Customs OK, I give up. DeSoto wagon brake issue.

My '52 DeSoto wagon has 4 wheel disk brakes, Explorer, an '01, rear. The axle came bare from the salvage yard, I bought new rotors, calipers, E-brake guts. I bled the brakes with a power bleeder but never felt like I'd gotten all the air from the rear lines, so this morning my wife helped me bleed the brakes. Indeed we did get some air from the rear lines.
It still has no, or very poorly functioning, rears. With the car running, in gear the tires spin. In neutral, with the brakes engaged, I am unable to turn the tires, so they do (barely) work.
Looking at the rotors, it's clear the pad is above the rotor by 1/8". These pads are about 3" long and and 1" high. The rotor is 11.2" diameter, the only one available, at least anywhere I've found, for this generation Explorer. I bought a pair of '02 rotors today, which are 11.89", after some "experts" on a FB page told me I had the wrong rotors. They newer ones have the rotor about 3.8" further out on the hat and the calipers will not mount with them.
I've cleaned the (new) pads with lacquer thinner, and the rotors, thinking I may have contaminated them with oil during assembly. No change. I've re-bled the entire brake system, no change. The master, a Corvette style dual chamber from Speedway and matched disk/disk proportioning valve, is new. All new 3/16" lines. All new rubber flex lines.
My next step is to check the pressure in the system, I'll buy a gauge if I have to but I have a friend who has a garage so I think I can borrow his. I initially suspected the proportioning valve might be faulty, but my understanding with a disk/disk system is there's no residual valve, so I don't think replacing that, or the master, is probably going to change anything.
The pedal has a good "feel", and engages after about an inch of free travel. Front brakes are GM style big rotors and calipers, from Speedway as well. It is mounted on the firewall in the usual position, not under the floor.
I'm trying to wrap up the mechanical aspect of this build before spring, this is frustrating as I thought bleeding the brakes would eliminate the no rear brake issue. I'm at the point that I'm sorry I didn't just put the Ford 8" I had in it with it's drum brakes and called it good enough. View attachment 4931613 View attachment 4931614 View attachment 4931615

 

I tried to add a couple more photos to show the relationship of the rotor to caliper, but get a message saying I don't have permission to view. I guess I can't build brakes or operate my Mac-book or iPhone...

 

I would say you have a master cylinder with two different bore diameters. The larger bore going to the front calipers. That would be the back line coming out of the master cylinder.

 

Most likely using GM metric "low drag" calipers on the front.

Either change the calipers or use an S10 stepped bore m/c


Edit: A simple way to check is to put a feeler gauge between the pad and disc and measure the pad knock off.

 

Hmmm. It's plumbed per the instructions with the MC, so I don't think I f'd that up, but it's possible.

 

Not to belabor the obvious, but are the bleeder screws oriented correctly? Right caliper on the right sides?

 

Oh yeah. They're in the "UP" position. That was one of the photos I wasn't permitted to load.

 

It really looks like your calipers are mounted wrong somehow. The whole pad should be contacting the rotor surface.

Proportioning is balancing the brakes between front and back. You need that.

Residual valves maintain pressure in the brake system when the brakes are not applied. This is needed with drum brake cylinders, and disk calipers when the master is below the caliper. You don’t need them with the described configuration here.



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Or the rotors are the wrong diameter.


Something in this mixture of parts does not match.

 

Eh? He has rear calipers that mount with the pads not fully hitting the rotors, possibly air in the system, and rear brakes that can’t stop the wheels from turning.

No mention of front brakes being the problem here.



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I wonder if those are 2002 (3rd gen) Explorer IRS parking brake/caliper brackets. Those, as far as I remember, will bolt on, but will not work with the other solid axle parts.

 

Nope. He said that they are the BIG GM calipers. The big GM calipers are inch calipers. The low-drag ones are only the smaller metric ones.

 

Check ALL your fittings for leaks, today's fittings are junk when it comes to leaks. You can pull air back in the system through the same fittings. You could have a bad master cylinder also.

 

One thing I've learned to do is wrap the bleeder threads with teflon tape; you'd be amazed at how much air can be drawn past them.

 

Not all. Up to mid 70s this is true but with the '77+ B bodies they were 73 or 75mm. I think the C/K trucks went metric in the mid 80s'. If you are not totally familiar with the calipers C/K truck and B/D body stuff looks similar. Eyeballing a 73mm vs a 3" caliper can be hard.

Yup. I like to use a new bleeder with yellow 'gas' Teflon tape, thicker than white Teflon, only takes a wrap and makes it pretty fool proof as it is quite forgiving.

 

I think you missed the point. I am not only totally familiar, I am a full-time automotive engineer at General Motors.

In GM nomenclature, the later more compact calipers used from 1978-1988 are referred to as Metric calipers.

It makes no difference what measurement the piston size is, as it is not a reference to the piston, but the era of GM production that they were made in, and the fact that they have Metric fasteners.

Pre-Metric era passenger car and light truck GM calipers have a pin spacing of 7-1/16", irrespective of piston size.

