Author Topic: Brake bleeding (Read 5967 times)

jtanguay · « **on:** June 24, 2008, 01:35:02 pm »

so i decided to bleed my brakes yesterday. while examining the front calipers they looked pretty worn... one side had the rubber for the piston all rotten. so i bought new calipers. installed them, and began bleeding the system.

i had bought a pressure bleeder last year and wanted to give it a go. so i attached it to the brake reservoir and pumped up the pressure to about 30 or so psi. i followed the correct bleeding procedure minus one part... the part about pulling the regulator all the way back. (mine is quite rusted, and will probably need changing by next year

) so i bled each till clean fluid came out and absolutely NO bubbles. probably flushed a pint or so through the system in total.

get in, the pedal feels nice and stiff, like a car should when there is no brake boosting. turn it on, and she feels kinda like before, but almost a bit worse? push the pedal and it feels stiff for about 1 second until it starts going to the floor. it takes a while to get there but eventually it'll reach.

now i'm thinking my master cylinder is bad and the pressure is bleeding past the piston and slowly going to the floor. surely there isn't enough air in the system to make it go to the floor???!!! a few pumps and it becomes stiffer, but after a second it goes right back to how it was.

does the rear proportioning valve really matter that much??? i want to try and squeeze another year out of that thing... try to spread out the repair bills wherever possible :lol:

thanks for any help!

gigaz2 · « **Reply #1 on:** June 24, 2008, 01:44:49 pm »

I screwed a master cylinder, and it felt like that.
debris get into the seals and scratch the sealing surface (or something like that)

if its just the valve, you can bleed again (correct way) and it will work right?

saurkraut · « **Reply #2 on:** June 24, 2008, 02:15:05 pm »

Quote from: "gigaz2"

if its just the valve, you can bleed again (correct way) and it will work right?

I've been using a pressure bleeder for over 5 years. Its the easiest and, due to the positive pressure with steady flow, probably the best way to get air out of the system.

What, pray tell, is the "(correct way)" in your world?

zukgod1 · « **Reply #3 on:** June 24, 2008, 02:18:00 pm »

I really like the pressure bleeders that attach to the master VS the ones that suck from the bleeder.
I've had a couple cars that fought me on using the sucker but on both I also found a loose line allowing it to suck air, very little but still.

jtanguay · « **Reply #4 on:** June 24, 2008, 03:27:38 pm »

the reason i think my master is gone is because last year it ran dry when one of my rear wheel cylinders started leaking the fluid. didn't really notice until there wasn't much left, only because i hardly use the brakes (downshifting... i bought new pads for the front but they look virtually brand new!!!)

so just wanted to know if someone had a similar problem and it was the proportioning valve... guess i'll have to buy a master cylinder and bleed the system AGAIN (the pressure bleeder is awesome! one man job FTW)

thanks!

burn_your_money · « **Reply #5 on:** June 24, 2008, 06:31:14 pm »

don't buy a new master, just take it apart and freshen it up. It's easy.

Did you ever run out of fluid when you were bleeding the brakes? It sounds like the master just has air in it. I'll come buy and give you a hand bench bleeding it or whatever if you'd like.

zukgod1 · « **Reply #6 on:** June 24, 2008, 09:24:43 pm »

Quote from: "burn_your_money"

don't buy a new master, just take it apart and freshen it up. It's easy.

And SOOOOOO much cheaper!!

I was up against the clock when I though my master was bad, $170. later it was a damn seal on the Audi calipers I rebuilt..

At least I have a good mk3 22mm master as a spare..

Dakotakid · « **Reply #7 on:** June 24, 2008, 09:42:01 pm »

JT:
Yes. Last summer I put the pristine "basket case" (actually makes sense) gas Jetta together and had my first encounter with that rear proportioning valve. I have to admit...it took me quite a while to figure it out. The futures price in brake fluid went high on Wall Street. But, my lines sure were clean!!!!!
Finally, I parked it on concrete and saw the puddle after sitting overnight. It would drip straight down and not really litter/wet itself as it leaked.
Luckily, I still had one parts Jetta that had a good one.
This was on an "85 Jet.

jtanguay · « **Reply #8 on:** June 25, 2008, 04:51:59 am »

at first i had a problem bleeding the rear left side (2nd in sequence) so i thought it was the proportioning valve. (pressure on bleeder was about 30 psi, so fluid should have been pissing out) so i smacked the proportioning valve and then depressed the brake pedal a few times for good measure. then fluid started coming out. wasn't bad fluid as it was bled the year before.

