A few brake questions...

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To this point my 79 g-body brake system is stock. I'm running a mostly stock 5.3 from a 2000 Tahoe and brakes from LS F-bodies converted on my drop spindles using g-body rotors cut down as hubs and some conversion brackets I already have. Out back is an original drum brake 9" Ford being converted to disc. I have the ability to make any custom brackets I need at school.

I've always run stock brakes on all my cars so conversions are new to me. Any input is helpful.


1. I need to buy calipers. The F-bod front ones are just a few bucks more than the rear and are dual piston compared to single on the rears. Anything inherently wrong (or stupid) with running front dual piston calipers on all four wheels?

2. Speedway Motors sells both braided and kevlar brake lines for g-body calipers for cheap cheap. To use their hoses you have to buy hose fittings for the calipers instead of using banjo fittings. Would the early g-body calipers have the same thread as the f-bod?

3. The price comparison is minimal difference. Kevlar is bullet proof, does that mean they'd be better brake hoses too?

4. I think there is a g-body at the local wrecking yard with hydroboost, I'm going Friday to check. There are also plenty of Astro vans too, which seems to be the popular swap. The g-body would be a direct bolt in, Astro requires some fab work. Is there a difference between the two making the newer Astro a better booster?

5. Is the Tahoe power steering pump compatible with both of these HB units?

6. I'm relocating brake hard lines for a cleaner look and to get them plenty clear of the header heat. In the process I had planned on getting a dial type single line proportioning valve like the Speedway or Willwood unit. I'd imagine there is some tuning involved so I thought I'd purchase a brake pressure gauge. I see in Speedway's catalog they have dual gauge kits. Should I have two gauges to compare front to rear? Or is that an unnecessary waste?

7. I was thinking of running a master cylinder for a late 90's Caprice wagon/ Police/ Impala SS with 4 wheel disc option, 1 1/8 bore. Something else I should use instead?

Thanks!

[Apogee]

I'll post my responses in blue below. Tobin @ KORE3


To this point my 79 g-body brake system is stock. I'm running a mostly stock 5.3 from a 2000 Tahoe and brakes from LS F-bodies converted on my drop spindles using g-body rotors cut down as hubs and some conversion brackets I already have. Out back is an original drum brake 9" Ford being converted to disc. I have the ability to make any custom brackets I need at school.

I've always run stock brakes on all my cars so conversions are new to me. Any input is helpful.


1. I need to buy calipers. The F-bod front ones are just a few bucks more than the rear and are dual piston compared to single on the rears. Anything inherently wrong (or stupid) with running front dual piston calipers on all four wheels? Yes, there are several inherent issues with running front calipers in the rear, first and foremost is your front to rear brake bias. Your front brakes typically provide about 70% of your overall braking, so the components are sized accordingly. Running proportionally larger rear calipers increases your rear brake bias and increases the likelihood of premature rear brake lockup. There are ways to mask the inherent issue of building a brake kit with unbalanced components, but unless you were planning on running dual master cylinders with a balance beam and incurring the associated costs, it isn't really worth discussing here.

2. Speedway Motors sells both braided and kevlar brake lines for g-body calipers for cheap cheap. To use their hoses you have to buy hose fittings for the calipers instead of using banjo fittings. Would the early g-body calipers have the same thread as the f-bod? Both calipers require banjo fittings...whether they're swaged to the hose assembly or an AN adapter fitting, they're still banjo fittings. The 98-02 F-body calipers have M10x1.0 inlet ports whereas the 1978-1988 G-body calipers are M10x1.5, so no, they're not the same.


3. The price comparison is minimal difference. Kevlar is bullet proof, does that mean they'd be better brake hoses too? The inner arimid fiber (Kevlar) braided sleeve around the PTFE Teflon tube results in a firmer hose with less compliance under pressure, so it is arguably better than a hose without it. The only downside I know of is that it typically increases the minimum acceptable bend radius.


4. I think there is a g-body at the local wrecking yard with hydroboost, I'm going Friday to check. There are also plenty of Astro vans too, which seems to be the popular swap. The g-body would be a direct bolt in, Astro requires some fab work. Is there a difference between the two making the newer Astro a better booster? The G-body "hydroboost" units were electric over hydraulic units, meaning they used a separate electric pump to power the booster. These were notoriously expensive to repair/replace and somewhat unreliable in my experience. The Astro hydroboost unit is a more conventional design that uses pressure from the power steering pump like most modern HB applications.


