Dot 4

[sdg3205]

I have been struggling with getting sufficient brake results on a few cars. At best I have replaced everything. From master cylinder, braided soft lines and Pistons to seals. At worst I have only upgraded the soft lines. When I bleed I do 2 go arounds with a pressure bleeder THEN use a buddy to do the pump method at least twice around. I also manually manipulate the outer piston on the front calipers (push back in to help get the air out of the chamber since the fill/bleed tunnels are the same) multiple times. I even elevate front and back to see if air is trapped anywhere.

The pedal is always still soft, which makes me wonder if I am using crappy DOT 4. Or perhaps I am missing something else?

[DMCMW Dave]

I have been struggling with getting sufficient brake results on a few cars. At best I have replaced everything. From master cylinder, braided soft lines and Pistons to seals. At worst I have only upgraded the soft lines. When I bleed I do 2 go arounds with a pressure bleeder THEN use a buddy to do the pump method at least twice around. I also manually manipulate the outer piston on the front calipers (push back in to help get the air out of the chamber since the fill/bleed tunnels are the same) multiple times. I even elevate front and back to see if air is trapped anywhere.

The pedal is always still soft, which makes me wonder if I am using crappy DOT 4. Or perhaps I am missing something else?

I've seen some rebuild kits where you put the car all together, drive it 50 miles or so using the brakes a lot, and then bleed it again. Not sure why but it works. Seems to depend on the source of the rebuild kits.

The only fluid that can cause this problem is DOT5, because it's very difficult to get air out of it.

[David T]

Air can get trapped in places difficult to bleed. Since you are having so much trouble I suggest you first rebleed the master cylinder on a bench. Once you are certain you have gotten all of the air out put it back on and start with the F/L wheel, F/R, L/R and then R/R. Keep the car level and do it at least twice. I like the pressure method using an assistant and a one man bleeder aka check valve on the bleeder nipple. Refill the master cylinder after doing each wheel. NEVER reuse brake fluid once removed. If the pedal is still soft watch each hose as the pedal is depressed. If you see one swelling up under pressure it is bad. To properly bleed the brakes you should use a quart of brake fluid total (1/4 of it for each wheel) and a pint for the master cylinder. If that doesn't fix it you probably have a bad master cylinder.

[Ron]

$.02

Actually, you should bleed from longest to shortest run for any vehicle -- Usually RR, LR, RF, then LF.

If all else fails, divide and conquor - After confirming all flex lines are OK, plug the master cylinder ports off and see if it firms up. If so, remove one or the other to determine which is the culprit (spongy). Leave the other plug in and move down to the Tee on the "bad" line and follow the same logic...

[sdg3205]

I think I may have found the culprit.

After running 3 litres of brake fluid though the system via pressure bleeder and the buddy system I decided to push the rear pistons back into the callipers the same way I do the outer front calliper pistons (essentially a manual burp of each side of the calliper). I got a big burp from the rear left. I was a little surprised given I felt like I was grasping at straws, but sure enough the pedal improved. Im not sure how the air was trapped in a rear calliper that never got opened, but it certainly did.

I'll do a test drive tomorrow and report back.

[Jonathan]

I think I may have found the culprit.

After running 3 litres of brake fluid though the system via pressure bleeder and the buddy system I decided to push the rear pistons back into the callipers the same way I do the outer front calliper pistons (essentially a manual burp of each side of the calliper). I got a big burp from the rear left. I was a little surprised given I felt like I was grasping at straws, but sure enough the pedal improved. Im not sure how the air was trapped in a rear calliper that never got opened, but it certainly did.

I'll do a test drive tomorrow and report back.

Can brake fluid syphon backwards towards the reservoir or other open lines even on a caliper that didn't get opened? There's no check valves in the lines anywhere to my knowledge. Maybe the cap on the reservoir and everything being closed up normally prevents this from naturally happening? Just thinking out loud...

[Bikercmbc]

I have the exact same issues on my car, just rebuilt everything and still has a bubble somewhere. last time i did this i had to driver it around a while and it helped. ill be pressure bleeding it again and hope it gets it out. ill try to do the individual pads like you are talking about also.

[sdg3205]

Yes, I don't know how but i had a big burp from the rear left INNER calliper. I kept the pressure bleeder on at 15-20 PSI, pushed the piston in and bleed a massive pocket. Pedal is rock solid again.