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  #1 (permalink)  
Old 02-10-2019, 08:15 AM
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Default Brake question

I had a close call last Fall with some driver cutting in front of me in order to exit the express way. So I need to do something to ramp up my braking system. What I've done so far last summer new softer pads, bleed all brake lines several times with Dot 4 brake fluid, ( positively no air whatsoever) new 7/8 Tilion master cylinder for the front and 3/4 for the rear, turn front rotors and double checked the brake balance adjustment all OK. My question is does anyone think replacing the 7/8 master cylinder with a 1" is worth trying? Safety is more important than going fast. It's not fun driving with so so braking. I do believe i've exhausted all possibilities to get this thing to stop decent. I know non power disk brakes take more effort to stop but this is not acceptable. Can any body out there have this issue?
Thanks for your time.
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Old 02-10-2019, 08:43 AM
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Larger master cylinders will move more volume, but create less pressure. It also shortens the movement of the brake pedal.

A smaller MC will increase the pressure, and move less fluid. But require more pedal movement. IMO, a little more pedal movement is good, because they are easier to modulate at the edge.

If you're going to replace the MC, I'd go smaller. Like a 3/4".
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Old 02-10-2019, 09:03 AM
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classical,

Maybe you took care of this, maybe not?

Your car's rotors may have a layer called "glaze" due to deposition of the prior pad material. If this isn't removed by a light turning or maybe some emery cloth, you may find the car won't stop well no matter how high the braking line pressure.

A layer of glaze definitely has a lower coefficient of friction.

I'd suggest looking at this before trying other sized cylinders.

Just another possibility...

Tom

PS: It looks like the front rotors were turned? If so, you could still check the rears. If they're OK then maybe do what Bob proposed.
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Old 02-10-2019, 01:26 PM
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I saw a Baer ad talking about 4 piston calipers for 11" rotors. Which should fit with 15" wheels. I'm going to look into them because I'm not thrilled with my brakes.
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Old 02-10-2019, 02:35 PM
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Here's what I'd do. First, I'd test the brakes in a safe place on a flat dry road by doing an emergency stop from about 35 MPH. It would help to have an assistant watch from a safe distance. My goal would be to (1) lock up the brakes and (2) confirm that the fronts locked before the rears. If I ran out of either leg strength or pedal travel before the brakes locked, I'd start evaluating the entire system. While there are many components in a brake system, it all comes down to pressure and travel at the pedal becoming pressure and travel at the calipers. The length of the pedal, diameter of MC, diameter of caliper puck and position of the pad on the rotor are just some of the things that determine how hard the pads press against the rotors and how much stopping torque the rotors apply to the wheels. There are web sites that will allow you to put all the factors in and it will tell you whether it should work.

If I could lock up the brakes but didn't like either the pedal travel or force required, I'd look at changing either the pedal ratio or the MC size. But know that nothing short of power brakes can help with both. With manual brakes you get to choose either lower leg force with longer travel or shorter travel with higher leg force.

One last observation - during an emergency stop with well configured brakes, the front brakes will do about 70% of the work. So don't skip the step about getting the front brakes to lock up first. They are the ones that you should work to get right first.
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Old 02-10-2019, 03:04 PM
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Quote:
Originally Posted by Karl Bebout View Post
I saw a Baer ad talking about 4 piston calipers for 11" rotors. Which should fit with 15" wheels. I'm going to look into them because I'm not thrilled with my brakes.
4 piston calipers for ERA cars are an easy option. Sierra is long gone, but here's a pic of mine to give you an idea. Just ring up Bob P. and ask him what the "big brake" option will cost you. It is not a difficult upgrade.

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Old 02-10-2019, 06:05 PM
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Quote:
Originally Posted by Tom Wells View Post
classical,

Maybe you took care of this, maybe not?

Your car's rotors may have a layer called "glaze" due to deposition of the prior pad material. If this isn't removed by a light turning or maybe some emery cloth, you may find the car won't stop well no matter how high the braking line pressure.

A layer of glaze definitely has a lower coefficient of friction.

I'd suggest looking at this before trying other sized cylinders.

Just another possibility...

Tom

PS: It looks like the front rotors were turned? If so, you could still check the rears. If they're OK then maybe do what Bob proposed.
The front brake rotors on my wife's car (Infiniti G35x) were worn beyond specification, so I ordered a 'Power Stop' brake kit from Rock Auto. It's nothing fancy or high performance, just OEM equivalent - Infiniti generally equipped them with decent brakes, so I didn't think I needed to go high end.

I installed the kit and went through the whole break-in procedure:
Break in the pads as follows: 5 moderate to aggressive stops at 40 mph to 5 mph without letting the brakes cool and do not come to a complete stop. Then do 5 moderate stops at 25 mph to 5 mph and let the rotors cool after each brake application. You should expect to smell some resin as the brakes get hot.
We live in a bedroom community of about 6,000 and we're only about a mile from a quiet, two lane rural highway. Perfect for breaking in a new set of brakes, right? I followed the above instructions carefully to ensure it was done right. Did I smell some resin? You bet! Did I have smoke coming out of the wheel wells? Not billowing clouds, but it was there.

