Specifically, the combination valve and master cylinder.
My understanding is that the combination valve is supposed to shift to isolate the front or rear brakes in the event of a blown hose, however, I thought this was also the whole idea behind modern master cylinders having tandem pistons, each piston feeding half of the brakes, front or rear. Yes most brake master cylinders have a common reservoir that can be drained, but they're typically divided midway up such that a leak on one side doesn't drain fluid from both.
The whole system seems very belt and suspenders, not that it would be a bad thing to have redundancy, but I just don't see the advantage.
is my understanding grossly flawed? the reason I ask, is because I'm planning on installing a line lock, and was considering an adjustable proportioning valve in the rear circuit, and eliminate the combination valve from the equation. Am I making a grand mistake by doing this?
Brake system hydraulics.
Moderators: The Dark Side of Will, Series8217
-
- Posts: 2841
- Joined: Mon May 24, 2010 5:34 pm
- Location: Aiken, SC
Brake system hydraulics.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
- neophile_17
- Posts: 89
- Joined: Tue Mar 03, 2015 1:33 am
- Location: Southbury, CT
Re: Brake system hydraulics.
Hello,
There is more involved in a well functioning braking system than most hotrodders understand. This is what I have learned trying to improve our braking system.
The combination valve does 3 things.
Proportioning
Indication
Timing
Proportioning adjusts the front/rear bias.
Indication lights the light to let you know something is wrong.
Timing adjusts how pressure is applied to the front/rear so that the car behaves well under braking. This is most evident in F disc R drum cars where it is needed to avoid excessive dive. The rear brakes are applied first until a certain pressure is reached and then the front brakes are applied.
Many GM cars use step bore master cylinder which at least doubles the complexity of designing a competent brake system. Our race car is (now) a single bore master because getting the rest of the variables right is hard enough.
If your system is similar enough to stock the combination valve is the path of least resistance. If your caliper bores and tire heights are different enough then removing the stock valve and using an adjustable proportioning valve is the second easiest. Pay attention to which port on the master cylinder is attached to the the front/rear. Many other cars are the reverse of the Fiero and where the ports are drilled affects front/rear apply timing.
Good luck!
There is more involved in a well functioning braking system than most hotrodders understand. This is what I have learned trying to improve our braking system.
The combination valve does 3 things.
Proportioning
Indication
Timing
Proportioning adjusts the front/rear bias.
Indication lights the light to let you know something is wrong.
Timing adjusts how pressure is applied to the front/rear so that the car behaves well under braking. This is most evident in F disc R drum cars where it is needed to avoid excessive dive. The rear brakes are applied first until a certain pressure is reached and then the front brakes are applied.
Many GM cars use step bore master cylinder which at least doubles the complexity of designing a competent brake system. Our race car is (now) a single bore master because getting the rest of the variables right is hard enough.
If your system is similar enough to stock the combination valve is the path of least resistance. If your caliper bores and tire heights are different enough then removing the stock valve and using an adjustable proportioning valve is the second easiest. Pay attention to which port on the master cylinder is attached to the the front/rear. Many other cars are the reverse of the Fiero and where the ports are drilled affects front/rear apply timing.
Good luck!
85 GT LeMons Car LA1/LX9 Hybrid
85 SE LZ4 Pending...
85 SE LZ4 Pending...
-
- Posts: 2841
- Joined: Mon May 24, 2010 5:34 pm
- Location: Aiken, SC
Re: Brake system hydraulics.
I think I may try and build and install one of Aaron88's adjusters in the stock combo valve, I put together a bracket to hold a line lock using the master cylinder bolts, and bent lines to a stock combination valve, so ditching it now doesn't make a ton of sense.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
- Series8217
- 1988 Fiero Track Car
- Posts: 5984
- Joined: Thu Jun 02, 2005 9:47 pm
- Location: Los Angeles, CA
Re: Brake system hydraulics.
I'll put my aaron88 brake bias adjuster up for sale after I have my new brake system installed this spring, if you can wait that long.
-
- Posts: 2841
- Joined: Mon May 24, 2010 5:34 pm
- Location: Aiken, SC
Re: Brake system hydraulics.
I may take you up on that, let me know when the time comes.Series8217 wrote: ↑Sat Nov 11, 2023 11:51 pm I'll put my aaron88 brake bias adjuster up for sale after I have my new brake system installed this spring, if you can wait that long.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."