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Big Brakes
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http://www.clubcobra.com/forums/all-cobra-talk/135810-big-brakes.html)
| cycleguy55 |
02-16-2016 05:33 AM |
Quote:
Originally Posted by pormgb
(Post 1380995)
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.
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The fact it's going soft says to me there's air in those lines. I went with 'speed bleeders' when I did my brake conversion (Wilwood 4 piston front, GM rear) and I'm convinced they're the way to go. Bleeding is never a 'fun' task, but using them took the real hassle out of doing it so much I'm also planning to install them on our daily drivers. |
| pormgb |
02-16-2016 10:48 AM |
Quote:
Originally Posted by cycleguy55
(Post 1381036)
The fact it's going soft says to me there's air in those lines. I went with 'speed bleeders' when I did my brake conversion (Wilwood 4 piston front, GM rear) and I'm convinced they're the way to go. Bleeding is never a 'fun' task, but using them took the real hassle out of doing it so much I'm also planning to install them on our daily drivers.
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Yep, I do have a power bleeder, I will pull it out this weekend and bleed all four corners, |
| DanEC |
02-16-2016 11:18 AM |
Quote:
Originally Posted by pormgb
(Post 1381056)
Yep, I do have a power bleeder, I will pull it out this weekend and bleed all four corners,
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He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.
They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ??? |
| cycleguy55 |
02-16-2016 12:24 PM |
Quote:
Originally Posted by DanEC
(Post 1381060)
He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.
They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ???
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Yes - you can see the Russell ones here: Aftermarket Brake Kit Application Guide - Speed Bleeders - Russell Performance Products
They're widely available in parts stores, speed shops, etc. and come in a variety of sizes to replace bleed screws in OEM and after-market calipers. For Wilwoods you only need a pair for each caliper to replace the upper bleed screws - you can leave the lower bleed screws in place as you'll never use them anyway.
BTW, my rear lines were pretty much completely dry when I bled them, and I was astounded how many pumps it took of the brake pedal before I got anything out. The key message is it may take a lot longer than you think before you get all the air out. Brake fluid is relatively cheap - don't be afraid to waste some, and always start with the wheel furthest from the MC and work closer as you go (RR, LR, RF, LF - for LH drive cars). |
| pormgb |
02-16-2016 07:08 PM |
Quote:
Originally Posted by DanEC
(Post 1381060)
He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.
They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ???
|
I have them on the rear calipers (GM Metric) and they are clean and work really well. The Sierra's have 1/8" bleeders, I could not find speed bleeders to fit the calipers. I take that back, I just found a 1/4-28 speed bleeder that fits in the 1/8" NPT housing. |
| pormgb |
02-16-2016 07:10 PM |
Quote:
Originally Posted by cycleguy55
(Post 1381065)
Yes - you can see the Russell ones here: Aftermarket Brake Kit Application Guide - Speed Bleeders - Russell Performance Products
They're widely available in parts stores, speed shops, etc. and come in a variety of sizes to replace bleed screws in OEM and after-market calipers. For Wilwoods you only need a pair for each caliper to replace the upper bleed screws - you can leave the lower bleed screws in place as you'll never use them anyway.
BTW, my rear lines were pretty much completely dry when I bled them, and I was astounded how many pumps it took of the brake pedal before I got anything out. The key message is it may take a lot longer than you think before you get all the air out. Brake fluid is relatively cheap - don't be afraid to waste some, and always start with the wheel furthest from the MC and work closer as you go (RR, LR, RF, LF - for LH drive cars).
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I just finished using my pressure bleeder, still no luck.
I will revert back to my wife's assistance and see how that goes. |
| pormgb |
02-16-2016 09:53 PM |
The fun continues!!
I decided to block the rear MC port, got rock hard front brakes.
I then blocked the brake line at the rear Tee, got rock hard front brakes.
The problem must be in the GM Metric calipers, there is either air trapped in them or there is an issue with the adjuster.
Since I'm using a 1" dual bore MC and it can drive 2x2" and 2x1.85 pistons, there must be enough volume to drive 2 pistons just over 2".
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| pormgb |
02-16-2016 11:21 PM |
I got this figured out!!
My problem is related to rear caliper piston position, GM Metric calipers have this weird adjustment that is related to the parking brake.
