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Hi guys
Just replaced my front calipers on my 76 highboy and I cannot seem to get the air bled outta the lines now.
i did fumble around a bit getting the drivers side line back on so likely got quite a bit of air in the line, and I didn’t gravity bleed them before I got to pumpin (rookie mistake).
Besides that and to the best of my knowledge, I’ve done the procedure properly. started back right, back left, no air. Fronts however, absolutely insane amount of air that never seems to end! I’ve gone through 3 quarts of brake fluid and still a **** ton of air coming out when I crack the bleeder on both sides.
I’ve got no fluid leaks that I can see and I’ve been diligent with keeping the master cylinder topped up.
How much air is normal and how much fluid should I expect to go through to get these brakes bled out? Something seems off. Had no air problems prior to changing these calipers.
in a perfect scenario, only enough fluid to fill each empty bore(s) of the calipers. describe your bleeding method. Are the bleeder screws at the top of the caliper? all lines from master tight and in good condition?
in a perfect scenario, only enough fluid to fill each empty bore(s) of the calipers. describe your bleeding method. Are the bleeder screws at the top of the caliper? all lines from master tight and in good condition?
I started out solo, ran a clear tube on the bleeders with a zip tie to keep it tight. Ran a loop up (to stop air from sucking back in) and then down into a plastic bottle to catch the old fluid. Crack the bleeder and pump the brakes. On the last pump I would prop the pedal down with a board then close off the bleeder.
After not succeeding with this technique I had a partner to try and help buddy bleed. We ran a whole quart through with him pumping the pedal 10 times and holding while I cracked the bleeder.
lots of air coming out every time in both techniques.
one thing I did find in my research is the need to pull or push the pin on the proportioning valve, which I had not been doing. The book says on GVWR over 6900lb to push the pin in. My truck says 7700 on the door tag, but I don’t think my proportioning valve is the type you push in, rather it seems to want to be pulled out (maybe someone replaced it with the wrong one at some point?) I’ll post a pic, maybe somebody can confirm which proportioning valve is the have and if I indeed need to pull that pin?
Last edited by Daveymoults; Feb 1, 2026 at 11:28 AM.
Reason: Adding photo
I've never had to mess with the pin...
Just to be clear...the bleeder is closed while you pump the pedal then hold...THEN open the bleeder then close it BEFORE the helper lets the pedal back up?
I've never had to mess with the pin...
Just to be clear...the bleeder is closed while you pump the pedal then hold...THEN open the bleeder then close it BEFORE the helper lets the pedal back up?
Sounds like you're doing it right, I use a mighty vac along with the two person bleeding and it always works.
Are you sure you're getting air ? sometimes the fluid looks like it has air but it's just from the pressure as it goes through the bleeder.. unless you're actually getting obvious air, I'd try the brakes and see if they're working properly.
The only place air can enter the system at this point is the master, and if you're keeping that full you can only bleed so much air.
If your just talking about bubbles, Thats could be air just entering around the hose, or through the loose bleeder threads.
How does the break pedal feel? Sometimes if the break pedal is low, it’s because the rear breaks aren’t adjusted.
I use a hand vacuum pump and I usually see bubbles because a loose connection on the vacuum hose and bleader screw, but the break pedal comes up tight.
If your just talking about bubbles, Thats could be air just entering around the hose, or through the loose bleeder threads.
How does the break pedal feel? Sometimes if the break pedal is low, it’s because the rear breaks aren’t adjusted.
I use a hand vacuum pump and I usually see bubbles because a loose connection on the vacuum hose and bleader screw, but the break pedal comes up tight.
thanks for the reply!
brake pedal is loose. I even put the wheels back on and was gonna go for a test drive but I barely had enough brake to keep me stopped when I put her in drive so I didn’t back out.
rear brakes could need adjustment, I’ll check that. But I think I have somethin else awry here. Copious amount of air
1. Check that all bleeders are closed.
2. Make sure the master cylinder is full.
3. One person pumps the brakes until the pedal is hard and he/she holds the brake pedal down with constant force.
4. Another person opens the bleeder, starting with the one furthest from the master cylinder.
5. When the pedal is pushed to the floor, he/she keeps it to the floor until the bleeder is closed. Verbal communication helps in this step.
6. Repeat 1-5 until all air is no longer coming out of the bleeder.
7. Move to the next bleeder and repeat 1-5.
This is the way that I have always done it and it has always worked. Do not pump the pedal with the bleeder open. It will suck air back into the caliper every time. I hope it helps.
X2 what SlickWillie said, BUT between step 5 and 6....EACH time you are done bleeding, like do it once and then (while the assistant person holds the brake pedal to the floor), and you close the bleeder. And once you yell "bleeder shut", then they take their foot off the pedal. And they go right to the master cylinder, take the cap off and refill the master cylinder. You must keep it full of fluid. I never have had to mess with the pin either. Some say in, some say out based of GVW.
Bleeder rod hold OUT tool, make out of a piece of sheet metal. The rod does not move very much.
Before you go test driving with questionial brakes, 100% make sure the emergency/park brake works. As in it sets AND releases.
Last edited by 77&79F250; Feb 2, 2026 at 05:44 PM.
The master is the only place air can get in the system once you finished changing parts, all it can do is leak now it can't pull air. and the system simply cannot hold much air it's physically not possible. so if you really are getting lots of air it has to be because your fluid level in the master going empty. maybe it's returning a little after the pedal is released and it just looks like it hasn't gone dry.
I have a '76 high boy with the same brakes as you, when I changed my calipers it took about 5 minutes to bleed them. there has to be a simple explanation, this is all I can guess.
I have a 20 ft piece of 3/16 vinyl tubing, connect one end to bleeder, made small hook out of a piece of brake line, connect to other end of tubing, hang it in the side of the full rez your doing, start pumping. Watch the tubing when doing this. Keep pumping till all the bubbles are gone, tighten bleeder. You might have to get creative on tubing connection to bleeder, like zip ties, etc. No fluid loss. Don't let the rez empty out or you will have to start over. Real easy, one man job, pedal doesn't need to be on floor when tightening bleeder. Cap the tubing on both ends when switching wheels, rez side first so minimal dripping.
And correct me if I am wrong, that you DO need the master cylinder cap ON (with the bail) when pushing the brake pedal. Other wise brake fluid will shoot straight up out of it? Or did I make a mistake one time?
Headloct I like that way, I need to try that so I can be a one man band bleeding brakes.
X2 what SlickWillie said, BUT between step 5 and 6....EACH time you are done bleeding, like do it once and then (while the assistant person holds the brake pedal to the floor), and you close the bleeder. And once you yell "bleeder shut", then they take their foot off the pedal. And they go right to the master cylinder, take the cap off and refill the master cylinder. You must keep it full of fluid. I never have had to mess with the pin either. Some say in, some say out based of GVW.
Bleeder rod hold OUT tool, make out of a piece of sheet metal. The rod does not move very much.
Before you go test driving with questionial brakes, 100% make sure the emergency/park brake works. As in it sets AND releases.
thanks for that info!
I’ll be digging into it again in the next couple days here. I’ll post back with how I make out
Last edited by 77&79F250; Feb 2, 2026 at 05:44 PM.
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