brake pressure fade

[renovationinnov]

Hi guyS i was just bleding my brakes for the first time with the help of my apprentice
i havent started the motor up but when bleeding the brakes the peddle has harden but still travels about 50mm on the foot pad to get firm but i can still turn the front wheels with a bit of force but the rears are locked solid
is this only that i have not got vaccum in the booster or has the master cylinder got a by pass problem from new or do i need a porsionvalve fitted to the rear to make the front work
HELP
ROB

[sevenohms]

Something wrong rob. Should easily resist your motion.

Maybe a bubble stuck somewhere. Worth leaving it overnight, let it settle, and try again in the moring.

[Rob. Smith]

Did you bleed the master cylinder before fitting it ? It is a pain in the bum but necessary

[Zedn]

Definitely sounds like air in the front lines. Keep bleeding!

[renovationinnov]

tried leaving it over night with the front up on stands
3 bottles of fluid thru now & still soft '
then tried the master cylinder bleed reconnected the lines & rebleed still the same
but did notice as my misses release the pedal till shot brake fluid up in the master cylinder


might ring grilock Monday & see if they have a idea
master cylinder is new xe falcon white fluid resevior all new lines & jag reconditioned calapers

[Rick Parker]

Did you bench bleed the Master cyl BEFORE instalation? Somtimes a bubble can be trapped within the master cylinder that is impossible to relieve once installed.

[Legless]

I'll second Ricks thoughts, if you haven't bench bled the MC, pull the master cylinder out and bench bleed it. I put a new master cylinder in without bench bleeding it once, bled it and bled it, then drove it 1500km, went to a race meeting bled it in the car again then went to another race, still had the same issue. I ended up pulling The MC out and bench bleeding it! Problem went away. If you did have the booster connected you'd probably find the brake peddle heading for the floor.

[sideshow]

get 4 vise grips

clamp off all 4 rubber brake lines that goto the wheels
then press the pedal it should be rock solid
if it is not rock solid then u have air in yr master cylinder or faulty master cylinder

if it is rock solid then unclamp each vise grip one at a time
and after each one test pedal again
the wheel that softens the pedal the most when the others are clamped up is the problem one

[sevenohms]

Originally Posted by renovationinnov

tried leaving it over night with the front up on stands
3 bottles of fluid thru now & still soft '
then tried the master cylinder bleed reconnected the lines & rebleed still the same
but did notice as my misses release the pedal till shot brake fluid up in the master cylinder


might ring grilock Monday & see if they have a idea
master cylinder is new xe falcon white fluid resevior all new lines & jag reconditioned calapers

depending on your installation the caliper might not be able to bleed all the air out. I'd do what sideshow suggested, clamp the hoses on the front, and see if they improve, then I'd take the caliper off and put the bleed nipple to the highest point possible and see if that helps. just make sure you put something between the pads

[Mrs flatchat]

Vacuum bleed --works for me

[Gaz64]

All your caliper nipples are at the high point of the caliper?

I knew one guy years ago that put his front calipers on the wrong side with the nipples facing down.

[renovationinnov]

ok !! i might be stupid but how do you vaccum bled brakes mrs flatchat

gaz 64 my calapers have the bleed nipple at ta the middle of the caliper but just below the flex hose on the caliper [ they may be upside down but i took a pick when i disassembled the front end then put them back as the pics but the front end was pulled apart before it got to me !!
might goole jag front ends & find out whats what

i'll try again tomorrow thanks again
ROB

[Mrs flatchat]

We use this thing (closest ref from Ebay) available from Super Cheap, Repco, Autobahn
Great for pulling old fluid and air through for fresh -- its a one man job and the pedal feel seems to be superior to the two man effort of push the pedal and crack the nipple type.
Plug this device to your compessed air source attach the bleed hose to the nipple - pull the trigger and crack the nipple open --watch the fluid and air into the container bowl until continuous -close nipple and move to the next one --job done --do the longest lines first and keep the reservoir full


Vacuum Brake Bleeder OTC8104 Brand NEW | eBay

this site is a PITA for loading pics

[Gaz64]

Rob,

The nipples are below the flex hose?

Perhaps my wording was confusing.

Are the bleed nipples at the highest point within the caliper piston/s bore?

Poor design makes it difficult, if not impossible to get all the air out.

[renovationinnov]

gary [ gaz 64 I couldn't sleep thinking I had put the calipers on upside down & wrong handed so when looked again but the pics I took had the nipples to the ground so to day is turn & swap then make new brake pipes to suit ;; as the front end came with no plumbing so any type so bled again & see what happens

mrs flatchat thanks ;i'm off to repco to get one of those vaccum bleeders

thanks rob

[boxhead]

Rob, put a picture up of your calipers fitted to the car, also make sure we know the orientation (which way is up)

Sounds like you may have them fitted left to right and vice versa.


Also, note to all, never, repeat NEVER use vice grips on your flex hoses.
You WILL damage the rubber if not external then internal, only way you will find out is when you jam your foot on the brakes and the hose ruptures.

If you need to clamp off a flex hose, spend teh $12 and buy the proper tool from supercheap (no sharp edges and not ratcheting so you can over squeeze them).

[sideshow]

vac bleeders work ok when the system is working good
and u use them for just flushing the system with new fluid every few years
they can help with removing air but not always
the best system is a pressure bleed but u push fluid from nipple back up toward and out master cylinder but dont ask me where to buy the tool

i am pretty sure the hole where the rubber brake hose goes into the caliper should be lower than the bleed nipple so maybe thats yr problem because if the nipple is lower u will never get the last bit of air out
this is where the vise grip check will prove its air in the calipers in 5 minutes
so if u have not tried the vise grip test it will take 5 minutes and prove if it calipers or master cylinder or u can keep fking round and waste time guessing hehehehe

[AC-460]

your displacements are incorrect...... Your problem is what you first suggested.... if you don't have a dual master cylinder setup eg one for front one for rear with a balance bar and you are relying on a single master cylinder your displacements are wrong eg your rears are locking up because your master cylinder has supplied more fluid to the rear than the front..... you need to fit a proportioning valve to bleed off pressure to the rears.... or reduce the piston size of the calipers on the front..... or increase the piston size of the calipers on the rear

[AC-460]

Best way I have found to bleed a system is simple....just use a big syringe first put it in your master cylinder an suck it dry... then put a bit of clear plastic hose on the front and push it fast back through the bleeder.... go to slow and the air will remain in the high spots....using the pedal to bleed wont clear the air out of the high points in the brake lines

[Legless]

Originally Posted by AC-460

Best way I have found to bleed a system is simple....just use a big syringe first put it in your master cylinder an suck it dry... then put a bit of clear plastic hose on the front and push it fast back through the bleeder.... go to slow and the air will remain in the high spots....using the pedal to bleed wont clear the air out of the high points in the brake lines

If the master cylinder is in situ wouldn't it still be possible to have air in it if the piston wasn't fully compressed where as with a bench bleed you can be sure the piston is fully compressed?