Technical brake master cylinder

[bilopapa]

howsit guys its me again looking for some expert advice...so i changed brake calipers and brake pads and blocked pipe...so i bleed the brakes while car is off and brakes catch but once i start the car and try to brake the pedal goes right in...i then bleed the brakes with the car idiling same story no brakes...i used dot 4 brake fluid and yes i bled brakes properly any suggestions or help?

 

[bugsymike]

howsit guys its me again looking for some expert advice...so i changed brake calipers and brake pads and blocked pipe...so i bleed the brakes while car is off and brakes catch but once i start the car and try to brake the pedal goes right in...i then bleed the brakes with the car idiling same story no brakes...i used dot 4 brake fluid and yes i bled brakes properly any suggestions or help?

It sounds to me as though you still have air in the brake system, when engine running the brake servo increases the pressure applied so pedal will feel softer.
Apart from a weak master cylinder allowing air back into system, the new brake pads will still be soft/not bedded into discs, this can be aggravated if the brake discs are grooved or have a wear ridge and will add to a soft pedal, driving the vehicle and using the brakes to bed in the brake pads may help , but do not do this too aggressively as it will glaze the pads and overheat the brake discs which will be bad.
All this is apart from if there is still air not bled out.

 

[Pugglt Auld Jock]

If you're sure you've bled it properly then it might be worth CAREFULY clamping off the brake flexible hoses to try to isolate where the problem is. You can do this in various sequences but in a case like yours where the pedal is very poor - you tell us it's going to the floor? - I'd pinch off all 4 flex hoses and see if the pedal goes effectively solid. If it does then you know for sure the problem is in one or more of the wheels so remove the clamps one at a time from the flex hoses, testing the pedal each time you remove a clamp, and when the pedal goes poor you know you've got the one that needs bleeding again. Of course there may be more than one wheel needing rebled. I don't like clamping off flex hoses because there's always the chance you'll internally damage one, especially if they're old, so use something without sharp edges and only tighten enough to just "pinch" the hose.

Something like these: https://www.sealey.co.uk/category/5637151039/hose-clamps

Edit. Brake bleeding can sometimes be a real problem. I remember many years ago we had a wee Simca - the one with the engine in the back - which we just couldn't get the front brakes to bleed out on. One of the lads suggested we leave it overnight with it's front end up in the air on the 4 poster - it was almost standing on end! Don't ask me why, but when we came in in the morning, put it back on "all fours" and tried the pedal, it was almost perfect and the small remaining amount of air still in there bled out easily with just a few pumps of the pedal! To this day I can't explain it!

 

[bilopapa]

thanks alot guys...let me get back to work will update u guys