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In a nutshell, you may or may not need a proportioning valve. They aren't linear -- they don't just reduce pressure by 25%. They reduce pressure proportionately -- on light braking they don't reduce it at all, but on sudden hard braking they close and reduce it by the percentage they are set at.
Exactly. There's a "knee" where pressure to the rear brakes starts to increase at a slower rate, or even levels off, depending on the design.
 

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What kind of money are you talking for Hydroboost???
It's a little pricey. You'll pay around $800 +/- for a full kit, but if safety is a concern. I was like you, the brakes stopped the vehicle OK, but I couldn't lock up the wheels. If I can't lock up the wheels, and I do not have ABS, I'm leaving braking power on the table. That is something I did not wish to do. The system uses the power steering pump to add boost to the brakes. No vacuum involved, so cams and other vacuum eating modifications are no longer a factor in stopping power. But it is kinda pricey.
 

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Hydroboost is great, as long as you already have power steering. The PS pump also powers the brakes. All Hydroboost types I know of have an accumulator that stores enough pressure for a couple good applications of the brakes if you loose power steering -- enough to pull off the side of the road safely if the PS pump goes out or a hose brakes. If you notice suddenly hard steering you better stop!

You can junkyard a Hydroboost from many different cars and trucks. Mostly diesel powered vehicles, but because it takes up less firewall space many large cars used a hydroboost system... using the name to describe any hydraulically boosted power brakes (using PS pump).

I comnplete kit is around $800, but a rebuilt GM Hydroboost unit can be found for under $200, minus master cylinder (which is a standard power brake unit). Mounts to the firewall pretty much like a vac booster. Plumbing to the hydoboost isn't that bad. The GM Hydroboost has a splitter built into the base. Most run from the PS pump to the Hydroboost, then from the Hydroboost to the PS box/rack. There are separate return lines. The return from the Hydroboost is added with a T in the low pressure return line from the PS box/rack, usually near the reservoir.
 
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Buy a entire hydroboost off a 1 ton chevy. Or build a system with that as a parts list. Eliminates alot of guess work. In 88 they went to a serpentine setup. 87 has a v belt/5 rib belt. 86 and earlier all used v belts.

The hydroboost does not care about ABS till around 2008. So if you buy a cheap (non moving/hit) truck you can part/scrap it out getting a hydroboost cheap that way.

Several vans also had hydroboost with remote resiviors.
 

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I think your master is to large.

Not knowing the ratio is a shot in the dark. But a smaller master yeilds higher pressures and should provide better stopping power with more pedal travel as the trade off.

You may also be able to find a smaller bore caliper that still fits in the bracket to adjust the braking that way.

Personally I would rather change 1 master then see how it feels before reducing the caliper bore.
You would have to increase the caliper piston bore size to increase braking force. Basic hydraulics 101. A smaller master cylinder bore will give dramatic increase in braking force with no increase in pedal force required. Four wheel disc brakes require very little pedal travel.
 

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You would have to increase the caliper piston bore size to increase braking force. Basic hydraulics 101. A smaller master cylinder bore will give dramatic increase in braking force with no increase in pedal force required. Four wheel disc brakes require very little pedal travel.
I discovered this^^ almost by accident being a cheap ass lol. It's very popular to believe all of what can be found on larger rotors, larger pad surface area and multiple piston calipers. Of the 3 I referenced, I've become a firm believer that more piston area is the most important factor for increasing brake effectiveness. Of course there is a limit to this also. It's obvious that a 15 or 16" rotor is going to be more effective than a 9" rotor. But the difference between a 10" rotor and 12 or 13" rotor is not as important as a larger caliper piston area.

I'm basing all of my opinion on G-bodies. My son started with a stock brake/drum setup. He went to a larger front rotor and 2 piston S10 caliper. It was better. Then went to a C6 front caliper and rotor setup and it was better yet. Then swapped the stock drums to a Seville rear disc setup and it was amazing after getting a properly matched master cylinder. He runs 26" - 26.5" tires. The final setup was very well balanced as described by Farna's testing method. It made it stop like a modern car from 120-130mph. But this setup is not cheap.

I took the cheap approach (as always lol). Stock brakes at 125mph on the drag strip left stripes in my britches. I swapped to an 8.8 rear and used the Explorer disc setup and it helped, but I still had some hair raising moments as I approached 135mph. I swapped out the fronts to an Afco oversized caliper (58mm) and it made a world of difference. No more panicking on shorter tracks. I ended up converting to manual brakes and at the same time installed a set of EBC Yellow Stuff pads on the fronts - it's almost like my son's car when climbing on the brakes at full speed of 140ish. And that's with a stock G-body metric rotor up front.

The EBC Yellow stuff pads are truly nuts. They work great in my application, but they are not very acceptable for street use because of the required heat needed to get them working.


