F250 front brakes drag. Help!

[guhfluh]

I converted my 67 to 73 F350 front spindles, caliper brackets, calipers, hubs, rotors and lines. Around the same time, but before the disk swap, my master cylinder blew the fitting and threads out of the side, so I replaced it with a questionable new reman for a 67 drum under warranty. I have checked the master and it does NOT have a residual valve behind the brass seat in the front brakes port. I am still using the 67 drum distribution block as well. Nothing else changed.

Since installing the disks though, I cannot get the front calipers from dragging. I have rebuilt one and bought another new, as well as new hoses.

I need some insight on how to diagnose. I'm thinking it has to be the master, but I'm not sure:(

[ultraranger]

Are your brakes manual or power?

If manual, grab the brake pedal and pull it towards the seat. There should be some free-play in the pedal.

If brakes are boosted, you will need to check the length of the boosters output rod compared to the depth of the bore on the back of the MC. If the tip is adjusted too far out, it'll be partially applying the brakes even when you aren't stepping on the pedal. You should have .005"-.010" clearance between the tip of the booster output rod to the bottom of the MC bore.

It would be best to install a disc/drum combination brake valve and a MC that's specifically designed for a disc/drum brake system.

[guhfluh]

It's still manual brakes. I have a booster to install, but want to do things one thing at a time. The combination valve will come later as well.

I do have play in the pedal still, but I'm not sure the master is returning the pedal all the way up as far as it should. It is not returning the pedal all the way back to a normal position very fast and because the pedal rod is not actually attached to the piston in the master, I cannot make the piston retract any faster or further by pulling the pedal. It is kept in the master body by the circlip though. When I first installed this master, I noticed it when bench bleeding as well as bleeding it in the truck. If I jiggle the pedal on top of the piston, it seems to want to return further sometimes than others and faster as well. It takes a few seconds for it to fully return, which seems like an eternity to me compared to others I'm used to.

As far as I know the only difference between this master and a disk/drum specific one will be a smaller bore size, and pedal effort right now is fine, even without a booster. I like a firm pedal without a whole bunch of travel, as it builds confidence, even if it's not actually working better.

I *am* actually interested in upgrading to a 86? Ford Ranger master if/when I need a new one, as I'm tired of battling rust. I need to figure out what fittings I'll need, if I need to rebend lines, and make sure it's the right one though.

Thanks for any help you can give; you seem to be the guru on brakes around here.

[ultraranger]

I forgot to ask earlier if the pressure differential valve wiring pigtail is hooked up and if the brake warning light is staying on (of course this also depends on having a known good bulb in the warning light). If it's staying lit, it could be causing just enough restriction to the fluid freely returning to the MC so that the pistons of the MC would be slow to return the pedal to its at-rest-position. The resistance would give a firm pedal but slow brake reaction, overall.

Two other possible causes of the pedal being slow to return to its at-rest-position could be a caliper piston(s) that's not moving freely or the MC pistons themselves could be sticking in the bore. --another reason I try to stay away from rebuilt MCs. They just don't have a good track record of lasting very long and I can think of better things to do than to change MCs every 6 months to a year.

The biggest difference between a drum/drum MC and an actual disc/drum MC is the size of the fluid reservoirs. A disc/drum MC will almost always have a higher fluid capacity than an all drum MC. Removing the RPV (Residual Pressure Valve) or, getting an all drum brake master that didn't have any RPVs installed to begin with, can be used in a disc/drum application but, I wouldn't recommend doing this. The reason goes back to fluid capacity of the MC. After all, if it wasn't necessary to change MCs to match the type of brake system that's being run, automotive manufacturers wouldn't have gone through the expense and time to design and install a different style of MC (or brake valves) if one type was good for all applications.

