Hey Guys,
When I re-did my 69 f-100, I had a 69' Ranger Donor truck,It had four drums and a power booster. I decided to use the booster on my truck to upgrade a little.
We pressure checked the Booster-Good. I used a new Master cylinder, We replaced ALL the rubber Lines, Both Front Wheel cylinders with a matching set, New Shoes,and turned the drums........After it was all said and done, The truck pulls to the right HARD on braking. It is also very late on the pedal and then Bam....it will stand you on your head almost. It will slide the right front wheel quickly,or easily in gravel...I have had everything apart three times, Moved drums from side to side........ Checked and rechecked the Mechanical part of everything...... Bled the Brakes Multiple times.... even replace parts on the back in the beginning making sure it wasn't the rear ......I have since replaced the wheel cylinders again to make sure it wasnt unequal pressure.......We're stumped. My best friend is a retired ford delearship mechanic of 40 years....so its not just my eyes/hands that have been on it....
I mean, does anyone know what might cause uneven fluid pressure to the right front........Sunday, after I changed everything out, It was fixed....Me and Terry both drove it 10 miles. It stopped straight/smooth and a nice even (although a little soft) pedal...You could not even hold the wheel and she would stop straight.....and as I'm driving it home,I hit the brakes in a roundabout and it slid the right front and literally jerked the wheel out of my hand....and now its back to being touchy and pulling hard to right again.....Terry (Ford mechanic) hypothesized a piece of rubber hose in line blocking left front line being sucked back and forth after bleeding?? we're really grasping at straws..........UltraRanger, I know You're a Brake specialist.....Any Ideas??
I dont know exactly which Booster I have......Also, How Can I tell if I have the Proper Master Cyl for Drum Drum ??

 

I am having my own brake issues so far from an expert, but sounds like something in the line to the left side. Can you disconnect it at the pressure differential junction and blow the lines out? Only other thought would be adjustment of the shoes but sounds like you have had it apart to double check the install for that and to make sure you have the adjuster installed correctly.

 

Fluid pressure in a contained system will be the same throughout the system (Pascal's Law).

The rear brakes will have the same amount of force being applied to them as the front brakes, so long as the tandem MC has the same bore diameter on both the primary and secondary sides. The only reason the front brakes do more work than the rears is because the front wheel cylinders/caliper pistons are larger than the rears and the front brake drums/rotors have a larger surface area than the rears.

Whatever pressure is being applied on one front wheel should be the same for the other, since the pressure is at the same common point from the MC to the two outlet ports on the primary side of the pressure differential valve. If they are not the same, the pressure is being reduced somewhere between the pressure differential valve out to the wheel cylinder of the offending side. Having a pressure gauge would help diagnosing if/where there's a pressure drop.

There could also be some mechanical binding of the shoes as they try to move. Check for wear groves in the drum backing plate that the shoes could be hanging up on and not wanting to freely extend or retract.

 

Thanks Steve....I'll see if I can get a pressure guage and check the line....I did look at the backing plate to make sure it wasn't bent and didnt see any contact area but will double check....and I switched the drum sides in case the drum wasn't cut deep enough when turned and pull didn't switch sides, so I think that ruled that out......

 

The best thing you could do for the front drums is to replace them with the front discs/suspension from a '73-'79 F100 or a '75-'79 F150. (I prefer the '75-'79 F100/F150 2WD front discs suspensions, since the radius arms on them are already configured to accept the endlink brackets for a factory swaybar from a '75-'79 F100-F350 2WD truck).

I have the front swaybar assembly from a '78 2WD F250 Camper Special and a rear swaybar assembly from a '79 Bronco, along with a front discs/suspension from a '77 F100 on my F100 Ranger. '74 model radius arms can be modified to accept the swaybar endlink brackets but, you're out of luck with '73 model radius arms, since they're made just like the '67-'72 radius arms --cast steel vs the changeover to the later stamped steel configuration.

I wish at the time I had rebuilt all 4 drums on my '69 F100 in 2011, that I had just spent the money/time on switching it over to discs then instead, like I finally did in 2014. Going to power front discs was a major improvement over the power drums I had, and before that, I had manual 4-wheel drums.

