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

At this point I think I’d be on the phone with some of the Aftermarket brake companies asking them about proven components.

 

@flynbrian48

Yep! And their answer to all your worldly problems just happens to involve buying something they have on their shelves.



The O/P needs to start measuring what he has.
Corvette M/C's were great when paired to Delco Moraine 4 pot callipers.

Later model Corvettes[C4] went to a smaller 15/16" M/C with a booster.
S10's used the same ^^^ as a stepped bore [quick uptake]

There is so many variables [and calculations] for brake systems , that many novices actually make a step backwards in their "improvements".
If he gets out of his depth all he needs to do is copy a factory set up.

A 95 Crown Vic has the same rear piston calipers as the Explorer, so if he used a Crown Vic master cylinder, and calipers with the same bores as a Crown Vic calipers, he would be close enough.
But the pedal ratio is wrong

The Front GM calipers are easy to swap, So is the master cylinder. [pedal ***embly not so easy]

I suggested earlier a 3rd to 4th Gen Camaro caliper! That should get the front /rear bias close enough.

Then start by going down in master cylinder bore sizes until the pressure is suitable.
Here is some psi ratings with a 4:1 pedal ratio with 100 lbs pressure applied by his foot

1-1/8" master cylinder = 402 psi
1" master cylinder = 509 psi
15/16" master cylinder = 580 psi
7/8" master cylinder = 665 psi
13/16" master cylinder = 772 psi
3/4" master cylinder = 906 psi

The 4:1 pedal ratio and 1-1/8" bore seems to reflect the psi that you already have.

Now if he changed the pedal ratio to 6:1 and applied the same 100 lbs pressure with his foot

1-1/8" master cylinder = 603 psi
1" master cylinder = 764 psi
15/16" master cylinder = 870 psi
7/8" master cylinder = 998 psi
13/16" master cylinder = 1158 psi
3/4" master cylinder = 1358 psi

So switching to a smaller 7/8" master cylinder will give him more gains, than keeping the 1-1/8" Corvette master cylinder and only altering the pedal ratio.

He should go down to the local "U-Pull" and vulture a few calipers and master cylinders to try out first. Then get new ones for the final build/***embly

Edit: 79-93 Fox body mustangs have a 21mm 7/8" master cylinder [they are plentiful in junkyards for an experiment]

 

That's good stuff.

I am curious though about the mounting distance on the studs for the M/C. They aren't universal on all boosters are they?

Not trying to be a smart @$$ here but, why wouldn't he just use a Ford Explorer M/C, if mixing and matching? We know it matches the rear end calipers.

 

I like how you guys talk about me in the third person, on my thread.... I'm RIGHT HERE. That said, that is good information, and fits the situation I found. I don't see the reason Mimilian thinks the pedal ***embly would be hard to swap, although it isn't a fun job with the dash in, which it wasn't almost a year ago when I put this stuff together. Other than being forced to be in a slightly awkward position to remove 4 14mm nuts, it took less than 5 minutes to have it out and the MC off the firewall. It's no big deal. I'm an old dog, but I can learn new tricks. The junk caliper and rotor I scrounged from the U-Pick yard to make sure I got the correct ones cost almost as much as the new parts, so, combined with time spend slogging through snow and slush, it's cheaper and less h***le
to buy new parts to experiment with. So, there's that.

 

Why would't he indeed? Because he wasn't born knowing everything, and asks for information and advice when something comes up that's out of his scope of knowledge.

 

I have been, and I have parts coming that I've been advised should work.

 

Please take no offence, It was originally a reply to another members post.
Then I got carried away with the answer , so I attached your username to it.

Because there needs a correction for the pedal ratio that has already been installed , so a smaller master cylinder is easier than re-engineering the pedal/ MC mounts [both are a step in the right direction]
I am only suggesting replacing one component [not 2]
The alternative is to replace the pedal ***embly and leave the existing Master cylinder as is.[or replace both]

What is needed is an increase in PSI to pedal effort [ there are many ways to do this ]
Adding a booster is not a fix for poor brakes [ a booster is needed to decrease pedal effort ]

You would be much better off talking to a brake engineer, than some "phone jockey" at a call centre. [all those people ask is ,what is your current setup? then sell from there]
How many of them have asked you for Fr and Rr weights, Wheelbase, CGH , Rolling Tyre Diameter etc etc [probably none]

I have given you some simple basic advice, [the best advice being, try to replicate a factory setup]


I have designed complete brake setups for road racing cars, and there is too many variables needed for calculating optimum braking performance.

I do have a basic grasp of the concept

 

That’s good,you have to trust someone for help with these issues, why not ask the people who work with products and develop them.

