2020 .. What are you doing today?

[WZ JUNK]

I am continuing work on the brakes on my 54 chevy with 4 wheel power disc.  I have narrowed the problem to the rear calipers.  When I isolate the calipers there is a 400 psi pressure difference.  When the calipers are in the system, the pressure is about 700 psi and when I isolate them, by taking a reading at the point where they connect to brake lines, I get a reading of near 1100 psi.  I have tried lots of different bleeding methods, even removing the caliper and rotating it into different position in hopes of removing any trapped air.  At least I have it narrowed down to the calipers.  Time for more pondering. :?

Is it a flow (volume) problem or a pressure problem, John?

Is it possible the master cylinder is not displacing enough fluid (volume) to satisfy the caliper volumes when the pistons are extended?

It seems to me the pressure is high when pumping against a "dead head,"  but as the pistons extend, the increased volume of the system is not being supplied by the m/c, thereby causing the pressure to drop.

Of course, I may be totally mistaken and F.O.S.!

Is it possible to isolate ONLY ONE rear caliper and re-test?

I have tested each of the rear calipers individually and both of them have pressure drops.  One has a little more than the other.  Since I have full pressure to the point where the fluid enters the caliper, and I have the caliper bled, I would think that the master cylinder could supply the needed pressure through the caliper.  However, if I knew the answer, I would not be asking for help.  I have another experiment it the works and I will give it a try soon.  Thanks

[chimp koose]

phat 46 , I can remember machining piston pin buttons many years ago (30+) for a blown alcohol donovan for a friends tractor puller . He was losing the pin retainers . I will be resizing and shortening some titanium valves for him soon . The pin buttons worked but were heavy .

[Bruce Dorsi]

I have tested each of the rear calipers individually and both of them have pressure drops.  One has a little more than the other.  Since I have full pressure to the point where the fluid enters the caliper, and I have the caliper bled, I would think that the master cylinder could supply the needed pressure through the caliper.  However, if I knew the answer, I would not be asking for help.  I have another experiment it the works and I will give it a try soon.  Thanks

I rarely have answers, John, but I always have questions!   ...We don't usually learn from jobs we've done 100 times before, so these unusual problems allow us to learn something new and challenge our brain.  ....I am here to learn.

My understanding is that pressure is created by resistance to flow.  ...Conversely, when resistance is decreased, pressure decreases as flow increases.
 
The brake circuit is closed, flow is created at the master cylinder.  ....This flow is what moves the pistons in the calipers.  ....Pressure does not significantly increase until the pads contact the rotors and the pistons can not move any further.  

If the pistons in the calipers are clamped in the retracted position, the pressure inside the calipers should be close to the 1100 psi reading.  ....As the pistons extend, the pressure reading will drop until piston travel stops.  ....If volume of fluid available is insufficient to clamp the rotors, pressure will not build to the 1100 psi.

One way I can think of to test this would be to vary the limit of travel of the pistons to see how pressure reading is affected.  

Are the calipers correct for the thickness of your rotors or vice-versa?

Please keep us informed as you work on your braking problem.  ....It gives us a chance to learn with you.

[Crosley.In.AZ]

I have tested each of the rear calipers individually and both of them have pressure drops.  One has a little more than the other.  Since I have full pressure to the point where the fluid enters the caliper, and I have the caliper bled, I would think that the master cylinder could supply the needed pressure through the caliper.  However, if I knew the answer, I would not be asking for help.  I have another experiment it the works and I will give it a try soon.  Thanks

Integrated parking brake calipers?  Friend of mine had huge problems with his Seville rear calipers till he went wild man on the adjusting - parking arm of the calipers to get the clearance of the pads tight

[Charlie Chops 1940]

Many years ago I tried to get those calipers and parking brakes to work. I gave up and put a pair of like sized front calipers on and they worked just fine .Don't remember what I change to adapt them but it wasn't a big deal as I recall. Don't like not having a parking brake though. Since I've just used the Ford 11" drum brakes in the rear.

