Need expert brake help

[Drummerdad]

So the truck is running good. A few annoying issues Ill address one at a time, but it works pretty good for now.

I noticed a rubbing noise in the back, so I investigated and found the problem. Pictures are below. The rearend has a casting number of 2881489, and a quick google search shows this to be a "medium" duty 8-3/4" chrysler, with a 1-7/8" tapered stem pinion out of something from 69-74. The noise was one of the brake drums rubbing against the inside flange (I think that's the name of it). The drums are different, so I am assuming the one rubbing is probably wrong, like maybe off of a different year. Is this correct?

Also, the park brake just wont work. It slows the wheels down if they are spinning, but it wont hold the truck from rolling. I added the Lokar handle (its in the build thread for Isaacs truck) but the handle is about the same length as the factory one, so the cable pull ratio should be about the same. I might have the park brake parts installed incorrectly. I looked for a diagram, but I couldnt find a good one. Does anyone know where I can find a good one?

I still have a lot of work to do on the brakes, because they just dont work as well as I think they should. They stop the truck, but if someone put me in a bad situation, I'm going to hit them.

[nutz]

hard to tell from pic but looks like the leading shoe is on the back
front shoe should be the smaller one

[martincom]

Ditto Nutz's comment on the brake shoes. The shoe with the shorter length lining (primary) is installed in the front position. The shoe with the longer lining (secondary) is installed in the rear. This is for the "self-energizing" action. Google Bendix self-energizing action for more info.

Also, I don't see an automatic adjuster cable. I can't tell from the photo if the automatic adjuster arm is in place. You'll need both to provide the automatic adjustment and to prevent the star wheel adjuster from loosening w/road vibration.

The stock emergency brake handle is adjustable. It is adjusted by turning the knob at the end of the handle. Sometimes the knob locks up or becomes stiff from lack of lubricant, but it doesn't usually take much to free them up so they can easily be turned by hand. I'm not familiar with the aftermarket Lokar handle that you utilized.

The factory service manual has excellent illustrations of each brake shoe/wheel assembly as well as the emergency brake system.

Also, measure the diameter and width of the brake shoes and compare it to the specifications in the factory service manual. You'll want to be sure they didn't become smaller with the rear axle change. I saw from glancing at the photo bucket that you went to disc brakes up front. If you haven't already done so, you'll need to add a proportioning valve in the rear brake hydraulic circuit. You'll probably want to go with an adjustable, so you can adjust it to balance the braking power between front and rear.

As the rear axle has been changed, you'll want to take a look at the pinion angle and make sure the U-joint is not going to encounter the limit of it's movement as the rear axle travels from full up to full down, of the suspension.

[Wildergarten]

If you haven't already done so, you'll need to add a proportioning valve in the rear brake hydraulic circuit. You'll probably want to go with an adjustable, so you can adjust it to balance the braking power between front and rear.

I consider that adjustable valve a must on all trucks that carry heavy loads. Else the front brakes can lock up and skid when the loads are heavy. On my old Dart, I actually piped the lines into the cab with aircraft hose so that I could adjust it from behind the wheel.

[Drummerdad]

I have an adjustable valve for the rear brakes, I just havent adjusted it yet. Ill change the shoes around this weekend if I can, and see if that helps. Hopefully itll fix the park brake problem as well.

[nutz]

the other thing that will greatly effect your braking is the size of your wheel cylinder bore
when adjusting your parking brake ,make sure to adjust your service brake first then take up the play in your cables
after you adjust your cable make sure the top of the shoe still rest on the top pin (that the brake spring is attached to)
if the cable is over adjusted it will lift the top of the shoe off
now swapping stuff around its possable that the p-brake lever in the wheel can hit the axle before it pushes the shoes out (just a thought)
back to wheel cylinder sizing ... a smaller one will travel more and needs to be sized with your master cylinder
so if adjusting your proportioning valve (witch is used control the speed the fluid gets to the rear ) doesn't give enough rear braking might
try a smaller w/c if it seems like the rears are over powering ,then a larger might be the fix
good luck truck looks great wish i had time to build something that cool

[martincom]

Also, if one return spring is weaker than the other, it'll be placed on the front shoe. The front shoe should engage the drum first, for proper self-energizing action.

[nutz]

yes good point
what a lot of people don't understand
is a drum brake system is more like a cam then both shoes pushing against the drum
what happens is the front shoe grabs the drum first then the twisting force pushes against the rear shoe and increases outward pressure on the drum
thats why it doesn't need a lot of hydro force
disk brakes are all hydro/friction materals

[PwrWgnDrvr]

yes good point
what a lot of people don't understand
is a drum brake system is more like a cam then both shoes pushing against the drum
what happens is the front shoe grabs the drum first then the twisting force pushes against the rear shoe and increases outward pressure on the drum
thats why it doesn't need a lot of hydro force

That's only true for duo-servo type systems. (100-200 trucks)
W300 front brakes are not like that, nor are two cylinder rear brakes on 400 and up models.
Don't remember what 400 and up front brakes are, but probably not duo-servo style.

[712edf]

My W600 has the two wheel cylinders (upper/lower) on front.

