Brake bleeding tips and tricks?
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I believe that air trapped in the U shape above the MC's causes a great deal of bleeding problems and shows up as soft pedal. My son and I ran into this on his race car where the pipe was above the MC. A Tee with a plug was useful here so that simply bleeding from the Tee plug would allo9w air bubble to be expelled. But a classic mini has the U which ttraps air. Simply installing a Tee at the top of the U would solve the problem. However purists would frown on this I'm sure.
I recognized that air would be trapped in my Mk1 so I did the following. With normal bleeding a helper would press,let off depress, hold while first person would bleed at the brake. and repeat several times until hard pedal. If there is an air pocket at the U it will never be expelled under normal bleeding. Installing the pipe on the MC I reasoned would result in an air bubble regardless of the care taken to fill the pipe and fill the MC plunger. I reasoned further that the air bubble must be driven out. since the RF bleed was the closest I chose to drive a volume of brake fluid thru the pipe and expell it into a waste bucket without drawing air into the MC. I then opened the bleed wide open an firmly, but not too fast, pumped the pedal. I guessed that the bubble would get expelled before the resevoir emptied.
Result was well adjusted brakes.
Here's what I did with new pipes all around and a Single LE sytem that needed to be filled without air.
Skim cut all drums to round them to make easier (and more precise) to adjust the adjuster nut.
Leak checked rear half of sytem with air at the fireall Tee. Held 80 psi for 10 minutes. Did the same for the front half. I was then assured that there were no leaks front to back.
Filled the MC with brake fluid and allowed fluid to drain out thru the bleeds by gravity and fill wheel cylinders.
Pumped the pedal as above to drive out any air bubble.
Adjusted nut tight the backed off quarter turn.
Bled all four brakes with helper in normal fashion.
Brake operation was flawless.
my two cents
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They require a certain velocity of fluid flow to "break them loose" because of surface tension -induced clinging to the pipe wall, or even to other bubbles.
This is a fluid dynamics issue not just in brake fluid. For example, and this is the way I learned about it, if you have enough flow while refilling a house hot -water radiator and pipe system, you can get the bubbles "blasted out" and not have much (or any) air to relieve at the bleed screws
Pretty esoteric stuff.
See //www.thermopedia.com/content/8/DOI:10.1615/AtoZ.b.bubble_flow
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I was able to do a driveway brake test... WHOA!!! Big improvement - nice firm pedal with better height and the Mini does a bit of a nose-dive compressing the front Smooth a Ride springs.
Thanks for all the guidance and encouragement guys!
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"Hang on a minute lads....I've got a great idea."
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If the rear hoses were not blocked and as the bleeders were not bleeding what was blocked?
Hard to blame it on Lucas, Prince of Darkness. Must be some other Mini diety/demon I upset.
I suspect there might have been some sludge in the bleeding orifices in the rear cylinders that eventually yielded. All I know is that it finally bled by gravity and the pedal feels more or less normal. I was too dirty to sit in the car and give it a proper foot test.
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"Hang on a minute lads....I've got a great idea."
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If the rear hoses were not blocked and as the bleeders were not bleedingwhat was blocked?
If in doubt, flat out. Colin Mc Rae MBE 1968-2007.
Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.
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A few fine points discovered:
- hose wrench size appears to be 11mm but nuts and hard line fittings seem to be 9/16 even though threads were correct.
- hard pipes on suspension trailing arms are copper - upper ends released OK but fittings to rear brake cylinders were stuck to copper tubing and risked twisting off (could not separate them).
- keeper nuts for each end of hose are different depth - fitting on copper pipe is deeper than on steel pipe. This was learned the hard way after getting the right-side hose almost completely installed but could not tighten the fitting on the copper pipe. So I got to re-and re- 3 rear pipes!
