Brake Bleeding Frustrations

[Andy W]

Hi, I have fitted new seals etc. to all four calipers, fitted a new proportioning valve, painted them and got them all pretty and then spent two hours and 2 1/2 litres of brake fluid bleeding the system and failed! - the pedal goes slowly to the floor.

Firstly, I have to say that the brakes were working perfectly before I striped and overhauled the calipers last weekend.

To bleed the system, I pumped a few litres of oil through with compressed air, there was no sign of bubbles from any of the calipers for the last litre or so of oil - I would have expected this method to have bled the master cylinder as well.

Anyway, the symptoms are as follows:-
- with the engine not running, the brake pedal is hard, and there is no movement of the pedal when I push on it and keep the pressure there for 10 seconds or so.
- with the engine running there seems to be more movement in the pedal and if I keep a gentle pressure on the pedal it gradually travels to the floor. Pumping it
makes very little difference.

So the problem seems to be when the servo is operating.

Tonight I had a go at bleeding the master cylinder; I slackened one front and one rear brake line connection to the master cylinder, pushed the pedal down, re-tightened the brake lines, let the pedal up and then repeated it a dozen or so times resulting in - no change.
Then I used compressed air on the reservoir to blow the fluid through; I slackened all four brake lines, held the pedal down, pressurised the reservoir and waited - nothing happened. So I tightened the brake lines, let the pedal up, pressurised it again with the pedal up, slackened all the brake lines and bled it until close to the minimum level, re-tightened everything and de-pressurised. Checked again and the same symptoms as above, engine not running - feels good, engine running - the pedal travels to the floor.

One thing I don't understand is that in the past if there was air in the system, the pedal felt spongy but this time when the pedal moves, it almost feels like the brake fluid is going past the master cylinder seals. When I say this I am sure that is not the case as the master cylinder is pretty new looking at it and everything was good until I started fiddling!

Needless to say, I am getting very frustrated and short of brake fluid!

Can anyone help please, thanks, Andy

[Mr. Flibble]

In the L400 you must bleed with the engine running due to the kind of ABS. Learned this the hard way after putting quite a lot of brake fluid through the system.

[thelazygreenfox]

Always frustrating, messy and never easy. My description of delica brake bleeding! Gotta love backyard mechanics, yup I'm one also .

It's simple.... Engine running (thx MF), van up on jacks, wheels removed, bleeder in place on (1) rear pass side brake, hose facing upwards to bottle mounted above the bleed screw. Fill up master cylinder,crack open the bleed screw, depress brake pedal till bubbles stop flowing up to the bleed bottle. Close the bleed screw and move to the (2)front drivers wheel, then(3) rear drivers wheel and finally(4) front passenger wheel.

"No you can't do it any other way", the manual say do it this way cuz the brakes bleed best this way. If you haven't bled the brakes before have a friend help you. If you don't have any friends pay the kid next door . LOL

If the bleed screw is wide open the screw threads will suck in air . Open it only as much as you need to bleed the brakes..

If a friend helps you, open and close the bleed screw as he pushes on the pedal but if you bleed by yourself use a one way flow valve in the clear plastic bleed line.

Continually fill the master cylinder as it empties........

Good luck
TLWF

[Andy W]

Thanks but I have done all that, with my son pumping the pedal and me underneath and also using compressed air to push the fluid through, both making little difference. Everything seems to be pointing to the master cylinder seals even though the master cylinder and reservoir both look very new. Guess what I am doing at the weekend!
Andy

[thelazygreenfox]

Don't use CA! If you used compressed air, start the bleed process again as there is air in the lines. Also ensure your son is not releasing the pedal until you have closed the bleed screw.

If you're underneath then the van is not up on blocks and the wheels aren't removed for easy access to the brake bleed.

Other than that I can't help you.
Good luck

[Mr. Flibble]

I am with TLGF on this one, don't push with compressed air. Instead, use your compressor to power a bleeder like this:


http://t.harborfreight.com/brake-fluid- ... 92924.html

This pulls the fluid through the system, no need to pump with your feet. It took me about 20 min to do the system once I was aware that I needed the engine running. Also, as mentioned above, the order you bleed the wheels in is very important.

[T2Small]

If further bleeding doesn't help, the pedal dropping to the floor sounds like a master failure. Likely you killed the master during your bleed procedure.

[Yukonflyer]

How'd you make out?

I changed the front right calliper and rotor a couple weeks ago and put new pads in the front right and left as well.

I also removed and re-greased the slide pins on the front left and ensured proper grease on the new front right calliper. (the old calliper pins were completely dry and the front left were not much better)

I then bled fluid into the new front calliper using a vacuum bleeder from Princess Auto. Once the new calliper was full I started the engine and bled the system in the prescribed order (RL, FR, RR, FL)
I went around twice, used less than half a litre of brake fluid and took max of 30 minutes (I'm slow, could have don't it in 20min I think)

Brakes are nice and firm.

I'm going to pull the pins on the rear callipers next to re-grease them, it looks to me like that will be one of the keys to keeping brakes functioning properly and not having to replace callipers to often. So I plan to add greasing the calliper slide pins to the regular maintenance, perhaps once or twice a year.

Hope you got your problem sorted.

Happy Landings
Cam