Not asking for help just because someone might sell you something as one guy posted seems counter productive and stubborn to me.

I’m not going to ask these guys for help they’ll just want money.

I’ll just bang my head on the workbench a little longer

By the way you seem to be one of the rare males in the species that will admit to not knowing everything.

 

It's a steep learning curve. I take free advicel, but always remember it's worth what I paid for it. Once in a while something worthwhile comes along. Part of the reason to ask is because I KNOW someone else out there is doing the same thing, with the same good intention, and they might not stumble over something like I did. One of the comments is a guy using the EXACT same combination of parts, that works, and one is building using the same, and is anxious to know if I get out of this trick bag.

 

Just another thought, do you have power steering? If you do a hydro-boost system might work out instead of another booster & hood hinge redesign.

Sent from my SM-G973U using The H.A.M.B. mobile app

 

I think I would have compared your Challenger pedal ratio to the pedal ratio Ford used on their Explorer P-up (the rear brake donor) before deciding your present pedal ***embly was part of the problem.

 

This pic shows a 90 degree bend in the pedal. Was that bend put in by you to fit your car or did the Challenger pedal arm come like that from the factory? If you put that bend in there and the pedal was originally straight, you drastically changed the pedal ratio when you bent it. Although you didn't technically shorten the arm (no metal was removed), you certainly shortened the distance between the pedal and the pushrod, drastically changing the pedal ratio, IF you put that bend in there.

 

i have no help for your issue but want to thank you for sharing this as the 8.8 rear has become so common these days
and you are making so many of us at minimum more aware of potential issues.

 

I know there is lots of good advice from all. I am surprised the used parts you bought were so expensive. Well now you have the correct caliper mounting! That's good. Ok here's my 2 cents. If you can figure out the piston diameter for the front calipers and the diameter of the rear pistons? You know the original master cylinder off the sport track or whatever its called is correct for the rear calipers. If you can find out what the original front piston diameter was in the sport truck and it happens to be the same as your front calipers then that master cylinder should work for you?? If not some other master cyl with same diameters as both front and rear piston diameters? My 56 truck is apples and oranges from yours but when I set up the brakes I used a master cylinder from a 85 f150. I found out that the rear drums were the same diameter and the wheel cylinder pistons on the 56 same size as on the 85. I also found out the GM calipers I used were the same piston diameter(or real close-can't remember), to the 85 stock calipers on the 85. Works good. Good luck on yours you will get it. I had a great old s**** yard that I could get used parts for pennies, that makes a difference also...

 

As an experiment, because I know it's going away, I lengthened the pedal 2.5", and put the pad on the very end without the end. The result was a shade under a 6:1 ratio, compared to the 3.5:1 of the original pedal. Pressure at the rear caliper? 400 PSI. The exact pressure with no change to the pedal at all. I don't need to have the pedal pad over that far, in fact, it turned out to be slightly awkward and too close to the gas pedal, so it'll be different with the new one. Honestly, I don't see what difference it could make, lots of cars had the pedal pad offset much more than this. I've used pedals from GM cars from the 60's, through early 00's that have a pad at least 4 or 5" long, offset from the arm. Not arguing, but seems like a lever is a lever a lever?

 

I was shocked when the counter person said, "Single piston caliper and rotor? $40." They were CLEARLY not usable, but I'd spent so much time finding them in the muck, and I wanted them in my hand to look at the new stuff. Cost of the new rotor and caliper? I think it was like $70. Junk parts aren't worth anywhere close to half of new. I asked how much I could buy the entire axle for, $350. For junk. I'm not wasting time pulling stuff on my back, in greasy, muddy slush and ice.

 

"As an experiment, because I know it's going away, I lengthened the pedal 2.5", and put the pad on the very end without the end. The result was a shade under a 6:1 ratio, compared to the 3.5:1 of the original pedal. Pressure at the rear caliper? 400 PSI. The exact pressure with no change to the pedal at all"

This is exactly what I was getting at ... if the pedal worked in a Challenger, why is it not working for you? What changed? I ***umed the change may be in the pedal IF the pedal is actually part of the problem. If you bent the pedal, you did affect the ratio but your latest test shows the pedal ratio doesn't actually matter that much as you are still at 400 psi with the 2.5 extension (which gives you the recommended ratio). Early on I stated that I really didn't think a lot of pedal pressure was needed for power brakes as the power part does the job for you.

Now, all that being said, I do not think your pedal ***embly is part of the problem. I realize you've already removed it but I really do not think it was the cause of your issues and your recent test seems to agree

Now that you have the rear brakes sorted, I think your present problem lies in the booster or the master or whatever valve/combination valve/proportioning valve you have in there. I am ***uming you don't have a leaky fitting somewhere.

