Kentite Posted April 14, 2018 Report Share Posted April 14, 2018 Our brake pedal is distrubingly soft when the vehicle is running, but rock solid when the engine is off. This was somewhat noticeable last time we ran the car (October), but seems to be worse now as we have just reassemble for the spring. We have a new brake booster and check valve, and I DO understand that the power assist will soften the pedal, but like I said it is softer than ever. New front calipers, but currently our old pads are installed (they have maybe 20% let on them) as we are waiting for the new ones to arrive. Also we are using a stock master cylinder, which is 5 years old, to push a single piston rear disc swap and dual piston front calipers as opposed to OE single piston. So it may need to be upgraded. It is a four port master with an individual line to each wheel. No ABS. Thoughts? I’m thinking maybe something internal in the MC, but I feel like that would be evident with the engine off. Maybe a bent pad or mounting bracket? We do have slight kink in one line from some ham fisted jacking by yours truly but the wheel it goes to is releasing fully. Quote Link to comment Share on other sites More sharing options...
mender Posted April 14, 2018 Report Share Posted April 14, 2018 Have you test driven the car to see if the new booster is adding more assist? I had one that allowed me to push the pedal to the floor but only because it had way too much boost! Just looking at the pedal locked up the brakes! 1 Quote Link to comment Share on other sites More sharing options...
Kentite Posted April 14, 2018 Author Report Share Posted April 14, 2018 36 minutes ago, mender said: Have you test driven the car to see if the new booster is adding more assist? I had one that allowed me to push the pedal to the floor but only because it had way too much boost! Just looking at the pedal locked up the brakes! We are about to load it for alignment. We will drive it in a couple hours, gonna be pouring rain though. Quote Link to comment Share on other sites More sharing options...
Ian Posted April 14, 2018 Report Share Posted April 14, 2018 If you went to disc rear, and dual piston front from drum/single piston, you likely need to increase the size of your master cylinder. You effectively doubled the surface area of your braking system, which means you need to move twice as much fluid for the same amount of brake force. Which means the pedal must travel further to move said fluid. On our car, if we made the same conversions, we'd need to switch from 7/8" master, to a 15/16", or 1" master. Quote Link to comment Share on other sites More sharing options...
Kentite Posted April 14, 2018 Author Report Share Posted April 14, 2018 40 minutes ago, SonsOfIrony said: If you went to disc rear, and dual piston front from drum/single piston, you likely need to increase the size of your master cylinder. You effectively doubled the surface area of your braking system, which means you need to move twice as much fluid for the same amount of brake force. Which means the pedal must travel further to move said fluid. On our car, if we made the same conversions, we'd need to switch from 7/8" master, to a 15/16", or 1" master. I’m going to look into something bigger at some point, but what we’ve had has worked for years. Pads just showed up so we will install those tomorrow and bleed the brakes again. I have a feeling that one of the internal prop valves in the master is bad. I had one brake line disconnected for a while to remake it and no fluid came out of the port. Quote Link to comment Share on other sites More sharing options...
Ron_e Posted April 14, 2018 Report Share Posted April 14, 2018 Air in the system? Regarding increasing the master cylinder size: We changed the rear from drum to disc, internet said we needed to increase the size of the master. We didn't. We changed the front from single piston to dual piston and larger area, internet said we needed to increase the size of the master. We didn't. We converted to manual without booster and moved the pivot point of the pedal, internet said we needed to increase the size of the master. We didn't. We changed the front to a different caliper with even larger area, internet said we needed to increase the size of the master. We didn't and it was still fine. Easy to swap to 94+ master with a larger piston but it was points at the time and our brake feel is exactly as much as I would want it to be. 2 Quote Link to comment Share on other sites More sharing options...
Team Infiniti Posted April 14, 2018 Report Share Posted April 14, 2018 2 hours ago, Kentite said: what we’ve had has worked for years Ok, so your saying there have been no system changes, just taken apart and reassembled? If so You need to drive to get pads settled in to their "grooves" (literally) also re-bleed and consider what Mender said, it may just be boost, putting pedal feel aside, how well does it stop after everything is settled in? 1 Quote Link to comment Share on other sites More sharing options...
