Brakes Wont Lockup

[jeremywatco]

Finally got my '73 onto the road today. Ran awesome. I recently added disc brakes to the front and kept the original drums in the back.

One thing I realized is it seemed the harder I pushed on the brakes the less braking power I got. If I pushed down moderaterly I got good braking. If I tried to lock the tires up and pushed the pedal hard as far as it goes it didnt seem to do much. I couldnt lock the tires up at any point regardless of how hard I tried. I went back and re-bled the system, no air.

I do not have a vaccum assist or hydroboost. Just have the master cyl right on the pedal. Its a new master cylinder as well.

Any thoughts? Curious where to start.

 

[joshd1971bronco]

Proportioning valve perhaps? Did you change or modify your original in any way?

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[jeremywatco]

Yes. The wildhorse kit I purchased came with a new one. I installed the new valve.

 

[Broncobowsher]

Anytime I hear of the disk conversion issues, first suspect is the knuckles ground enough? If there is even a hint of contact there will be problems.

The other big one (I don't suspect that much but still worth checking) is the calipers on the correct sides. The bleeder can face about 12 o'clock or lower (4 or 8 o'clock) in reference to the piston bore. The straight up 12 o'clock position is the only correct position.

Those are just the basic things I always start with for any Bronco disk conversion.

 

[jeremywatco]

Anytime I hear of the disk conversion issues, first suspect is the knuckles ground enough? If there is even a hint of contact there will be problems.

The other big one (I don't suspect that much but still worth checking) is the calipers on the correct sides. The bleeder can face about 12 o'clock or lower (4 or 8 o'clock) in reference to the piston bore. The straight up 12 o'clock position is the only correct position.

Those are just the basic things I always start with for any Bronco disk conversion.

Thanks. I've checked all those things. Bleeders are facing straight up. The knuckle has plenty of room. I may try bleeding again.

Should the brakes lock up when I mash the pedal? The rear don't either.

 

[nvrstuk]

New m/c but what bore?

Remember that a caliper for discs requires more pressure than a wheel cylinder does for drum brakes... this is probably why you can't "lock up" the brakes but I'm not really sure it has anything to do with why with less pressure on your pedal you have "better" brakes and the harder you push the less brakes you have...

 

[DirtDonk]

What kind of proportioning valve did you get? Lower mounted brass block type that gets all the lines and doubles as a distribution block, or the manually adjusting type that just goes in the rear line?

If your pedal is firm and high you don't have air in the system. If when you mash on it you come up hard against the end of your travel pretty quickly, you don't have air in the system.
Or at least it's not showing it in the traditional way.

What master cylinder did you get? If the larger heavy duty type with 1.125" bore, the required pedal pressure will be quite hard, but it should not feel like your braking power is diminished the harder you push.
If it's a stock size/type master of either 15/16" or 1" diameter you should be able to lock up at least the rears pretty easily.

But that all leads to the last question... What size tires and wheels are you running?
If you're running larger than 33's, and especially on heavy steel wheels, you might find the stock setup not as responsive. Even with the front discs.
Though with the larger piston size of the front calipers now, the rear brakes should apply pretty quickly. If you have the brass type prop valve it would be my first suspect. After tire size that is.

But just to rule out stuff, how firm up have you adjusted the rear brakes? Do they rub quite a bit when you turn the drums, or is there very little to no scuffing sound?
If little to none, try applying the parking brake one or two notches to see how that might help.
When my rear brakes would wear down and the self-adjusting feature was not working (which they almost never did) I could tell by the pedal feel that the rears were getting out of adjustment. Driving around with the parking brake applied to the first notch firmed my pedal up again until I could make the time to re-adjust the rear brakes again.

Happened every few months back then because it was my daily driver.

Paul

 

[jeremywatco]

What kind of proportioning valve did you get? Lower mounted brass block type that gets all the lines and doubles as a distribution block, or the manually adjusting type that just goes in the rear line?

If your pedal is firm and high you don't have air in the system. If when you mash on it you come up hard against the end of your travel pretty quickly, you don't have air in the system.
Or at least it's not showing it in the traditional way.

What master cylinder did you get? If the larger heavy duty type with 1.125" bore, the required pedal pressure will be quite hard, but it should not feel like your braking power is diminished the harder you push.
If it's a stock size/type master of either 15/16" or 1" diameter you should be able to lock up at least the rears pretty easily.

But that all leads to the last question... What size tires and wheels are you running?
If you're running larger than 33's, and especially on heavy steel wheels, you might find the stock setup not as responsive. Even with the front discs.
Though with the larger piston size of the front calipers now, the rear brakes should apply pretty quickly. If you have the brass type prop valve it would be my first suspect. After tire size that is.

But just to rule out stuff, how firm up have you adjusted the rear brakes? Do they rub quite a bit when you turn the drums, or is there very little to no scuffing sound?
If little to none, try applying the parking brake one or two notches to see how that might help.
When my rear brakes would wear down and the self-adjusting feature was not working (which they almost never did) I could tell by the pedal feel that the rears were getting out of adjustment. Driving around with the parking brake applied to the first notch firmed my pedal up again until I could make the time to re-adjust the rear brakes again.