I don't believe the pedal ***embly needs to be changed.

 

Interestingly, the bore size of a Sport Track MC is 1.065". I didn't look to see if an Explorer is different, but the pistons in the rear calipers, at least of the ones I have (both kinds) are the same. The fronts, on a Sport Trac, are 2.95", 75mm. Compared to the GM (Speedway's) caliper of 2.75. The volumes should be then, roughly equal and would seem to be to be, from a volume/pressure standpoint, tone compatible, no? (edited for grammar and spelling)

 

Right there is the reason I am sharing this very frustrating issue. It'd be great if power-braking burnouts was a priority, or used a s Line Lock, but we're pulling a 25', 6,000 travel trailer and an enclosed car trailer with this thing.

 

It’s not the pedal offset, it’s that bending the arm shortens the effective length of the lever.



Sent from my iPad using The H.A.M.B. mobile app

 

did you full stroke bench bleed the brake master cylinder

is the tail at the brake master a little pinched

 

A lot has be discussed and a lot of advice. I’m especially interested in diameters of everything. When I did my system and did not want power ***ist and the rear wheel cylinders were also changed by me on the advice of a brake system manufacturer to a smaller diameter. It all must work together.

 

My post was merely asking the difference between the Crown Vic m/c and the Explorer. Wasn’t questioning your knowledge. I was just saying if the Crown Vic would work with the rear calipers instead of the Corvette, then why not use a matched own set from the Explorer.

Sheesh.

 

Did you check the front and compare?

 

Given that little tid-bit of 'new' information about a travel trailer caper....
How comparable is the weight of the wagon to the weight of the Exploder? Havig had one years ago I recall them being ok for small trailer towing, per Ford. Your brake system must be designed for the same 'gross workload' as is any factory system and maybe the Exploder is a good sample or, the Vic mentioned.
IMHO, you need to step back and make some comparisons to actual oem combinations based on your curb weight and intended usage rather than buying more door stops.
No bashing intended, I wish you an excellent result as you might be the car near me on the highway......

 

Sport trac wright, 4600+, depending on options. ***le weight of the DeSoto, ,4100 lbs. Tow capacity 5,300. I'm close enough for horseshoes. Longer wheelbase. More than twice the power, same brakes, but close enough. If I can get brakes...

 

Adding brakes on the trailer axles will also add a safety margin as well. I even have surge brakes on my box trailer

 

I had a look at Explorer Fr / Rr calliper piston sizes to compare. [excuse the metric measurements]

Explorers have 47.9mm bore rear calipers.
Early Explorers have 65.9 bore front calipers
Late Explorers have twin 45.9 bore front calipers [ twin 45.9 has the same swept volume as a single 65.mm]
The Explorer has a 1" or 25.4mm M/C,
Explorer's also has a 305mm front disc diameter and 301mm rear disc diameter

Now I compared a Crown Vic [1996-97]
Crown Vic's have 47.9mm bore rear calipers.
[1995-97] Crown Vic's also have 65.9 bore front calipers [single piston]
The Crown Vic also has a 1" or 25.4mm M/C

As soon as @flynbrian48 gets decent psi from a smaller bore M/C [or pedal leverage] he will end up with front wheel lock-up due to having 70mm [2.75" bore calipers]
I recommended reducing the bore size by fitting 3rd / 4th Gen Camaro calipers [which are 2.5" or 64mm]
This is how restore bias to the Fr /Rr [unless he plays around with disc rolling radius ,which requires new caliper brackets etc]

The Crown Vic M/C would be the ideal candidate if the pedal ratio was the same. But with a 4:1 he would need a smaller bore 7/8" [22mm] or smaller
I suggested Fox Body, but Chevy Monza will also do the same.

I will be deleting all my postings here later [because I have been advised to]
I don't want the liability of someone misinterpreting advice and killing themselves.

Line pressure is equal throughout the system [up to the point where a "proportioning" valve limits rear pressure]
The only way to have different Fr / Rr circuit pressures is to have 2 Master cylinders with an adjustable balance bar [which Road Racers use]

 

You aren't giving advice, just stating facts. I think the info you posted was most insightful. It's interesting to see real life numbers. Maybe, you could post the formulas for those that want to do their own math.

 

Sorry, I was admittedly irked about about the entire thing, and I admit this has been a stressful week for a lot of reasons, not all of them centered on this aggravating problem. Apologies, I realize you guys are trying to help. I'm not usually this thin skinned.