Bleeding brakes a warning
 

Today I've been fitting new calipers to improve the brake performance of the front brakes, one of them was sticking slightly.

Hoses clamped off and calipers changed with no problems

Time to bleed the brakes and thought I'd do it properly on the T4, the sequence is as follows:

Select brake to be bled on screen menu after fitting bleed tube to bleed nipple.
Open bleed nipple and depress pedal to expell air until it runs clear ensuring resevoir is topped up.
Next press continue on the T4 menu to bleed the secondary circuit with the ABS pump until clear.
Finally tighten bleed nipple while pedal is depressed.

All was going well until it came to bleed the secondary circuit........... Absolutely full of air

Took a total of 4 bleed sequences on each side to get it free of air and 1/2 litre of fluid.
The pedal is now solid when depressed.

The problem for members is that normal bleeding or pressure bleed kits only bleed the primary circuit, in order to bleed the secondary circuit you will need to use suitable diagnostic equipment capable of using the ABS pump to bleed it properly.

I wonder if this is why some owners suffer from sinking pedal syndrome.

Russ

hi
 

thanks for the info .but i am now quite worried as i intend to change my rear brake pipes pretty soon as both sides are badly corroded i was going to do this myself i am no not so sure anyone got any thoughts advice on this ?:confused:

Are you saying the car doesn't exhibit the Sinking Pedal Phenomenon? Did you physically check this aspect after doing this bleed? If so it's an important new observation.

TC

ive seen this on a sierra 4x4 once , many a year ago , i pulled the abs fuse out then bleed the brakes , may not work on the 75 , anyone ?

The pedal is definately more firm but will comment more once I've also bled the rear brakes using the same method didn't have enough time today. It's not being moved until it's been done.

The brakes were properly bled using a pressure bleeding kit last year but I think at some point they haven't been bled properly.( probably when the main brake lines were changed before I bought the car).

If there's air in the system it can find it's way into the abs modulator where it will stay unless the system is bled as described above because the valves in the abs system only open when the ABS system operates.
You can bleed the system properly then when the ABS kicks in it can let the air trapped in the modulator into the brake system again.

Russ

My 75 cdti has recently suffered sinking pedal syndrome, and traction control has also been coming on at 90mph on a straight road and slowing the car down to 80mph then going off, then on again and slowing the car down to 70mph this problem started when my 75 started getting the dreaded S.P.S, i then went though a process of elimination so i changed the master cylinder twice and then the servo and the S.P.S still remained so i then changed the brake hoses and had the A.B.S unit sent away to be tested which came back no faults found it was bench tested 10 times and i still the S.P.S persists i then took the 75 to the main dealers (Teeside Rover) and they used T4 to bleed A.B.S. back to having a hard brake pedal now, problem solved and no more premature traction control problems

What we need is a non T4 method for opening the ABS valves to get a correct bleed.

JCW

Top Tip Russ !!

(thankfully I have access to a T4)

This info is rather worrying, I wonder how many of us are running around with no back up brake systems at all?? :shrug: :confused:
...

If you braked at a VERY low speed on loose gravel so that the ABS came into play would this not purge the system of trapped air ???? :shrug::shrug::shrug:
This could then be bled in the usual fashion.


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