Brake experts, advice please.
- Thread starter OC_
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I cant really be sure from the picture but it looks like only the front of the car is jacked up, if this is the case the orientation of the caliper on the hub is not leaving the bleed nipple in the vertical position . That small amount of air left trapped in the tops of eight pistons could stack up to a lot of pedal travel. It would affect all eight as well because of the way the piston feed channels are drilled. Try bleeding them off the mounts with the pistons blocked.
Just thoughts
Bob
Just thoughts
Bob
Terry Oxandale
Skinny Man
I'm using a similar adapter with my C4 uprights, and must (as Bob noted), remove the upper bolt, rotate the caliper to place the bleeds at the top of the bores, and bleed the caliper. Then remount the caliper's top bolt.
This is a pic of the bracket thickness, but dont let this deceiving, its pretty heavy duty and the material its made of seems extremely hard and tough, it is not mild steel but some sort of stainless. I did not make this part, but have been in communication with the guy who did about my issue.
Pads are wearing evenly.
Pads are wearing evenly.
Attachments
Howard Jones
Supporter
Here's what I need to know and I'll try and help you.
1. Master cylinders size's front and rear.
2. Front caliper piston sizes and number of pistons.
3. Rear caliper piston sizes and number of pistons.
Here's good baseline. My GT40 stops like a cat at the beach.
Masters are both 5/8 inch. Front calipers are 1.75 X 4 and the rears are 1.375 X 4. all rotors are 12 inch in diameter.
I have the original GTD vacuum assist and the rather short 4 to 1 peddle ratio. If yours is about 1 to 6 and un assisted then they would be roughly equivalent. I also use a P-valve to reduce rear pressures about 6-7%.
My guess is the front master is too big and you are using the proportioning valve to reduce rear caliper pressure to balance the car front to rear. Thus very low caliper pressures, but we'll see.
Here's another calculator that is a bit less comprehensive:
Bias Calculator
1. Master cylinders size's front and rear.
2. Front caliper piston sizes and number of pistons.
3. Rear caliper piston sizes and number of pistons.
Here's good baseline. My GT40 stops like a cat at the beach.
Masters are both 5/8 inch. Front calipers are 1.75 X 4 and the rears are 1.375 X 4. all rotors are 12 inch in diameter.
I have the original GTD vacuum assist and the rather short 4 to 1 peddle ratio. If yours is about 1 to 6 and un assisted then they would be roughly equivalent. I also use a P-valve to reduce rear pressures about 6-7%.
My guess is the front master is too big and you are using the proportioning valve to reduce rear caliper pressure to balance the car front to rear. Thus very low caliper pressures, but we'll see.
Here's another calculator that is a bit less comprehensive:
Bias Calculator
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Terry Oxandale
Skinny Man
If this is a "muscle car", the front bias will be much stronger than our mid-engined cars with lower CGs. Even a front engined, rear drive car with better than 50/50 weight distribution requires a drop in rear pressure. The brake design program I've used for my project, indicated an identical front/rear set-up, which appears to be correct thus far.
Based on the photo, I would guess the caliper is parallel with the rotor unless the upright (looks to be an OEM piece) is damaged. The adapter plate appears to be plenty strong, and probably made from plate, indicating it is most likely straight and parallel as well.
Based on the photo, I would guess the caliper is parallel with the rotor unless the upright (looks to be an OEM piece) is damaged. The adapter plate appears to be plenty strong, and probably made from plate, indicating it is most likely straight and parallel as well.
Here's the specs to the system:
System is vacuum boosted.
1" mc bore
piston area of front calipers 3.0"^2. Four piston calipers with 1.38 pistons.
piston area of rear calipers 1.58"^2. Four piston calipers with 1" pistons.
Front rotor size is 13"
Rear rotor size is 12.19"
Car is 3540lbs wet with driver and has 55% of its weight over the front.
I have a p-valve in car and have the rears turned down a bit. These cars suffer tremendous rear wheel hop issues due to the torque arm rear suspension.
I have new front calipers on order that have an area of 4.12^2 and the piston size is 1.62".
I used the calculator above and it says that i have about 70% front brake bias with my 3.0^2 calipers and it will be about 76.5% with the new ones on order. If i got the 4.8^2 calipers, it says it would be 79%.
System is vacuum boosted.
1" mc bore
piston area of front calipers 3.0"^2. Four piston calipers with 1.38 pistons.
piston area of rear calipers 1.58"^2. Four piston calipers with 1" pistons.
Front rotor size is 13"
Rear rotor size is 12.19"
Car is 3540lbs wet with driver and has 55% of its weight over the front.
