Big Brakes

[patrickt]

Originally Posted by pormgb

Yep, they are 1".

Pumping the pedal builds good pressure, I can't imagine where air could still be in the system.

Try putting 1/8" shims, for test purposes only (not driving) between your pads and rotors and see if you can firm up the pedal feel in the garage. That will at least answer the "do I need a fatter rotor" question.

[pormgb]

Originally Posted by patrickt

Try putting 1/8" shims, for test purposes only (not driving) between your pads and rotors and see if you can firm up the pedal feel in the garage. That will at least answer the "do I need a fatter rotor" question.

Put shims behind the four front pads, pistons were as far back as possible but there was no difference in the pedal, still goes to the floor.

I am thinking I either don't have enough volume due to the 1" MC or there is still air somewhere in the system.

[patrickt]

Originally Posted by pormgb

I am thinking I either don't have enough volume due to the 1" MC or there is still air somewhere in the system.

I would temporarily cap off the rear lines and see if you can firm up the pedal using nothing but the front Sierras. If you can't do it, then it's got to be air in the lines.

[DanEC]

Originally Posted by pormgb

A funny thing; When I have the power bleeder attached and pumped up to about 15lb, the brake pedal does get quite hard, when the pressure from the bleeder is removes the pedal goes soft.

I'm thinking it's a MC issue. Have you looked closely at your pedal and linkage adjustment to make sure the pedal is returning the piston past the compensation port(s) in the cylinder? If the piston doesn't return past the port it can't refill with fluid and if the last press on the brake pedal moved the pads tighter against the rotors the system is short of fluid for the next application. If your linkage from the pedal to the MC is adjustable try shortening it a little.

[patrickt]

Dan might be right. Disconnect the rear lines from the splitter and plug them. Then bleed it again and if you can't get a firm feel with, essentially, a "front wheel brake system" only then it has to be hidden air bubbles or it's not assembled properly. That 1" MC is more than enough to handle the Sierras only. Whether it can handle the rears as well remains to be seen.

[razerwire]

Are you replacing brake system or is this a new brake system? Lots of information on new setups from Wilwood and others on internet. Sometimes it's very very hard to get all air out. Perhaps someone local can come by and get second set of eyes on your setup.I think you need to set back and do some reading and measuring, sometimes you come back the next day and the problem jumps right out at you.

[DanEC]

Razorwire's post does remind me that ERA recommends jacking the rear of the car up in the air as high as you reasonably can to facilitate bleeding all the air out. Seems like that was another thing that helped me get all the air out.

[patrickt]

Originally Posted by DanEC

Razorwire's post does remind me that ERA recommends jacking the rear of the car up in the air as high as you reasonably can to facilitate bleeding all the air out. Seems like that was another thing that helped me get all the air out.

No, the front of the car goes up. See page four here: http://www.erareplicas.com/427man/br...conversion.pdf

[pormgb]

Originally Posted by razerwire

Are you replacing brake system or is this a new brake system? Lots of information on new setups from Wilwood and others on internet. Sometimes it's very very hard to get all air out. Perhaps someone local can come by and get second set of eyes on your setup.I think you need to set back and do some reading and measuring, sometimes you come back the next day and the problem jumps right out at you.

No, I built the system myself, looking at all possibilities since I'm using different parts from different manufactures.

[pormgb]

I found another possible issue last night. I think I had the brake lines connected to the wrong master cylinder ports. My MC has a large reservoir and one small; I had the rear brakes on the large and the fronts on the small. After doing reading, I think older Ford MCs has a primary cylinder nearest to the firewall that feeds the front brakes and the primary has a higher pressure. I switched the lines and notice a stiffer pedal; I still need to do a full bleed to see if there is a real difference.

[pormgb]

Originally Posted by patrickt

No, the front of the car goes up. See page four here: http://www.erareplicas.com/427man/br...conversion.pdf

That's a great idea, defiantly something I can try.

[razerwire]

Good progress. I called wilwood to get their advice and talked to two different guys and had friend go to wilwood booth at sema and got 3 slightly different answer's. Shook all 3 in a bag and met in middle lol. Difference was small so it will be alright. I went with single master because it would be less work on Bennett car to replace JFZ parts. The csx car has great brakes but I would have to completely change everything to duplicate on Bennett car. When I get engine back from Rex Racing engines and installed . we shall see.