In summary, I'd recommend the oversized calipers to anyone. They were $50 apiece from the local circle track shop and they were the single largest improvement in the system. Take this for what it's worth.
 

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Discussion Starter · #31 ·
Well all I continue to have brake issues... If I had it to do over again I would have just installed a dual master cylinder and booster.

After more testing with booster connected and disconnected I still can't stop this car quickly enough in a panic stop. I measured the master cylinder bore again and it's 1.125" and according to the tech guy the kit I have is supposed to use a 1" master cylinder. That being said they are sending me a replacement.

I'm tired of waiting to see if it's a hydraulic issue so tonight I stopped and bought a 1969 Corvette master cylinder and it is just under a 1" bore. I will try to put it on in a day or two.

I will say after putting on the vacuum pump I can almost get the rears to lock up. My rear tires are almost 10" in width and fronts are 8".

This whole system is based on the 79 Eldorado and the surface area of the pads also looks very small to stop a 3,800 cruise vessel like my Impala yet other people say their brakes work great.

Time will tell I guess. I will post more info asap.

Thanks all.
 

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Hang in there my friend. I suspect the replacement m/c will help. I threw out my LMC m/c and booster and purchased a Camaro rebuild m/c and booster for my F100, not perfect but boy at least I can stop now. This kit stuff, I feel is not worth the risk to spend in the hope that it will work.

I like large diameter double diaphram boosters and 1" bore m/c's and that forms a basis for a potentially a good out come in the brakes dept...
Oh and drum at the rear for me all day long.
Call me old fashioned but I stick to the recipe that works and is cost effective...
 

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Discussion Starter · #33 ·
I hope to get at it again tomorrow. I pulled the kit master cylinder off today. I'll install the 1" master cylinder and hope it doesn't drastically change the pedal travel. I'm pretty certain the kit master cylinder is bad. I say this because when the vacuum pump is running at 20" of vacuum... I can push the brake pedal to where it's firms up and then if I continue to hold the brake it will creep on down to the floor. So I believe it's letting fluid by the seals.

When this happens I also got under the car and checked every line, fitting and caliper for leaks and found no problems.

I read all the info. about hydro boost systems and it would be a real pain to install on a 64 Impala. They do work well but frankly with good vacuum and a well engineered kit you shouldn't need it.
 

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Discussion Starter · #34 ·
UPDATE for all- my new replacement master cylinder arrived from the vendor today. I will have say they have been good to work with I just wish the system they sell would have been better thought out, so to speak.

I installed the master cylinder and immediately noticed an improvement in the firmness of the pedal. So I connected the vacuum booster to manifold vacuum just to give it a try. The 409 with the solid cam is pulling about 12. 5 to 13 in. of vacuum.

Much to my surprise the brakes worked much better but not what I would say was perfect. I layed into the pedal normally a few times and wow it pulled the car down pretty good. So I did a panic stop at around 40 mph and noted a huge improvement. First time the passenger seat back ever flew forward in this boat.

I went back to the the shop and checked my rotor temperatures and it was consistent around 125 to 140 at all 4-wheels. Next I bled the system one more time.

Then I disconnected the manifold vacuum and connected the vacuum pump directly to the the booster check valve. I turned on the pump and used a gauge to test and found the pump is pulling between 20 and 25 in of vacuum while I was pumping the pedel.

I went out for another drive on a 40 degree country road and everything improved even MORE. The car slows quickly now at highway speeds and if I panic stop at 40 mph the wheels don't lock completely but all of them just start to skid with the back skidding just a little bit more than the front. It also stop straight as an arrow.

I guess I'm okay with it now but dang it was a pain. Now I have to decide just how much I want to run the vacuum pump, so do I run it constantly or install a vacuum can and vacuum switch to come on at a preferred vacuum signal?


Thanks all hope every one had a good Thanksgiving.
 

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Congrats, it is always nice to read a strory with a successful outcome. You call on the final vacuum adjustments. I'd be more annoyed with the rear brakes wanting to lock first. That can be deadly in a crisis situation...
 

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Discussion Starter · #36 ·
I think the rear being more aggressive is my very tired front coil springs.... and weight transfer.

My next project is coilovers on all 4 corners. I actually think that will solve the problem.

I will start a new thread on that project.
 

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Say you triggered the pump using wiring like this: brake light switch -> relay -> pump. Would vacuum get down to around 18"hg fast enough to do any good? Or would it take several seconds or longer?

Also, you might want to look at more aggressive brake pad material. If your calipers use D52 pads, you might try Wilwood pads with their BP-10 compound which has better bite than most OEM-type pad material, but doesn't need a lot of heat to start working..
 

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Discussion Starter · #39 ·
The pump I have hits 25" of vacuum pretty quick but I really don't want the pump running all the time. If I don't have too. My thought was to use a vacuum switch, that triggers the pump at anything less than 18".

Honestly I wasnt aware of special compound pads for street use but I will certainly check on it too.

Thanks.
 
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