I have a p-valve in car and have the rears turned down a bit. These cars suffer tremendous rear wheel hop issues due to the torque arm rear suspension.
I have new front calipers on order that have an area of 4.12^2 and the piston size is 1.62".
I used the calculator above and it says that i have about 70% front brake bias with my 3.0^2 calipers and it will be about 76.5% with the new ones on order. If i got the 4.8^2 calipers, it says it would be 79%.
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Terry Oxandale
Skinny Man
Sounds like you headed in the right direction. My assumption is your using a tandem MC similiar to all the usually OEM parts. You should be able to dial down the bias with the new larger front calipers.
Looks sturdy enough but I wondered if the caliper was properly centered on the disc. Its not very clear on the picture but does look like its to one side of the disc more than the other.
Bob
This is true in the pic. At the time the pic was taken, it was off and I was in the process of sizing a spacer to center it. The calipers are for 1.25" thick rotors and the rotors im using are actually 1.10", the new calipers i have on order are for the correct thickness.
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Howard Jones
Supporter
Good, the math is saying that you have a pretty good piston size selection. I was going to add when I got your data that a front engine car (my experience is with a GT350 mustang) will be about correct with 70-75/25-30% F/R bias unless you really run much wider tires on the back, lower the car a lot, and run it very stiffly sprung.
The Mustang is at about 69% front. It is very stiff, really light, running 10"/12"wheels and slicks.
So now you have me wanting to know if the car stops straight even if it seams weak. Does it pull in one direction under breaking? If it does then one of the front calipers is bad. (blow or melted seal, or stuck piston)
Keep in mind that both front calipers may have been badly overheated and the pistons have scored the cylinders. Something is amiss at the front of the car. From what you are saying the applied friction is being effected. Could be badly glazed pads or rotors.
So look in the calipers and see if the piston bores are nice and polished. No scores or blue metal.
Same with the rotors nice and smooth with no glazed material.
Look at pads and forward pad type/number. My race pads do take a bit to get warm and until they do there is a bit less friction. Nothing like you report. Could you have a old set of burn up race pads on the front?
Are the pads being swept completely? Full surface area of the pad in contact with the rotor?
The new calipers should tell you something, one way or the other. What pads are you going to put in them?
The Mustang is at about 69% front. It is very stiff, really light, running 10"/12"wheels and slicks.
So now you have me wanting to know if the car stops straight even if it seams weak. Does it pull in one direction under breaking? If it does then one of the front calipers is bad. (blow or melted seal, or stuck piston)
Keep in mind that both front calipers may have been badly overheated and the pistons have scored the cylinders. Something is amiss at the front of the car. From what you are saying the applied friction is being effected. Could be badly glazed pads or rotors.
So look in the calipers and see if the piston bores are nice and polished. No scores or blue metal.
Same with the rotors nice and smooth with no glazed material.
Look at pads and forward pad type/number. My race pads do take a bit to get warm and until they do there is a bit less friction. Nothing like you report. Could you have a old set of burn up race pads on the front?
Are the pads being swept completely? Full surface area of the pad in contact with the rotor?
The new calipers should tell you something, one way or the other. What pads are you going to put in them?
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Everything looks good as far as condition goes. These calipers are old but they were unused for years and dont have much time on them. I will continue to run the PF01's, in fact, im just going to move them from my old calipers to the new ones since they use the same pad.
Fronts are ducted which has worked very well so far. 3" ducts, the backing plates are carbon fiber, but I can smell my resin burning when they are hot. I needed to use a specialized high temp resin or maybe just aluminum.
This is the rear setup. I'm running fixed mount 4 piston calipers on a c-clipped rear axle without knockback issues. Contrary to what people say, it can be done and done well.
Fronts are ducted which has worked very well so far. 3" ducts, the backing plates are carbon fiber, but I can smell my resin burning when they are hot. I needed to use a specialized high temp resin or maybe just aluminum.
This is the rear setup. I'm running fixed mount 4 piston calipers on a c-clipped rear axle without knockback issues. Contrary to what people say, it can be done and done well.
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Howard Jones
Supporter
I though of something else last night. Do you have a tandem Master? Could be a issue with the front piston (seal) and the rear piston OK.
Also I would have made that shield out of aluminum myself if I did it that way. Another way would be to direct the ducting towards the center of the rotor so that the air can flow into the center and out the vanes, leaving the face of the rotor exposed to free air or cooled with additional ducting.
In any case I wouldn't want the heat held in on the rotor by insulating it from outside air as yours does. But if you are going to try that, an alum shield would pull the heat away and dissipate it much better.
Lastly, you might want to try 4 X 1.75 calipers on the front if it's not to late to change your order. Then if they work better you can upgrade the rears with 1.38 you have and put the 1.0 on the shelf. I think that the overall piston size's may be a little small overall.
