Bleeding the brakes

[IHdieselfan]

I've been working on a truck for a friend of mine. did a total brake overhaul. front brakes pads, calipers, hoses, rotors. rear shoes, drums, wheel cyl, axle drop hose, hardware kits. brake booster, master cyl. I mean the whole system. and it seems every time I open the brake system on one of these trucks. it always has a sinking pedal for a while. I bleed and bleed by the book and bleed at the rabs valve. and it always does it like this. what am I not doing right. when I bleed the system I have the truck off. work all the air out and it has a good pedal. then crank up the truck and get some vaccum on the booster and then it starts sinking to the floor.

 

[racin460]

id like to know myself, one time I ran half a gal of brake fluid throw one and still had the same feeling. soft peddle but when driving the truck a very little pressure on the peddle stops the truck easy, heck some times you can press so light on the peddle the tail lights wont even light. but once you stop you can push the peddle 3/4 to the floor.

 

[icanfixall]

The rear brake shoes usuallyare the issue for soft or sinking brake peddle. Whats happening is the rear shoes wont self adjust. So the fronts do all the stopping and after you stop the rears are still wanting more fluid to fill the wheel cylinders. So the peddle continues to push fluid back there and sinks. Test this my seeing how far the parking brake arm needs to go to set the brakes. If you near the floor you bet the rears are way out of adjustment. Now apply the parking brake about 1/4 to 1/3 and test drive the truck. See where the brake peddle stops the truck and what the feel is. I'm betting it wont sink because to have already added the needed brake adjustment by applying the parking brake. Then you need to adjust the rear shoes with a brake spoon manually like many of us do all the time. Using the parking brake as the guide to seeing how bad the rear shoes has worked well for many of us.

 

[HammerDown]

The rear brake shoes usuallyare the issue for soft or sinking brake peddle. Whats happening is the rear shoes wont self adjust. So the fronts do all the stopping and after you stop the rears are still wanting more fluid to fill the wheel cylinders. So the peddle continues to push fluid back there and sinks. Test this my seeing how far the parking brake arm needs to go to set the brakes. If you near the floor you bet the rears are way out of adjustment. Now apply the parking brake about 1/4 to 1/3 and test drive the truck. See where the brake peddle stops the truck and what the feel is. I'm betting it wont sink because to have already added the needed brake adjustment by applying the parking brake. Then you need to adjust the rear shoes with a brake spoon manually like many of us do all the time. Using the parking brake as the guide to seeing how bad the rear shoes has worked well for many of us.

I never would have though of doing that ... brilliant!

 

[icanfixall]

Thanks for the brilliant idea comment but.. I was just thinking thru the braking system years ago and figured if the parking brake was slightly applied then the brakes would be kind of adjusted up. Out thinking these silly self adjusters is something I have worked on for years. I still don't know why they don't work very well. Kind of have given up on that fix..

 

[G. Mann]

I completely removed the self adjusters on my 87 F250 4x4.... When the brake peddle starts to get low, I know it's time to adjust the rear brakes... With a floor jack and a brake spoon, takes all of 10 minutes and I'm in control.. instead of forgetting about it, relying on the self adjusters that never work anyway.

It's a system that has worked fine for me for quite a while now. Your mileage may vary.

Bleeding brakes: I use a cheap electric fuel pump hooked to the longest line wheel first, to suck the old fluid out, then the next shorter line , etc.. close all the bleed screws as you move to the next wheel..

Then: reverse the connection lines [use cheap poly lines from your hardware store.. one use, discard] start at the longest line, drop the pump pickup line in a clean bottle of brake fluid and pump fluid from the bottom UP to the master reservoir. When you get about 1/4 inch of fluid and no air, close the bleed screw and move to the next longest line, repeat for each wheel. Keep a watch on your master reservoir and you can of brake fluid, don't suck and pump air [of course] and don't over fill the master.

What you will do is push the air in the lines UP which is what air wants to do. When you are done, you will have lines and master that have no air in system, you don't need two people, and you have brakes first time, every time.

I use a cheapy fuel pump and a 12v battery out of a house alarm system [got it for free] so it's all easy to move from wheel to wheel..

