Line lock question

Mark Ugrich · 05-11-2015, 08:22 PM

Quote:

Originally Posted by tommy d

Speaking of line-locks. Has anyone ever had a spongy pedal because of a line lock problem? Every single piece of the hydraulic system has been replaced except for the roll control and I still have a spongy pedal. It wil come around on the second stab and work great. I even installed a front disc conversion and went with a G.M. Corvette style master cylinder and still soft. Arrrgh!

Is the pedal ratio correct for the conversion/disc brakes?

Eman · 05-11-2015, 10:28 PM

Buy a couple of plugs that will fit the MC. Plug off 1 section and see what it feels like. If it's still spongy plug off the other and try it, spongy with both plugged you've got air in the MC. If plugging 1 section makes the pedal firm you have air in the section or a hose ballooning.

tommy d · 05-12-2015, 12:06 AM

Thanks for the ideas guys. I like the idea about blocking off a chamber on the m/c and see what happens. The disc conversion company says to pick up the $30.00 Harbor Freight pressure bleeder and use it. Gonna try that tomorrow. I hear pedal ratio thrown around on other forums. Maybe I'm going to have to learn about that next. Thanks.

HandOverFist · 05-12-2015, 01:29 AM

Yes, I use a 2 pound residual valve in the rear of both the Camaro and Mustang (Aerospace 4-pistons).

Eman · 05-14-2015, 08:38 AM

Pedal ratio should be 6:1 so if the pedal is 12" long from the pivot to the bottom you want the rod attachment at 2" down from the pivot.
I guess 2lb isn't much but most class racers don't want any drag on their brakes and have gone as far as installing springs to release the calipers so the pads don't rub the rotors. Since disc brakes don't have return springs there should be no need for residual valves unless the MC is below the wheel cyl and fluid could drain back. Residual valves on old drum brake cars were to stop the return springs from pushing back the wheel cyl pistons way back and causing a low pedal. Much of that was overcome with those strainer looking things in the wheel cyl on the wheel cyl springs. Which is why they did away with residual ck valves in factory MC's years ago even with drum brakes.
You can back bleed brakes pretty simple and easy. Go buy a large animal syringe and a piece of clear tubing to fit it. Load the syringe with brake fluid and remove the air, just like you saw the nurses do before they inject you. Push the fluid back thru the bleeder with the syringe. This is OK but I've never had to do it on brakes, only on clutch hydraulic systems that were hard to bleed.. On calipers tapping the caliper with a rubber mallet will bring the air to the top and out the bleeder. Be sure the calipers are installed correctly with the bleeders at the top. I have seen them reversed and the bleeders at the bottom.

pmrphil · 05-15-2015, 06:13 PM

I have had issues with the caliper not being perfectly square to the rotor, causing the caliper to "move" or twist (just a few thousandths) but it was enough to affect the pedal movement similar to what you say, a bit "mushy" on the first hit.
After squaring the caliper to the rotor the problem went away.

Bob Mulry · 05-15-2015, 09:19 PM

Give me a call at 650 922 0407 and I'll give a trick for bleeding disc brakes....

bob

05-11-2015, 10:28 PM	#2
Eman Member Join Date: May 2014 Location: E TN Posts: 473 Likes: 16 Liked 133 Times in 76 Posts	Re: Line lock question Buy a couple of plugs that will fit the MC. Plug off 1 section and see what it feels like. If it's still spongy plug off the other and try it, spongy with both plugged you've got air in the MC. If plugging 1 section makes the pedal firm you have air in the section or a hose ballooning.

05-12-2015, 12:06 AM	#3
tommy d Senior Member Join Date: Oct 2010 Location: Indiana Posts: 830 Likes: 1,625 Liked 359 Times in 135 Posts	Re: Line lock question Thanks for the ideas guys. I like the idea about blocking off a chamber on the m/c and see what happens. The disc conversion company says to pick up the $30.00 Harbor Freight pressure bleeder and use it. Gonna try that tomorrow. I hear pedal ratio thrown around on other forums. Maybe I'm going to have to learn about that next. Thanks. __________________ Who owns this car, with the peace sign,mag wheels, and four on the floor?

05-12-2015, 01:29 AM	#4
HandOverFist VIP Member Join Date: Oct 2013 Location: Gulf Breeze, FL Posts: 1,651 Likes: 8 Liked 33 Times in 16 Posts	Re: Line lock question Yes, I use a 2 pound residual valve in the rear of both the Camaro and Mustang (Aerospace 4-pistons). __________________ Rich Taylor I/SA - 321

05-14-2015, 08:38 AM	#5
Eman Member Join Date: May 2014 Location: E TN Posts: 473 Likes: 16 Liked 133 Times in 76 Posts	Re: Line lock question Pedal ratio should be 6:1 so if the pedal is 12" long from the pivot to the bottom you want the rod attachment at 2" down from the pivot. I guess 2lb isn't much but most class racers don't want any drag on their brakes and have gone as far as installing springs to release the calipers so the pads don't rub the rotors. Since disc brakes don't have return springs there should be no need for residual valves unless the MC is below the wheel cyl and fluid could drain back. Residual valves on old drum brake cars were to stop the return springs from pushing back the wheel cyl pistons way back and causing a low pedal. Much of that was overcome with those strainer looking things in the wheel cyl on the wheel cyl springs. Which is why they did away with residual ck valves in factory MC's years ago even with drum brakes. You can back bleed brakes pretty simple and easy. Go buy a large animal syringe and a piece of clear tubing to fit it. Load the syringe with brake fluid and remove the air, just like you saw the nurses do before they inject you. Push the fluid back thru the bleeder with the syringe. This is OK but I've never had to do it on brakes, only on clutch hydraulic systems that were hard to bleed.. On calipers tapping the caliper with a rubber mallet will bring the air to the top and out the bleeder. Be sure the calipers are installed correctly with the bleeders at the top. I have seen them reversed and the bleeders at the bottom.

05-15-2015, 06:13 PM	#6
pmrphil Member Join Date: Aug 2010 Location: CT Posts: 462 Likes: 1,832 Liked 348 Times in 152 Posts	Re: Line lock question I have had issues with the caliper not being perfectly square to the rotor, causing the caliper to "move" or twist (just a few thousandths) but it was enough to affect the pedal movement similar to what you say, a bit "mushy" on the first hit. After squaring the caliper to the rotor the problem went away. __________________ Phil Molski PMR Performance S/C 1623

05-15-2015, 09:19 PM	#7
Bob Mulry VIP Member Join Date: Apr 2002 Location: Coarsegold, CA Posts: 1,016 Likes: 57 Liked 320 Times in 102 Posts	Re: Line lock question Give me a call at 650 922 0407 and I'll give a trick for bleeding disc brakes.... bob __________________ Bob Mulry 7516 STK A & M Motorsports