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Old 01-23-2006, 08:38 PM
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Ford Rear Discs, revisited 1/26/2006

Hey gang..

Refresh your memory.

Ford Rear Discs Cobbled Together

I finished this past weekend.



Explorer rear discs on a 78 XR7.

I actually swapped total housings from my Elite project, now I have 3.55:1 posi, versus 2.47:1. LOL. Like night and day, even with a 2v 351W.

I managed to get the rear ebrake cables from the explorer to work with the Cougar cables, using no extra parts, except maybe a zip tie.



I still need to clip in the cables so they stay put, but the ebrake works nicely.



I simpy adjusted it a bit longer.

My parts list so far
Master Cylinder - Lincoln Mark V 77-79 with 4 wheel discs
Proportioning valve - Lincoln Mark V 77-79 with 4 wheel discs.. I gutted it and used the ford prop valve brass plug.
Power Booster.. 76 Ford Elite (same as 77-79 Cougar, I just had this one already painted with POR15).
Front calipers - Stock Cougar (midsized ford)
Rear calipers - Ford Explorer (unsure of years.. that same kit Ford sells)

that's if anyone wants to ever try this and searches this.

Now.. my problems (always problems)
1. The pedal is super slow coming back up, and the car drags with that.. I've read that if the rod between the master and booster is adjusted too long, that will happen, I DO remember making it as long as I could when I did the swap in the Elite a few years ago in a futile attempt at getting a pedal (didn't work). What is the "proper" length? any guidelines?

2. This rear axle is a 3.55:1 9". When I put it in gear, it seems a bunch louder than the 2.47:1s did. This center section only has a few hundred miles on it, and is "tight" no noises while driving, etc.. Could that just be the nature of the beast here?

3. I can't lock the wheels up at all. I barely can in the rain.. Now, I don't remember ever being able to do so BEFORE, as I'm running heavy-*** 17" cragars with large tires.. However, the car seems to, well, stop as it did before, at least from 30 - 0. Should I be worried? perhaps that rod is a bit too long?

And yes.. those are bilsteins.. this car handles remarkably well for it's size.

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Last edited by Psquare75; 01-25-2006 at 11:36 PM.
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Old 01-23-2006, 08:54 PM
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Might want to check the master cylinder. Some master cylinders have a residual pressure valve in them. This would keep approx 10lbs of pressure on the drum brakes so the wheel cylinders don't collapse. Disc brakes would not like that at all.

Also when adjusting the brake rod it is important that the refill hole at the bottom of the fluid cup can refill the cylinder if there was ever a leak. Look down the hole and have someone depress the brake do you see the hole close as the piston goes by? You should.

Was that an 8" ford or 9"?

Looks great.
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Old 01-23-2006, 09:14 PM
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Quote:
Originally Posted by evltwin
Might want to check the master cylinder. Some master cylinders have a residual pressure valve in them. This would keep approx 10lbs of pressure on the drum brakes so the wheel cylinders don't collapse. Disc brakes would not like that at all.

Also when adjusting the brake rod it is important that the refill hole at the bottom of the fluid cup can refill the cylinder if there was ever a leak. Look down the hole and have someone depress the brake do you see the hole close as the piston goes by? You should.

Was that an 8" ford or 9"?

Looks great.

This master should not have a residual valve, as it's a 4 wheel disc master.

It's a 9".
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Old 01-25-2006, 11:48 PM
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Well.. I did some measuring, and the cup for the booster pushrod is the same depth for both the disc/disc master (lincoln mark V) as the disc/drum master (XR7)

Lincoln mark V disc/disc1 1/8" bore ** in use

Stock Cougar disc/drum 1" bore

My problem is.. the pedal seems, well, low. I've tried the following

1. Bench bled master, then gravity bled system.
2. Used hose in bottle to bleed
3. Mity Vac setup.

As for the rears, I even went so far as to pull the calipers and clock them so the bleeders were at a true (bore) 12 oclock.


The rear calipers are working, judging from the now rust free rotors, and the fact that I have to struggle some to break the rear tires free in a brake stand.

However. the pedal just feels..... weird. I put some line locks on the rear axle rubber line, and the front hoses, and the pedal was noticably harder.

I haven't touched the fronts at all, and the rear axle hose is what was there before. I DO have two axle > caliper hoses.. but could the hoses be swelling THAT much? I think I'd see it/feel it when someone else applied the brakes.