Bucky

[nutz]

yes 2 wheel cylinders one piston top to the front rear bottom to the rear
still a twisting cam effect
think the duel servo uses an s-cam instead of wheel cylinders

[PwrWgnDrvr]

yes 2 wheel cylinders one piston top to the front rear bottom to the rear
still a twisting cam effect
think the duel servo uses an s-cam instead of wheel cylinders

No, not like that at all. 2 cylinders, one top, one bottom, BOTH push both ways on both shoes, the anchor point is in the center of each shoe. The W300 anchors EACH shoe individually at the bottom. There is NO cam effect on them.
Duo-servo is the name for the basic style on most cars and light trucks. "Duo" because they cam up both forward and reverse, wedging against the single anchor point at the top, where the cylinder is mounted. "Uni" servo only cams up one direction - moving forward.
This is all clearly detailed, illustrated and described in the FSM "Service Brakes", section 5.

[712edf]

MY FSM does say that the system on my W600 is "energized" by forward motion, but it looks & works exactly like PwrWgnDrvr mentioned.

I think my rear drums are 15"x5", fronts are narrower.

Bucky

[nutz]

ok was only speculating on those
was thinking duel wheel cylinders like my 50 dodge
haven't done much work on anything over 1 ton trucks
other then schooling for hd trucks ...40 years ago
so 2 duel piston wheel cylinders ,is there 2 anchor points ? in the middle thats something i've never seen
guess i'll have look them up

[Drummerdad]

Sorry its been a few days. I have been crazy busy and couldnt get back on the truck.
Good catch on the shoes being backwards. I didnt see that at all. Only the passenger side was wrong, the drivers side was okay.

I changed the shoes around, and re-adjusted them. I also put the other new parts in, that I neglected to put in when I put the brakes on. Also one of the springs I had replaced with a new one just didnt seem to be shaped right, so I cleaned up the old one and put it back on.

But the brakes are still not good. The truck stops, but I cant lock any wheels up. The pedal has what I think is good pressure, and it feels tight. I can push it so hard I hear a squeak from under the hood, which I assume is fluid going through the MC. But they are just weak.

After reading about the problem (hard pedal/weak brakes) on a few hotrod forums, it very well could be one of a few issues. 1) the booster is too small or it isnt getting enough vacuum. and 2) the master cylinder might be too big. I bought a conversion kit specifically for 67 D-100, but it was one of those universal type kits, so take that with a grain of salt. It was from Pirate 4x4 I think, but it listed the 67 D100 and I bought the one for front disc brakes. I assume they were expecting a poly 318 with a single barrel carb, so the vacuum would probably be higher than in this LA 318 with a 4-bbl. It appears to be an 8" booster, so I might have to get a 10" or a 12". Someone mentioned a dual diaphram. Ill have to check the vacuum at idle. Also the squeak seems to be when fluid is passing through the master, and the hotrod guys say the MC might be too big. Im not sure what the piston diameter is, so Ill have to look into that. It might have been sized for the larger trucks, with bigger brakes. This brake kit has been an issue altogether. Not as bad as the mustang 2 suspension, but this thing is fighting me.

Someone mentioned it could be the design on the modern metric disc brake calipers, and them being a mismatch to a standard PV-1/2 combo valve. Im not sure. Ill start with the vacuum and look at the booster. If that doesnt work, Ill look at re-sizing the master. If that doesnt work, Im not really sure where to go.

[nutz]

might be easier to just get different size wheel cylinders
just not sure witch way to go
smaller will give more travel but will require more effort
larger will apply more pressure but will need more travel
then the proportioning valve will balance it out

[martincom]

You may want to give the rammaninc.com a call. He has a lot of knowledge on brake systems. I know he offers a disc conversion kit for sweptlines, but it appears you went with an independent front suspension kit.

Disc brakes do not have the stopping power of drum brakes, as their contact area is smaller and they don't have the self-energizing action. So most disc brake application have some form of assist, such as vacuum or hydraulic. However, a larger vacuum booster maybe treating the symptom and not the problem. You still need to be able to stop the truck, if the engine dies.

[nutz]

the other thing that could be a problem is the brake pads them self
the lining might be too hard
if run into this problem with euro cars i work on
if the pads are too hard you need a lot more effort to stop until you heat into them
ceramic pads last long but have no bite
and organic pad will have more bite

[Drummerdad]

Another thing I need to check is the proportioning valve. Its a PV-2, so it could be tripped to the front or the back, and not providing pressure to both. And Ill also have to check the vacuum. I think I read online that it needs 18" of vacuum at idle, so Ill look at that, but its going to be a few weeks. Ill update if there is a change.

[Drummerdad]

So I did a little checking. I started by hitting the brakes when the truck was cold, then starting it, and trying again. The pedal feels the same in both situations. I checked for vacuum at the booster, and it has it going in (im not sure how much, Im going to get a gauge), and there is a valve that is working on the booster. I moved the vacuum hose to another port on the manifold, and even replaced the hose with a better, stiffer hose to eliminate the possibility of it collapsing under vacuum, which I havent seen, but just in case. Still works the same. Then it occured to me, they feel like manual brakes. It feels like the pedal on the F100, which is manual. Again, the truck stops, but it wont lock up a wheel.

Im going to get a vacuum gauge and see what its making. The internet says it should be 18" minimum. Then Ill go from there. So far, I think my booster isnt working. Its either undersized, or Im not making enough vacuum. We will see.