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Discussion Starter #1 (Edited)
My race car is a 89 mustang coupe with all wheel disc brake conversion... All new brake lines new calapers etc. The brakes dont work unless I pump them a few times first? The system has been bled correctly but still the same.? it has a manuel brake conversion on it aswell.. all air is out of all four corners. the brake pedal is real soft feeling.Any ideas? Maybe manuel brakes dont push enough foru calapers? Anyone run front brakes only on there race car?
 

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You first mistake was allowing Manuel to do your brake conversion.
 

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you need a modulator valve for the rear brakes.with man.brakes you need a valve to stop the fluid from bleeding back into the master cylinder.put a 5 lb valve on it
 

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residual valve inline to hold pressure...wilwood sells them
 

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yea, prob need a residual valve, but not a 5 lb one, could lock up you brakes-try a 2 lb one
also make sure the p/r is long enough, if its at the wrong angle, might not be in correctly
also needs the proper size piston in the MC, and the correct ratios, as mentioned-some people use to big a piston, lose pressure
 

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Discussion Starter #13
Ok I got all the lines where they need to be and bled the brakes and the brakes only will work if I pump then a bunch of times..?? I went to the performance shop here in town and they told me the only time I need the residual valve is if I had willwood brakes all the way around. I have stock cobra dics brakes all the way around..??????????? any ideas?
 

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Ok I got all the lines where they need to be and bled the brakes and the brakes only will work if I pump then a bunch of times..?? I went to the performance shop here in town and they told me the only time I need the residual valve is if I had willwood brakes all the way around. I have stock cobra dics brakes all the way around..??????????? any ideas?
What master cylinder are you using? What is your pedal ratio? ? I would still put a residual valve in line as stated.
 

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you need a 2lb residual valve for the rear brakes, regardless of what the guy at the shop told you

so the rear brake fluid needs a valve because the fluid might suddenly not be effected by gravity and travel uphill towards the master cylinder thats higher than calipers?-all while allowing an air bubble to travel downward to the caliper?
 

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Discussion Starter #17
alright... Ill pick one up tomorrow and give it a try... Im using a man. brake kit with stock style cylinder.. I have used this same setup on my last car and worked GREAT! but it has drum brakes in the rear..
 

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alright... Ill pick one up tomorrow and give it a try... Im using a man. brake kit with stock style cylinder.. I have used this same setup on my last car and worked GREAT! but it has drum brakes in the rear..
i don't know how well a stock style master cylinder will work with disk rear. the racecraft kit i got has 2 different bores, one is larger which pushes more fluid, you use that line to the brakes you want to do most of the braking. in the instructions it says to use a 10lb residual valve for drum rear, and a 2lb residual valve for disk rear.
 

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i don't know how well a stock style master cylinder will work with disk rear. the racecraft kit i got has 2 different bores, one is larger which pushes more fluid, you use that line to the brakes you want to do most of the braking. in the instructions it says to use a 10lb residual valve for drum rear, and a 2lb residual valve for disk rear.
yeah... I think the disc conversion on the rear is what is getting you, and you might not have enough bore on the MC.
 
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