PDA

View Full Version : Yes another question about bleeding the brakes


nwcherokee
September 16th, 2010, 15:57
I am installing extedended SS brake lines, front & rear. I've only bled brakes on a 60's VW Bug before. Is there anything different that I should know before trying this? My XJ is equipped with ABS, is that going to change things? I've heard it's best to go in order of RR, LR, RF, LF. The way we did it back in the day was pump up the brake, crack the screw, close, pump some more and so on. Any better methods i'm unaware of?

Thanks
-Nick-

jeep ride
September 16th, 2010, 18:43
That's the way I do mine with no problems.

EMSJEEP
September 16th, 2010, 19:03
Vac. bleed is best, but that should work for ya too.

UKJEEP
September 17th, 2010, 04:03
In my limited (no pun intended) experience, bleeding XJ brakes is well nigh impossible because - like just about everything else - the bleed nipples will be seized solid!

Matthew Currie
September 17th, 2010, 07:22
Pumping the pedal and opening the screw, etc., is OK, especially if you have a patient partner, but if you're replacing whole lines it will take a long time. Vacuum bleeding is a bit quicker, as well as convenient for doing alone.

For small occasional bleeds, I have an old tailgate strut to which I put a little U-shaped block at one end to hook under the steering wheel. Pump up brakes, hold pedal down with strut, then go down and open the bleeder. It's slow and tedious, but effective if you're working alone without a vacuum pump.

ehall
September 17th, 2010, 07:28
vacuum bleeding sucks (:rof:), pressure bleeding is best way to do it. Motive sells one like this but you can make your own with a spare master cylinder cap and a garden pump

http://ecx.images-amazon.com/images/I/21tZ4owVJOL._SL500_AA300_.jpg

Fill it with brake fluid and force the old crap out

kastein
September 17th, 2010, 08:12
In my limited (no pun intended) experience, bleeding XJ brakes is well nigh impossible because - like just about everything else - the bleed nipples will be seized solid!
X2, you are missing the first steps - torque off old bleeder screws, curse a lot, walk to parts store, buy new drum brake cylinders, replace drum brake cylinders!

I have never had a problem with the front bleed screws, they seem to be more out of the weather and are a larger size so they can still be turned after corroding somewhat. The rears are often a disaster however.

EMSJEEP
September 17th, 2010, 10:46
X2, you are missing the first steps - torque off old bleeder screws, curse a lot, walk to parts store, buy new drum brake cylinders, replace drum brake cylinders!

I have never had a problem with the front bleed screws, they seem to be more out of the weather and are a larger size so they can still be turned after corroding somewhat. The rears are often a disaster however.

Having converted my D35 drums I have no problems with the rear caliper bleeder screws...when the differential isn't exploded in one manner or another. I have always had problems getting a good bleed, stock or otherwise, a vac is probly the best way. I will be buying one next time, I'm sick of fighting with the whole system.

Please explain more about pressure bleeding??

sjx40250
September 17th, 2010, 13:38
Gravity works if you have the time. Just keep fluid in res and a jar for each wheel. It will get all the air out. Vacuum will also suck air by the bleeder connectors leading you to think there is still air in the system.

joe_peters
September 17th, 2010, 15:33
One thing being overlooked is the ABS.

You need to bleed the brakes--gravity, pressure, foot pump.

Then you need to take it to a shop with a DRB scanner or equivalent so the ABS can be properly bled.

Good luck.

ehall
September 17th, 2010, 17:34
Please explain more about pressure bleeding??
Basically what the name says, it pressurizes the system and then you go around and crack the bleeders. This ways the old fluid is forced out, and there's no real opportunity for air to work back into the system, unlike gravity and vacuum bleeders.

http://www.youtube.com/watch?v=d0h5bMoW-aw

http://faculty.ccp.edu/faculty/dreed/campingart/jettatech/bleeder/index.htm

I still use a home-made bleeder that works under pedal pressure (uses a check valve at the catch bottle) that is less sophisticated but not as effective. My setup can work with vacuum bleeding but my experience it never works right since I can't get a good enough seal to create suction and air always gets in.

