Front brake problems

[CA.XSer]

I am having a problem with my front brakes on a 79SF. I am not getting a solid feel on the lever. The lever will go about halfway before starting to brake then feel mushy. I have rebuilt the m/c, calipers and installed s/s brake lines. I used a mity vac to bleed, and not getting anymore air. There is a little fluid squirting back through the spooge hole when applying brake lever. Any ideas?

I did the same rebuild on my 78 and the lever is rock solid.

[Snow]

Is it possible that you got some brake fluid on the pads/rotors? Are all connections tight?

[CA.XSer]

Is it possible that you got some brake fluid on the pads/rotors? Are all connections tight?

Haven't taken it out of the garage yet, all connections are tight. Just bleed again and same problem.

[Mike Hart]

seems odd. spongey feel usually is air, but if you've bled twice and are sure, then it must be the cylinder rebuild at fault? Plunger not quite right? O-ring?

[CA.XSer]

seems odd. spongey feel usually is air, but if you've bled twice and are sure, then it must be the cylinder rebuild at fault? Plunger not quite right? O-ring?

Thats what has me stumped, I have taken the m/c apart again but it looks ok. It does seems to be doing the same thing as before I did the rebuild and changed to s/s lines.

[Snow]

I ended up rebuilding my mc twice, I had the black cap in backwards the first time, and I just couldnt build up much pressure

[schpiff]

Two things to check
1 Make sure your caliper are free to move and caliper is lined up.
2 make double sure all the air is out of master. (sounds dumb but it happened to me)..I bled alot and didnt get anymore air out of lines or caliper. I took line off the master and bled that first. I got a couple little tiny bubbles...thats all it was.

[Hobbit]

I just had the same problem with my 79 XS. After rebuilding the calipers and master cylinder and bleeding the system every way that I could think of, I still had no stopping power.

The problem seemed to be that the caliper pistons would return to far, never taking up the free play needed to make the pads contact the rotors. I removed the calipers one at a time and using a pair of internal snapring pliers, I worked the master cylinder and would not let the piston return. When the piston was far enough out of the caliper, I reinstalled the caliper and did the other side. Now they work perfect.

I did the same thing with the rear system and have great brake feel front and rear.

[newmaac]

It is possible, and common, to have trapped air in the fittings where 2 lines come into one. Try laying the bike over as far as possible, both to the right and then left to try to dislodge any trapped air bubbles.
Since the master cyl is the highest part of the system, holding the brake lever squeezed, (with a rubber band), overnight often allows trapped air to release. I haven't tried that one myself, but have read several posts that reccommend it.

Good luck.
Mike

[Jeff]

That rubber band on the front brakes at least makes sense since applying pressure would make any trapped air bubbles smaller and more likely to rise thru the system to the MC since all the lines run nearly vertical.

I did have a question though. Is it necessary to "bench bleed" the MC prior to hooking up the lines to it..... similar to what is required for an automotive MC? In a car.... this is normally done by attaching hoses to the outlets of the MC and running them back up to the reservoir.... to remove any trapped air in the MC piston bore.

[newmaac]

For bench bleeding, what have done is to simply cover the outlet hole with a finger, while slowly pumping the lever. You are going to lose fluid, but if all painted areas, (and eyes) are covered, it works well to remove any air from the m/c before attaching the fluid line.

[graybird78]

air in m/c

I had same problem after I changed front tire.brakes wouldn't pump back up. I did the miteyvac ,bled normal way , even cracked open bleeders to no avail. still had spongey brakes. bled the thing till I was blue in the face. Finally decided to put brake fluid in a small glass jar,put a piece of vac line on bleeder and submerge vac line in glass jar making sure it was in fluid.then opened bleeder and pumped. Idid forget one thing I took brake handle off and used small needle nose vise grips on end of plunger to pump brakes. So when you pump brakes you push and pull on m/c,was amazed at how much air was still in system.this method worked very well for me ,cuz when you push you force fluid out and can see air bubbles in fluid.when you pull back on m/c it will pull fluid back into system not letting any air in. You might also try tapping on various brake parts to dislodge any air bubbles that might still be trapped in system.This also works very well on auto brake and clutch systems. It's how we do it at my job when these systems are hard to bleed in conventional ways.all most all the time you should get good results. If not there is something else wrong or air is finding a way into system.

[NOMAD]

Gary,
Just a couple more ideas. Try putting teflon tape around your bleeder screws so they seal-up while using the Mighty-Vac.
Check the size of the master cylinder. My P O had installed a 14mm on my 80SG where I needed a 5/8" bore. The master cylinder is marked on the bottom, either 14 or 5/8. You need the larger one.

Just an idea, Nomad