Two 1975 GLs front brakes.

[6adan]

I have rebuild on these two bikes front brakes, new pistons, new o ring kits, cleaned very good. Now my problem is one bike (red) I get good brakes or as good as possible with stock lines but the other one (green) I cannot get good brakes, the lever will go to handlebar. The red bike was in good shape when I got it just setting for several years the other bike had not had such a good life although it is in good shape now. Could this have anything to do with the problem, maybe because the green bike sat outside a long time and the red bike was inside most of its life? Could this fact make the brake lines softer on the green bike? looking for any help on this one.

[cfairweather]

Here are a few ideas you can verify:
1. Air in the lines. Try bleeding the brakes again.
2. The seal that goes around the piston might not be sealing correctly. Did you polish the cylinder when you cleaned it?
3. Did you make sure the tiny hole from the reservoir to the cylinder was open?

[MikeNTexas]

Does the handle firm up after pumping it several times? And if it does’ does it hold pressure if keep squeezing it? If yes to both questions there is still air in the system.

If it never builds pressure do you at least get fluid from the bleeder when you pump the handle? If yes then the MC is probably bad. If no then the spooge hole on the MC may be stopped up not letting fluid get to the piston.

[low-side]

Really bad hoses can cause the lever to the bar situation by ballooning under pressure. On both my '78s, the master cylinders and calipers were fine, but nothing worked right until I changed out the brake hoses.

[BillW]

Did you rebuild master cylinder as well or just calipers?

[6adan]

Thanks for the replies, I used a vacuum bleeder on the breaks. The handle dose not firm up like it should. I am getting fluid through the bleed valve. I even let it set overnight with the lever held down to the handlebar and the MC moved on the handlebar to be sure it was at the highest point. I did not rebuild the MC on either bike but I did try a good MC from another bike with the same results. I will keep at it and will let you know.

[MikeNTexas]

The best results I have had are first to put some Teflon tape on the threads of the bleeder to keep fluid from seeping by them and assure that it only goes through the nipple. Place the clear hose of my vacuum bleeder on the nipple. Hook the other end of the hose to the catch bottle. Place the bottle somewhat higher than the caliper. Fill up the MC and slowly pump it watching the fluid come up through the hose. Observe any air bubbles coming out of the caliper no matter how minute. Keep refilling the MC reservoir and pumping until no more air bubbles are observed. Then do it some more for good measure. If the fluid is clean and clear you can recycle it back to the MC reservoir.

I get much better results this way than using the vacuum pump.

[Track T 2411]

I typically use the vacuum pump to get everything started, then continue manually. When I do have to tie the lever back, I don't go all the way back to the handle, 1/2 to 3/4 inch space...

[6adan]

Mike, I do use Teflon tape but have not thought of using clear line. Track, I will try it that way.

[Fred Camper]

Eliminating the splitter in the middle and using dual banjos at the master makes bleeding the brakes really easy.

[gltriker]

Correctly Rebuild at least one of those 3 front brake master cylinders. First. Perhaps two would be prudent.

Don't skimp on the length of the clear tubing which will be routed vertically into a catch container.

If you can get an attentive helper to continually keep the vertical clear tubing attached to the open bleeder screw while you are purging air out of the whole system, that is a BIG PLUS to allow you to concentrate on the job.

Keeping a column of brake fluid in that vertical clear tubing will prevent air from re-entering the brake caliper it is attached
onto when the brake lever is slowly released, with the bleeder screw remaining opened. Take your time. It is not a race.
Give the master cylinder fluid reservoir adequate time to gravity refill the fluid piston bore before you slowly squeeze the brake lever, again. Take your time. It is not a race. Close the bleeder screw only after there is no more witness of air leaving the brake system.
It is not necessary to squeeze the brake lever all the way to the handgrip. Discouraged, actually, because the Honda Shop Manual has an illustration of temporarily placing a 15mm spacer between the hand grip and the brake lever to limit the master cylinder's internal fluid piston stroke. My trike has an aftermarket lever so I very carefully limit each lever stroke.

Constantly check and renew the brake fluid level in the master cylinder reservoir.

Turn the handlebars all the way left, attach the clear tubing to and open the right side caliper bleeder screw.
After the caliper is purged, close the bleeder screw.

Turn the handlebars all the way right, attach the clear tubing to and open the left side caliper bleeder screw.
After the caliper is purged, close the bleeder screw.

If the master cylinder brake lever doesn't give you correct, repeatable feedback after both side's caliper piston are fully , hydraulically extended to clamp the pads onto the brake rotor, bleed both sides' calipers again.

Reminder! Rebuild at least one of those three front brake master cylinders. First.
New brake hoses are a Best Practice, too. (advises the old guy that just replaced the 45 years old, factory installed front brake hoses on his '75 GL1000 )

20210705_222705_resized.jpg

[cfairweather]

You shouldn't use Teflon tape on brake lines or brake components.

[Shadowjack]

I use plumbers' silicone grease on the bleed nipple threads to seal against air backflow.
I find that if I can orient the master cylinder in such a way as to make the plunger diaphragm the highest point of the assembly, then when I work the lever, air in the lines will migrate up to it. The MC has to be level so the spooge hole is at the top of the cylinder, but have just a little tilt so the plunger is highest. Then just work the lever the littlest bit, several times, making sure that the plunger seal doesn't pass the spooge hole, and the air will come out. You have to have the cover off to see it, of course, and be prepared to loosen and twist some things to get the proper attitude.

[Sidecar Bob]

My son & I wasted a couple of bottles of brake fluid trying to bleed the rear brake on my 1000 one time many years ago. I never did get it to work properly until I bought a good used master cylinder and rebuilt it, then it bled easily and worked perfectly.

You mentioned the brake lines and the conditions the bikes were stored in. Are you aware that rubber brake lines should be replaced every 2-3 brake fluid changes (-5-6 years)? If you still have the original 40+ year old ones I'd advise replacing them with modern stainless braided ones that will last practically forever and double the life of the fluid before wasting any more time and brake fluid bleeding with the old ones.

FWIW, I find that vacuum bleeding works much better and faster for me.

[6adan]

I want to thank all of you for the suggestions. I have used them and now have brakes as good as they will get with the old lines. I am working on this for another guy so he will have to decide about new lines. Thanks again Dannie