For the calipers to function correctly, the pistons have to be adjusted so the pads are close but no obstructing wheel moment. The parking brake also has to be attached.
The rear pistons are sitting so far back there is excessive pedal travel taking up the slack, I moved the pistons up using the parking brake levers and the brakes are now functioning correctly.
|
| cycleguy55 |
02-17-2016 05:51 AM |
Quote:
Originally Posted by pormgb
(Post 1381134)
I got this figured out!!
My problem is related to rear caliper piston position, GM Metric calipers have this weird adjustment that is related to the parking brake.
For the calipers to function correctly, the pistons have to be adjusted so the pads are close but no obstructing wheel moment. The parking brake also has to be attached.
The rear pistons are sitting so far back there is excessive pedal travel taking up the slack, I moved the pistons up using the parking brake levers and the brakes are now functioning correctly.
|
I have the larger, non-metric GM calipers on mine, and your comment jogged my memory about those adjusters. Here's the text from the installation manual:
REAR CALIPER ADJUSTMENT
When installing rear disc brakes with calipers that have an internal parking brake you must adjust or set the calipers when installing. Failure to do so will prevent you from getting a firm pedal and you will have no rear brake function. Only do this adjustment with the caliper and rotor installed on the vehicle. You must set the parking brake every time you park to keep the calipers adjusted.
INITIAL ADJUSTMENT
1. remove the spring.
2. crank the lever or turn the retention nut to actuate the lever forward.
3. after cranking the lever forward as far as it will go, rotate it back the other way until you hit the stop. you may need to use a long screwdriver to lever the lever back into place.
4. The rear caliper should now be correctly adjusted.
5. re-install spring
Important: You must use the parking brake mechanism on a regular basis to set the self adjusting calipers. Failure to use the rear parking brake will result in rear brake loss!
Interesting note at the end - obviously important to note!
Sorry I didn't remember this sooner - it sounds like you could have saved some time and frustration had you been armed with this.
BTW, there is another procedure you'll need to know in order to be able to rack the piston back out for brake pad replacement - but hopefully it will be a while before you need to deal with that. You also need to know that procedure should you "crank the lever or turn the retention nut to actuate the lever forward" prior to installation of the calipers." Don't ask why I needed to discover that... |
| DanEC |
02-17-2016 06:08 AM |
Well, that's interesting. Good job of tracking it down and correcting. Hope that takes care of everything with the brakes.
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| patrickt |
02-17-2016 06:23 AM |
Quote:
Originally Posted by pormgb
(Post 1381134)
I got this figured out!!
|
Nice. Now on to the next issue....:LOL: |
| pormgb |
02-17-2016 10:24 AM |
Quote:
Originally Posted by cycleguy55
(Post 1381144)
I have the larger, non-metric GM calipers on mine, and your comment jogged my memory about those adjusters. Here's the text from the installation manual:
REAR CALIPER ADJUSTMENT
When installing rear disc brakes with calipers that have an internal parking brake you must adjust or set the calipers when installing. Failure to do so will prevent you from getting a firm pedal and you will have no rear brake function. Only do this adjustment with the caliper and rotor installed on the vehicle. You must set the parking brake every time you park to keep the calipers adjusted.
INITIAL ADJUSTMENT
1. remove the spring.
2. crank the lever or turn the retention nut to actuate the lever forward.
3. after cranking the lever forward as far as it will go, rotate it back the other way until you hit the stop. you may need to use a long screwdriver to lever the lever back into place.
4. The rear caliper should now be correctly adjusted.
5. re-install spring
Important: You must use the parking brake mechanism on a regular basis to set the self adjusting calipers. Failure to use the rear parking brake will result in rear brake loss!
Interesting note at the end - obviously important to note!
Sorry I didn't remember this sooner - it sounds like you could have saved some time and frustration had you been armed with this.
BTW, there is another procedure you'll need to know in order to be able to rack the piston back out for brake pad replacement - but hopefully it will be a while before you need to deal with that. You also need to know that procedure should you "crank the lever or turn the retention nut to actuate the lever forward" prior to installation of the calipers." Don't ask why I needed to discover that...
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Yea, read this a few times but didn't really think it had such a profound affect on pedal feel.
This write up is actually more detailed, thanks!! |
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