Upon initial installation, a drum/drum MC, in a disc/drum application, it will operate the disc and drum brake circuits of the system. However, disc brake linings are generally much thicker than drum brake linings. As the disc brake linings wear down, it takes more fluid volume from the MC to fill the void in the calipers as the pistons move further outward in the caliper bores. This in turn drops the brake fluid level in the primary reservoir of the MC. A disc/drum MC is designed with enough fluid reserve to compensate for this. A drum/drum MC is not. If the level drops enough in the drum/drum MC (being used in a disc/drum application), you will run out of both reserve and brakes too.

[ultraranger]

RANGER MC:

An '87 Ranger MC had a cylindrical aluminum body with a plastic reservoir. It came in two versions; power and manual brake applications. Both versions had a 0.0937" [15/16"] bore.

The power brake version has a 7/16"-24 primary port and a 9/16"-18 secondary port.

The manual MC version has a 3/8"-24 primary port and a 1/2"-20 secondary port.

I'm not sure if I'm correct on this but it seems like sometime back, I remember you saying you had an F-350 dual-diaphragm booster (?).

The 15/16" bore of the Ranger MC will generate a lot of output pressure but you may experience a long travel of the brake pedal. If it's mounted on the F-350 booster, you may also find that's it's too sensitive. ... hard to know for sure without actually installing it but, these are very probable (potential) problems you could experience with it.

[guhfluh]

The light actually hasn't been working and I haven't thought about it thus far. I did notice it came on one time when I first started the truck, with the oil and alt lights, but had never come on before and hasn't come on since. I'm sure it has a bad bulb or poor connection in the circuit right now and it's something I should go ahead and check.

I believe it's probably the master cylinder piston sticking in the bore and not the calipers, or it could be both. I guess I should jack up the front and see if it frees up a wheel if I crack a bleeder?

My booster is just a Cardone unit for a 67 F250 from OReilly Auto. It's a single diaphragm I'm sure, but I'm not sure of the diameter. I have the normal brackets and not the cantilevered ones.

The Ranger master does sound small for use with a booster...Your old pictures from 2012 don't work anymore showing a Windstar vs Explorer master, would one of those be a better fit and have easily adaptable ports from stock or easily made non-bubble flares?

[ultraranger]

Both the Explorer and Windstar MCs have metric ISO bubble flare ports that exit on the drivers side and have a 1.062" [1-1/16"] bore diameter.

The '95-2001 Explorer MC has a 10 mm x 1.0 port and a 12 mm x 1.0 port. Approx overall MC length is 7-1/2". The plastic reservoir is basically 'level.'

The '95-'98 Windstar MC has (2) 10 mm x 1.0 ports --and one 3/8"-24 port that's on the bottom, front end of the MC body. Approx overall MC length is 8-1/8". The plastic reservoir is level and physically larger than the Explorer MC (greater fluid capacity than Explorer).

Explorer MC






Windstar MC






Explorer MC on left, Windstar MC on right.

[tqwrench]

I do have play in the pedal still, but I'm not sure the master is returning the pedal all the way up as far as it should. It is not returning the pedal all the way back to a normal position very fast and because the pedal rod is not actually attached to the piston in the master, I cannot make the piston retract any faster or further by pulling the pedal. It is kept in the master body by the circlip though. When I first installed this master, I noticed it when bench bleeding as well as bleeding it in the truck. If I jiggle the pedal on top of the piston, it seems to want to return further sometimes than others and faster as well. It takes a few seconds for it to fully return, which seems like an eternity to me compared to others I'm used to.

Seems pretty straightforward. You depress the piston in the bore and it's not returning all the way. Fix that first. Calipers rely on the square cut O-ring deforming during application and returning to normal to pull the pistons back after application is over. They're not overly complicated. Perhaps it's time to start fresh with a 73 F350 master cylinder? Check rockauto, they typically have more selection than Autozombie's Cardone or Chinese white box parts. Maybe a nice Bendix reman or new master is in order? I personally have had multiple brake components from the fast food parts stores come with shot or debris in them. If I'm stuck and have to use their stuff, I prepare to disassemble, clean and reassemble before using it. QC is garbage on this stuff.

