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  #11  
Old 01-30-2006, 04:37 PM
Doc Doc is offline
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Default Re: The Final Word on front disc brakes

Dave,

Tires are a little different than brakes. The reason is that tire contact isn't strictly limited to friction alone. There is the "stickiness" of the rubber, and also the fact that the rubber is soft and conforms to the rough road surface. Friction does not account for this kind of behavior. Consequently, larger tires have some non-friction advantages. (They also have better heat handling characteristics). Don't forget that one of the major advantages of drag tires is not just the size, but also the wrinklewall design.


Back to brakes: Personally, I would not use the BAER kits. This is because in my opinion they are dreadfully expensive. I admit that I have not used them personally, but I simply cannot see that their braking performance would be THAT good.

A few things to consider, assuming that your brake system is properly bled, etc.

1. Generally, softer pads (organics) give better braking than some of the long-wearing pad designs. I would consider using a soft pad, or a pad specifically designed for performance braking. You probably won't find the latter at a typical auto parts store. Try Summit.

2. Make sure you have a check valve in the vacuum hose that goes to your power booster.

3. If you are going to consider upgrade parts:

I would first try using the US Brake or Wilwood OEM style but oversize calipers. They are quite inexpensive, and will yield a solid 20% in clamping force. That's probably your best bang for the buck.

If that's not good enough, then I would consider the Wilwood kit if you want an "easy to do" swap. Everything is in the kit, and it should be far less expensive than the Baer kit. If you'd rather take a more hands-on approach, then I'd go with the 12" swap using GM parts, while utlizing the oversize OEM style calipers mentioned above.

4. Don't forget about your rear brakes. You can always swap in larger pistons back there as well.
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  #12  
Old 01-31-2006, 08:22 PM
Dave Burchfiel Dave Burchfiel is offline
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Default Re: The Final Word on front disc brakes

Doc, thanks for the input. I have the check valve and the brakes are properly bled etc. I've been doing a lot of research on this site and others.
and I've found I'm not the only one who has converted to vacuum brakes who's still having problems. The following is a post and reply from Hydratech. I've ordered a hydraboost unit (not cheap) and I'll let everyone know the results when it's installed. Probably be a few weeks. Even if it performs as advertised I'll be upgrading to 12" front and putting discs on the rear sometime in the future.

I have a Buick GN that has terrible brakes. I converted from the powermaster to vacuum brakes about 14 years ago. I'm running 16x8" wheels with 245/50 tires. I have three problems; the first was present with the powermaster and that is no matter what I can't lock the brakes. the 2nd and third are only with the vacuum conversion. The pedal travels a long way before the brakes even start to engage and on occasion, usually when the car is cold the brakes have no power assist at all and standing on the brakes with both feet barely stops the car from a slow roll.
I've changed the master cylinder three times and the booster twice. The vacuum canister doesn't leak, the lines are all good and have been replaced several times. I'm stumped. Could the combination valve be causing some of the problems. I guess the master cylinder has a "quick take up spool" (not sure what that is) but I think it stops the front brakes from applying before the rear drums have begun to engage. The master is from a 1987 Monte Carlo SS. The rest of the brakes are stock except for semi-metalic pads and soft compound shoes.

I'm pretty certain i'm going to convert to hydraboost. Will this take care of my problems? Do I need a different master cylinder? I'm eventually converting to Baer brakes. 13" front 12" rear. Are thera any special considerations for the hydraboost kit with that setup?

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Posted: Mon Jan 30, 2006 12:02 pm Post subject:

--------------------------------------------------------------------------------

Hi Dave - Yes, our GN systems will definitely knock your socks off with the power that they can produce! (guaranteed in writing or your money back in full). These systems are also totally consistent, with the same brake response at all times - whether it's cold or hot, whether you're running ten mph or 120 mph. Reliability is also second to none, which is why GM has decided to start installing these types of systems on most all of their truck lineup these days.

