Problem bleeding the brakes

[Pboden]

Changed the front brake-lines on my -74, and after installation, I struggle to bleed the brakes. Been at the job for several days, but I can not get the brake-pedal hard.
Bought a tool for fluid suction and also had help from my father pushing the pedal, but with no luck.

Have made an order for a new brakecylinder, but not sure if that is the culprit.

Any others with a similar problem ?

[mfiazzo]

I had a similar problem bleeding my back brakes.

What finally worked was I had my son in the car pumping the brakes 10 times then he held the pedal down and I opened the bleeder. We just kept repeating this process. It took a really long time but I finally got them bled.

[H-viken]

Add a longer bleed hose to the right rear caliper and mount the end higher than the reservoir

Then open the nipple and let gravity do the work for you

Power bleeder also work really well

[trond]

should be very easy if all is in order. I had problems when I had a dodgy master cylinder

[chrismorse]

When I worked at a dealership, as a service writer, I was often asked to do the up-down with the brake pedal, while the real mechanic bled the calipers/wheel cylinders.
On older cars, (10+ years), we began to occasionally see master cylinder failure after manual, (foot), bleeding.
Power bleeding prevented this, (vacuum bleeding works well too).
My thoughts were that moisture, rust and small bits of deteriorated brake components, like rubber hoses would collect in the master cylinder. Each brake application would sweep the bore clean -to a mid point in the bore. Over time, this debris, solidifies and it is easy for a full brake pedal stroke to push the seal over the trash, occasionally cutting the master cylinder piston seal.
With newer master cylinders or annually flushed systems cutting a seal would be highly unlikely, but 20, 30- 40 year old cars, especially infrequently driven or flushed may be at risk.
Pressure, vacuum or gravity bleeding avoids this risk.
chris

[ChrisBennet]

Did you remove the brake pads or push the caliper pistons back for some reason?
Sometimes the pads have a "commute" until they actually reach the disc. Because of the huge mechanical advantage the brake system has, a lot of pedal movement results in a tiny movement at the caliper end.
The symptom of this is a soft pedal that gets real hard at the end of the brake pedal stroke - it's not bouncy.

If this is the case:

1. Try pulling a brake pad (one at a time) out, moving the caliper piston in (press on brake pedal a *little* at time) until pad won't fit.

2. Pry the piston back until you can just tap (with rubber tipped hammer or large frozen fish like say a Pickerel) the pad.

3. Rinse and repeat for all calipers

[shadowjack1]

Pboden
Post our location, someone may make a house call. Lots of good guys on this board. You never know.

[yelcab1]

Motive power bleeder, works every time.

[sugarwood]

I had a car that would not get firm, and it was the master cylinder.

I tried fluid suction that pulled the fluid.
That was total garbage.
Pushing the fluid is the accepted way, either by Motiv or pedal.

[dicklague]

Originally Posted by yelcab1

Motive power bleeder, works every time.

AGREED. Motive works like a charm every time. Pushes the fluid through from the master resevoir.

[Bill Douglas]

It sounds like some air in the brake line that is working it's way back up after each pedal push.

I put speed bleeders on my brakes. In your case I'd do the same then give them half a dozen quick succession pumps of the brake pedal then close them off.

Good luck.

[trond]

old 911 brakes are so easy to bleed. It is enough to just open bleen nipples and let gravity do it. Close nipple when no more air is coming out and you are done. If this does not work it is either the master cylinder, or the pistons not all the way out. If the last drive slowly around the block and see if it does improve by itself.

[Trackrash]

If you have S calipers, I, and others, have had a similar problem.

Only solution was to drive the car enough to get the brakes warmed up. Then bleed again. Took me years to figure this out. I always use a pressure bleeder and have a fairly new MC.

Here is how you can tell. If you push down on the pedal and after a half inch or so of sponge, it gets hard, you still have air in the calipers.

If you can push on the pedal and it slowly sinks down after it feels hard, it is the MC.

[juanbenae]

if while pedal bleeding you depressed the pedal to the floor you could have fouled the master cylinder. when bleeding brakes I only depress the pedal like 2/3 of the travel as to not push the piston to where it's not been regularly. I use speed bleeders and never go full travel on the pedal.

look in the MC reservoir when pumping the pedal and see if there is any turbulence being created. it won't bubble or anything that obvious, but if the MC bore and O-rings have been compromised you might see some turbulence in there. the less full the reservoir the better for this exercise.

also tap the calipers with a rubber hammer or even a piece of wood if they were emptied at all. sometimes air bubbles can affix themselves to the inner chambers of the caliper and cause you grief.

[Rawknees'Turbo]

Originally Posted by sugarwood

I had a car that would not get firm, and it was the master cylinder.

I tried fluid suction that pulled the fluid.
That was total garbage.
Pushing the fluid is the accepted way, either by Motiv or pedal.

Don't even need a Motive if one has an air compressor - just hook the air source to the vent nipple () on the reservoir (an air gun with a suitable sized rubber hose on the end works great) and use about 15psi of pressure. This method is a super quick, easy one-person operation, and requires no pedal bleeding at all. I have not pedal bled any machine, including aircraft, in over 10 years, and glad to be done messing with that method.

PS - glad to see you back, Wood!

[Bill Douglas]

Originally Posted by Rawknees'Turbo

just hook the air source to the vent nipple () on the reservoir (an air gun with a suitable sized rubber hose on the end works great) and use about 15psi of pressure.

Oh Jeezus, good thinking. I can't wait to try that out.

[Rawknees'Turbo]

^^^

Unlike the 911 reservoirs, many don't have actual vent nips () on them (as I'm sure you know), so in that case, you can just add a hose barb to a spare cap. It really is amazing how quickly that gets the job done, including with systems like many aircraft have, where the caliper bleed nips () are on the bottom of the calipers and facing downward - just fires air and fluid right out. Of course, you can experiment with pressures to see what you're comfortable with - 15-17psi being about max.

[Bill Douglas]

I went out and had a look. Yes the 911SC has a vent going to a braided rubber hose that goes "upwards".

I have various air fittings and adapters from using my Paasche air brush with the big compressor. So a big thanks.

[Rawknees'Turbo]

No problem.

One other tip (just the! ) to mention is that it is good to wrap a rag around the cap on the reservoir - just in case a little fluid is pushed out past the cap seal (if air pressure is a little too high, the seal isn't the greatest, etc.).

Also, as you've probably figured, you have to keep a close eye on the fluid level - moves fairly quickly, but not ridiculously so. That's why an airgun works so well - you can shut the air supply off instantly by releasing the trigger. I use a strip of Velcro wrapped around the gun to hold the trigger down while I check out the flow from whichever caliper I have open (a rubber band works, too) - that way you can start the air, and then walk to the caliper to see what is happening.

[Bill Douglas]

Thanks - god advice.

I've got a on/off setup just after the regulator and air drier setup. And I'll start with 5 or 10 psi so I don't have bits of connectors flying around LOL