5. Is the Tahoe power steering pump compatible with both of these HB units? Yes, so long as it is plumbed correctly.


6. I'm relocating brake hard lines for a cleaner look and to get them plenty clear of the header heat. In the process I had planned on getting a dial type single line proportioning valve like the Speedway or Willwood unit. I'd imagine there is some tuning involved so I thought I'd purchase a brake pressure gauge. I see in Speedway's catalog they have dual gauge kits. Should I have two gauges to compare front to rear? Or is that an unnecessary waste? Most of the tuning with the 11-turn infinitely adjustable proportioning valves (APVs) is seat of the pants, performance based and not something that a brake pressure guage will necessarily help with. Guages can be extremely helpful in debugging and troubleshooting, but I don't typically get the guages out to set the APV. It's also worth noting that an APV is really meant for fine tuning a brake system, not correcting for major componets mismatches as you're limited in terms of what you can accomplish with an APV. If your APV is maxed out to either extreme (full open or full closed), then you could probably benefit greatly by reworking/rethinking either your front brakes, rear brakes or both.


7. I was thinking of running a master cylinder for a late 90's Caprice wagon/ Police/ Impala SS with 4 wheel disc option, 1 1/8 bore. Something else I should use instead? You should choose your master cylinder based primarily on your caliper piston areas, booster gain levels and pad CoF.


Thanks!

[Hydratech®]

The '81-'85 G cars did have PS driven hydroboost on some of the diesel models, though they were the highly inferior internal accumulator models that were quickly put out of production (only used from '80-'85 then QUICKLY put out of production per problematic design flaws). While the G body system will bolt into the firewall, it CANNOT be use with a vacuum spec brake pedal = you will be doing mods to graft this unit into your '79 G car. On the other hand, the Astro units are a highly superior design to the early G car units, as they have the EXTERNAL ACCUMULATOR design - the problem is that that these units will not bolt into the G cars without mods either. The '93-'94 units have the correct firewall bolt pattern, but the brake pedal rod specs are incompatible requiring further fabrication on the DIY level...

If you want no muss / no fuss / direct plug n play bolt in, OR just want to pick his brain for tech, call our guy Jim Petty to discuss: http://www.hydratechbraking.com/contact.html

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Paul- Thanks! Good info, pm sent.

Tobin- Man, thanks a lot! You mentioned things I never thought of. You also created more questions. :naughty:

In response to answer...

2.- Thanks for clarifying. When I saw the photos in the catalog, I saw the hoses with AN fittings on both ends. I assumed they sold adapters to take the place of the banjos, but I went back and saw that they sell banjos with an style ends on them. I will be going ordering the steel braided lines, 2 new banjos with an ends, and the M10-1.0 banjo bolts. Thanks again for pointing me straight on that.

4. Great info! I scoured the junk yard today to see what was there, I found a few Astros, one in particular looked well maintained inside and had the cleanest engine bay. I will probably go back in the next couple of days to grab it for $25. I noticed the lines come out of the top and the emergency reservoir is on the passenger side. Most conversions seem just the opposite. Are those conversion installations simply rotating the pump 180 deg.?

6.- Seems I've read that discs require less pressure than drums, so if I use my factory prop valve there may be too much pressure directed to the now rear discs increasing lockup. So in using the APV is it then wise to put it the rear line between the master and prop valve, then effectively turn down the pressure?

7. Lol! I'm a designer not an engineer! ;) I had to look up the acronym CoF but I couldn't find anything related to brakes. So in theory I would imagine an LS F-body master would be the ideal one to use? I wonder if that would bolt to an Astro boost pump? They're fairly pricey for my budget, can I save the $ for something else and simply use my 1 1/8" bore G-body master and be o.k.?

[cheapthrillz]

I'm a designer not an engineer! ;) I had to look up the acronym CoF but I couldn't find anything related to brakes. So in theory I would imagine an LS F-body master would be the ideal one to use? I wonder if that would bolt to an Astro boost pump? They're fairly pricey for my budget, can I save the $ for something else and simply use my 1 1/8" bore G-body master and be o.k.?

