[chuckies76ta]

Ok, I think we may have gone off track from the start. Your title referenced Hydro-boost Conversion sent me in that direction. Seeing that you have already installed larger rotors (I'm assuming) and calipers, and your making 15 inches of vacuum, you should have no problem with current braking system. My understanding is that with Disc brakes you need a 1-1/8" Master cylinder. You also need a Proportional valve that is designed for Disc/Disc brakes. Other issue I can think of maybe your brake line size to the rear brakes is designed for drum brakes. The 7/8" bore master cylinder is not gonna have enough fluid to apply brakes properly with a disc/disc system. The Disc calipers use a large amount of fluid because of there size, hence the larger M/C. bore. The other issue maybe you current Brake booster unit. I read it's a 9" single diagram, which in my opinion is too small. (As was mentioned) The dual 9" or even the 11" booster would be much better. Also the pin between the booster and M/C has to be the correct length for the system to work properly. What vacuum line are you using to feed the Brake booster and do you have the check valve located at the booster.?

My advice to you is to forget about the Hydro-boost system, and find a mechanic that can diagnose your current setup and get it working properly. So going back to post #3 Tininjun I understand what you were referencing now. my apologizes.

[chuckies76ta]

I'd also like to add this. We ran my wife's 68 Firebird with stock brakes, front disc, rear drums with close to 600 h/p and around 12" of vacuum. We ran an 11" brake booster with a 1-1/8" master cylinder. The car stopped very well. Never an issue. We went to a hydro-boost unit from Jim at Hyda-tech with the new engine, because of low vacuum.

I also run the same unit from Jim at Hydra-tech on my 76 T/A with stock rotors and calipers. Disc/Drum setup. I use a 1-1/8" M/C. The hydra-boost unit will look up all four wheels. It's incredible the stopping power.

[Formulajones]

Originally Posted by vertigto

Long story short, the shop installed a Right Stuff 4 disc big brake conversion kit on my 70 GTO that will not adequately stop the car (will not lock up). Right Stuff sent a 7/8" bore master cylinder and installed performance pads that helped a little in stopping distance, but didn't solve the problem. FWIW...original 400 newly rebuilt (30 over) with mild cam pulling 15' at idle. Should have enough vacuum, but whatever.

Last resort is to try http://"https://rpui.com/-The-Right-... kit (HBUK001).

Unfortunately, the hoses included in the kit are backordered and they can't provide an accurate date. This is the last part/issue to complete the restoration, so a little impatient and not wantingto wait indefinitely.

So...looking for recommendations/other hydroboost kits to use with the rest of my Right Stuff brake kit/installation. I see CPP sells their own version and even sells two hose kits separately (braided or rubber), but not sure if compatible with what I already have from Right Stuff.

Any experience with other hydroboost kits that you would recommend? Any help/advice would be greatly appreciated. FWIW...not interested in trying vacuum cans or pumps, just want to do this right and finish/drive the car.

<Frustrated in NC>

As far as your hose question goes, I never use the supplied hoses in the hydroboost kits. I always have them custom made to the lengths I want and run the hoses behind the fender so they are hidden. In fact the best way I've found rather than trying to have someone crimp fittings and hope you have them clocked correctly, is to use the screw together fittings and assemble them exactly the way I need it. They go together much like AN lines. This is what is usually supplied in most hydroboost kits, CPP being one of them, they just don't supply long enough hoses, and the hose you can get just about anywhere locally. I have 3 choices just in the small town I live in. Even Napa sells it and will make it if you wish.

[Formulajones]

Originally Posted by Lemans64

Just another question here, Why is it that some people opt for the improved Bigger braking system when the original system is very good?
Was there a Problem with the original system or just figured the upgrade would be nice? As noted above my 64 has 69-72 GM factory calipers and drums
and stops very well, if not wearing seat one could hurt themselves. Sounds as though Right Stuff my have got it WRONG in the development part??

I've never really jumped on that bandwagon either. I've found the factory disc/drum power brake setup to work exceptionally well, and we continue to daily drive stuff just like that to this day. In fact they have no issue at all overpowering the tires in a hard brake situation and that's really what it boils down to. And I'm talking tires that are slightly bigger than stock. If you're already overpowering the tires, bigger brakes aren't going to do anything for you accept overpower the tires even more. Besides that, I don't like much of anything over a 15" wheel on my muscle cars anyway, so big brakes aren't going to fit.

