Brake bleeding

[Nelson]

I just replaced all my brake lines and the m/c on my Mk2 Sprite. With the help of a friend pumping the brake pedal I bled all four wheels and do not get anymore bubbles. However, the pedal goes almost to the floor on the first pump. It improves with the next couple of pumps but we could not get it to stay up on the first stroke. I have new wheel cylinders in the rear and a new disc brake conversion in the front. Could air still be trapped in the lines? Would waiting a day to let whatever air bubbles there are join together so I can expel them? There are no leaks of fluid apparent anywhere.

Nelson
Medina, Ohio

 

[Trevor Jessie]

Have you adjusted the rear drums?

 

[Nelson]

I have played with adjusting them but they don't seem to be centered and are loose for part of a rotation and then have resistance for the remainder of the rotation. Do I need to remove the drums to get the linings centere? I thought that they would pretty much move into position when the pedal is pressed. The linings are also new. I don't recall if I lubed the areas where they contact the backing plate.

Nelson

 

[Trevor Jessie]

I was thinking that maybe you had them too loose and the excess travel is where your fluid was being consumed. Most likely you just have an air bubble. What order did you bleed them?

 

[Nelson]

I've done them all multiple times. I started with the driver's side rear as that is the longest distance for the lines from the m/c. Then the passenger side rear, the driver's side front and finally the passenger front. I've seen that the right rear is the place to start but that line is shorter than the left rear and my understanding is that it should be farthest to closest.

 

[jlaird]

First you adjust the brakes then you bleed.

 

[Nelson]

Having disc brakes up front is new to me. Is there a way to adjust them or are they just supposed to work? I guess I'll pull the rear drums and see if their contact area on the backing plates need a dab of lube.

 

[JPSmit]

and yes, you still have air - it took me three times to really get it right - especially if you have used DOT5 since it can foam.

 

[Nelson]

I am using DOT4 but when I was bleeding the clutch slave I had all kinds of froth coming out of the bleeder. Looks like I should let it sit over night and try again tomorrow.

 

[JPSmit]

slow and steady. I had a friend make me a jar with tube to go over the bleeder nipple. helped a lot - pushed the air through the liquid and meant I could recycle the fluid. You probably don't have to wait - just don't be skimpy on the fluid coming out. Let it flow thoroughly

 

[highhilleer]

slow and steady. I had a friend make me a jar with tube to go over the bleeder nipple. helped a lot - pushed the air through the liquid and meant I could recycle the fluid. You probably don't have to wait - just don't be skimpy on the fluid coming out. Let it flow thoroughly

I would never recycle brake fluid; too much potential for contamination. Since you shouldn't use brake fluid after the container has been opened for a few days, you cann't (or shouldn't) save what is "left over". There is no advantage to recycling brake fluid when bleeding the brakes. At least that's the way I see it.

 

[aeronca65t]

Keep winding in the square-head rear brake adjuster (#57 below) until the drums won't turn. Then back off until they will turn without too much drag.

Front disk brakes are self adjusting...no adjustment possible.

 

[jvandyke]

I don't know. Once you've flushed the old stuff through, bleeding through the new and dumping it back in as you bleed everything seems more environmentally sound then dumping it for no good reason. The silly M/C caps are vented anyway, the fluid goes bad in the car by design, should be flushed out routinely anyway so I say go ahead, put the stuff back in. (not the old dirty dark moisturized stuff) the stuff that was clean and perfect a minute ago before you bleed it through, it's plenty good to serve until the next flush though...IMHO. If the jar is capped, it's only going to absorb the moisture that's in the air of the can it's in. It should be fine. IMHO
As long as you flush it out every so often.

 

[Bayless]

If you can pump the pedal and bring it up then the odds are really long that you need to adjust the rear brakes. The disks are self adjusting. As mentioned above, keep edjusting both rears until you cannot turn them at all then back off until you get just a little scrape when turning by hand. Do this back-and-forth a few times to be sure the shoes are as centered as they can get. If the linings are new, you will probably have to adjust again after a few miles.

 

[JPSmit]

I would never recycle brake fluid; too much potential for contamination.

recycle is probably the wrong word - thinking more of not letting it go to waste - especially DOT5 which is pricy.

coming to the other posts, if you need to pump up the brake, there is still air - adjusting the brakes won't address that.

 

[jlaird]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]adjusting the brakes won't address that. [/QUOTE]

But brakes have to be adjusted before you can get em bleed properly.

 

[dklawson]

As Jack and others have said, if your drums aren't adjusted properly you will get excessive pedal travel on the first pump. No amount of bleeding will address that and the drums do need to be adjusted properly before bleeding.

This is a question as much as a suggestion. On other BMC cars I've worked on the friction material has been relieved at one end of the brake shoe. That is to say... the friction material isn't centered on the shoe. The relieved end should make contact with the drum first in the direction of normal forward wheel rotation. I haven't worked on Spridget brakes so I don't know if that applies here. However, if it does... putting the shoes on in the wrong order can result in a soft pedal with excessive travel.

Regardless, as Nial said, the drums need to be adjusted so they will turn with a bit of drag.

 

[JerryB]

Having disc brakes up front is new to me. Is there a way to adjust them or are they just supposed to work? I guess I'll pull the rear drums and see if their contact area on the backing plates need a dab of lube.

remove the drums...

take the shoe assembly and push it up and then down...about 3/16"

the assembly should slide rather freely. If not lube the backing plates where the inside of the shoe rubs the backing plate, adjuster cam and pins, and wheel cyl to shoe contact. Use only lube made for brakes (very hi temp).

The drums may be bell mouthed or out of round if , on rotation of the drums is free then grabs. The arc of the shoes MAY be wrong also. In this exercise you MUST put two lug nuts torqued .....backwards so the flat of the nut is against the drum. Or the wheel on...but its hard to work with wheels on.

Try tightening up the adjuting screw on both drums....then see if the pedal comes up. It should, as it sounds like excessive clearance shoe to drum is your problem.

Adjusting screws....pull tire "down" with one hand on the tread forward rotation. Pull and tighten screw. When you cant pull down any more with one hand then go back 5 or maybe 6 clicks. Wheel should roll free going forward (pulling down)...you might hear feel a very slight noise at some o-clocks but thats ok. Any more than 6 clicks you have out of round.

P.S. Never reuse brake fluid. Never compress caliper pistons or wheel cylinders so fluid runs backwards up the lines. Always open the bleeder sruz. Hardware store get Tygon clear tubing. Rear bleed scruz need smaller tubing.

Have fun.

 

[Nelson]

Thanks for the good suggestions. I don't have any of the brake lube so I will get some along with a couple more bottles of brake fluid. My brake linings and drums are brand new so I wouldn't expect them to be troublesome. Once I've got the pieces properly lubed I'll do the adjustment again. It doesn't look like my helper will be available for a while again so I today I ordered a set of Speed Bleeders to hopefully make bleeding easier. My MityVac can't get the flow that I got when he used the brake pedal and I think I will need a good flow to purge the last bits of air from the system.

 

[Roger]

I've found it helpful to bleed brakes with the handbrake full on. This tends to centre the shoes on the drum as well as helping the pistons to fully extend in the wheel cylinders.