This is the first time I’ve had to bleed the system. so any pointers would be most welcome.
I’ve changed the front calipers, disks and caliper mounting brackets to those from a +2. After bleeding the system with an Eezi bleed kit, the pedal is soft on the first press, then solid on the 2nd.
This is about how it was before I started.
If I start the car, then I need about 4/5/6 pumps to get a solid pedal (presumably because of the servo). Before I only needed one pump to get to a solid pedal.
When I replaced all of the system on my Sprint, including +2 front calipers but without a servo (well except the rear calipers ) it took ages to get rid of all the air, must have bled it half a dozen times. To be frank, it is still ever so slightly spongey on first press, after two years; heck, I guess it’s time to change the fluid again!
Why would you want +2 calipers AND a servo? Put it on e-Bay, add more lightness.
You should have no problem bleeding the brakes on such a simple system unless something is wrong with one or more of the components. Also as long as you have someone to help you should need no special equipment other than a jar and a bit of hose. The thought of putting compressed air over hygroscopic fluid never seamed right to me.
Make sure that the brake pedal is returning fully allowing the master cylinder to recuperate.
The servo if fitted should be mounted at an angle.
Should have no leaks!
Starting with the brake nearest to master cylinder open the bleed screw a ? of a turn only and get helper to push pedal fairly quickly to the floor and hold it down, lock off the bleed screw and let the pedal fully return. Repeat until you can see no more bubbles ? 4 or 5 apps
Next do the other front and after that any rear.
Do not open bleed screw more than ? of a turn and do not lift your foot off the pedal until the bleed screw is locked off other wise you will suck air back into the system via the threaded part of the bleed screw. This is particularly important on worn threads or alloy calipers with coarse threads.
System should be fully bled but if you are not completely happy you could try the following but you will need a suitable tool to easily push the caliper piston back.
Remove the out board pad from one caliper (opposite side to bleed screw).
Gently push the piston out ? enough so that you can still get the piston return tool in.
Using the jar and hose open the bleed screw as before and push the piston fully back in to the housing lock off the bleed screw.
Refit the pad and bleed that brake the standard way ? should only need one or two pumps.
Do this to all four calipers. If you have rebuilt the calipers wet you shouldn?t need to do this, actually if you have rebuilt them dry you shouldn?t have to do this but it will help. This procedure also removes the old fluid from behind the outboard piston which is obviously a good thing if you take your car on track days etc.
The pedal should feel firm but on the second application it should feel shorter still. This is not air in the system it is just that the pistons haven?t had time to move back into their resting position. The amount the piston moves back can be quite high on newly rebuilt calipers but should reduce with time. Also changing from the standard chrome plated pistons will affect this and there is no telling how well after market pistons are produced.
When changing from standard Type 14 calipers to Type 16 (+2 upgrade) then the pedal will be longer as the larger pistons will require more master cylinder displacement but dynamically this will be partly off set by the increased torque output.
Spent much of Saturday checking over the system for leaks, and must have bled it with new fluid at least 3 times (including by your method).
I managed to get two or three tiny bubbles out, but that was the total.
Without the engine running, the pedal is solid after two-three pumps. When running, it takes 4-5 pumps.
I cleaned all bleed screws and then wedged the pedal full-on overnight. This morning, checked and found no leaks, and no drop in fluid level. Bled the system and no air came out.
Pedal is as before. Can only think there must be a trapped air pocket(s) somewhere. I will prise back the pistons and make sure they are working correctly.
I now use speed bleeders. speedbleeder.com/main.htm. This allows me to bleed the brakes easily on my own, without making a mess. Touch-wood, I haven’t had any difficulty since.
I think it was SB3824DH for the back and clutch and SB1010 for the front - I have metric calipers - otherwise it is the same as the others. I cannot remember how much they were, but I thought it was a good enough deal, compared with the amount of brake fluid I can get through!
Are you sure you haven’t got air trapped in the master cylinder? I fitted a new one and tried to bleed it on the car with the result that I had the same troubles as you. I took the master cylinder back off and bench bled it. (this allows you to tilt it around as well as keeping the output port as the highest point) Quite a few bubbles came out.
Hamish, good point about the master cylinder. I’m loath to remove it again (been off 3 times already) so would the holding the pedal down overnight thing work as it did for my clutch?
Maybe if I opened a bleed screw, wedged the pedal down, closed the nipple and left it overnight?
You mentioned that you replaced the calipers. Which way are the bleeders pointing? Up or down?
This happens enough it must be mentioned, particularly given your symptoms. Many neophytes assume the bleeder goes down to “drain” the fluid, rather than up to allow trapped air to escape. They therefore install the calipers on the wrong sides, a mistake not prevented by the caliper design. This results in a large pocket of air trapped in the top of each caliper that cannot be extracted except by turning the car upside down to bleed the brakes.
If you got this right, did you bench bleed the master cylinder? Lots of air up there won’t ever make it down to the bleeders. Instead, bleed at the pipe fitting on the MC by loosening the fitting. Careful, this can get messy, and brake fluid is a great paint deglosser.
The calipers are the correct way up. That one I knew.
What I didn’t expect, was this amount of trouble with such a simple system. For the future, I think I’ll knock up some sort of tool so that I can disconnect the brake pipe from the caliper and then immediately connect it into the tool - hopefully preserving much of the system from air.
I think the suggestions regarding air in the master cylinder must be correct - there can’t be anywhere else for air to be. Pitty really, because as already said, it will be a messy business (will think on this, before rushing in).
As for wedging the pedal - this did not move air through the system for me. I think that will only work for air in the system which is after the master.
Hi Stuart
Are you sure you still have a problem what?s the pedal like when you are driving - does it still feel long?
I think that the brake system is probably bled and the pump up your experiencing might be down to the rollback on the new calipers ? gently put a feeler gauge between the pad backplates and the caliper pistons and tell me what they are for each - but make sure you don?t push the pistons back and get the wrong measurement.
Where are you anyway?
Regards
Steve
Had a night off, last night, so just pumped up the pedal and confirmed there is still air in there somewhere (I believe).
Nothing done since then so here are ‘cold’ readings:
n/s front: inner piston clearance to back of pad plate is 30+ thou
outer is < 3 thou
o/s front: inner 6 thou
outer is 10 thou
Despite a rebuild … sticking piston ? Bear in mind this is not a fully refurbished set of calipers, just seals etc.
Haven’t driven the car for 10 days, since gingerly testing it and discovering the brake problem. Certainly if I start it up, there appears to be extra travel on the pedal.
As regards my location, near Cambridge, East Anglia.
I think extra travel with the engine running is typical even when the problem is not directly related to the servo. At least that is what i have found. The logic is that servo adds extra force, making the pedal sink more easily. My money is still on the master cylinder, probably air caught in it. I like the idea of loosening the union on the output of MC and trying to bleed the air out like that. Otherwise, how about one of those desperate kits that pressurizes the MC resevoir? Gunson Eezibleed?(careful you don’t get brake fluid everywhere!)
I am already using the Eesi-bleed kit. If there is air in the master cylinder, then it doesn’t seem able to shift it.
I think I’ll connect the eesi kit up, then try to concoct some sort of plastic bag type of arrangement around the exit pipe from the m/c, and open it up a little. If I can contain the fluid enough, then I think a pump or two on the pedal might help.
Well Stuart, looks like you have found your problem, no actuation can cope with clearances like that! Get them all down to 0.003? and the pedal feel will be okay
) it took ages to get rid of all the air, must have bled it half a dozen times. To be frank, it is still ever so slightly spongey on first press, after two years; heck, I guess it’s time to change the fluid again!
