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Help With a spongy Brake Pedal

T

TK5

1/2 ton status
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May 29, 2002
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Fairview , Tennessee
Just finished my install of my 3/4 ton front and rear axles. Everything is hooked up and brakes have been bled. I am using a 3/4 ton dana 44 and 14 bolt converted to disc brakes Evrything is new pads and calipers. After bleeding the brakes and getting all the air from the lines I still have spongy brakes.

My thoughts is probably the combination valve has something to do with it. Or my master cylinder may be going bad. All this is in an '83 K-5 blazer with a 6.2 diesel with hydro boost.

Any suggestions what I should do now?

I have driven the vehicle at speeds of about 35 mph and seems to stop fairly decent but I feel needs soemthing else to make stop quicker. The bias seems to good between the front rear, but it is hard to tell right now. I really don't want to put it on the highway until I get get this problem solved.

Thanks in advance.
 
did the master cylinder stay full during the whole swap? or did it get empty? if it got empty? give it a couple bleeds, have someone pump the pedal twice then hold it to the ground while you crack the bleeder, or lines loose, then do the same starting with the rear wheels..are all the hoses ok? nothing rotted and expanding on ya?
 
Did the master cylinder work fine before the swap? If not, install a new one.

If it did work fine, take the truck somewhere and have it power bled. Sometimes just doing the 1 or 2 man bleeding by hand just won't do it. Gotta have it power bled. /forums/images/graemlins/wink.gif
 
I believe the rear disc conversion article on the main site covers this. The guy had the same thing with spongy brakes. He put in an aftermarket adjustable proportioning valve for the rear brakes. Remember discs have much larger pistons and will use more fluid as the shoes wear so keep checking it. The proportioning valve sends more pressure to the front brakes than the back, accounting for the soft pedal I believe.
 
ive run into this problem a few times before. we bled them forever and still had the spongy pedal. the only thing that seems to work someties is gravity bledding. crack all the bleeders open at the same time with the cap off of the master cylinder. they should drip slowly. let it do this for about a half hour, while keeping an eye on the fluid level. dont let it get dry! good luck. /forums/images/graemlins/thumb.gif
 
The master cylinder went dry. I gravity bled first and them went back pump bled a couple of imes. I had to remove the caliper to get the bleed screw at the top. I put a block of wood in between the piston and pads to keep from blowing out the piston. I have brand new stainless braided lines fromnt and rear.
 
did you bleed the master cylinder before you tried to bleed the rest of the system? if not you have a lot of air hiding in there. it probably wont do any good to try and bleed the master cylinder now, so you might as well just keep bleeding the whole system. i would bleed keep bleeding each wheel until the air stops of course, then try the gravity bleed trick for as long as it takes. Make sure whoever is opening the bleeders when your on the pedal starts with the wheel farthest from the master cylinder and works up to the wheel closest to the master cylinder.
 
What calipers are you using in the rear? If they're the Caddy calipers, you have to manually adjust the e-brake mechanism first, to snug the pads up to the rotors. Then bleed the brakes. Otherwise you'll never get rid of the spongy pedal feel. /forums/images/graemlins/frown.gif
 
You can get your own power bleeder kit. Mityvac makes it. Its the same guys who make the hand vaccuum pumps. They are around $30 at Car Quest. They make bleeding brakes a lot easier. You can get more air out in less time and it is a one-man operation. I bought mine a few years back and I am very happy with it.
 
If disk take more fluid and 3/4ton hard lines are bigger then you need somthing that will push more fluid right? 1ton master cylinder SHOULD do it thats what Im gonna try on mine. /forums/images/graemlins/thumb.gif
 
If the system ran empty it's air trapped in the Combination valve (part on the front crooss member).

Get uder the truck and loosen the line on the top of the CV on the passenger side. Don't take it completely loos just a few turns so it starts leak and tap on the CV with a wrench. Watch the fluid level in the rear of the MC. That will probably get it to burp some air. You can bleed that system for a month with the pump method and not get that air out of the CV. The inlet is on the top and the outlet is facing down hill.
 
Which model of corvette master cylinder did you use? A friend of mine at the auto parts store gave 2 models to possibly ue. These are big bore. First was 85 model special edition, the second was '89 ZR Editon with dual piston calipers front & rear. He's got the last on ecoming in tomorrow and we check it out.
 
Which model of corvette master cylinder did you use? A friend of mine at the auto parts store gave 2 models to possibly ue. These are big bore. First was 85 model special edition, the second was '89 ZR Editon with dual piston calipers front & rear. He's got the last one coming in tomorrow and we check it out.
 
[ QUOTE ]
Did the master cylinder work fine before the swap? If not, install a new one.

If it did work fine, take the truck somewhere and have it power bled. Sometimes just doing the 1 or 2 man bleeding by hand just won't do it. Gotta have it power bled. /forums/images/graemlins/wink.gif

[/ QUOTE ]

Well sometimes an old master would be fine before but if you power bleed it you could blow it out.
The old seals would be still holding ok, but a big rush of fluid brakes them.
Just gravity bleeding has worked fine for me everytime.
/forums/images/graemlins/thumb.gif
 
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