Hope this helps... This system will also work for bleeding clutch slave / master systems.. Really well.. Pain free system.. been using it for about 10 years on all kinds of vehicles.

edit: Forgot to mention. When you are pumping fluid from the wheel cylinder back up to the master, put the cap on the master loosely. If you don't it will squirt brake juice where you don't want it.. This is particularly important if you are bleeding the clutch from the bottom up.. you will spray brake fluid [which isn't good for paint]. Just set the cap in place, no worries then.

 

[HammerDown]

Thanks for the brilliant idea comment but.. I was just thinking thru the braking system years ago and figured if the parking brake was slightly applied then the brakes would be kind of adjusted up. Out thinking these silly self adjusters is something I have worked on for years. I still don't know why they don't work very well. Kind of have given up on that fix..

I too have a lower pedal > I know my rear shoes could use a little adjustment so, for giggles (today) I tried your experiment.
Can't say there was any difference, and that got me thinking.

When you slightly apply the e-brake the rear shoes are expanding 'mechanically' (not via hydraulics) so in reality (I'm thinking) the pedal will stay low because there will still be slop at the cylinder-push rods...in when the brake pedal is pressed the MC still sends fluid to the wheel cylinders to expand it's push-rods 'after' the front discs gets the fluid.

Now, the more the e-brake is being applied that could maybe effect pedal height. I only applied the e-brake just to where I felt the truck starting to slow down...and the brake pedal didn't seem any higher.

Suppose I'll adjust-up the rear shoes > when the snow clears

 

[TWeatherford]

How often are you all having to adjust your rear brakes? When I did them on my 94, it stopped great. But I had to adjust them constantly, once a week at least. Even a weekend getting firewood and it was time for adjustment. I figured, maybe with tougher pads I would have been better off. ******* drums, but at least I wouldn't have to jack with it every weekend. I'm wanting to do a disk brake swap on the dually to avoid this.

 

[HammerDown]

How often are you all having to adjust your rear brakes? When I did them on my 94, it stopped great. But I had to adjust them constantly, once a week at least. Even a weekend getting firewood and it was time for adjustment. I figured, maybe with tougher pads I would have been better off. ******* drums, but at least I wouldn't have to jack with it every weekend. I'm wanting to do a disk brake swap on the dually to avoid this.

I may adjust mine once a year...a lot depend on how you drive and, if your in a open or stop-go area.
Where I live, there's a stop sign or traffic light every 50-100 yards, you can wear out a set of brakes in record time!
However, I drive like I'm in a funeral procession.

 

[Zaggnutt]

I completely removed the self adjusters on my 87 F250 4x4.... When the brake peddle starts to get low, I know it's time to adjust the rear brakes... With a floor jack and a brake spoon, takes all of 10 minutes and I'm in control.. instead of forgetting about it, relying on the self adjusters that never work anyway.

It's a system that has worked fine for me for quite a while now. Your mileage may vary.

Bleeding brakes: I use a cheap electric fuel pump hooked to the longest line wheel first, to suck the old fluid out, then the next shorter line , etc.. close all the bleed screws as you move to the next wheel..

Then: reverse the connection lines [use cheap poly lines from your hardware store.. one use, discard] start at the longest line, drop the pump pickup line in a clean bottle of brake fluid and pump fluid from the bottom UP to the master reservoir. When you get about 1/4 inch of fluid and no air, close the bleed screw and move to the next longest line, repeat for each wheel. Keep a watch on your master reservoir and you can of brake fluid, don't suck and pump air [of course] and don't over fill the master.

What you will do is push the air in the lines UP which is what air wants to do. When you are done, you will have lines and master that have no air in system, you don't need two people, and you have brakes first time, every time.

I use a cheapy fuel pump and a 12v battery out of a house alarm system [got it for free] so it's all easy to move from wheel to wheel..

Hope this helps... This system will also work for bleeding clutch slave / master systems.. Really well.. Pain free system.. been using it for about 10 years on all kinds of vehicles.

I like it. Smart thinkin', Mister!

 

[riotwarrior]

I've a rather large supersuckerdomajiggy thingamabob that does this for me. Or, I'll use a special jigged up bottle and clear hose setup I've made, Extra long hose held up super high.

Next brake job I do, I'll setup all my toys (cough tools cough) and do a tech 101 on brakes and how I roll or stop the rolling buwa ha ha