CoF just mean Coefficient of Friction...

[cheapthrillz]

http://www.jakelatham.com/radical/info/brake_calculators.shtml

See if you can use step 3 on this site.... might help some

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Thanks JC. I'll have to play with that some.

[Apogee]

...4. Great info! I scoured the junk yard today to see what was there, I found a few Astros, one in particular looked well maintained inside and had the cleanest engine bay. I will probably go back in the next couple of days to grab it for $25. I noticed the lines come out of the top and the emergency reservoir is on the passenger side. Most conversions seem just the opposite. Are those conversion installations simply rotating the pump 180 deg.?

6.- Seems I've read that discs require less pressure than drums, so if I use my factory prop valve there may be too much pressure directed to the now rear discs increasing lockup. So in using the APV is it then wise to put it the rear line between the master and prop valve, then effectively turn down the pressure?

7. Lol! I'm a designer not an engineer! ;) I had to look up the acronym CoF but I couldn't find anything related to brakes. So in theory I would imagine an LS F-body master would be the ideal one to use? I wonder if that would bolt to an Astro boost pump? They're fairly pricey for my budget, can I save the $ for something else and simply use my 1 1/8" bore G-body master and be o.k.?

4. The orientation of the hydroboost unit is determined by the application it came from, however I've seen many Astro units rotated for better hose routing and clearance and never heard of any issues, although it would probably be wise to relocate the weep groove to the bottom of the mounting flange so that leaks are readily apparent should they occur.

6. Discs actually require more pressure than drums for the most part due to the self-energizing servo action of drum brake shoes in operation. Drum brake torque increases at a rising rate relative to input pressure whereas brake torque on a disc application rises at a constant rate linear with the brake pressure. Running a disc/disc system with a disc/drum proportioning valve typically results in the rear calipers getting too little pressure, thereby not contributing as much braking to the overall equation as they could if they were properly set up. Proportioning valves should only be used in a rear brake circuit, never in the front, so yes, it would be wise to put the APV somewhere between the master cylinder and the rear center hose where it splits to the rear calipers.

7. Sorry...JC answered the CoF question. The 98-01 LS1 F-body master cylinder is a 1" bore unit and came mounted to a dual-9" diaphragm vacuum booster. Using this master cylinder on an Astro type HB will give you an on/off brake pedal feel, hence most people running 1-1/8" bore master cylinders with their HB kits and comparable caliper piston areas to yours. As for your G-body master cylinder, I wasn't aware that their was a 1-1/8" option that year/make/model.

Tobin
KORE3

[Apogee]

...The '81-'85 G cars did have PS driven hydroboost on some of the diesel models, though they were the highly inferior internal accumulator models that were quickly put out of production (only used from '80-'85 then QUICKLY put out of production per problematic design flaws)....

Paul, thanks for the correction, I had totally forgotten about the internal accumulator hydroboost units...and for good reason.

Tobin
KORE3

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Thanks again Tobin! Good call, my '79 Cutlass vac booster came with a small bore master, I didn't even bother measuring it. I grabbed another vac booster from the junkyard, can't remember if it was a Regal or another Cutlass, either way it was an 82+ vintage with a 1 1/8 master if I measured it right. Doesn't matter either way as I'll be using the Astro hydroboost now instead of that vac booster.

Just wanted to verify what you're saying- The APV should take the place of the proportioning valve for the rear brakes, i.e to avoid re-plumbing the whole (front and rear) system I can merely set up the rear system so it bypasses the factory valve and the APV will control the rear brake bias. Correct?

This is all great info, I'm learning each time I come back to the thread. Your help is really appreciated.

[Apogee]

...Just wanted to verify what you're saying- The APV should take the place of the proportioning valve for the rear brakes, i.e to avoid re-plumbing the whole (front and rear) system I can merely set up the rear system so it bypasses the factory valve and the APV will control the rear brake bias. Correct?...

Yes, you are correct. Depending on the valve, you can either gut it and use it like a distribution block or just bypass it altogether and run through an inline adjustable proportioning valve. What you don't want are two proportioning valves in any given circuit as the results are far from predictable.

Happy to help,
Tobin
KORE3

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Again, thanks for the info Tobin. I hope this has helped some other folks that are new to modifying brakes too.