brake dragging or something else

Hi all! i have finished the disc brake conversion on a d25 axle.
Also i replaced the stock pedals and master cylinder with hanging pedals and power brakes.
So i went for a test drive to see the results.
Before the disc swap i had a problem with the front right drum, it was dragging,
while i was driving and a lot more while i was braking, also i did an alignment to see if everything was fine.
So now that i made the disc swap i still have the same dragging while i'm braking but less while i'm driving.
I went to a brake shop to check if there is a difference while braking on left and right side.
The front end had a little difference from left to right, but the rear end was quite big.
So is it possible the dragging to be caused from the rear drum brake?

 

Sure is. Right rear adjusted too tight will jerk the front around to the right and same is true for the other side.

 

Just like a tractor only you are going faster.

 

I have to disagree. Tractors have mechanical brakes. Hydraulic brakes have equal pressure to each wheel. What could cause one rear wheel to brake more than the other is wet with oil, or brake fluid. That's assuming everything else is in good working order, like no pinched lines, or frozen parts.

 

If the drums are not adjusted correctly, you will get drag and pull to one side. I know this from experience. Doesn't matter front or rear. If one of the drums is adjusted tighter than the other, it'll pull to that side. They don't have to be exact but, if they aren't somewhat close, the tighter one will grab first.

 

After the disc swap, to get a firmer pedal, i placed in line a 10lb residual pressure valve as i read. It really did the work.
But can this valve affect something since it retains pressure in line?
Are the drum brakes still adjustable with the valve? How can you adjust them since the valve keeps the brake shoes close to the drum?
Would it be a good idea the set the brake shoes loose to test it?

 

Here is a link to a great article on brakes. Look at the section "valving" which specifically notes "When converting from drums to discs, you will need to remove any metering valve in the circuit.

http://www.pirate4x4.com/tech/billavista/Brakes/#Valving

Hope this helps.

 

'Tis a great article, to be sure. However the writer overlooked one reason for the cross-drilled, and/or slotted rotors.

Rain!

Those rotors are slotted and drilled to give the water somewhere to go, instead of causing a causing a hydro-planing effect which reduces brake power to nothing during rainy seasons.

 

Well i've put the 10lbs valve which is supposed to be for drum brakes, but my concern is that i had the drag before the disc swap and i didn't have the valve that time.
Back then i checked the drum brakes and i saw that the front right brake shoes were sticking open and i thought that was the reason for dragging.
But now i have discs in front and as i mentioned they don't have much difference from left to right to cause the drag.

 

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]I've worked with cars, street and race for over 40 years, my father was a life long mechanic and had multiple certifications including one in brake systems from NIASE (now ASE). I have rebuilt, modified and built from scratch brake systems for both street and track vehicles. Not an expert, just well versed in both mechanical and engineering principles.[/FONT]


[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]With a hydraulic system having more than one slave cylinder, such as hydraulic brakes, the slave pistons will move with little pressure until they meet their mechanical limit. That is, until the shoes hit the drums, then the pressures will equallize and then increase on each as the pressure on the master cylinder is increased. You cannot build up pressure on one wheel until the others have reached their mechanical limit. Then and only then, will the pressures start to increase. Google Pascal's Principles to find out more about hydraulic systems.[/FONT]


[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]For a drum brake to drag from adjustment, that particular wheel has to have the shoes adjusted tight enough to drag from the start. It also will not cause that shoe to have more pressure exerted on it via its slave cylinder, the principles of hydraulics makes this impossible. Differences in the mechanical distance between the shoe and the drum will not cause a difference in brake pressure to any one wheel.

A note on residual pressure valves, they are necessary on drum brakes because of the springs that pull the shoes away from the drums. Keeping a residual pressure prevents the pistons in the slave cylinders from being pulled too far back into the cylinder, without that residual pressure valve, you would have to pump the brakes every time you used them to move the shoes back out to contact the drum. Disc brakes to need them because the piston is retracted only by the twist on the rubber seal. If you look at the o-ring on a disc brake, you will find that they are usually rectangular in cross-section. Any residual pressure in a disc system will keep the brakes partially on all the time, resulting in premature wear and overheating of the brakes.[/FONT]


[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]That is why hydraulic brakes were such an improvement from the old mechanical brakes that preceded them. Unequal braking will be caused by frozen slave cylinders, contaminated shoes or drums, bad flex lines and improper components.[/FONT]


[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Worked on a car with severe pull and I mean severe enough to pull the steering wheel from your grip under panic braking. What we found was that someone had done a brake job and had replaced the right front slave cylinder with a rear wheel slave cylinder. One side had a 3/4 inch front slave cylinder and the other a 5/8 inch rear slave cylinder. That is a 20% increase in piston area from on slave to the other. [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]On disc brake rotors, the holes or slots are to allow hot gasses to escape on performance brakes. Under extreme cases, these gasses can affect brake performance. They have little to nothing to do with the wet performance of the discs. Disc brakes have a natural squeegee action that will get rid of any water that might affect braking performance. Drum brakes were affected by water because they tended to trap water. In deep water at slow speeds water can affect disc brakes because they aren't spinning fast enough to sling off the water. For the majority of street vehicles, drilling or slotting is more for looks than actual performance increases.[/FONT]

 

and that is why I love this forum.

 

Thank you LesT21

 

the mc is dual reservoir and the valve is only for the rear line, also is for disc/drum set up,
I think i should check the slave cylinder first and the rest of the parts, if something is in bad condition.
Thanks for all the info, i'll update as soon as i have news........

 

I agree with this. I would like to add this however. If one set of brake shoes, say the right rear, are adjusted too far in, and the left rear are correctly adjusted. This is what can happen:
The left rear shoes have very little distance to travel before application. The right rear has a long distance to travel. When the left rear shoes make contact with the drum any and all pressure not being utilized transmits to the right rear. This means in effect the right rear shoes will be expanding outward twice as fast as they should be. They then make very hard contact against the drum. Coupled with a duo servo braking system (self-energizing) this can cause a brake pull initially or until pressure and mechanical advantage equalizes on both side of the vehicle. This also makes the assumption that all mechanicals and hydraulics are working as designed.

 

As said, "Unequal braking will be caused by frozen slave cylinders, contaminated shoes or drums, bad flex lines and improper components."

And also, "This also makes the assumption that all mechanicals and hydraulics are working as designed."

....Perhaps it doesn't apply here, but random stuff such as corrosion in wheel cylinders (and so on) certainly can create strange effects, due to a individual brake not activating, or dragging after activation.

 

Well after an inspection at the rear drum brakes, the conclusion is that the
right brake shoes where too tight and it was dragging all the time and the left cylinder was stuck.
So this is a good combination for the steering to drag while braking.
Because i didn't have the parts to rebuild the rear cylinders,
i had a "brilliant" idea to replace the rear cylinders(3/4" bore) with the front ones(1" bore) i had from the disc swap which are in good working condition.
Has someone done this before after a disc swap? Because i test it on a rainy day and the rear brakes where locking too easy?
I still haven't tested on dry road though.

 

Larger slaves may use up a bit more travel on the master, and thus the pedal. And ditto on Warloch's comment.