It sounds like your vac setup isn't running all that well due to the SFI Turbo V6 not particularly pulling enough vacuum, especially when cold. The factory G-body QTU (quick take up) design 3 piston master cylinders are pesky, as the valving inside usually doesn't work right - this could also be a factor in your situation. I am actually currently running a dead stock '86 442 (55k original miles), and have installed one of our hydraulic brake assist systems in this vehicle, (what a difference in braking with no other changes!), to find that I can't wait to get rid of the stock QTU design mc. Depending on just how fast and hard you hit the brakes, the pesky QTU design MC will just simply drive me nuts in use per inconsistent braking actions. I have swapped out the MC with a brand new AC Delco unit in thinking that maybe the original MC was tired, just to find that there was no improvement = I now recommend against the use of these types of master cylinders, as the idea seemed to be great "on paper", though just doesn't seem to really work properly in actual use. GM has also discontinued use of these types of MC's in many various applications (where they were used for years), apparently for the same reasons why I don't like these things. My experience tells me that your MC is most likely suffering an internal check valve problem, to where the QTU function isn't working correctly to cause your low pedal complaints. The idea behind these designs is this: When you first hit the brakes, the high volume oversized rearmost piston is *supposed* to take up any slack in the system first, then a check valve kicks in to shut off the QTU function and then follow through with the forward two conventional smaller MC pistons to produce the pressures the brakes need. As you can imagine, this action is subject to various little metering / check valves inside of this type of MC working properly, which can malfunction with even the slightest little piece of dirt or wear. If the internal valves aren't working correctly, you can experience so many different problems that it would even be quite a challenge to list all the possible symptoms. Again, this is exactly why I don't like these designs, and generally recommend against their use...

QUOTE: I'm pretty certain i'm going to convert to hydraboost. Will this take care of my problems?

REPLY: YES - satisfaction guaranteed of your money back in full.

QUOTE: Do I need a different master cylinder?

REPLY: Yes - the QTU design oversized rear register of the '87 Monte SS MC (the rear part that actually fits into the booster) will not fit the "mouth" of the replacement hydraulic assist unit, so a conventional 2 piston design mc will be needed. We have bored the assist units open larger to fit the factory G body QTU MC's in testing, (like my 442), to find that even though we *can* make them fit, that we simply just out and out do not recommend the use of this type of MC. To that end, there are quite a few various factory type of MC's and a host of aftermarket MC's that you could consider installing (as the assist unit is designed to accept most all '77 and newer design GM non-QTU power brake master cylinders - you could even use a '96-'02 Z-28 or '97-'02 C5 Corvette plastic / aluminum if you wanted to). The target bore size should be 1 1/8", though the 1" bore versions will work OK too.

QUOTE: I'm eventually converting to Baer brakes. 13" front 12" rear. Are thera any special considerations for the hydraboost kit with that setup?

REPLY: Even though the booster is hydraulic, all of the usual conventional wisdoms still apply from the MC forward. To that end, there really isn't anything you would particularly have to do differently because of having a hydraulic brake assist unit (as opposed to a vac booster).
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Last edited by Dave Burchfiel; 01-31-2006 at 08:26 PM.
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  #13  
Old 03-01-2008, 07:31 PM
POWERBRAKEBOB POWERBRAKEBOB is offline
 
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Default Re: The Final Word on front disc brakes

Interesting to see that all those High Perf calipers always show less stopping power over stock. The real problem with the g.N. is that weak Powermaster booster system. Now, after 20 years the electric motor pumps are all failing. Those pumps had to use phenolic vanes inside to be able to run without galling, since brake fluid is not a high pressure lubricant. The other problem with the pumps, is when the seal leaks between the pump and the windings. When the elec. side fills with brake fluid, it shorts out. Buick never used the standard Regal vacuum booster on their supercharged cars. Vacuum boosters need vacuum, (20") and a 231 ci. motor with a turbo, cruising along in overdrive, has very little. The G.N. is a heavy fast car, and was built when G.M. was downsizing cars. They used all S10 brakes on the fast car. Not good. We have been converting the Powermasters to brand new Hydroboost units. They bolt right on, and use the same pedal as the powermaster. We use stainless braided hose to connect to hte pump, and box. The master is replaceable, easily, and we them in aluminum. Guys are reporting being able to hold up to 22lbs of boost, with their foot on the brake. The car stops like any new car, at any speed, with less rotor heat. Hydroboosts run off of the p/s pump, and need no vacuum, and no electricity. They can last up to 200,000 miles with just an occasional p/s fluid replacement.
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  #14  
Old 07-23-2008, 12:07 PM
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Default Re: The Final Word on front disc brakes

Quote:
Originally Posted by POWERBRAKEBOB
Vacuum boosters need vacuum, (20") and a 231 ci. motor with a turbo, cruising along in overdrive, has very little. The G.N. is a heavy fast car, and was built when G.M. was downsizing cars.
HB systems work but lets look at some basic facts here.