Also I would have made that shield out of aluminum myself if I did it that way. Another way would be to direct the ducting towards the center of the rotor so that the air can flow into the center and out the vanes, leaving the face of the rotor exposed to free air or cooled with additional ducting.
In any case I wouldn't want the heat held in on the rotor by insulating it from outside air as yours does. But if you are going to try that, an alum shield would pull the heat away and dissipate it much better.
Lastly, you might want to try 4 X 1.75 calipers on the front if it's not to late to change your order. Then if they work better you can upgrade the rears with 1.38 you have and put the 1.0 on the shelf. I think that the overall piston size's may be a little small overall.
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Howard Jones
Supporter
Called my GT350 friend and he is running Superlight 6 piston calipers on the front and Dynalight 4 piston calipers on the rear with duel piston masters un aided.
Masters are both 1.75
Fronts are Superlight 6 piston 1.62,1.12,1.12, piston area 4.04, 13X 1.25 rotors ducted
Rear Dynalight 4 piston 1.38 piston area 3.0, 12 X .85 rotors ducted
He has a bias bar and it is usually adjusted about 50/50ish full tank gas and 60/40ish low
on gas. 20 gal tank. That's about a 100 pound swing. Total weight of car is about 3100. It's run very low with very stiff front springs and a big ass roll bar. Rear bar is about half the front and springs are quite a bit softer.
He also said to set the front shock compression setting pretty high to help reduce the chassis weight transfer forward under breaking until the car settles from initial brake application. BUT, this can be a tradeoff on slower corner off power push (more).
I have ridden in this car. It is pretty quick but I wouldn't EVER say it is road worthy. Way too stiff. The brakes however are very good and will lock up a set of Hoosiers at will.
Masters are both 1.75
Fronts are Superlight 6 piston 1.62,1.12,1.12, piston area 4.04, 13X 1.25 rotors ducted
Rear Dynalight 4 piston 1.38 piston area 3.0, 12 X .85 rotors ducted
He has a bias bar and it is usually adjusted about 50/50ish full tank gas and 60/40ish low
on gas. 20 gal tank. That's about a 100 pound swing. Total weight of car is about 3100. It's run very low with very stiff front springs and a big ass roll bar. Rear bar is about half the front and springs are quite a bit softer.
He also said to set the front shock compression setting pretty high to help reduce the chassis weight transfer forward under breaking until the car settles from initial brake application. BUT, this can be a tradeoff on slower corner off power push (more).
I have ridden in this car. It is pretty quick but I wouldn't EVER say it is road worthy. Way too stiff. The brakes however are very good and will lock up a set of Hoosiers at will.
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Howard, My ducts are as to the center of the rotor as I can get them. I think 80% of the hole is in the center area. They are working well so far, when these burn up I'll redo out of aluminum. Whats your friends overall f/r weight distribution? Mine is pretty horrible, around 58% front without driver and a full tank of gas. This makes for very inefficient use of the tires and also the reason for why my brake biasing is what it is.
My 1" MC and new 4.12^2 calipers should be able to generate more force for a given pressure than your friends. That 1.75" MC your friend is using is huge! Are you sure thats right? 1.125 is the biggest wilwood makes..
Now i dont know what to do! I dont know if the pistons I got in the new calipers are going to work out. 4.8"^2 is OE size, and i think i would like more "feel" than that. The ones i have on order, which are 4.12"^2, are the next size down. This is a pretty substantial increase from the 3.0 which i have now...
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Howard Jones
Supporter
Sorry. The masters are .75 on my friends car. I had calipers sizes on the brain. Not to sure on weight distribution but it has a full on cage in it and everything that can be in the back is like battery, fire bottle, fuel pumps fuel tank, etc.
It may be a bit more centered without all the road interior pieces, bumpers, lights and stuff like that but basically those cars are about 60% of the weight on the front tires.
It may be a bit more centered without all the road interior pieces, bumpers, lights and stuff like that but basically those cars are about 60% of the weight on the front tires.
Howard, is your mustang friends brakes boosted?
I dont know if i should stick with the 4.12^2 calipers and see if they work with my current rears, or i should just scrap everything and start over with a 4.8^2 caliper in the front and get a new larger rear. I'd rather not have to get new rear calipers, and If i go the the 4.8^2 caliper, im pretty sure i would have to.
I dont know if i should stick with the 4.12^2 calipers and see if they work with my current rears, or i should just scrap everything and start over with a 4.8^2 caliper in the front and get a new larger rear. I'd rather not have to get new rear calipers, and If i go the the 4.8^2 caliper, im pretty sure i would have to.