To recap, front brakes are stock mid 70s Ford pieces, rears are Ford Explorer.

On a side note, I do have an adjustable valve in there from SSBC for the rear discs, immediately after the disc/disc valve (gutted Mark V).. which is actually all the way clockwise for max rear brake pressure... and the rears still won't lock up, at least in the drive way at 20/25 mph. Even on wet pavement.. the fronts will lock, rears will not.

What am I missing? I know the explorer calipers arent optimal, but, I think in a panic stop the rears should be able to be slowed.. My father thinks I should try the original wheels/tires, as perhaps my 255/50/17s and 275/50/17s are throwing off the rears, making rear lockup harder?

Actually, I found this in reference to another thread..

http://www.ford-trucks.com/article/idx/13/092/article/Complete_Brake_Upgrade_for_1978__1979_Ford_Broncos .html

His/her setup mimics mine, same components.... the only difference I see is the proportioning valve... hmmmm

Anyway.. comments?

Last edited by Psquare75; 01-25-2006 at 11:55 PM. Reason: Added link
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Old 01-27-2006, 11:42 AM
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The article I read in that link said he gutted the stock combination valve and used an adjustable valve for the rear brakes. Sounds just like yours, unless I am reading something wrong.

He is also using a dual stage booster, while you are using a single stage. This means it is most likely easier for him to get high line pressure than you can. Ford often preferrs to use hydroboost with 4wl disc to obtain high enough line pressure.

In my, and Ford's opinions, your rear calipers are too small compared to your fronts (or your fronts are too big compared to the rears) for that vehicle, but you knew I was going to say that
The rear brakes will not do as much as they ought. This goes for the Bronco in the article too, as well as some of his information is inaccurate, though it was overall a good article.
With the rears being underpowered, the fronts have to work even harder than normal to slow the vehicle. You probably aren't producing enough line pressure to stop as well as you'd like.

If the pedal is not returning like it should, it is a problem in the booster, master cylinder, or linkage/pushrods. Nothing in the system past the master cylinder can cause that, including residual valves. Even if the brakes were totally seized hydraulically or otherwise, the master cylinder springs should return, the booster spring should return, and the pedal should come up.

At this time I haven't much of a clue as to why the pedal is low, but if pinching the hoses made it better, that indicates a possible problem at one or more wheel. Maybe there is just still a little air in a caliper.

Put your hose locks on the 4 hoses leading to the wheels, and remove individually and test pedal, then replace, and go to the next. Hopefully you can isolate the main drop to one or 2 wheels. The pedal moves down as the caliper pistons move out, so there will always be some movement, and often 4wl disc has more travel than disc/drum. Dont put so much pressre on that the fluid bleeds past the locks, or you will get a false reading.

Check your lining clearences on your new rears, and check that the pads are seated to the caliper properly. Sometimes the shims dont match the pads and can cause a sort of 'spring' action, severely increasing pedal travel. Observe caliper and pad movement while someone else hits the pedal. Check the fronts too.

And take your Dad's advice about trying the smaller wheels. I don't know if it will help it stop better, but it might, and it cant hurt.

I don't know why it clunks (I guess it is a clunk?) when you go into gear now with the new gear ratio, but since it is transmitting substantially more torque to the axles now than before, it might just be normal. A higher stall converter can sometimes reduce that clunk.
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Old 01-28-2006, 02:19 PM
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Yesgo, I knew you were going to say that.

In a continuing quest. I've tried the following
Removed adjustable valve
Changed factory prop valve to a non gutted 4 wheel disc unit.

I checked all the fittings, each one is dry.

With the front brakes blocked off, the rears barely even coast the car to a stop. They won't even hold the back wheels during a holeshot (you're telling me that this 351w has that much power?) Even on dirt, the back wheels simply won't lock.. and the pedal is lousy. I'm thinking either.
A. both calipers in the rear are bad (I doubt that, as they bleed fine, and move fine/no hangups).
B. I need to try that other dual diaphragm vacuum booster.. But I feel like that would only apply if my pedal was too hard, and I couldn't press it.
C. Both rear hoses are collapsed.. But again..
D. The master doesn't put out enough pressure for the rear discs. ** This one I'm not sure of.