Explain why the vac brake system was factory equipped on the 89 Turbo Trans Am that had the SAME turbo V6 engine and 2004r OD trans as the GN / turbo regals????

Furthermore the TTA was used as a Pace car and was definitely in overdrive doing considerable speeds while performing this task and stopped just fine.

Last edited by Keller; 07-23-2008 at 01:55 PM. Reason: Fixed quotes and spelling
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  #15  
Old 07-23-2008, 02:07 PM
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Exclamation Re: The Final Word on front disc brakes

You may forget that the TTA had four wheel disc brakes, and their front rotors were larger than those of the G-body fronts. The 16" wheels were required to fit their rotors. The swept area is much larger than the TRs! The rear brakes on our cars are about as good as Fred Flintstone and his feet at high speed.

This is like comparing apples and cumquats. the 1LE package on the TTA is light years better than the 1960's era braking system (sans Powermaster) in the TRs.
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  #16  
Old 07-24-2008, 05:35 PM
turbofish38 turbofish38 is offline
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Default Re: The Final Word on front disc brakes

I never found PBBob to have much credibilty as far as any turbo'd car goes. Just check out his threads over on the other boards. As far as I'm concerned he is a gypsy selling snake oil.

I dont think the matter is so much the type of booster but the size and capacity of the brake system in general. I've done some wild stunts with the stock brakes on my 455 Regal and equally wierder things with the PM and vacuum brakes on the GN. I would say you're sitting good if you have a firm brake pedal and can lock up the fronts at will reguardless of the calipers and how sticky the tires are.

Funny thing how you never hear anyone complain about the lack of ABS on these cars. In other words, just like there is a technique to making our cars go fast there is also a technique to slowing them down....fast.
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  #17  
Old 07-24-2008, 07:49 PM
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Default Re: The Final Word on front disc brakes

Quote:
Originally Posted by Keller
You may forget that the TTA had four wheel disc brakes, and their front rotors were larger than those of the G-body fronts. The 16" wheels were required to fit their rotors. The swept area is much larger than the TRs! The rear brakes on our cars are about as good as Fred Flintstone and his feet at high speed.

This is like comparing apples and cumquats. the 1LE package on the TTA is light years better than the 1960's era braking system (sans Powermaster) in the TRs.
Lets not get confused here PB Bob is stating that the turbo V6 does not pull enough vac for the vac brakes to work properly.
The TTA with 1LE, larger disc, 4 discs or whatever is besides the point. And yes the brake torque from the larger rotors on the TTA is way better than the G Bodys not doubting that a bit and that fact never came under question or scrutiny....thats not the point!

Your saying that since the TTA had bigger rotors and the 1LE package is the reason the VAC brake system works on the TTA and you cant compare the 2 since the turbo regals brakes are 60's tech.
I guess the N/A engines in the GTA's and other equally brake equppied N/A powered TA's that pull vac more than the no vac pulling Turbo v6 stop 100 foot shorter than the TTA.
Its not a question of which car is better equipped from the factory brake wise i'm talking the engine ability to pull vac and the vac brakes ability to work.
I.e- PB Bob says the Turbo V6 doesnt have the vac to support a vac brake system.
I saying the TTA has it and if it would not pull enough vac I dont car if you had 14" brakes its not gonna stop properly.
My GN has the swap and I have not had one downside and can hold the exact same boost as with the PM. I have to admit i was nervous on the vac brakes ability tio hold boost but was pleasently surprised that it held the same amount.
MHO FWIW
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  #18  
Old 07-24-2008, 08:38 PM
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Lightbulb Re: The Final Word on front disc brakes

I believe the only issue where brake "holding" with the TR's is really at issue is at the line, where someone may be on the pedal for a long time. A good booster should be all you need to hold them awhile. Otherwise, they should do just as well as a Powermaster.
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  #19  
Old 07-26-2008, 09:13 PM
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Default Re: The Final Word on front disc brakes

Dave: Did you ever install the Hydraboost unit? The accumulator failed again on my Powermaster unit and I just can't see putting another $200 into it. I already have the B body spindles and the 1LE rotors. I also have the large wheel cylinders in the back, but would like to install rear disks also. My car tends to nosedive with the additional braking force up front. The Hydraboost costs much more that the vacuum assist, but seems to me that it would be more consistent. I don't mind spending more for a better system. We spend lots to make them go fast. I wanted to get an opinion from someone that has the Hydraboost to see if they are happy with it. Thanks for the info guys, this discussion has been interesting.
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Old 10-01-2009, 04:03 PM
joe_schindler joe_schindler is offline
 
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Default Re: The Final Word on front disc brakes

Sorry; Iíve not looked over here in a while. Other sites are linking back to this; so:

Quote:
Originally Posted by Doc View Post
As you can see from the other threads I've been doing a lot of thinking and research regarding front brake options. I decided to compile a list of some of the common options to aid in planning.