[DanEC]

Originally Posted by patrickt

No, the front of the car goes up. See page four here: http://www.erareplicas.com/427man/br...conversion.pdf

You had me going for a minute but it's bleeding the slave cylinder they want the front of the car raised. For brakes the 427 manual says to hike the rear up.

See page 143.

[patrickt]

Originally Posted by DanEC

You had me going for a minute but it's bleeding the slave cylinder they want the front of the car raised. For brakes the 427 manual says to hike the rear up.

See page 143.

... and right you are. What's funny is I just finished flushing and bleeding both the fronts and rears just last weekend... and I didn't elevate either the front or back. You know, if you think you have a funky air bubble in there, if tilting the car in one direction doesn't work, then tilt it in the other.

[DanEC]

Originally Posted by patrickt

... and right you are. What's funny is I just finished flushing and bleeding both the fronts and rears just last weekend... and I didn't elevate either the front or back. You know, if you think you have a funky air bubble in there, if tilting the car in one direction doesn't work, then tilt it in the other.

Actually I wonder if the front should be raised to bleed the front brakes and the rear raised to bleed the rear - sort of makes sense doesn't it? But the back are harder to bleed.

Still thinking it's the MC.

[pormgb]

Checked the car again today, I defiantly have more brake than ever after switching the MC lines, the pedal still goes to the floor but I'm pressing hard to do so. Over the weekend, I will bleed the brakes again using some of the discussed techniques.

How much travel do you have on your cars with manual brakes? does the pedal go to a point where it can no longer be pressed but the MC is not fully depressed?

I am using this MC;

http://www.ebay.com/itm/Brake-Master...kijq5Q&vxp=mtr

[cdnus]

No brake expert here but, it seems most decent brake systems on these cars use dual 3/4 or 7/8 masters.
Is it possible with the large calipers you are using there is just not enough capacity with a 1" single cylinder?
Just asking
There is probably a hydraulics expert here that can calculate that for you.

[patrickt]

Originally Posted by pormgb

How much travel do you have on your cars with manual brakes? does the pedal go to a point where it can no longer be pressed but the MC is not fully depressed?

OK, I'm going to say that pedal slack gets taken up in about an inch of foot travel and then you get another inch and a half or two travel at the max. The dual Tilton setup is quite firm.

[DanEC]

That would be a tough question to answer - it will depend on the car. You would need to total the area of all the caliper piston bores, assume an amount of piston travel to bring the pads against the rotors and compute a volume of fluid from that. Then convert that volume in to piston travel based on the area of the 1 inch piston in the MC.


For instance - the combined piston area of your front brakes is 11.65 sq inches each or 23.3 in sq for both fronts. I don't know what your rear brakes are but for example use a 2-piston caliper with 2 inch pistons. They would be 6.14 in sq per caliper or 12.28 in sq for both. All brakes would total 35.58 in sq piston area.

Assume the pistons travel 1/32 inch on each side to bring the pads into contact with the rotor - that's 1.112 cu inches of brake fluid.

The 1 inch MC piston is .785 sq inches. 1.112 cu in / .785 in sq = 1.417 inches MC piston travel.

Not sure if that 1/32 inch travel is reasonable or not. The MC definitely should not bottom when applying the brakes.

[pormgb]

Originally Posted by DanEC

That would be a tough question to answer - it will depend on the car. You would need to total the area of all the caliper piston bores, assume an amount of piston travel to bring the pads against the rotors and compute a volume of fluid from that. Then convert that volume in to piston travel based on the area of the 1 inch piston in the MC.


For instance - the combined piston area of your front brakes is 11.65 sq inches each or 23.3 in sq for both fronts. I don't know what your rear brakes are but for example use a 2-piston caliper with 2 inch pistons. They would be 6.14 in sq per caliper or 12.28 in sq for both. All brakes would total 35.58 in sq piston area.

Assume the pistons travel 1/32 inch on each side to bring the pads into contact with the rotor - that's 1.112 cu inches of brake fluid.

The 1 inch MC piston is .785 sq inches. 1.112 cu in / .785 in sq = 1.417 inches MC piston travel.

Not sure if that 1/32 inch travel is reasonable or not. The MC definitely should not bottom when applying the brakes.

Hmm, make sense and means I have way too much travel.

I am using GM Metric rear calipers, the type found on Cadallac Eldorado's with built in parking brake. These calipers have 2.380 in pistons.

To state again, when I pump the brakes the pedal gets quite hard, wait a minute and it soft.