I'm stumped, and about to put these parts on eBay and try something else.
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Old 01-30-2006, 01:00 PM
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Just an update, I ordered a brake pressure gauge.. I'll stick it in each ports, and various places in the system, and see what I come up with...
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Old 01-30-2006, 03:54 PM
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Man, I hope you get this figured out and update the post, My Son's 70 Nova project has a new ford nine inch in it with the Explorer disc package but the project is far from done and haven't tried the brakes yet. A good friend of mine has the same problem with his 32 Ford running discs front and rear- it is a nightmare in a sudden stop situation the car just won't lock up the brakes and won't respond. He is running the same 1.125" ford disc/disc master as you. I've been told he needs to lose the factory style proportioning valve completely and add one adjustable inline to the rear brakes to cure the problem. I'll be watching for your final cure to this problem, good luck, keep us updated. Bob

With the Nova we are planning on running the stock disc/drum master cylinder since the Explorer calipers have about the same bore diameter as the original drum wheel cylinders.
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Old 01-30-2006, 06:28 PM
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Tonight I tried my original 1" disc/drum master (only difference should be diameter and the reservoir size)..

Again, same deal. In fact, I had all the wheels clamped off except the left rear... pedal felt fine.. but, it just doesnt stop, or do anything. You'd figure one wheel would spike pressure to lockup.. Nope.. it just barely grabs, and still rolls along. The Ebrake in the center of the hub stops the car better and locks up the rears better.. I'm almost tempted to put the drums back and say forget it.

It's at the point where I'm about to drop the $499 for the 11.5" cobra rear disc kit, but I'm VERY afraid that I'll still have the same problem.
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Old 01-31-2006, 07:26 AM
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Psquare75, when you get that pressure gage be sure and let us know the details. Do you have to put a bleed port in the line before the gage or is it built into the gage? Or it doesn't need to be bled after gage install. I hope it pinpoints your problem, I've got some of my own and have been thinking of getting a gage.

Moon
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Old 02-01-2006, 05:16 PM
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Well, my gauge showed up.. I installed it.. pumped the pedal once, as the gauge said.. and I got a whopping.


*drum roll*

850!?!?! PSI, and that was with both feet-oh-my-god-there's-a-50-foot-tall-alien-in-front-of-me-pressure. It spiked to that.
What the gay? (as a friend would say).

I am going to try the gauge in FRONT of the rear hose, as I have a feeling that hose is bad. I'll let everyone know more over the next few days.
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Old 02-01-2006, 05:59 PM
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Don't you have a prop valve in there?
If you had a prop valve spec'd at 400/.45 for an example, at 1000psi front, the rears would show in the neighborhood of 670psi.
Your caliper piston force with the 1 7/8" Explorer piston @ 850psi is ~2346lbs.
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Old 02-01-2006, 06:08 PM
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I have hte original unit back in there for now (disc/disc), so I was expecting more along the lines of 1000+ psi.

These brakes don't do *anything*. For kicks, I tried my boss' Explorer, and clamped his front hoses..
Guess what didn't spin.. at all, well, with a lot of pedal they did :-x..

You're telling me with the pedal down and the rears-only applied, I should be able to push the car by hand with some footwork?
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Old 02-01-2006, 06:11 PM
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Maybe if your car outweighs the caliper force.
The rear brakes that go with the valve you are using put out ~4478lbs @ 850psi. That is per wheel.

The Explorer likely runs at a higher overall line pressure as well.

Edit: I'm not saying this is your problem, but it could be. There could just be a problem at the calipers or pads where they are not clamping properly.
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Old 02-01-2006, 06:24 PM
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that 850psi was with a 1" master and the mark V disc/disc prop. gutted/non-gutted/adjustable made no difference concerning the pedal... so I have a feeling it's not there. Just in case, I can look up the split point of the prop valve later tonight in my FSM. I *Haven't* been able to find the necessary PSI for the Explorer rear discs. That should help some. An Explorer should weigh about the same, +/- 100 or 200 lbs as my Cougar, and their tire diameter is the same (roughly, if not larger on the SUV)

What bothers me is that article I posted with that Bronco... he managed to get his rear wheels to lock up, and he had both larger tires, and more weight.. Seems like every article I've read online, people have rear wheels locking up inducing spin... I have the opposite problem. With the front brakes blocked, these rear wheels should skid down the street.. they barely hold the car at idle.
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