| Username | Post: Manual Brakes-Master Bore Size? (Topic#187599) |
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Winmon
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| 04-18-08 04:29 PM - Post#1414544
I have made to decision to swap out my power brakes for manual brakes due to low vaccum. Just seems like the easiest and cheapest way to go.
I have 4 piston Wilwood discs on the front with drums on the rear. Craig Morrison suggested I may need to increase to a 1' bore master cylinder to help the rear drums.
Anyone else running manual brakes with front discs and rear drums? What size master cylinder are you running?
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Rick_L
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| 04-18-08 04:51 PM - Post#1414549
In response to Winmon
Contrary to what your intuition tells you to do, if you switch from power to manual brakes, you need to DECREASE the master cylinder bore size if it was correct for the power brakes.
For instance, if you were using the typical GM calipers that a lot of us use, from either a Chevelle or a Malibu, you need a 1' bore for manual brakes and a 1-1/8' bore for power brakes.
I would call Wilwood or a dealer (Morrison probably is one). You need to match the master cylinder to the calipers you have.
Seems like Craig posted he was using a 7/8' master on the GT55. But his calipers may not be the same as yours.
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Chevyfanatic
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| 04-18-08 09:16 PM - Post#1414707
In response to Winmon
1'bore, no larger. You can use smaller but 1' will work great.
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MikeB
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| 04-19-08 04:13 AM - Post#1414790
In response to Winmon
My 55 has 10.5' GM metric discs in front and small drums from a 79 Malibu in back. I have a 1' MC that does a decent job, but requires lots of pedal pressure to even slightly squeal the tires. I could probably use 15/16' for a bit more force to the brakes. However, if I had 11' brakes and larger caliper pistons, I'm sure the 1' would be perfect.
If the pushrod has been lowered on your brake pedal, you will want to raise it up to the original hole for more mechanical leverage.
Oh, make sure to get a true manual MC with a deep pushrod bore.
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
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Winmon
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| 04-20-08 09:03 AM - Post#1415580
In response to MikeB
Thanks guys!
Bagged '62 Bel Air - 450hp LS2 - T56 - 9' Rear End
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zio7
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| 04-20-08 01:15 PM - Post#1415750
In response to Winmon
I am thinking I might need a new master for my car. I was wondering where you are purchasing yours from.
thanks
Tom
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Winmon
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| 04-20-08 01:57 PM - Post#1415771
In response to zio7
I think I am going with a Wilwood...
Bagged '62 Bel Air - 450hp LS2 - T56 - 9' Rear End
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zio7
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| 04-20-08 03:18 PM - Post#1415812
In response to Winmon
Do you know if that is a direct bolt up to our cars? Also do I need to run a proportioning valave with that? (front disk rear drum).
thanks
Tom
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Winmon
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| 04-20-08 07:16 PM - Post#1416003
In response to zio7
Tom. I am about to find out, right now I am not sure. I was told that I might need a proportioning valve, but that I would for sure need a #10 residual pressure valve for the rear and maybe a #2 residual pressure valve in front.
Bagged '62 Bel Air - 450hp LS2 - T56 - 9' Rear End
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MikeB
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| 04-21-08 12:34 PM - Post#1416539
In response to Winmon
IMO, you don't need a prop valve unless your rear brakes lock-up prematurely. This is a problem on un-loaded pickups in panic stops, but not necessarily on a passenger car with better weight distribution. Other variables also come into play, such as swept drum and rotor area, pad/shoe friction material type, etc. I have never understood how a one-size-fits-all prop valve can work for any application. You can always plumb in an adjustable valve and tune it for proper balance.
Some say it's a good idea to use a 10 psi residual valve in line with rear drums, and a 2 psi valve for front disc. But others say this is only necessary if the MC is lower than the wheel cylinders and calipers. However, I don't see how using them can hurt anything. The idea is to keep a little pressure on the wheel cylinders and calipers, thus reducing pedal travel when you hit the brakes.
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
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Edited by MikeB on 04-21-08 12:48 PM. Reason for edit: No reason given.
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leons57belair
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| 04-21-08 03:27 PM - Post#1416678
In response to MikeB
By keeping pressure applied to the brakes won't they drag slightly causing them to wear prematurely as well as a decrease in fuel economy from the constant drag?
| Black 57 Chevy Belair 2 door Sport Coupe. 350 engine, edelbrock performer rpm intake, 600 cfm edelbrock carb, K&N filter. Th350 trans. |
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zio7
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| 04-21-08 06:45 PM - Post#1416863
In response to leons57belair
Sorry for all the questions. Does anyone know of a 1' bore master that will work from another car? I really do not have the money for the wilwood right now, since I just bought a house.
thanks
Tom
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jk56chevy
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| 04-22-08 05:47 AM - Post#1417201
In response to Winmon
Winmon:
For what its worth, I am running the same setup as you are planning, manual brakes, 4 piston wilwoods up front, drums in the rear, wilwood master cylinder, 1 inch bore, wilwood prop valve, and a line lock. I am very happy with my set up. Good Luck with yours!
John
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MikeB
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| 04-22-08 06:43 AM - Post#1417252
In response to leons57belair
By keeping pressure applied to the brakes won't they drag slightly causing them to wear prematurely as well as a decrease in fuel economy from the constant drag?
I suspect 2 psi on the calipers piston won't make the pads drag. And 10 psi on the rear wheel cylinders is only enough to keep the springs from pulling the shoes too far away form the drums. In fact many OE drum brake MCs had a residual valve built in.
