1963 GMC K10 stock BRAKE question-problem wont stop

[aerotruk63]

[padresag]

jon . re w/c as they are new as off the shelf. but how long have they been on the shelf and what are. the rubbers like? could they have been stuck and tore a bit when pressure applied. they could have sat on the shelf for 50 years??.
the system is pretty basic so it has to be something oddball or is so obvious that one cannot see it for looking.
hoses can cause problem with collapsing(or swelling), but the odds of both fronts doing it are pretty high odds
ron

[jtrichard]

IT is said that bonded lining is just as good as riveted BUT I have had better stopping power with riveted my self .... I would have someone press the brake pedal and crack the front and rear bleeders and see if the pressure looks to be the same .... then as a last resort take the shoes to a brake shop that relines shoes and have top quality riveted lining put on the shoes same size on all four shoes.................: "" New wheel cylinders front and rear , fronts 1 1/8 bore rear 1 inch . Why if the fronts require more pressure aren't they 1" inch ? Parts book I believe confirms 1 1/8 size as correct.""... The bigger the wheel CYL. is in relation to the master the more pressure ......They probably don't make it but 1-1/4" fronts would make it stop

[padresag]

if the backs can lock up then that should isolate the mc/ and the rears as it is a single line down from the mc
ron

[luvbowties]

Originally Posted by 60-66

Nothing

I think you said you replaced front flex hoses. At this point(I'd have done this earlier, but I had run into that rare scenario before!)it may be wise to remove both front flex lines and ensure they are FULLY open on both ends.

One instance on a new car: I 'stole' a 1978 Regency in 1979 from a consulting firm with like 8000 miles on it. Their employees were afraid to drive it due to somewhat similar symptoms as yours, just not as severe. The small selling dealership could not find the problem, and even after sending it thru a much larger dealership 40 miles away, no cause nor cure.

Sure enough, I luckily hit paydirt: left front hose had not been drilled on the caliper end where a solid fitting required the drilling as 1 step in the mfg. process. Less than $14 & a new hose later, brakes were perfect.

Please remove your front hoses and verify they are ok. And, I HTH!
Sam

[60-66]

Originally Posted by jtrichard

IT is said that bonded lining is just as good as riveted BUT I have had better stopping power with riveted my self .... I would have someone press the brake pedal and crack the front and rear bleeders and see if the pressure looks to be the same .... then as a last resort take the shoes to a brake shop that relines shoes and have top quality riveted lining put on the shoes same size on all four shoes.................: "" New wheel cylinders front and rear , fronts 1 1/8 bore rear 1 inch . Why if the fronts require more pressure aren't they 1" inch ? Parts book I believe confirms 1 1/8 size as correct.""... The bigger the wheel CYL. is in relation to the master the more pressure ......They probably don't make it but 1-1/4" fronts would make it stop

I have an NOS set of shoes coming Im going to try, might still be asbestos .

Im getting conflicting answers here on wheel cylinder bore size, three people have said small bore and small brake lines Front equal more pressure, not larger bore . This truck has the same size brake line front to back .

Originally Posted by luvbowties

Please remove your front hoses and verify they are ok. And, I HTH!
Sam

Im thinking along those lines also, I bought two sets so I will check.

[padresag]

it is all the same size brake line
your parts books should confirm that
ron

[jtrichard]

Originally Posted by 60-66

I have an NOS set of shoes coming Im going to try, might still be asbestos .

Im getting conflicting answers here on wheel cylinder bore size, three people have said small bore and small brake lines Front equal more pressure, not larger bore . This truck has the same size brake line front to back .
.

When one hundred (100) pounds of force are applied to a piston that is two (2) inches in diameter, a force equivalent to that is applied on an adjoining piston of the same size.

If the diameter of the second piston were six (6) inches, the same force of one hundred (100) pounds would be applied to the entire surface of the larger piston. The surface area of the larger piston is nine (9) times greater than that of the first piston, therefore there would be nine (9) times the force applied to the piston. However, the first piston would have to travel nine (9) times as far as the second piston in order to exert this force.


line size is meaningless for the PRESSURE.. line size is VOLUME= speed to apply/release

[60-66]

Originally Posted by padresag

it is all the same size brake line
your parts books should confirm that
ron

Yes I know, Ron , just mentioning it because if you want more pressure to the front such as, like a disc brake setup , the front lines would be smaller . Its been said these Lockheed brakes need more pressure yet the bore size is larger and lines same as back.

[padresag]

did you try backing the adj off in the back a bit. it shouldn't make any diff, but
ron

[jtrichard]

Originally Posted by 60-66

Yes I know, Ron , just mentioning it because if you want more pressure to the front such as, like a disc brake setup , the front lines would be smaller . Its been said these Lockheed brakes need more pressure yet the bore size is larger and lines same as back.

