Disc brakes woes

[mezzmo]

Hi guys and gals,

i need to pick some brains here......As you may or may not be aware, we take our beloved 'Magic Bus' on the Variety Bash every year, last year i invested a fair amount in trying to get the brakes fixed, they have never really worked effectively. I have come to the conclusion the the professionals out there have absolutely no idea and as a hack myself, its like the blind leading the blind!

So, here's what i have. fully reconditioned Brake Booster and master cylinder, pbr callipers. What we are finding is serious brake fade but only intermittently, not all the time - at one stage we had no pedal at all and that could be a little scary heading down a mountain!!!!

Please, if there is someone out there that has done this conversion successfully your assistance will be greatly appreciated -

Thanks in advance!

Mezz

[johnxb351]

are you useing the brakes alot when this happens. like going down a hill ranges. if so your brakes  can get hot and it  can transfer heat to your brake fluid  and boils which causes air bubbles in your brake fluid. so when you push you brake petal  the brake fluid compresses the air bubbles that are taking up space in your brake line so you lose  hyd pressure.  also check that you are useing the wright brake fluid  for example  only  DOT 3.   check that your brake lines are not near hot spots  like  .extrators .  check that brakes are not draging good time to do this after a good long drive jack up van  on level with wheels chooked and van in gear if manual  . and spin wheels to see if the brakes are draging. brake draging will build up heat. they might smell hot too. do one wheel at a time so other 3 wheels are on ground. while doing this CARFULLY check if the brakes calipers and drums are hot.  just a note. if your van is a auto you use your brakes more than a manual gearbox.

[johnxb351]

when you spin rear wheel van will have to be out of gear

[mezzmo]

Thanks John, none of that you mentioned seems to be the issue, it's like you can be driving not using the brakes and then when you do they are incredibly spongy then the next time you use them they could be fine etc etc

[johnxb351]

sounds like air in brake lines. may need a good long bleedling of brake lines.  the longer your brake lines are the more bleeding they need as air has a lot ferther to travel.  was it doing it before you fitted new master cyl.

[Merlin]

heres a few things to check :rear shoes adjustment ( if to loose will give excessive peddle travel ) also check front wheel bearings for freeplay as this will push the caliper pistons back in the bore (worse when you do more cornering ) to check for air in the system pump the peddle 4 times to get a firm peddle the remove foot for aprox 10 secs and push the peddle again if its not firm then you have air in the system .you can localise where by clamping the flex line at each end and repete the process
                                                              Cheers Merlin

[rumax]

Hi Mezzmo, never fun....
Starting with the basics... I am assuming there is no evidence of brake fluid escaping from anywhere....
Could be anything, but start with the master cylinder. If there is a mark in the bore that aligns with a nick in the cylinder rubber.. as they rotate, it can cause an issue.. had this in a car in the 70's. Also, if the system doesn't release the pressure completely, it could hold on the brakes, causing them to overheat. This could be either the master cylinder or the booster, but generally the booster. The other option is the hoses. If they are old/damaged, under pressure, they "expand" reducing the pressure to the wheel cylinders/callipers... but that would be all the time. Just because the items are recon (or new), doesn't mean there not at fault!

[Rogerfied]

Have had this similar problem in the past, checked everything as you have just to find the vacuum hose to the booster was old and the hose had collapsed on the inside so this made the fault hart to predict. Installed new hose and made sure all fittings were leak free, end result was excellent.. Give it a look at might help

[Gordon]

Mezz, I had a similar issue and no amount of bleeding would solve the issue. In desperation I ended up bleeding the master cylinder by filling up the reservoir and loosening the front and back circuit connectors where they go into the master cylinder. Just enough until you start to leak fluid from the joints and then just tighten them up again. Solved the issue for me. Seems like air can get trapped up there especially after a master cylinder rebuild.

[mezzmo]

Thanks for the tips guys, i'll try the various combo's this weekend.