The combination of a power brake booster, front & rear swaybars and discs on the front have made a dramatic improvement in the way my truck handles and stops from the way it was when I initially bought the truck.

 

It does sound a lot like some crap in the lines doesn't it?

Good call on checking for grooves or gouges on the backing plate shoe pads. There are 6 per side, 3 for each shoe. They ride and slide on these and must be flat in order to retract smartly when brake is released.

 

You may want to double check the the shoes are installed in the correct location. As I recall you will have a shorter shoe on each side. If booth short shoes were installed on one side trying to get things adjusted properly will be difficult. Also look at the self adjusting cables. Good luck.

 

At each wheel, the shorter drum brake shoe will be installed towards the front end of the vehicle and the longer shoe gets installed on the side towards the rear of the vehicle.

 

Since it drove correctly right after the work was done but now doesn't makes me believe everything was done correctly. With the possible exception the parts supplier sent you (2) right side adjusters. So the left side would be backing off. But I have the faith OP checked the adjusters before installing.
So that gets us back to the hydraulic system. I'll bet it's a bad L/F rubber brake hose. The Inside is hosed (pun intended).

 

Had this exact problem on a vehicle years ago and it was exactly that a piece of crud in the lines, a chunk of rust in that case. Disconnect the affected circuit's line from the master cylinder and then the next coupling point (junction block ?) and blow it out with unregulated shop air in both directions, then rinse out with brake clean and blow dry with shop air. Do this will all the lines on that circuit and any junction blocks, be sure to blow it out in both directions. Do not use brake clean on the rubber flex hoses ,unless it one that is safe for use on rubber.

Also check the inlets to the slave cylinders. If the rubber brake hoses are not new replace them as they can degrade from the inside out and flake off chunks of rubber that can block things up. It would not hurt to pull the slave cylinders take them apart and clean/check them even if new out as a chunks of rust can jam up between the the pistons when the brakes were bled. If only one piston in the slave cylinder is working to full potential you can lose the self energizing feature of the brakes and it will drastically cut down braking effort on that wheel.

With modern shoe materials and power assist, in later vehicles fitted with 4 wheel drums they are more than adequate in most cases.
If you are hauling heavy loads, towing, or live in hilly or mountainous terrain or see lots of stop and go traffic then the the upgrade to disks is definitely advisable.

Some light auto applications were using 4 wheel drums in to the mid 80's and worked as good a disks, mind you they were fitted with 2 slave cylinders on each wheel.

 

You should use caution when blowing compressed air into the plumbing of a brake system or into its brake components. It's not unusual to have minute particles of petroleum-based oil in the air line from an air compressor. If this oil gets forced into the brake system plumbing and comes in contact with any of the seals in the brake components, it will cause the seals to swell, rupture and fail and it only takes a small amount of it to do this.

DOT 3, 4 & 5.1 brake fluid is synthetic and not petroleum-based. The seals are only compatible with synthetic or silicone (DOT 5) fluids but not petroleum fluids.

If you're going to use compressed air to blow out brake lines or its components, it would be good insurance to install a new (out of the package) inline air filter between the air line and the blow gun, before blowing the parts out.

 

Good point Ranger I just always assume that if you have a compressor you are going to have a water/oil separator installed, just a common sense sort of thing but then again common sense is not so common.

DOT 3, 4 brake fluid are not synthetic but true Glycol Ethers (some DOT 4's may be synthetic or blends) in short they are a type of solvent. Dot 5.1 is a true fully synthetic Glycol Ether based fluid. The old DOT 2 was castor based now obsolete. And of course DOT 5 is Silicone based. If you rebuild a brake system (all new parts and lines) then DOT 5 is a no brainer. modern replacement seals/rubbers in reman parts are compatible with DOT 5

 

All glycol-based brake fluids: DOT3, 4 & 5.1 brake fluids (fluids that are not silicone or mineral-based) are a composition of synthetic blended glycol materials.

See 3rd paragraph in the following link.

