Rear Brake Issues - Need Help!

[TDI_Cubed]

We have rebuilt the brakes on the 2K Golf, front and rear: new calipers, rotors, master brake cylinder, and new fluid. During the brake bleeding, it was very difficult to bleed the rear brakes, to the point that I had to press on the brake pedal to accomplish the bleeding. Once fully bled, during the test drive, a lot of pressure needed to be applied to get any rear brake action.

I'm stumped - do the rear brake lines need to be replaced, or?

 

[Genesis]

Sounds like there's some trash (or corrosion, etc) in the proportioning valve that distributes braking force between front and rear. I don't know where it is on these cars (I haven't had to screw with mine) but that would be my first guess on what's going on.

 

[Nutsnbolts]

How do you know that it requires greater pressure to get the rears to apply, as opposed to the whole brake system? If it takes a great deal of force to apply the brakes, then that is usually related to a booster issue.

If you mean that the pedal travel is greater than normal, then the issue sometimes has to do with the rear calipers themselves taking a longer time to seat up.

-Rich

 

[TDI_Cubed]

How do you know that it requires greater pressure to get the rears to apply, as opposed to the whole brake system? If it takes a great deal of force to apply the brakes, then that is usually related to a booster issue.

If you mean that the pedal travel is greater than normal, then the issue sometimes has to do with the rear calipers themselves taking a longer time to seat up.

-Rich

Would a booster failure cause resistenace in bleeding the rear brake lines?

 

[BobnOH]

Would a booster failure cause resistenace in bleeding the rear brake lines?

no
What method are you using to bled the brakes?
(I didn't understand the statement it was very difficult to bleed the rear brakes, to the point that I had to press on the brake pedal to accomplish the bleeding)

 

[TDI_Cubed]

no
What method are you using to bled the brakes?
(I didn't understand the statement it was very difficult to bleed the rear brakes, to the point that I had to press on the brake pedal to accomplish the bleeding)

I use a motive brake bleeder. As I mentioned earlier, we replaced all of the components, than began a systematic brake fluid flush off all 4 brakes. When we started on the rear brakes, we were not getting the flow one would expect, and had to revert to applying the brake pedal to get an appropriate flow and volume.

 

[BobnOH]

yes, with the Motive at 12 lbs (I used 15) first check that it hold pressure for say 10 minutes. If yes, the fluid should flow (it'll be slow) out of those brand new rear calipers. If not, there is debris in the master cylinder or the brake lines.

 

[TDI_Cubed]

Thanks BobnOH for the info related to the Motive and bleeding the rear brakes.

I am still concerned with the difficulty we are experiencing in stopping (a lot of brake pressure required). I am looking at replacing the brake lines (car has 265K + miles on it). The only thing we would not have replaced than would be the booster. I will be verifying we don't have any vacuum leaks as well.

 

[TDI_Cubed]

Bounce!

Anyone have any suggestions on direction I should take to determine why, after replacing all brake componenets except the booster and actul lines, it is still difficult when applying the brakes?

 

[Nutsnbolts]

I just want to make sure that we understand- you are pressing the pedal more firmly than normal, correct? If so, then the booster coud indeed be causing your trouble.

I think that you should measure the vacuum in the system at idle with the booster disconnected and the hose plugged, then plug the booster in and see what the vacuum level drops to. You may discover that you have a leak internally in the booster.

-Rich

 

[TDI_Cubed]

Thanks Rich! This is what I was hoping to hear from someone.