This is from an article by Dean Oshiro:
Residual Valves: Residual valves are pressure valve use to retain pressure in the lines. The most common use is on a hotrod when there is a floor mounted brake pedal and master cylinder. Mounting the master cylinder (M/C) below the floor positions it below the calipers. Gravity will cause the fluid to flow away from the calipers. The residual valve will retain pressure within the lines. (i.e. 2 pounds residual valve will retain 2 pounds of pressure, 10 pound will retain 10 pounds.) Drum brake master cylinders have residual valve(s) built into the master cylinder. This is needed to maintain pressure against the cup seals in the wheel cylinders. If you are using a disc brake master cylinder or after market you will need to install a 10 pound residual valve for the drum brakes. Do not install a residual valve if your master cylinder already has one in it. This will cause the brakes to lock up after the second application to the brake pedal.
Distribution Blocks or Combination Valves: One of the biggest misconceptions is the distribution block or combination valve. Almost every factory car has one. This usually serves as a metering block to adjust the proportioning to the rear brakes, as a 'T' fitting for your front left and right front brake lines and brake light warning switch. What people fail to understand is that each car is 'engineering' for a specific distribution block based on weight, braking characteristics and tires. So generally most factory cars have different blocks.
Ask yourself this. How can one distribution block be engineered for all applications? So, we have this 23T with tiny tires in front and big tires in the back, we have a 57 Caddy and a 57 Chevy pick up. Do you really think the braking is the same for all three vehicles?
Save yourself some headaches install a adjustable proportional valve in the rear brake lines.
Entire article is here: http://www.hotrodheaven.com/tech/brakes/brakes1_i n...
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
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MikeB
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| 04-22-08 08:03 AM - Post#1417297
In response to Winmon
Found this description of how CPP's MCPV-1 master cylinder works. Seems like they have all bases covered.
The MCPV-1 has two circuits...front and rear. The front circuit of the MCPV-1 contains the metering valve, which is required on cars that have disc brakes on the front wheels and drum brakes on the rear wheels. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in. Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line.
The rear circuit of the MCPV-1 contains the adjustable proportioning valve and the maximum rear pressure adjustment. The adjustable proportioning valve controls the balance of pressure between the front and rear brakes. For example, if the adjustable proportioning valve was set to 70 percent and the brake pressure was 1000psi, the front brake would get 1000psi and the rear brakes would get 700psi, regardless of what type of brakes a car has. The Maximum Rear Pressure Adjustment controls the maximum rear pressure allowed to the rear brakes to help prevent rear wheel lock up. If the Max Rear Pressure Adjustment is set to 500psi and the adjustable valve set at 70 percent, the front brakes get 30 percent more until the rear reaches 500psi.
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
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leons57belair
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| 04-22-08 07:57 PM - Post#1417870
In response to MikeB
Thanks Mike, that was some good info!
| Black 57 Chevy Belair 2 door Sport Coupe. 350 engine, edelbrock performer rpm intake, 600 cfm edelbrock carb, K&N filter. Th350 trans. |
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HYPR
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| 04-22-08 08:01 PM - Post#1417879
In response to MikeB
Dave,
When CPP could not deliver the 1.125' Billet MCPV-1 to me after being on hold for a year I went ahead and ordered the Wilwood for my car. My only regret was ordering the polished version which IMO was a waste of money since the casting marks on this unit are so great. I ended up spending about 4 hours of wet sanding and polishing to get it to an acceptable show.
Save your money and order the plain version and polish it your self.
The performance of the unit is outstanding. I have the 4 piston Wilwoods at all 4 corners and on the advice of Orem Brothers I installed the Wilwood proportioning valve and the brakes are just awsume. The '56 will out brake my '06 GTO hands down from any speed.
Bob
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tri5ss
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| 04-23-08 04:59 AM - Post#1418041
In response to zio7
Sorry for all the questions. Does anyone know of a 1' bore master that will work from another car? I really do not have the money for the wilwood right now, since I just bought a house.
thanks
Tom
I think a M/C from an early 70's Corvette will work. Get the one for the manual 4 wheel disk. I believe I paid around $28-$30 for mine at Autozone. Got me through the season and allowed me to save up for the new chrome one!
Randy
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MikeB
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| 04-23-08 07:06 AM - Post#1418140
In response to HYPR
The '56 will out brake my '06 GTO hands down from any speed.
That is just too cool!
Any power boost?
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
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HYPR
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| 04-23-08 07:13 AM - Post#1418145
In response to MikeB
The '56 will out brake my '06 GTO hands down from any speed.
That is just too cool! Any power boost?
Hydraboost.
Bob
http://www.cardomain.com/ride/222599
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Winmon
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| 04-24-08 07:15 PM - Post#1419542
In response to HYPR
Thanks again guys!
For what its worth, I am running the same setup as you are planning, manual brakes, 4 piston wilwoods up front, drums in the rear, wilwood master cylinder, 1 inch bore, wilwood prop valve, and a line lock. I am very happy with my set up. Good Luck with yours!
Thanks John, I just ordered the 1' from Craig Morrison. Sounds like I made the right choice
My only regret was ordering the polished version which IMO was a waste of money since the casting marks on this unit are so great. I ended up spending about 4 hours of wet sanding and polishing to get it to an acceptable show.
Save your money and order the plain version and polish it your self
Too late, I already did
Bagged '62 Bel Air - 450hp LS2 - T56 - 9' Rear End
Pictures Here:
Photobucket |
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