Disc brake conversion stopping power and proportioning valve adjustment

[gladkin]

Hello,

I just installed the wildhorses4x4 front disc brake conversion kit with new everything, including proportioning valve. I do still have manual m/c (no power brakes). I bled the brakes multiple times from backs to front and I am getting a stiff brake pedal now. The issue that I have is it does not feel to me like I have the stopping power that I had with all 4 drum brakes. Is this common for a break-in period with new disc brakes or should I be able to lock 'em up? Or does it come down to more brake bleeding? I would think if there was any air left in the line that I would have a mushy pedal?

In addition I am told that the proportioning valve is adjustable to bring more or less braking to the front/rear brakes. How do I adjust this to get the correct proportions? It wasn't clear to me from the wildhorses instructions.

Thank you!

Michael

 

[infinite monkey]

Proportioning valve will only affect how soon your rear brakes will lock up as compared to the fronts. You do not want the rear to lock up before the front.

Once you get it going again, do some hard stops and dial in the valve so front and rears lock up at the same time. I'm not sure if I have any suggestions on the low pressure issue, other than I think disks require a larger amount of fluid to operate than drums. Your old MC may not be up to the task.
Did you remove your old proportioning valve?

 

[StnePny]

Did you pull the check ball out of the M/C for the front reservoir ... ?

 

[DirtDonk]

If it's our master, it would not (should not at least) have a residual pressure check valve.

And yes gladkin, you should feel more braking power as well. Not night and day differences, as it's still set up as a manual system so would mostly be more consistent and predictable than the drum brakes they're replacing. But still, you should feel it as more powerful to a certain extent too.

Which proportioning valve did you get? The standard one that looks similar to the factory type (brass color and mounts to a steel plate bracket) is non-adjustable.
If you bought the Wilwood adjustable one, then it's sole function as a prop valve is to reduce pressure to the rear brakes only. Should only be adjusted down if your rear brakes are locking up too soon.

One thing I can think of is the grinding of the knuckles. Did you grind enough that you can see daylight between the knuckle casting and the caliper when you look down on them?

If none of that works out, give us a call in the morning. Or if you can call within the next three minutes you can still get someone! ;D

Without your last name, I can't look up your order to see what you have.
Someone should be able to help out though.

Good luck.

Paul

 

[broncnaz]

Drum brakes are self engergizing so they do tend to feel like they stop better. Only issue is when they get hot they fade. Disc brakes take a lot longer to fade. Also new brakes need some time to Wear in so to speak, You can burnish them to help wear them in sooner. Basically do some low speed driving with the brake pedal pushed down slightly so the pads seat into the rotor.
There are other factors that affect the stopping power. one is pad material some pads just dont stop well until you build some heat up in them.
Some MC's with larger piston bores will give a stiff pedal but less overall braking pressure. Problem is with disc brakes you may need the larger bore to get a good pedal. So the braking differance between the old drums and new discs seems like its less because it takes more foot pressure to stop.

 

[gladkin]

Thank you for the replies! I did take out the residual check valve on my master cylinder as wild hoses said to do so in the instructions with the brake kit (thank you!). In addition, the knuckles are ground down far enough not to interfere with greater than 1/8" of daylight at all spots that may interfere with the caliper. I also installed the wild horses proportioning valve. One problem that I have found is I have a small leak on the SS brake hose where it meets the coupler that attaches to the caliper. The hose is bent where it was pressed into the coupler.

After work I confirmed that leak on a test run yesterday (previously I thought that it was just bent but not leaking). The leak is suuuuuuper small, but a leak none the less. Due to the bent line (I told wild horses yesterday) they shipped me a new hose that should be in today and I will install after work.

 

[70_Steve]

!~!

I did take out the residual check valve on my master cylinder ...

Hey Mike!

So, are you using the same master cylinder as you were using for your drum brakes?

It might all come down to leverage. And that change in leverage is the diameter (bore) of the master cylinder. The larger the bore, the firmer the pedal, but the more pedal effort to get a certain braking. The smaller the bore, the more pedal travel (to displace the same amount of fluid) so, not so much pedal effort to get that same braking.

You may need to change your master cylinder...

 

[Timmy390]

X 2 ^^^^^

Sounds like you did a Chevy conversion and are using your stock drum/drum MC.

That works for the Ford conversion (I'm living proof) but for the Chevy, you need a different M/C with a bigger bore. The calipers on the chevy are bigger and need more fluid movement.

Tim

 

[Rustytruck]

Whats your tire size? 28 inch tires are much easier than 33" or worse yet 35" tires to stop. Pad compound on the front disc's make a difference too. On my Chevy conversion I was hard pressed to lock up a tire with 33" x 12.50" X 15" tires and manual effort. But the truck stopped in a shorter distance and stopped straight. Adding Hydraboost made all the difference in the world. My conversion with the larger Blazer calipers would not work with a 1" bore master cylinder, I used everything from 1.250 bore to 1.00 bore through the years and have settled on 1-1/16" bore working the best for me and my set-up.

 

[gladkin]

Yes, I am using the chevy conversion front disc braking kit and yes I am currently using a stock dual m/c from ford for the 4 drum brakes. I am currently running 33x12.50x15 BFG Mud Terrains and was going to go up to 35x12.50x15 in the next week or two. This all means that I am getting real short on money...

So that being said, I am not sure what to do about the m/c. I clearly need something with a bigger bore so, which m/c do I go with? I don't know if I have the time or the money at this point to do the Hydroboost prior to the Bronco stampede on March 13, but I do know that I need good solid braking to run Terminator and some other trails.

Suggestions vs. cost vs. performance from anyone for the different options?

 

[70_Steve]

So that being said, I am not sure what to do about the m/c. I clearly need something with a bigger bore so, which m/c do I go with?

If I understand your problem, I'm not sure I can agree with Timmy390's conclusion that you need a bigger bore.

If your problem is that you now need greater pedal pressure to achieve the same stopping, and you have a firm pedal, then you'll need a MC with a slightly smaller bore.

To displace a certail amount of fluid, the larger the bore, the shorter the pedal travel required to displace that fluid, but the more pedal effort required. The smaller the bore, the longer the pedal stroke required, but the less pedal effort.

And yes, it could be a couple of other factors as well, including your choice of pad material...

 

[treihesse]

Use the f250 camper special mc. Its a bigger bore and works really good.

 

[gladkin]

What year? 1976?

 

[gladkin]

Success! Just to let everyone know that the 1974 F250 M/C with the dual piston caliper and a 1.25" bore works amazingly well. I now have great manual stopping power. Thank you for everyone for your help!!!

 

[68ford]

Great effort Steve at spreading badly needed knowledge. But I fear the grade school academics required to comprehend the most basic fluid mechanics is lacking here.

Exactly, most off-road race trucks with manual,brakes and 39 in tires these days usually run a 3/4 master for front and 7/8 master for rear. And that's with massive 6 piston calkpers and long brake pedal.