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Topic Review (Newest First)
02-23-2007 08:26 PM
Scarebird well put. ..................
02-23-2007 06:11 PM
joe_padavano
Quote:
Originally Posted by Scarebird
no. their job is to limit pressure AFTER a certain point is reached. when you stamp on the brake hard they kick in, but during normal stops, they allow full pressure to the rears, allowing the rears to help stop the car.
Maybe I'm misunderstanding what you're trying to say, but as I read it, that is confusing. Tilton has graphs showing the output pressure curves of their proportioning valves in their installation instructions here:

http://www.tiltonracing.com/pdfs/29.pdf

The output pressure will ramp up at the same rate as input pressure up to a preset pressure (usually a very low pressure) then at a certain point the ramp rate changes and output pressure becomes proportional to the input pressure but lower (hence the term PROPORTIONING valve). The peak output pressure is also always less than the peak input pressure. I think the confusion is in your statement that "during normal stops, they allow full pressure to the rears". I think what you mean is that under light braking, the pressures are the same, but under light braking you won't be locking up the rears anyway.

On factory units this proportioning is not adjustable, but the whole purpose of aftermarket adjustable units is to allow you to change the output to input ratio. Under NO condition does the rear brake see the full input pressure that the front sees when using a proportioning valve unless you back it off to the point that it's disabled.

Proportioning valves are used in disc/disc systems all the time to account for front/rear weight distribution. The factories leave them out when possible to save cost. Pickup trucks use load-sensing proportioning valves to change the front/rear bias depending on whether the truck is full or empty.

There's nothing magic about a proportioning valve. It does not change how it operates due to the rate of pressure rise. It is essentially a pressure regulator, but rather than limiting the output pressure to a fixed PSI, it is designed to reduce the output pressure to a percentage of the input pressure. Yes, you CAN use a proportioning valve to prevent premature lockup if you have bigger rotors on the back than the front. The only issue is that you're potentially wasting money installing those bigger rear rotors if you're just going to reduce their effectiveness by dropping the line pressure.
02-23-2007 03:06 PM
BonzoHansen
Quote:
Originally Posted by Scarebird
this is a bad idea from several angles:

1. 1979 Seville rotors are 5 on 5 bolt pattern for starters. And they are 11-3/8" in diameter. Your 81 Monte rotors are 10-1/2", so you will easily lockup the rears due to grooss bias mismatch.

2. Crossdrilled are ridiculous for the street; they are guaranteed to crack from stress risers between the vanes.

www.scarebird.com
He probably has WS6 Trans Am rotors (5x4.75). Similar setup.

Holes = cracks - slotted or solid is the way to go. Modern pads do not outgas like pads of the olds days.
02-14-2007 07:08 PM
matt167
Quote:
Originally Posted by Scarebird
no. their job is to limit pressure AFTER a certain point is reached. when you stamp on the brake hard they kick in, but during normal stops, they allow full pressure to the rears, allowing the rears to help stop the car.
right, and not only that. most disc/disc applications do not use them. they are used because of the self energizing ( duo servo ) drum brakes, they don't need as much brake preassure, once they rotate over ( self energize )
02-14-2007 06:58 PM
Scarebird
Quote:
Originally Posted by xntrik
What about rear wheel proportioning valves? I thought that was their purpose.
no. their job is to limit pressure AFTER a certain point is reached. when you stamp on the brake hard they kick in, but during normal stops, they allow full pressure to the rears, allowing the rears to help stop the car.
02-14-2007 03:49 PM
xntrik
Quote:
Originally Posted by Scarebird
this is a bad idea from several angles:

1. 1979 Seville rotors are 5 on 5 bolt pattern for starters. And they are 11-3/8" in diameter. Your 81 Monte rotors are 10-1/2", so you will easily lockup the rears due to grooss bias mismatch.

www.scarebird.com

What about rear wheel proportioning valves? I thought that was their purpose.
02-14-2007 11:10 AM
Scarebird Ian, you are corect about Girlock, Lockheed was also a pioneer, though theirs was originally on aircraft.
02-14-2007 01:29 AM
IanRiordan
Quote:
Originally Posted by Scarebird
It is pressure from marketing; the kids like to see the holes. I asked Brembo about this at SEMA, as they wrote the book (literally) about disc brake design. If you have solid rotors, it is not an issue as you can countersink the holes and remove the risers.
I always thought Girlock suplied the first commercial discs in the 50s. I'm guessing that Brembo market their products very well, just as mazda are famous for the rotary - an NSU (wankel) design.
I may still have a steel girlock disc off a mid 70s sports sedan Monaro in the shed. Like most of the running gear on this car it is alledged to be ex Le Mans GT40. It has holes drilled and heat cracks. Funny how people want 'high tech' but will accept BAD 'old tech' as long as it doesn't work and looks trick.
02-13-2007 10:44 AM
Scarebird It is pressure from marketing; the kids like to see the holes. I asked Brembo about this at SEMA, as they wrote the book (literally) about disc brake design. If you have solid rotors, it is not an issue as you can countersink the holes and remove the risers.
02-13-2007 01:49 AM
IanRiordan Amen, here, most disc manufacturers reccomend slotted only for a high perf or race application. I've seen cracks out of the holes on standard AMG discs (M/B C32 and E55). Thank christ they no longer use them, some engineers should be cleaning toilets at the factory.
02-12-2007 11:37 PM
Scarebird
Quote:
Originally Posted by m.docken
I need crosss drilled & slotted rotors that will match front and rear on my 67 chevelle. Rear rotors are 1979 Cadilac sevelle, and front rotors are 1981 monte carlo. Does anyone know what company will make these rotors so they will match front and bvack??????? Thanks
this is a bad idea from several angles:

1. 1979 Seville rotors are 5 on 5 bolt pattern for starters. And they are 11-3/8" in diameter. Your 81 Monte rotors are 10-1/2", so you will easily lockup the rears due to grooss bias mismatch.

2. Crossdrilled are ridiculous for the street; they are guaranteed to crack from stress risers between the vanes.

www.scarebird.com
02-09-2007 09:14 PM
m.docken I have rear bolt on caliper hangers for 12 bolt rear end from King Tek enginering.
02-09-2007 09:11 PM
poncho62 How are you mounting your calipers?..........just wondering.
02-09-2007 09:09 PM
m.docken
cross drilled rotors on a 67 chevelle

I need crosss drilled & slotted rotors that will match front and rear on my 67 chevelle. Rear rotors are 1979 Cadilac sevelle, and front rotors are 1981 monte carlo. Does anyone know what company will make these rotors so they will match front and bvack??????? Thanks

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