- car must be level to get every wheel to bleed: I had the car up on all 4 axle stands to do the front part and to bleed as far as the T- fitting at the rear subframe. When it came to replacing the rear hoses, I took the car down and turned it around to get the rear end close to the work bench. Since I "just needed to change the hoses", I lifted the rear end. I got the hoses fully installed but again was unable to get anything out of the rear bleeders. So, I lifted the front end to replace the broken bleeder while I thought about the problem. Then on each side, I loosened the fitting from the copper pipe to the hose and let fluid drain and observed some small bubbles escaping. That told me I had flow as far as the copper pipes. Back under the car, I tried opening the other ends of the copper pipes but stopped as noted above. In despair, I tried the bleeders once more, giving the brake pedal a few pumps. Lo and behold, when I looked at the bleeders, they were damp! At first, they would barely weep but the flow slowly increased to a proper gravity flow.
I think I have most of the air out but a road test is needed to verify pedal feel and stop-ability. I'll put the insurance on it tomorrow.
Once more thing... the rear hoses were not blocked at all.
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"Hang on a minute lads....I've got a great idea."
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Until the parts arrive, there are yard chores and the boat needs spring cleaning, waxing and polishing for the upcoming sailing season.
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"Hang on a minute lads....I've got a great idea."
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When I got my car as a project the rear hoses had collapsed inside. They were working like check valves. You'd come to a stop and the rears would stay "locked" when you went to move again.
FWIW, the braided hoses cost a bit more than stock rubber ones but have been good investments for me.
Glad you are getting it sorted Dan i have run into collapsed hoses (and broken nipples for that matter) a number of times.
If in doubt, flat out. Colin Mc Rae MBE 1968-2007.
Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.
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Kinda extra funny considering I had a mastectomy (took away one "fitting") and radiation which took away most of the hair on that side.
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URL: [img]https://s5.postimg.cc/uzrlzxxzb/Dripping.jpg[/img]
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This afternoon I was able to disconnect the long rear line from the limiter valve and get gravity and pedal flow through it.
Next step was to disconnect one of the pipes at the T-fitting at the rear subframe. All three pipes must have been tightened by the same 600 lb gorilla, but one finally gave in and opened up. Good gravity and pedal flow to this point. Even with the joint opened up I was unable to get any flow from either rear adjuster.
Time for new flex hoses.
Side note: brake fluid will attack epoxy floor paint.
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"Hang on a minute lads....I've got a great idea."
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So far, I've flushed and bled the front system. Both front bleeders opened with little wrench effort and flowed freely, including under gravity alone. I will probably re-flush one I've got the rears flowing. Since the front circuit is short, I decided to try bleeding it first - if it bled OK, I didn't need to crack its joints individually.
On the right-side front caliper, I had trouble keeping a wring wrench firmly seated on the bleeder but it opened OK. Even though my clear-tubing bleed line was securely connected, and the bleeder was barely cracked open, there was some fluid dribbling down the caliper and tire onto the floor. Annoying bit not critical. As I rotated the bleeder, I noticed the bleeding tube seemed to not be in line with the axis of the bleeder, even though I reset it several times. Not being able to get my head in there for a good look, I cap-sealed the master cylinder and removed the bleeder completely. Once I got it out and cleaned, I could see the problem - see photo. Most likely the brakes were last done by a 600 lb gorilla. I put the bleeder back in and tightened it gently - I wouldn't want it to snap off in the caliper.
Time for lunch. This afternoon, I'm having a look at the rear system.
Since this is a long weekend in Canada, I won't be able to go shopping for bleeders until Tuesday.
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"Hang on a minute lads....I've got a great idea."
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When I got my car as a project the rear hoses had collapsed inside. They were working like check valves. You'd come to a stop and the rears would stay "locked" when you went to move again.
FWIW, the braided hoses cost a bit more than stock rubber ones but have been good investments for me.
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If in doubt, flat out. Colin Mc Rae MBE 1968-2007.
Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.
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"Hang on a minute lads....I've got a great idea."