Happened every few months back then because it was my daily driver.

Paul

Thanks for the response.

I have the brass valve that goes to all brakes. Also have 33's on steel wheels.

Maybe need hydroboost?

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[DirtDonk]

Maybe... But maybe there is something wrong with the proportioning/combination valve too. Too hard to say at this point.
But if none of the other stuff pans out, it might come down to the prop valve.

I don't actually know what can go wrong with them (other than leaky delay valves under the rubber boot) but maybe it's as simple as debris getting in and blocking flow. Just know that some issues have cropped up now and then that were traced back to the aftermarket valve.

Which master did you go with?

Paul

 

[jeremywatco]

Maybe... But maybe there is something wrong with the proportioning/combination valve too. Too hard to say at this point.
But if none of the other stuff pans out, it might come down to the prop valve.

I don't actually know what can go wrong with them (other than leaky delay valves under the rubber boot) but maybe it's as simple as debris getting in and blocking flow. Just know that some issues have cropped up now and then that were traced back to the aftermarket valve.

Which master did you go with?

Paul

I got a new master from wild horse.

I think part of the issue is this is my first bronco and up until this point I've never driven one. So have zero clue what to expect. Maybe it's normal. But I'd think If I push the pedal as far as it goes I'd have a lockup.

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[bronconut73]

Not neccesarily lock up but yes you should be able to nose dive it pretty hard when you slam on the brakes. When this happens the rear lightens up as it lifts from the front end nose diving. That will usually allow the rears to lock up a little bit because you taking so much load off of them by nose-diving the front.

So my question is did you get the lines reversed for your brake lines when you were installing the new master cylinder?

Typically the rear Reservoir operates the front brakes and the front Reservoir operates the rear brakes. Check that out as that could have the symptoms that you describe at least to some degree

 

[bronconut73]

One more thing about the knuckle grinding. You need a good bit of room for the caliper to move as the pads wear and for Flex in the caliper mounting bracket that is more excessive with the Chevy Conversion then it is with the Ford conversion obviously. So if you ground the knuckles enough to just fit the calipers that will not be enough. I'm sorry to say I don't know exactly what is enough but I would start with the thickness of your inner PAD as your guideline for how much room you need to create for the caliper.

 

[Apogee]

System compliance can also create the symptoms you describe, where above a certain pressure, the expansion of the hoses, flex of the calipers, etc create what is essentially a zero net gain in pressure with additional pedal travel. Caliper spread isn't generally an issue with iron calipers, so are you running rubber brake hoses or braided stainless?

What's the bore size of your MC as has been asked previously above? If this is the typical 15/16" to 1" bore, then it's odd that you're not able to lock up the rear brakes, even if the knuckles weren't clearanced enough. It would indicate to me that the rear drums may not be functioning like they should.

Tobin

 

[Rustytruck]

If you have access through your rims do a couple of hot braking passes and then aim a temperature heat gun at the rotors and brake drums and try to find a wheel with an unusually low temperture reading. Then solve the problem why that wheel isnt pulling its weight.

 

[jeremywatco]

Master is 1 1/8" bore

I did notice prop valve had a small pool of fluid on it. I tightened Everything down tight again and will retest today/Tomorrow although it was a small amount of fluid so I doubt it was enough of a leak to throw it off

 

[jeremywatco]

UPDATE.. So i took it out in the driveway (which is SUPER STEEP)... brakes seem to work "ok". Now if I leave in drive while holding the brakes all the way to the floor and barely push the gas, the bronco will crawl.

I was able to get the rear to skid a little bit.

I crawled under and verified the knuckles. There is about 1/8 of an inch between the caliper and the knuckle.

I am going to bleed the brakes again. Maybe air got in the system with those little leaks I had.

 

[ntsqd]

Which front calipers did you use?

For Ford front calipers set up manual, no booster I'd suggest a 1-1/32" bore MC (93.3:1) with a 1" bore MC (99.2:1) optional.

Fro GM front calipers set up manual, no booster I'd suggest a 1-1/16" bore MC (91.7:1) with a 1-1/32" bore MC (97.4:1) optional.

1/8" may not be enough clearance long term, the friction material on the outboard pad should be thicker than that. There needs to be enough clearance that the caliper body can not hit the knuckle with only the outboard pad plate (no friction material present) pressed tight against the rotor by the caliper. Need not clear by a lot, but it does need to clear.

 

[bronconut73]

If it's the vendor supplied GM caliper bracket they do tend to flex a bit too. And it is okay that they flex, but that also needs to be accounted for when clearancing the knuckles.

 

[DirtDonk]

Alert! Long-winded reply warning!
As if I'd do it any different. But hey, you've been warned...

I did notice prop valve had a small pool of fluid on it. I tightened Everything down tight again and will retest today/Tomorrow although it was a small amount of fluid so I doubt it was enough of a leak to throw it off

Probably right, but good to check.
If it's leaking out of that rubber boot, peel it back and check the fitting for looseness too. This is an unfortunately too common leak area for some reason. It's a delay valve, and sometimes (if you're lucky) it's just loose. Other times it leaks from the o-ring or seat. A member here just went through this last week and was talking about the fix.