98stocker
September 17th, 2010, 17:53
Start at wheel furthest from mc.

Fill mc.

Put some fluid in a jar, attach vacuum tube to bleeder, and drop end of tube into jar of fluid.

Crack bleeder open, have assistant in drivers seat press brake pedal slowly down.

Close bleeder, have assistant let brake pedal up. Repeat last two steps about 20 times.

Fill mc again, move on to next furthest wheel.

Repeat open, press, close, let up cycle about 10 times.

Fill mc again, move on to final wheels and repeat.


Don't press pedal up or down too fast, can cause air in lines to turn into tiny bubbles which don't like to leave the system for some reason. Dunno why.

Oh yeah. If you let the mc run dry accidently, bench bleed it and start over.

kastein
September 17th, 2010, 18:04
Don't press pedal up or down too fast, can cause air in lines to turn into tiny bubbles which don't like to leave the system for some reason. Dunno why.
likely hydrodynamic cavitation. I've noticed this as well. Let the pedal up too quickly and the localized pressure in the brake fluid temporarily drops below the vapor pressure, so the fluid boils in tiny spots.

http://en.wikipedia.org/wiki/Cavitation#Hydrodynamic_cavitation

Unrelated, but "7 degrees of wikipedia" found it, isn't science awesome? Sonoluminescence, i.e. making a fluid glow by subjecting it to intense sound waves. http://en.wikipedia.org/wiki/Sonoluminesence

lawsoncl
September 18th, 2010, 13:45
Sonoluminescence, i.e. making a fluid glow by subjecting it to intense sound waves. http://en.wikipedia.org/wiki/Sonoluminesence


Pretty cool stuff. Most of my cavitation experience is on the acoustics side. Cavitation emits lots of acoustic energy and can eat away metal pretty quick.

winterbeater
September 18th, 2010, 16:29
Bleeding brakes: The best way is the GRAVITY method. The only problem is it takes a lot of beer and you don't want to drive right after. (CAUTION: YOU MUST BE 21 TO BLEED YOUR BRAKES THIS WAY!) I use it whenever I replace brake cylinders or calipers, but mostly it's just to change the brake fluid, which I do whenever I change shoes or pads. Ideally you change brake fluid at least every other year. If you worked on old cars and saw rusty pistons, you'd know why, but people also say that old brake fluid boils and won't stop you right.

1.) Get the car in a position where you can open up the bleeders. I always like to break them loose with a 6 point socket being careful not to break them off. If you can, spray them with breakaway or similar a day before.)
2) Starting with the bleeder furthest away from the master (pass. rear), open it about 1 turn. You can put a little hose and cup on it if you want to keep the old fluid from running all over. Make SURE to keep the master cylinder topped off with fluid and DON'T let it get down to where air gets back into the master cyl. Let it flow this way until the fluid comes out of the bleeder clean. This will take at least 2 cups or so of brake fluid. Using gravity alone, you can drink 2 beers while topping off the master cylinder for the first corner. (CAUTION: Do not store brake fluid in beer cans or put beer into master cylinder. Drinking a little brake fluid however will probably not kill you. Beer in your brake lines might.) Snug up bleeder good when you're done.
3.) Proceed to drivers rear and repeat. It won't take as long because the long brake line has already been purged of the old fluid. So you have to drink your beer faster.
4.) Pass front. Drink even faster.
5.) Drivers front. Etc.

Patience can be substituted for beers, but that's no fun.

This prevents the rubber pieces from going any further than they are used to and self destructing.

This should work fine with ABS systems too.

garr
September 18th, 2010, 17:00
vacuum bleeding sucks (:rof:), pressure bleeding is best way to do it. Motive sells one like this but you can make your own with a spare master cylinder cap and a garden pump

http://ecx.images-amazon.com/images/I/21tZ4owVJOL._SL500_AA300_.jpg

Fill it with brake fluid and force the old crap out

+1, pressure bleeders & speed bleeder valves (with the internal check valve) have made properly bleeding brakes a simple job.

Vacume bleeders suck!