Metric era passenger car and small light truck GM calipers have a pin spacing of 5-1/2", irrespective of piston size.

GM low-drag calipers were only made after the Metric-era began, are only the small body calipers, and therefore cannot be Inch-era calipers, which are the big calipers.

 

Some thing that happened to me one time may be worth looking at. I purchased new rubber hoses for a car I was working on and had a similar event happen on a front wheel. All new parts but the brake for that wheel just wouldn't work right. Turned out the rubber hose was assembled wrong. They peeled the inner lining of the hose when they inserted the fitting and the rubber "flap" in the hose acted like a check valve when pressure was applied thus causing the brake to malfunction. It seemed to bleed fine, just wouldn't work under pressure. Found it by taking the hose off and was looking for a restriction. Just take a welding rod or similar wire that will fit in the hose and polish the end so it will not abrade the inside of the hose , and see if it will go through the hose without resistance.

 

If you think you still have air in the system then I would reverse bleed the brakes.

 

Just a FYI....
The calipers and rotors are DIFFERENT between o1 and o2 Xploder

 

I think the master has too small of a bore.
an easy test is to block one line going to a rear caliper,the other side should clamp harder.

 

Well, I don't know how the calipers can be mounted wrong, there's only one possible way to mount them. There's no residual valve, it's a MC and distribution block for disk/disk (unless of course it isn't, but it's sold as such) and distribution block for front and rear disks, sold as a package. I plumbed it per the instructions.

I think the first thing to do is to re-bleed, for the 4th time, the entire system, front and rear. We didn't bleed the front yesterday. The rear brakes have tiny pads, it seemed wrong to me as well that the top 1/8" of them doesn't contact the rotor, being above it. Even if they were completely on the rotor, they're about an inch wide, so the contact area in no way is the entire width of the rotor. The E-brakes are drums, again tiny, inside the "hat" of the rotor and are mechanical.

I have some adjustment at the pedal and pushrod, so I can see if I get result by lengthening that a bit, but it sure "feels" right as is. I'm also going to make sure I indeed have an '01 axle, I know for a fact it's not newer as the '02 rotors don't work on it.

To say that I'm disappointed with my selection of parts for this project is an understatement. I should have followed the "KISS" method, which is how I've always tried to build a car, this certainly isn't working as I'd hoped.

 

They are indeed the metric front calipers, they're big in the sense that they're on the larger rotors on the Heidt's front end.

 

I am painfully aware of that, having gotten both styles. View attachment 4931944

 

Brian, I see you're in Kazoo, can you go to a local salvage yard that will let you go out and look at a 01 or 02 Explorer (or whatever year the rear end was from)? Many times wheels are already off and hopefully you can find the stock setup to compare to. Measure it up.etc. This would at least get your rotor-pad correct. You know they would never make a pad too big for the rotor surface from the factory. The pads will wear in if the rest was working properly and create a big "step" in the pad. As far as the hydraulic problem you seem to have I dunno... Good luck !!

 

I see a visit to "KLQ" U-pick in my immediate future as well.

 

one day someone is going to redo the mustang 2 front end and use the
spindle nad rotor and even the top control arm from a gen 1
2wd 1999 ford explorer
then you could use its complete brake system, going even as far as
using the pedal and stock ratio of that.
-I mean its not as if you can't even buy a new 2wd spindle and upper arm from the lieks of rock auto for buttons
PLUS you'd get a air bag through it
PLUS of course, due to them having tone rings in them, you could actually run abs on that 100 thousand dollar
street rod
cheese
n.b the rotors are 11.30
dual piston progressive caliper - pistons on one side
rotor is really shallow, same as a stock 9'' stang 2 rotor
upper arms available in 2 peice style
upper ball joint is cotter pinned , pressed in, the whole arm is real cheap
lower arm stock is torsion bar
shock towers real short
blah blah blah

oh i forgot.
the steering racks are the same i think across all ford platforms of the era
so and I>E> the TIE rods of the explorer - where they screw into the steering rack, have extra meat there so as to place the pivots farther out board,
I>E stock the wheel mount face is say 59''
so - by simply swapping the tie rods you simply move the pivots inboard - probably one inch per side, then get to 57, which is nice
not really hamb friendly I know , but there you go!

 

a lot of posts to say not enough rear pressure and you need SMALLER bore M/C on the rear[NOT larger-smaller=more pressure,larger=more volume}don't worry about the pads not being all the way on the disc

 

Everything I read prior to assembling my brake system said I needed 2# RPV's. Especially if the MC is mounted low on the frame.

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The master is mounted high on the firewall, not on the frame below the calipers.

 

Something isn't matched up on those rear brakes if the pad is sitting above the rotor. Of all of the brakes I have done on Explorers and Rangers I have NEVER seen one with the pads like those are sitting. If you look at the photo above of the rear end sitting in the bed of the truck, there is a rust line above the pads.... which is the way it should be.

What is the original application for the proportioning valve you are using? Some applications put minimal pressure to the rear brakes to prevent lockup. I would try the brakes without that valve in it.