Disc Brakes

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73fj552

73fj552

10 Year
Joined
Oct 17, 2011
Threads
36
Messages
119
Location
Orange, CA
Here we go,

I just performed a disc brake conversion on my 73 FJ55 by swapping in a front axle from a donor 76. I completely rebuilt the front axle with all new factory parts. Im running a new disc master cylinder for a 76 on the booster for a 73.

I put everything together on the car and after driving the truck for a few days i cant help but feel that the brakes are not working to their full potential. They have a numb feeling and dont "bite" as well as the drum brakes I had on before. The system bleeds really well so I dont believe it to be a hydraulic issue. The only other thing I can guess it may be is the pads Im using. I currently have organic pads but am looking to switch to metallics hoping to increase the "bite". It feels as if the brakes reach a threshold and dont want to stop any better. On a side note, I reversed the car and braked hard and was able to lock up the front tires and noticed a definite increase in braking. I repeated this process going forward and had less than stellar results.

Id like to know your ideas on what I can do to increase the brake performance. How long for the pads to bed in? What material pads are best?

Any info would be helpful.

Thanks
 
Quick question: did you bed the brakes properly after install? If they were new pads and rotors you might have glazed them if you didn't put them through the proper heat cycle, which could be a/the reason you are having trouble.
 
jdog35 said:
Quick question: did you bed the brakes properly after install? If they were new pads and rotors you might have glazed them if you didn't put them through the proper heat cycle, which could be a/the reason you are having trouble.
Click to expand...

Can you describe jdog?
What is proper heat cycle?

I am wondering if you started with new surface on the rotors?
Or did you drop new pads in on an old rotor surface?
 
Heat cycling is another way of saying bedding i guess. Basically every brand of pad has a specific sequence to follow to properly bed the pads and rotors. Usually they are set up by braking from certain speeds and distances until they properly seat. If you don't put them through these heat cycles they wont work worth a darn.
 
I havent done a sequenced heat cycle. I just put them in and started driving. I have gotten them pretty hot in an effort to test the boundaries of the braking performance.

The rotors and pads are new. I wiped down the rotor surface with brake cleaner to free it from any oils. I have read that the rotors should be turned before installation otherwise the pads wont properly grab. I put them on without turning them.

The braking improves slightly when the system warms up but its only marginal. I am going to pull the pds and sand the surface of them with some 80 grit sand paper to try and roigh them up a bit.

Keep questions and suggestions coming.

What is an example of a bedding in heat treat cycle?

Thanks
 
I would definitely say if you didn't do any bedding or cycling that is a big part of your problem.

When we cycle pads at the race track they are very aggressive, so don't try this with your pig:) But an example would be getting the car up to 80 mph then hard braking to 30 mph. Ramp back up to 60 mph then drop to 20 mph. Go back up again in the 80 mph ballpark and drop way down to 10-20 mph. Then a couple short quick stops from 30 mph to zero and they are set.

Obviously those numbers are for track pads on our Audi, but the principle remains the same. Your pads should have instructions on what the proper bedding process is. No amount of sanding will get what you need compared to that kind of heat cycle.

Hope that helps!
 
Thanks. After doing some research I think that may be my problem. Now time to try and locate a bedding proceedure for my setup.

Thanks again.
 
73fj552 said:
The rotors and pads are new. I wiped down the rotor surface with brake cleaner to free it from any oils. I have read that the rotors should be turned before installation otherwise the pads wont properly grab. I put them on without turning them.

I am going to pull the pds and sand the surface of them with some 80 grit sand paper to try and roigh them up a bit.
Click to expand...

Don't turn your new rotors! That makes no sense!

Do clean your new rotors w/brake cleaner before you bed in the new pads - just as you did before, to removes any grease & oils etc... & start fresh.

While it's certainly possible you did, I doubt you glazed your new pads. I might hit them lightly w/some finer sandpaper than 80, maybe 120 - lightly. There is enough friction between the pads and rotors to do the required stopping - the surfaces don't need to be rough or gritty etc...

I would look up the proper bedding procedure for whatever pads you have and follow it. After that, just drive it a bit - as long as it's safe. Things sometimes take a few miles to break in & get happy.

Like jdog, my disk brake experience comes from my '74 Porsche 911 track car (my pig has drums all around still). If you rebuilt the calipers, sometimes the piston seals can force the piston to retract (when not under pressure) away from the pad & disk until you get a few miles on them & break them in. This can make the brakes feel a bit soft w/a longer pedal. . .

Finally, bleed the system. . . again and again. Did you bench bleed the MC? Sometimes it takes some miles and a bunch of bleeds to really get ALL the air out of the system.

Stick w/it!

Tom
 
Thanks for all the info. I went through the bed in procedure and out seems to have worked. I'm going to drive the car for a while and monitor performance. I will keep you guys informed on what happens.

Thanks again. You guys are a wealth of knowledge.
 
Just thought id post an update.

The car is stopping better the more i drive it. I do notice a dramatic difference between when the brakes are cold and when theyre warm. Is it normal for the brakes to feel like im using two sticks of butter for pads when they are cold? Otherwise when warmed up they seem to work okay.

Im going to put in a set of caramic heavy duty truck pads to see if i can cure this issue. I will post my findings.
 
Keep in mind on those ceramic pads they may have a higher initial operating temperature range. That means you might not get better response but worse depending on the pad. If they are built for a much heavier vehicle then they are built to withstand those much higher temps generated by the increased friction (due to the weight).

In real-world terms, your braking might be worse with them because your rig isn't really heavy enough to utilize the materials in those pads effectively. Again, that is entirely dependent on the specific pad and materials in it. The manufacturer will have specs for use that you should definitely check before applying to your pig.
 
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