Tech Article: Brake Fluid

Unfortunately, oil mists in a compressed air system are lighter than moisture droplets travelling through the plumbing and can still get past the separator. An additional (new) inline filter just before the blow gun will greatly reduce the chances of blowing petroleum residue into the brake system.

DOT 5 doesn't attack paint and isn't hygroscopic but, it does have 2X the aeration (compressibilty) of glycol brake fluids under normal braking conditions. This tends to cause a more spongy feeling brake pedal.

 

I would not take that article as gospel. Dot 3 Fluids are based on glycol eithers formulated from ethylene glycol an organic compound, DOT 4 contains synthetic borate esters in addition to what is contained in DOT 3, DOT 4 Super (superseded by Dot 5.1 in North America) is based on Synthetic borate esters and synthethtic polyethylene glycol

There is also LHM brake fluid (green in colour) which is mineral based and used by Jaguar , Rolls Royce and others

Dot 5 silicone brake fluid contains at least 70% diorgano polysiloxane.


Aeration and compressibility are not the same thing.

Dot 5 fluids will actually compress, the higher the temp the more they will compress, up to 2x times more than conventional fluids when heated . This can lead to a more spongy pedal feel. In unassisted (non power brakes) braking systems this may prove a benefit as it may lessen perceived pedal effort.

Dot 5 fluids have a much higher aeration capability (ability to hold air bubbles) over conventional fluids.
This is only an issue during fill and in applications where successive rapid brake applications are experienced (such as racing).

With the higher aeration factor and compressibility issues DOT 5 is not recommended for race applications or high performance braking systems.
But even then Dot 5 is the OEM fluid for Harley Davidson and others.

Dot 5 was developed for to meet a US mil requirement for a hydrophobic brake fluid.

In vehicles that sit for extended periods of time (sound familiar) conventional brake fluids will absorb moisture from the atmosphere. When brake systems see constant use the moisture content will tend to stay lower as heating of the brake components from constant use and surrounding components will help "cook" out /prevent moisture absorption.

Prior to the adoption of DOT 5 the military was having huge issues with brake system failures in vehicles that been parked for long periods of time (months maybe years) and was not uncommon with mil vehicles in service, owing to the hygroscopic nature of conventional brake fluids and the fact that most of these vehicles were stored out of doors in all types of weather the braking system components would corrode internally and many even larger trucks used juice brakes with air over hydraulic systems. The vehicles would then be put in to use only to find that the braking systems had degraded/corroded rendering them unusable with out repair. The development of DOT 5 alleviated this problem.

All the CUCV's other MIlCOTS and the HMMWV's all use DOT 5 with all the same brake components found in civilian units.

Some procedures need to be followed when initially filling a system with DOT 5 or converting to DOT 5.

If converting to DOT 5 the whole brake/clutch system needs to be thoroughly cleaned of all traces of conventional brake fluid as mixing DOT 5 and brake fluids based on organic glycol eithers results in jello. So wheel cylinders, calipers, master cylinders and slave cylinders need to be disassembled and thoroughly cleaned. This may even apply to new in the box parts.
And last time I checked Jello is not a viable hydraulic fluid.
DOT 5.1 fluid and DOT 5 fluids do not mix and will separate out but do not react with each other and gel up to form Jello.

Most all issues people experience when using or switching to DOT 5 are from improper system filling or not properly cleaning the braking system of conventional fluid.

DOT 5 is more viscous than conventional brake fluid and is not recommended for use with most ABS systems. But it is more viciously stable with changes in temperature than conventional fluids.

I have vehicles that have been filled with DOT 5 for over 35 years and are still using the same fluid and all the same hydraulic brake components with not a single failure. There was not noticeable difference in pedal feel when they were switched to DOT 5 but our old trucks have any thing but a performance braking system and pedal feel was an after thought at best.

Switching to DOT 5 fluid is a no brainer if you are restoring an old vehicle that is not going to see daily or regular use this makes even more sense if you are doing a full restoration where all the brake components are new.

Using DOT 5 essentially makes for a life time install and increases the life span of the braking system hydraulic components to decades rather than years.