[Crosley.In.AZ]

Road trip today...  thru Show Low , Payson , Snowflake, Pine Top Arizona...   Looking at property, houses, ect.

We drove down the AZ State RT 87 from Payson.. That is the area where wild fires burned thousands of acres of land in the mountains along the highway weeks ago.  They had to replace thousands of feet of guard rail that burned down along the roadway.

When you see the burned land in person , it brings it home.  We have seen the burned land before  on previous fires over the years ...  The view of the burned land really stays with you.

[WZ JUNK]

I tried another brake experiment this morning on the 54 Chevy.  I flip/flopped the brake lines on the master cylinder to see if that would make a difference.  It did not.  I am going to set the car aside for the time being and come back to it at a later date.  I have had enough disappointment and frustration for the time being.

[phat46]

Having fun today, I forgot how much fun ths can be! BTW, yes, that piston is out of the hole, .0165 to be exact, I'll need a .060 gasket to get the quench in the ballpark.

[kb426]

^^^^
What ring combination do you have? What comp. ratio are you supposed to end up with? To get a thick head gasket, is solid copper the only option?

[enjenjo]

I drove to Lasalle In today, about 80 miles one way, to pick up some parts. Two S10 transmissions, three bell housings, and a shifter. It was a good deal.

[phat46]

^^^^
What ring combination do you have? What comp. ratio are you supposed to end up with? To get a thick head gasket, is solid copper the only option?

The rings are what came with the Wiseco Pistons, the compression ratio should be 10.2 with the 62 cc heads I have.  It looks like there is a variety of gaskets, some are composite. And they are NOT cheap! 😮

[chimp koose]

Why not take the pistons out and face them down .010" . Then they would sit .005 proud of the deck, you could get a cheap fel pro gasket .045 thick and have .040 piston to head , perfect quench . I think you may have a higher CR than you think . Each cyl swept vol is 47.833" ( 2.015x2.015x3.14159x3.75=47.833"), 62cc=3.783"(2.54x2.54x2.54=16.387cc/cu in)(62/16.387=3.783") , head gsk @ .040 x 4.100 dia =.528"(2.05x2.05x3.14159x.040=.528") those work out to 52.144" at bdc . Vol at tdc = 4.311  . 52.144/4.311=12.09:1CR That is a little much for pump gas . I did not calculate the difference of the piston head dia sitting in the last .005" of head gskt . That would be a piston head dia of roughly 3.990 sitting in a head gasket of 4.100dia at a depth of .005"

[phat46]

Why not take the pistons out and face them down .010" . Then they would sit .005 proud of the deck, you could get a cheap fel pro gasket .045 thick and have .040 piston to head , perfect quench . I think you may have a higher CR than you think . Each cyl swept vol is 47.833" ( 2.015x2.015x3.14159x3.75=47.833"), 62cc=3.783"(2.54x2.54x2.54=16.387cc/cu in)(62/16.387=3.783") , head gsk @ .040 x 4.100 dia =.528"(2.05x2.05x3.14159x.040=.528") those work out to 52.144" at bdc . Vol at tdc = 4.311  . 52.144/4.311=12.09:1CR That is a little much for pump gas . I did not calculate the difference of the piston head dia sitting in the last .005" of head gskt . That would be a piston head dia of roughly 3.990 sitting in a head gasket of 4.100dia at a depth of .005"

You're right I may have a little more compression, but that may not be a problem, I have been building this to run e85, that seems to run best about 13-1. I thought about milling the pistons too, just seems like a lot of work and expense to buy cheaper gaskets.

[chimp koose]

I was wondering if you were considering e85 as you mentioned your relative running it with success. 12:1 would be easy on e85 I would think .

[Charlie Chops 1940]

Whatever you do be sure to clay check the clearance... don't even ask how I know....