Line size does NOT affect pressure only VOLUME ... IE larger line less restriction
And larger front wheel cylinder is more braking force then rear hence 1-1/8" front and 1" rear

[luvbowties]

We are mixing up terminology. Pressure out = pressure in, and is measured in pounds per square inch(psi). However, force out is NOT equal to force in; and it is measured in pounds. Pressure out of mc when depressing brake, say is 20 psi and force out of a 1" mc bore is 20 psi X 3.14 X1/2" X 1/2", which is 20 X 3.14 X .25 = 5 lbs. [20 lbs/sq in X 3.14 X radius squared, or 20 X 3.14 X 1/2" X 1/2"; which equals 20lbs/sq in X .25 sq in, which = 5 lbs of force.]

Now going into a wheel cylinder of 1.25" diameter, we get the following force: 20 psi X 3.14 X 1.25"/2(the radius) X 1.25"/2, which = 20lbs/sq in X 3.14 X .625" X .625", which = 20lbs/sq in X 3.14 X .39sq in , which = 24.5 lbs of force.

The above combo looks like magic but you hafta move the mc pedal 24.5/5 times as far as the wc moves; i.e., force in lbs X distance moved in inches on the mc end always equals force in lbs X distance moved on the wc end......or, inch-lbs out equals inch-lbs in.

All above based on formula for area of a circle being pi X r-squared = 3.14 X (diam/2) X diam/2.

Now, if his braking system would just incorporate all that mathematical mumbo-jumbo, his truck might stop!
Sam

[vince1]

Smaller M/C bore size and larger wheel cylinder bore size both give more force to the shoes. On some dual master cylinders bore sizes between front and back are different but probably unavailable for our trucks.

My 66 truck has the regular Bendix style and IMO it doesn't stop that great either but probably par for the course back in its day. I have considered disc brakes but my brother, who has owned many of these trucks, says that just putting on a booster makes a big difference for the better.

[61K10]

Put one of these on it as they were an option. I have disc with 1/4" lines and they work perfect.

[Matt's k5]

did you figure it out?

[61K10]

funny haw many never post the fix. As far as my opinion the design is 1930's. All my stuff was new everything and even with the (org rebuilt power booster) the brakes were just ok. They changed the front brakes in late 63 or 64 models to the newer style adjusters. spoiled by the new tks i guess. Try a panic stop on dry pavement with anti lock brakes. Thats another story lol.

[60-66]

Haven't driven the truck since . Busy with other projects ( K10 GMC Panel ). Im converting the front to 64-66 backing plates but Im still waiting for a couple parts . Prefer to keep this one as stock as possible. With NOS drums and shoes , like my other two , I have no problem getting them to stop as good as they possibly can or like new. This setup though I could not get to work , gave up trying . Should have it ready in May.

[61K10]

I figured you were busy with other stuff. You should be fine with the new set-up. Mine did pretty close to what yours was doing. Not good.

[60-66]

Originally Posted by 61K10

I figured you were busy with other stuff. You should be fine with the new set-up. Mine did pretty close to what yours was doing. Not good.

Thats what I dont get , Why ? There "should be" a way to make it work , they made this style of brakes in many vehicles. Something is still missing and I feel Ive tried everything.

[Matt's k5]

I'll have my wheels on soon and report back how mine stops, on my 63, it's the same design as yours

[padresag]

you have to adj. each shoe separately don't you with this setup?. the cam for each shoe is working. in this setup are you adj each shoe up fully at the same time and adj each off accordingly at the same time or are you doing each separately?
ron

[60-66]

Doing each separately but both at zero or all the way in , then turn cam till shoe just touches the drum as I spin the drum , then do the next same way. I did this , then once they were both out and nothing worked I put sand paper with a sticky back inside the drum , then spun the drum till I had 100% contact by the shoes . Still nothing. I see your point , possibly only one shoe is making contact ?

[padresag]

yes. this problem is more than likely some small item that keeps getting overlooked for being to simple to cause a problem.
if the m/c and the w/c are good as are the lines and the shoes are installed correctly what else is there , perhaps some small mechanical obstacle that no one is thinking about.
if you are getting good pedal then the hydraulics must be working and the shoes must be making contact in order to get pedal. are the shoes hitting just on one side or both. not saying that this is what is happening but could it be a probability with this setup. the shoes are not on backwards; believe this was brought up before.
ron

[61K10]

Hi ron--everything on mine was new, even all b/lines, adjusters in the front also (a jeep part) I guess mine worked ok as everything worked. back would lock up first. I like the way it stops with the disc/b. 60-66 has other problems. something simple as you said.

[60-66]

Again , I went through 4 master cylinders, new wheel cylinders and rubber hoses ( I realize that new doesn't mean its working) although I checked the function of each part , disassembled cleaned and went through everything at least twice. Front metal lines were blown out , ran a wire through them with no sign of any resistance or crud in the lines. Did my best to make sure the shoes all made contact with the drum and checked that they were expanding without the drum on. This is why Im simply going to the later setup and if there is still something not letting it stop, I know I missed something , although I doubt it. Might get the truck out one more time and pull the drums.