i would imagine that since fluid was coming out, i should be in the clear, right??? :lol:

now since i was doing some 'heavy duty' bleeding, the pressure reservoir went dry :oops: but when i took it off there was still fluid in the brake reservoir, so i should be ok right? air pressure basically pushing the fluid into the system? i topped off the fluid.

after driving today i'd say the brakes aren't too bad. i would say that they are more touchy than before, but theres still a bit of travel before they come on. then again i dont think i've ever had a vw with sensitive brakes :lol:

tyler i have to bring back my Giles pump for him to 'tweak' it a bit more, so maybe then you can take a look at it? i'm really thinking its the master cyl though. probably the same one from '92 :roll: plus me letting it run dry probably didn't do it any good :oops: (and the fact that the fluid was nassstayyyy :lol:)

where can i buy the seals to freshen up my master cyl? there's also a nice honing kit at princess auto that would fix it up nicely :wink:

this might be a good time to install a rear disc system :twisted:

thanks

Kneale Brownson · « **Reply #9 on:** June 25, 2008, 12:27:13 pm »

When I use a pressure bleeder, I keep it to around 15 psi.

I don't think you should pump the brake pedal with the pressure bleeder operating. Especially with 30 psi.

Most modern cars there's no way to rebuild the MC. I used to hone and reseal cast iron MCs back in the 1950s and 60s, but then I started driving cars with alloy MCs.

madmedix · « **Reply #10 on:** June 25, 2008, 01:31:11 pm »

On the pressure regulator mounted amidships; there is an eyelet on the main body and another on the tab itself that moves during pressure regulation. On the instruction sheet that came with my new one; it stated I am supposed to grab the tab (that moves with regulating the pressure) and pull it to the main body and run a stick or twist tie through the eyelets to hold it open. THEN you can bleed the rear end....

Andy

smutts · « **Reply #11 on:** June 28, 2008, 12:58:08 pm »

If you pumped the brake pedal further than it has been the last twenty years, then it is possible that the master cylinder seal caught on some rust or crap that has sat undisturbed for yonks. My old Renault drank brake fluid by the pint, but could I find the leak? :? It was only after the servo filled up with half a gallon it started dumping itself into the intake manifold. Then it said hello by huge clouds of acrid exhaust smoke. :idea: This won't happen as the diesel uses an air pump for the brakes, but cracking the master cylinder bolts/nuts that hold it onto the servo might release a dribble of brake fluid and put you in the picture. :wink:

commuter boy · « **Reply #12 on:** July 03, 2008, 01:03:44 pm »

+1 on putting the brake pedal down farther than it ever went before, and scoring the master.

You should always put a block of wood or something under the brake pedal when you're pumping it to make sure that it doesn't happen.

Farmermike · « **Reply #13 on:** July 08, 2008, 03:56:20 pm »

have you found the source of the problem? im new to this stuff but id really like to know if it is your master cyl. ive got a mk2 gtd and have exactly the same problem. with the engine on the pedals there for a few seconds, then slowly sinks to the floor. i replaced the master with one out of my old petrol mk2 and its still the same. not loosing fluid and have new callipers and rear wheel cylinders. im left with two choices either the spare master cyliner is leaking aswell although it was working fine on the other car (but has been stood for a year) or could the regulator is somthing to do with it :? my brakes have been the same for months now and i was just about to post a big help message when i saw this situation was identical.

jtanguay · « **Reply #14 on:** July 08, 2008, 04:34:55 pm »

Quote from: "Farmermike"

have you found the source of the problem? im new to this stuff but id really like to know if it is your master cyl. ive got a mk2 gtd and have exactly the same problem. with the engine on the pedals there for a few seconds, then slowly sinks to the floor. i replaced the master with one out of my old petrol mk2 and its still the same. not loosing fluid and have new callipers and rear wheel cylinders. im left with two choices either the spare master cyliner is leaking aswell although it was working fine on the other car (but has been stood for a year) or could the regulator is somthing to do with it :? my brakes have been the same for months now and i was just about to post a big help message when i saw this situation was identical.

i have a sneaky suspicion that it is the rear proportioning valve... it looks soo rusty in there so i would really like to just get in and replace it, along with the lines... and do some more work while i'm in there :wink: i don't want to give up on the master cyl just yet. the car is quite driveable the way it is with using the clutch to slow me down.