[guhfluh]

Okay, I've now gotten a chance to test the system and try a few things that didn't work out so well it seems. I work offshore 3 weeks at a time, so it takes me a while sometimes.

I checked the distribution block and it is centered and the switch is not grounded. The brake light bulb is good as well.

I jacked the driver front wheel off the ground, depressed the brake pedal and let off, then tried to turn the wheel, making sure it was binding up, then cracked the fitting at the master. Doing so freed up the wheel, so I knew it was the master.

I then pulled the brass fittings out of the master and double checked that I didn't have any RPV's in there, and as I suspected there weren't ANY front or rear in this reman drum/drum master.

So, I proceeded to change the master cylinder to a 89 Ford Ranger master with a 15/16" bore and remade my lines to the distribution block with new fittings for the master. I then had trouble getting the brake pedal rod the correct length without purchasing a $50 adjustable rod, or spending another $50 to purchase a tap and die set to thread mine and make one. So, instead of running it without a booster, I installed the booster I already had, since I knew it's rod fit, and I just adjusted the booster output rod for the new Ranger master.

Now, the brakes don't stay engaged or drag, but they feel horrible. It feels like there is still a huge amount of air in the system. Even with the truck not running, the pedal is soft and will go all the way to the floor pretty easily. I did bench bleed the master before installing it, then gravity bled about a 6oz. Through the front lines(half a small bottle). After that my wife got home and helped me manual bleed all four in order from back to front. I bled quite a bit through and continued after air quit, though it still feels like there is some air in there to me.

Aggravated, I went ahead and purchased a 2000 Ford Explorer 4dr. master cylinder, more line(because I don't trust my bubble flare skills yet), fittings and fluid. I plan on installing it tomorrow, BUT I have some questions:

1) What is with the bleeder screw fitting on the passenger side of the master?
2) Is there a special bleeding procedure for this master?
3) Is this the correct master? It's # and it has a 3/16" double flare port coming out of the front top as well as a 10x1.0 front and 12x1.0 rear port AND the bleeder on the pass side.

[ultraranger]

The Explorer MC from my photo in this thread was for a 1995 or 1996 model. I bought it at NAPA. I believe the part number was M3246. It was without cruise control and didn't have the bleeder on the side.

The MC you have is for a vehicle with cruise control, as denoted by the threaded boss on top at the front of the MC. In its original application, there would be a pressure activated switch in that port to cancel the cruise control setting when the brake pedal is stepped on. You could simply take a 3/16" inverted flare plug and cap off that port or, swap it for an Explorer MC w/o cruise control.

A 15/16" bore MC will produce more output pressure than a 1-1/16" bore but, the 15/16" MC will have a longer pedal travel compared to the 1-1/16". Even so, the pedal should not be going all the way to the floor with the 15/16" bore MC. This sounds like there is either a good amount of air in the system or, there is a leak in the brake line(s) that's keeping the pressure from building.

Double check the hard line connections to see if brake fluid is seeping out of any of them. I'm not sure on those twin-piston calipers if it's possible to install them on either side but, make sure the bleeder on the calipers is pointing upward. If they are swapped and pointing downward, you will not be able to get the air out of them.

Also, check the shoe adjustment on the rear drums. If they aren't adjusted out enough, it can make the pedal have a very long travel. Adjust the rear brakes up until you cannot turn the wheels. Once they are tight enough you can't turn them, back the adjusters off 10 clicks.

Here is a procedure for setting the output rod-to-MC bore depth when installing a MC on a power brake booster:

http://www.maximummotorsports.com/asset ... AK-1r1.pdf

[guhfluh]

Thanks for the reply Steve!

My calipers are on the correct sides, with the breeders pointed up. Yes, I believe they can be swapped, but not upside down.

Today I pulled the Ranger master cylinder and put on the Explorer master. I bench bled the master out of every port on it before putting it on the truck and after connecting the lines I bled through the front top port and side bleeder, just to make sure. I remade the lines to the distribution block with metric bubbles for the new master and gravity bled them before tightening, and before rebleeding the master on the truck. I then bled each wheel, but got nothing more from them.