First off, DISCS. A larger disc is effectively a larger lever arm for the brakes to act against. I made a little table to compare the expected effectiveness of larger rotors. The brake pad rides towards the outside of the disc, but the force is spread over a wide band of contact, not just the outermost edge. In my calculations I assumed that the pad was 1.5" wide. Therefore the center of the pad (or 0.75" in from the edge of the disc) was where the force would be concentrated. This may not be 100% accurate but it should yield a good comparison as long as it is consistently applied.

Keep in mind that this chart is Disc properties ONLY:

Disc OD: Effective Radius: Theoretical improvement:

10" 4.25" 0% (OEM size)
11" 4.75" 12% (Standard B-body brakes; also used in some aftermarket kits)
12" 5.25" 24% (B-Body heavy duty rotor such as IROC or "police brakes"; also aftermarket kits offered by Baer, Wilwood, etc.)
13" 5.75" 35% (Largest aftermarket kit offered by BAER)
14" 6.25" 47% (Listed for custom purposes only)

....as you can see the trend is roughly 12% per inch.


Now for the calipers. The effectiveness of a caliper is based on the area of the piston(s). In the case of 4-piston calipers where there are two pistons on each side of the disc, only the area of one side of the caliper counts.

Caliper: Piston Dia & Count: Effective Area: Improvement:

Stock GN 1x 2.48" 4.8 sq. in. 0%
OEM- Oversize* 1x 2.75" 5.9 sq. in. 20%
Wilwood Dynalite 4x 1.75" 4.8 sq. in. 0%
S-10 Blazer 2x 40mm 3.9 sq. in. -19% (performance LOSS!)
PBR Caliper (Baer)** 2x 38mm 3.5 sq. in. -27% (again, LOSS!)

*"OEM-Oversize" is the OEM style aftermarket calipers such as those made by Wilwood and US Brakes. They are the same style as the stock GM calipers but they have a larger piston. These calipers would be a direct swap for factory GN calipers. This is also the same piston size as the "big brake" option for the B body GM cars. If you use the "Police Package" brakes from a Caprice those also have a single 2.75" piston. However, the B Body calipers are a different style than the GN caliper; to use the B body calipers you have to use B body spindles.


**The often lauded Camaro/Corvette calipers are also 2x 38mm like the PBR, etc.


The Caliper info is interesting because it seems that the only real upgrade to be had here is the OEM style oversize calipers. That's interesting becasue they are among the most inexpensive as well.

These numbers are multiplied together when considering a full conversion. So, some examples might be:

B body swap with IROC rotors and Police Package Calipers 1.24 x 1.20 = 49% improvement

Wilwood aftermarket kit (12" rotors and Dynalite caliper)= 1.24 x 1.00 = 24% improvement

10" Discs + Overize OEM style caliper such as the US Brake = 1.00 x 1.20 = 20% improvement

12" Discs + Blazer calipers = 1.24 x 0.81 = Almost no improvement

13" Discs + PBR calipers (Baer kit) = 1.35 x 0.73 = 2% LOSS! (Perhaps this is why Baer recommends swapping in a smaller bore master cylinder???)

Of course, this information is only part of the puzzle. Larger discs are also good for better cooling. So, even though the above example of the Baer kit would respond in a small LOSS in braking power, the 13" discs in that kit WOULD have much better fading resistance compared to stock. For autocross or road course driving they would be far superior to stock due to this.

Likewise, some calipers are stiffer than others. My comparison was of clamping pressure only. Perhaps some of the calipers are stiffer than others, which might offer a benefit that I did not take into account.
4 piston calipers donít work off of 2 pistons. You get the clamping force of all 4 pistons; not just 2. Otherwise; thereíd be little advantage to 4 piston calipers.

Rotor diameter does not help the braking system. Swept Area is what youíre looking for; and you usually get that from a larger rotor.
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