I thought that car stopped pretty well before - but what a world of difference. After that I took my Infiniti FX35 through a similar procedure - the gains weren't as dramatic, but they were there.

Moral of the story - proper break-in makes a world of difference. Even repeating it with old rotors and pads can help - I imagine more improvement if they're glazed.

BTW, I'd also recommend cleaning the rotors with brake cleaner before the break-in procedure, even with old rotors and pads. It might not be a bad idea to take some sandpaper or a grinder to the old pads to knock off any glaze you find.
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Old 02-10-2019, 06:07 PM
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What chassis number is your car? what wheels do you have?
I have owned several ERA cars and they all stop very confidently when properly setup. I suspect many (like a few I've had) are improperly set up. Some are never right from the start. You may think you have all the air out and the balance bar setup, but you may not. Did you also replace all the rubber lines from the reservoir to the MCs? Hard line from front to back as well as front and rear brake hoses? Depending on the age and miles (lack of use) these areas may all need to be addressed.

The stock ERA brakes should be more than capable for all the street driving I can think of, unless something isn't right.
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Old 02-11-2019, 11:41 AM
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Quote:
Originally Posted by patrickt View Post
4 piston calipers for ERA cars are an easy option. Sierra is long gone, but here's a pic of mine to give you an idea. Just ring up Bob P. and ask him what the "big brake" option will cost you. It is not a difficult upgrade.

I also have Sierra brakes on my car, but I also noticed that my wear pattern on my rotors are nothing like yours. What I mean is I do not have the circular pattern that your rotor is showing. Now I'm wondering if there is an issue with my calipers maybe frozen up or stuck. When I first got the car (6 are ago) I rebuilt all the master cylinders and clutch hydraulics. The master cylinders were loaded with sludge and rust. I have flushed out the system at least 4 or 5 times until all fluid was clear, but now I'm thinking that there is something going on inside the calipers. I have since then installed 2 new masters, flushed the lines again (dot 4)and replaced the brake pads (the same ones you suggested in a prior thread. Time to pull apart and see if there is something frozen up. Your thoughts ?
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Old 02-11-2019, 11:46 AM
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Originally Posted by classical glass View Post
Your thoughts ?
Since you have "kinda new" pads on there, pull the cotter pin, yank 'em out, and see how they compare to the images found here: https://www.phoenixfriction.com/t-di...-patterns.aspx especially the funky pattern that can indicate a Caliper or Caliper Piston Hanging Up. Then post some pics.
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Old 02-11-2019, 01:09 PM
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Quote:
Originally Posted by patrickt View Post
Since you have "kinda new" pads on there, pull the cotter pin, yank 'em out, and see how they compare to the images found here: https://www.phoenixfriction.com/t-di...-patterns.aspx especially the funky pattern that can indicate a Caliper or Caliper Piston Hanging Up. Then post some pics.
Pads are worn evenly. I only have about 200 miles since last fall so there's not much wear. I.m going to remove the calipers tomorrow and bench test them at a local brake shop. That's about the last and only thing left that I can think of. Maybe I'm expecting too much, but it's still not safe.
Thanks
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Old 02-11-2019, 02:21 PM
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If you're going down the highway at 50+ mph, can you lock the wheels up without breaking your leg to do so?
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Old 02-11-2019, 02:36 PM
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Making sure the car is cross-balanced will also make sure you are breaking evenly side-to-side.
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Old 02-11-2019, 07:29 PM
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You could install a remote power brake booster, that would minimize your leg effort and multiply your master cylinders pressure output. This would be an easier way to apply more braking effort without having to go to the gym to workout.

By the way, I fully agree with bobcowan’s explanation above about the smaller the bore of the brake master cylinder the more pressure the master cylinder generates.

Last edited by CompClassics; 02-11-2019 at 10:04 PM..
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Old 02-12-2019, 08:08 AM
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If you're going down the highway at 50+ mph, can you lock the wheels up without breaking your leg to do so?
NO....not even close.
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Old 02-12-2019, 08:53 AM
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NO....not even close.
Well then I can definitively say that something is not right.
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Old 02-12-2019, 04:17 PM
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Quote:
Originally Posted by classical glass View Post
What I've done so far last summer new softer pads, bleed all brake lines several times
When you say you put on "softer" pads, what exactly did you install?

I have the same type of performance that you describe and my first step was going to be a more aggressive pad material coupled with turned rotors. My car stops ok but I can feel the pedal flexing before I get anywhere near lockup. I do have Avons on the car so grip may be higher than average, but still...

My 1969 911 has non-boosted brakes, 12" rotors with 4 piston front and 2 piston rear calipers. It stops SUBSTANTIALLY better than the Cobra although it is about 200lbs lighter.
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Old 02-12-2019, 04:53 PM
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Don't forget tires! It doesn't do much good if you've got the best brakes in the world if the tires just lock up.
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Old 02-12-2019, 05:07 PM
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I went from a 3/4 to 1 inch as the pedal ran out of travel. Now it takes a lot of pressure to stop it. I'll be going to instal a booster. Now the booster guy says to install a 3/4 inch booster which will double the pressure. But doesn't mean I'll be running out of pedal again? JD
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Old 02-12-2019, 05:48 PM
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The remote booster I just installed on a CSX6000 Series multiplies the brake pedal x2.
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