The pedal is much better and firmer. It will stop before reaching the floor, but still doesn't feel right to me. I will adjust the rear again to make sure, but that is the procedure I did when I had the original manual master.

What I have found is that the booster doesn't want to return the pedal fully when it has vacuum. With the truck off and vacuum pumped out, the pedal springs all the way back to the top without any issue or hesitation. With the engine running, the pedal will sloooowly get there, but until that point it keeps the brakes partially applied and dragging. If I pull the pedal back up with my foot, it releases immediately with no brake drag. Is there supposed to be a pedal return spring on power brake trucks?

[ultraranger]

The spring is internal to the booster. Is this a wrecking yard take-off booster, a booster that was already on the truck or, is this a new/rebuilt parts store booster?

[guhfluh]

It's a reman parts store booster.

[ultraranger]

Before changing or swapping any parts, the first thing you will need to know is how much vacuum you have to the booster. For the booster to work at optimum potential, you need at least 18"-20" of vacuum. Put a vacuum gauge on the vacuum port of the engine. If the vacuum signal is good there, take the vacuum line loose at the booster and read the vacuum at that point.

If there's a drop in vacuum on the end of the hose to the booster, then the hose may have a blockage inside it or, the hose is not clamped tightly at the engine fitting or, there may be a problem with the check valve on the booster.

If the vacuum tests are good, the next thing to checkout is the brake booster. The booster has vacuum in the chamber on the front side of the diaphragm. When you step on the brake pedal, the booster input rod moves forward. Simultaneous to this, the vacuum valve inside the booster is closed off while at the same time the atmospheric valve opens up. This allows atmospheric air pressure to rush into the back side of the booster housing (through the opening where the brake pedal input rod goes into the back of the booster).

The stronger the vacuum signal is, the greater the force of the atmospheric air pressure will be against the booster diaphragm to push it forward. --as an example, 20" of vacuum on an 8" diameter brake booster will provide 240 lb of brake assist.

If your vacuum signal is good, then there may be an internal problem with the vacuum port in the booster not sealing off when you step on the brake pedal, which may be why the pedal doesn't return to its at-rest-position unless you pull it back up with your foot or, until the vacuum is removed by turning the engine off. Aside from the spring on the reaction disc inside the booster, the primary and secondary MC piston return springs should also assist in returning the brake pedal to its static position.

If the vacuum from the engine, the vacuum hose and the booster check valve are all good, here are some steps to take to determine if you have a defective vacuum booster:

http://www.mbmbrakeboosters.com/index.p ... &Itemid=15

[guhfluh]

Thanks again Steve.

I do know that I have strong engine vacuum. It's a stock cam 300 and I have it adjustable in idle speed by the choke cable from 700-1000 rpm. I don't have a gage in it right now, but I've checked it before while setting the carb and dizzy.

The booster will hold vacuum for a few pumps after the engine is off, so I believe the external check valve should be good.

The line to the booster is teed above the PCV valve and then run to the manifold. It's all new lines and tight and could be collapsing, but I can tell the booster is getting vacuum as soon as I start the truck and while driving by the feel of the pedal. It's a little mushy at the top of travel(which I hate), but firms up nicely at the bottom and stops well.

Another thing I have a suspicion of is the boosters output rod adjustment. I have it set so that it is very close to the master's plunger. Maybe too close? I remember reading somewhere that there should be .010" of clearance? (Nevermind, its in the link you posted as .005" to .010") I'm thinking that I may be able to at least stop dragging by adjusting it for more clearance or that it may be binding ever so slightly right now. I set the depth originally for the Ranger master, by measuring with my dial calipers, and coming up with 0.945" in the master and 0.925" or slightly less on the booster rod. I checked that the Explorer master depth was the same before installing and checked by feel when I installed it on the booster for any bind.

So, in the morning I plan on checking the adjustment on my rear drums and checking the adjustment on the booster again. Any others?

I can take a video and post it on YouTube if there's anything to see that might help.