UPDATE.. So i took it out in the driveway (which is SUPER STEEP)... brakes seem to work "ok".

That's maybe almost possibly some good news. But still doesn't sound quite right even for someone not used to Broncos.
Thanks for the clear descriptions by the way

Now if I leave in drive while holding the brakes all the way to the floor and barely push the gas, the bronco will crawl.

Now that's a good indicator that all is not well. And in the clear-descriptions category, by "to the floor" do you literally mean to the floor? Or just pressing as hard as you can?
Because if it's indeed going that far down, you still have air in your system, or a leak is letting air in/fluid out, your pushrod is too short, or as mentioned your soft lines are expanding.
If they're braided, this is unlikely. If they're older rubber, it's very likely.

The last thing that can cause excess travel is the rear brakes not being adjusted properly. But even at their worst, this is only going to make for a little extra pedal travel. Not enough to cause it to go to the floor.

I was able to get the rear to skid a little bit.

Again, a tiny bit of good news in the mix.

I crawled under and verified the knuckles. There is about 1/8 of an inch between the caliper and the knuckle.

Sounds good. As long as you can see that 1/8" of daylight between the components, you're in good shape.

I am going to bleed the brakes again. Maybe air got in the system with those little leaks I had.

Very good idea at this point. Sorry you're having to go through it, but if your description of going to the floor is correct, there is very possibly some air in the system

I think part of the issue is this is my first bronco and up until this point I've never driven one. So have zero clue what to expect.

I think this is a key factor. But it might not be the only thing at work here either.
You are still fighting a larger diameter piston in the master than is normal without a booster of some kind. And you may still have something wrong. It's just very hard to tell from here yet.

I'm a fan of manual brakes in fact, and that's how my '71 is set up. Albeit with a 1" master.
And there are other members here using your exact setup and like it.
But it's still a compromise using the larger master. Good firm pedal feel and short travel, but you have to push harder to get it to stop.
Not that I don't appreciate a boosted setup, but after spending years on the trails and dealing with stalled engines where boosted brakes would be useless, a boosted setup is last on my list.
Heck, I just graduated to power steering!

Not just Broncos, but is this also your first older truck in general with manual brakes? As you suspect there is a huge difference in feel and power between any modern car or truck and a heavily modified older manual brake utility vehicle.
The key word there is modified. As in, larger tires, larger calipers and master cylinder.
If stock size master and stock size tires, the brakes you have would work "better" to a point and maybe even passably well. You'd probably be able to lock them up a little easier perhaps, but you'd also probably still feel the brakes were sub-par to what you're used to. Because in fact they were!
But you should still be able to expect a reasonably safe driving experience as well.

As a comparison, with that same master and brake setup, with those same 33" tires, adding a hydro-boost setup would probably push you towards the windshield when you hit the pedal.
Even the factory style vacuum boosters are not that impressive compared to the hydro-boost, or most other more modern vehicles. The cost is more impressive too though, as you've probably seen.
And vacuum boosters are also still perhaps better suited to the stock 1" bore master than the 1.125" size. More pedal travel, but easier on the leg muscles.
My newer rig (the '68) has a vacuum booster and 1" bore master, and it's not all that impressive either. And that's with just 31" tires!
Can't lock up the tires when it's cold at all, but it does get a little better when warmed up. Might be the pad material in my case though. Just not sure yet because I have not messed with it enough.

So your larger piston is still an advantage to gaining a firmer pedal with the larger size of the front brakes that you have. Just takes more leg pressure.
But pedal travel should be negligible too. No way it should go to the floor.

Maybe it's normal. But I'd think If I push the pedal as far as it goes I'd have a lockup.

It's not really normal, but it it's not uncommon either with larger tires. And it is something that others do deal with too.
As mentioned a few members here are using your exact setup and give it good reports. But they may be coming from a different place in their vehicle experiences too. Or maybe they're just young and have strong legs! How are yours doing these days?
I know I don't enjoy it as much as I did when I was 25.
But for that heavy-pedal reason I would say most who are sticking with manual brakes also stick with the stock size master.

Which brings me to an important question. How did you come to choose that particular master? Did we recommend it, knowing that you were sticking with manual brakes? Or were we not aware of your setup exactly perhaps? We sell a lot of that master for all the right reasons, but not as often for manual brake systems.
Just curious because I don't want us to ever steer someone down the wrong path for that person in particular. Every customer is different, but we should know how everything is going to work and let them know to the best of our knowledge too.
Let me know.

And we still have to keep the proportioning valve in mind at this point too.

Thanks. Hang in there!

Paul

 

[A/C AL]

When I was having problems with my breaks I picked up a break pressure testing kit. It comes with a gauge and adapters. I took readings at the calipers and wheel cylinders then worked back toward the master . If I remember correctly you need around 500#s to look up drums and around 900# s for disc.