less aggressive pad.
Is there something I'm missing or is hydroboost on a street driven car a solution looking for a problem?

[mnm99]

I went through this before and know how you feel. The 1 1/8" master is fine. The problem is getting use to the system. I was the same way when I put mine in. You get use to it. As look as the brakes arent dragging it will just take some time.

[Rick Dorion]

I too got used to it except when something unexpected and sudden would happen! I even lowered my brake pedal so I could just slide my foot over.

[Apogee]

Tobin,
While I do absolutely understand the reasoning for the more or less aggressive pads, I'm beginning to wonder why I'm contemplating a hydroboost to begin with. Would there be any advantage of using a hydroboost with less aggressive pads? My engine combo should still pull a moderate amount of vacuum, so that's a non issue.

Correct me if I'm wrong, but I would imagine that it would wear faster in a hydraulic boosted application in comparison to a vacuum booster given the same pad. This decrease in pad life negates the only advantage I could think in running a less aggressive pad.
Is there something I'm missing or is hydroboost on a street driven car a solution looking for a problem?

It all comes down to your overall brake torque generated for a given pedal force. Since the hydro generates so much boost or gain, lockup torques occur sooner in the pedal stroke and at much lower pedal forces, forcing the driver to compensate. This can be somewhat difficult since the range of force used to modulate the brakes is becoming narrower than a similar vacuum booster or manual system. Compensating during normal driving is one thing, but not stabbing the pedal during a panic "deer in the headlight" stop can be a difficult if not impossible thing not to do. Without ABS to do the modulating for you, I really like manual brakes for maximum control.

Hydro certainly has it's place, but like anything it has it's pros and cons. It has historically been a solution for the OE's in applications were there either wasn't a vacuum source (diesel engines) or the space available to mount a conventional vacuum booster. The hydro units are heavier, more costly, and more complicated than vacuum, so it's not something the OEM's would choose lightly if they had better engineered solutions.

As for pads, running hydro versus anything else shouldn't decrease your pad life given the same driving conditions. You just achieve the same deceleration rates with less pedal effort...just because there is more boost/gain available, doesn't mean that you can use it. You're still limited by your tires. The reason we suggest a lower coefficient of friction pad with hydro (assuming a 1-1/8" MC and C5/C6 type brakes) is because it reduces the initial bite of the pad which can help with the "touchy" feeling that hydro can give.

Tobin
KORE3

[Rhino]

Thanks Tobin. I do appreciate your input. The more I think about it, I'm leaning more and more toward less assist all the time. If it's not broke, don't fix it.

I completely understand the "deer in the headlight" stop, and that's the exact reason I want more modulation in my brakes. While I'm dealing with cornering and braking forces within the car, I don't want to worry about treating the brakes with kid gloves.

[Skip Fix]

Sounds like when I swapped on the TA 4 WD with booster nut did not change the pedal to the lower ratio pedal. Good stop no feel until I decreased the ratio.

[GetMore]

Would there be any advantage of using a hydroboost with less aggressive pads?

Correct me if I'm wrong, but I would imagine that it would wear faster in a hydraulic boosted application in comparison to a vacuum booster given the same pad.
I may be completely wrong, but a less aggressive pad should be a better street pad. It will be quieter and make less dust.

They might even last longer, but I don't know nearly enough about brake materials to guess at that.

For instance, ceramic pads last a long time, are almost dust free, and are quiet, but they don't offer maximum stopping power. With hydroboost to add pressure they might be just the ticket!