Now if you're into road racing and/or run some sort of fancy low profile super wide sticky tires then that's a different story.

[Scarebird]

Originally Posted by chuckies76ta

...My understanding is that with Disc brakes you need a 1-1/8" Master cylinder.

There is a lot of wrong here to unpack! We'll start with this - power GM units up to the late 70's used the 1-1/8" bore commonly, other than stuff like Vegas, Skyhawks, etc.

Ford and Mopar both used 1" or less. Mopar was really smart and used the same master for both power and manual: just had a nice deep pocket in the master piston for the 2 push rods.

Originally Posted by chuckies76ta

You also need a Proportional valve that is designed for Disc/Disc brakes.

Not true either - a simple adjustable prop valve will work well, the dirt track guys use them exclusively and dial them in during races for track conditions.

Originally Posted by chuckies76ta

Other issue I can think of maybe your brake line size to the rear brakes is designed for drum brakes.

Irrelevant - certainly not giving the OP his issues.

Originally Posted by chuckies76ta

The 7/8" bore master cylinder is not gonna have enough fluid to apply brakes properly with a disc/disc system.

Depends on the number and size of the caliper piston bores. Fairmont 7/8's works quite nicely with our 1961-63 Tempest kit which use a single 2-1/2" caliper per side.

Originally Posted by chuckies76ta

The Disc calipers use a large amount of fluid because of there size, hence the larger M/C. bore. The other issue maybe you current Brake booster unit.

Again, not true. Caliper pistons are much bigger, but they move very little compared to wheel cylinders on drums. As a test we swapped a 69-72 "A" kit onto a local 4 drum 1968 Firebird. Manual master, distribution block, lines remained the same drum stuff: car performed perfectly with no changes. Excellent pedal and balance.

Originally Posted by chuckies76ta

I read it's a 9" single diagram, which in my opinion is too small. (As was mentioned) The dual 9" or even the 11" booster would be much better.

The link the OP provided shows a dual 7"; a shameful trade habit of one size fits none. A dual 9" will help but not fix a gross hydraulic mismatch. I would wager his master bore is 1-1/8" too, adding more misery to the mix.

[vertigto]

Just remembered that I should have the 11" OEM replacement booster that was on the car when I bought it for the original disc/drum setup. Looked like it was recently replaced and in good condition.

[chuckies76ta]

Well, Scarbird I know you know alot more about brakes than I do. I tried 1" bore master cylinder, new 11" brake booster on my 76 T/A, even changed the Combination valve and had no luck. Went to the hydra-boost brake setup and never looked back.
Anyway, was trying to help the O/P with his braking system. I'm done.

[bawdgoat]

I currently run a 1-1/8" with a disc/disc master/proportional valve. 91 Camaro 1LE (D52?) front calipers and 04 Cadillac CTS rear calipers. The car stops exceptionally well.

Moved to this master from a 7/8" due to excessive pedal travel when first getting it going. Never drove the car with that setup as it didn't feel right so can't testify to if the braking was poor or not.

Ran the system for 4 years like that with a "tee" for the return lines and it was fine.

Just converted to a dedicated return and a new Tuff Stuff 1300psi pump. Cannot confirm what the previous pumps pressure was, but it was lower (from examining the difference between relief valves) and the system still performed quite well.

I would be looking at your master and proportional valve setup if you aren't seeing the braking performance desired. Also recall having to watch for some calipers as they withdrew (to prevent drag) and needed a lot more fluid movement to get them back to contact with the rotor.

[Scarebird]

Chuckie: this is NOT personal, but simply trying to knock down some of the myths promoted that are not true and constantly promoted as fact.

[chuckies76ta]

Originally Posted by Scarebird

Chuckie: this is NOT personal, but simply trying to knock down some of the myths promoted that are not true and constantly promoted as fact.

No worries. I very much value your input. All good here. Thank you.

[vertigto]

Originally Posted by Lemans64

I used Hydratech booster, they sell a hose kit that is braided, But I made my own with kits from Russell Hose.
Also used their fittings. Isn't the power system supposed to use a 1 1/8th master? My 64 stops on a dime, stock 69-72 GM disc in front
and stock 64 drum in rear. Make sure you wear your seat belt the first time you drive it. I am using a 1- 1/8th wilwood master.

http://www.hydratechbraking.com/GM_A_Body.html

Thanks for the info. A little pricey, but looks to be worth it, especially from your description. Anybody else?

Also, keep the troubleshooting tips coming...