Bleeding brakes - front only?

iani · Post by **iani** » Thu Apr 17, 2014 10:48 am

I swapped the two front calipers over this week, one of the caliper pipes fractured resulting in the reservoir emptying. I have filled it up and have bled the front brakes several times but still have a spongy pedal. On inspection, the rear brake nipples don't look like they're going to budge, obviously I don't want to risk shearing them in situ. Given that I only disturbed the front system, should I have to bleed the rears as well? I have tried bleeding both with the engine running and off, when the brake pedal is pressed, the rear pads move straight away so I don't believe they are having to take up slack.

Ian

Post by **Heuer** » Thu Apr 17, 2014 10:52 am

Two separate circuits so disturbing the fronts should not affect the rears. What method are you using to bleed - pressure, suction or pedal?

iani · Post by **iani** » Thu Apr 17, 2014 10:52 am

Pedal only.

Post by **Heuer** » Thu Apr 17, 2014 11:01 am

Arm yourself with plenty of brake fluid and an understanding helper! It can take a full reservoir of fluid per side to clear out any bubbles.

iani · Post by **iani** » Thu Apr 17, 2014 11:06 am

More than happy to spend the time if that's all it takes, I'll find a suitable assistant, thanks.

iani · Post by **iani** » Thu Apr 17, 2014 11:15 am

On the plus side, the new calipers & greenstuff pads are working very well, from the 2nd press of the pedal anyway.

ALAN COCHRANE · Post by **ALAN COCHRANE** » Thu Apr 17, 2014 2:07 pm

Ian

I recently went through the same pain as you are experiencing. I had to change two of the front brake pistons which were corroded and the cause of an MOT failure.
Perseverance is the name of the game. I used two litre bottles of DOT4 before I had a firm pedal again. I found the best way, if you have the time, is to bleed them until there are no bubbles apparent in the bleed tube and then leave it overnight. You will be amazed at the amount of air that will be expelled the following day. I think the design of the calipers allows some air to be trapped in certain internal recesses. I have Zeus calipers up front so I don't know if they are better or worse for this than the original S1 brakes.
Another trick I learned while bleeding my GT6 brakes was to leave the master cylinder cap off and pump the brakes repeatedly before starting. I managed to expel a considerable amount of air without any loss off fluid.
A note of caution-if you opt for a hand operated bleed pump, beware of over pressurising it. I was fooled into thinking that there was a tremendous amount of air in the system but actually the suction was so great that it was literally pulling apart the brake fluid flow into individual droplets.

Alan

iani · Post by **iani** » Thu Apr 17, 2014 2:35 pm

Thanks Alan, I will stock up on another bottle of fluid and give it another go tomorrow. I have owned a couple of GT6 myself, I'd have one now if I could fit in it.

Ian

iani · Post by **iani** » Fri Apr 18, 2014 4:20 pm

Having bled the fronts again I can report no change, I still have a spongy pedal on first press then good braking. I thought I'd try using freeze spray on the rear caliper bleed nipple, that was unsuccessful and I now have a sheared off bleed nipple, at least it sheared fully closed so I'm no worse off than I was before. I guess the IRS will have to come out now, I can feel the shipwrights disease spreading here.

Ian

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Bleeding brakes - front only?

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