Ogren-Engineering Posted April 16, 2018 Report Share Posted April 16, 2018 I have reduced my booster value by porting the vacuum line . The best way is to fit a metal fuel filter in line and drill holes in it to lower the vacuum value. Also I drilled the check valve straight through so there is no check valve and the hole is open at the booster itself. I have a Ford brake peddle assembly . The largest Ford MC I could find is a 96 F150 with ABS @ 1.25 in. This increased peddle pressure and works pretty well with the reduced vacuum. I have pad kickback due to having a solid axle with some endplay required and the rotors hung on the ends. One short stab sets the pads and the brakes stop great after contact . I still get drivers complaints about a low initial peddle tho. I toyed with floating the rotors , mounted inside of the axles on extended wheel bolts/bushings etc. Quote Link to comment Share on other sites More sharing options...
Technical Advisory Committee NigelStu Posted April 16, 2018 Technical Advisory Committee Report Share Posted April 16, 2018 On 4/14/2018 at 12:00 PM, Kentite said: . We have a new brake booster and check valve, Is the check valve installed the right way? Worth double checking. Quote Link to comment Share on other sites More sharing options...
Black Magic Posted April 16, 2018 Report Share Posted April 16, 2018 1 hour ago, Ogren-Engineering said: I have reduced my booster value by porting the vacuum line . The best way is to fit a metal fuel filter in line and drill holes in it to lower the vacuum value. Also I drilled the check valve straight through so there is no check valve and the hole is open at the booster itself. I have a Ford brake peddle assembly . The largest Ford MC I could find is a 96 F150 with ABS @ 1.25 in. This increased peddle pressure and works pretty well with the reduced vacuum. I have pad kickback due to having a solid axle with some endplay required and the rotors hung on the ends. One short stab sets the pads and the brakes stop great after contact . I still get drivers complaints about a low initial peddle tho. I toyed with floating the rotors , mounted inside of the axles on extended wheel bolts/bushings etc. Have you tried floating caliper mounts? Fixed mounts on a c clip style axle are trouble for this reason. Quote Link to comment Share on other sites More sharing options...
Ogren-Engineering Posted April 16, 2018 Report Share Posted April 16, 2018 The truck has BA GM Impala calipers X4 . They float a little and maybe more check valves in the lines might improve it some . I dont find it as a problem, but my candyass drivers dont trust the brakes 100%. Quote Link to comment Share on other sites More sharing options...
Kentite Posted April 16, 2018 Author Report Share Posted April 16, 2018 2 hours ago, NigelStu said: Is the check valve installed the right way? Worth double checking. Yep. Problem was starting to appear at the end of last year, we have since replaced booster and check valve. We were bleeding yesterday and were able to get the pedal back to normal. Then it went away again. Leaning towards a prop valve of which there are two in the master cylinder. After the pedal went away again I removed a line from the master cylinder on the port I’m suspicious of. No static fluid flow. We have had the same MC on the car for 5 years so I have one ordered. I’ll chalk the $40 and a little labor up to maintence if it doesn’t solve the problem, but I’m thinking it will. 2 Quote Link to comment Share on other sites More sharing options...
Administrators E. Tyler Pedersen Posted April 16, 2018 Administrators Report Share Posted April 16, 2018 How much movement does your MC have when you press your pedal? Worth making a brace for it to not move so much? Quote Link to comment Share on other sites More sharing options...
Kentite Posted April 16, 2018 Author Report Share Posted April 16, 2018 6 minutes ago, Crank Yankers Racing said: How much movement is your MC moving when you press your pedal? Worth making a brace for it to not move so much? More than we’d like, which to us is any movement at all. Already on the list. Unfortunately the list is LONG. Quote Link to comment Share on other sites More sharing options...
Administrators E. Tyler Pedersen Posted April 16, 2018 Administrators Report Share Posted April 16, 2018 5 minutes ago, Kentite said: More than we’d like, which to us is any movement at all. Already on the list. Unfortunately the list is LONG. Replacing the MC is a great start. I need to make a bracket myself. Just more other things that are pressing now 1 Quote Link to comment Share on other sites More sharing options...
wvumtnbkr Posted April 16, 2018 Report Share Posted April 16, 2018 It doesnt look like anybody mentioned a soft line issue. They can balloon and cause the soft pedal feel. Mash on the brakes while somebody checks each hose. It will probably be visible if there is an issue with the hoses. 1 Quote Link to comment Share on other sites More sharing options...
Black Magic Posted April 16, 2018 Report Share Posted April 16, 2018 You probably already have it, but if not pressure brake bleeders are a gift from god when it comes to getting the air out. 1 Quote Link to comment Share on other sites More sharing options...
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