Technical Question on Brake Pad Bedding

Hi all,

I installed a disc brake kit on my 53 Chevy. The driver side caliper was tougher to get on than the p***enger side even with brake lube and anti-seize on threads.

I notice leaving the spindle bolts loose helps to get the caliper on. On the driver side, as soon as I tighten the lower caliper bracket to spindle bolt, I notice there is a gap between the outer brake pad and the rotor on the bottom side, yet the top is perfectly flush. Prior to tightening that lower bolt, the top and bottom of that pad were perfectly flush against the rotor. The rotor is quite hard to turn by hand once that lower bracket to spindle bolt is tightened. I also tried pushing the piston of the caliper in carefully with a plate and c-clamp and bleeder open and it went in just a little but then came back to the same position. I provided some photos below. It looks like a 1/32" gap (maybe a little less).





The p***enger side looks ok so far. I haven't bled the brakes with the new calipers but the gap looks parallel I think? (I provided photos) and everything went on easier on this side.



I didn't want to bleed the brakes and drive it like this without knowing the cause. Does this point to the left side caliper bracket perhaps being slightly off center, perhaps with the roid being welded to the bracket during manufacturing? Speedway says this is normal and nothing looks off and I just need to drive it and follow bedding procedures.

 

Don't sweat it !! After a few miles the pads will wear so as to make full contact.

 

Great thanks! I will bleed the brakes, follow bedding procedures and cruise.

 

Normal for parts that weren't made very well...but then again, it's normal for brake pads to wear unevenly. But being difficult to install the caliper might mean there is something wrong, and the brake will drag and get hot.

I'd consider sanding some of the lining off the pad that's dragging...using co**** sandpaper, and a flat surface under the sandpaper.

 

Thanks, it's a kit from speedway but the brake pads are ultra premium semi-metallics from Napa. It's hard to get the driver side caliper on because of the thickness of the pads and rotor and position of the piston. I can push the piston in just a pinch but it returns to the same position.

 

Something is amiss between center of rotor to center of caliper.
This after market **** parts gets you close. I've had to file, grind, weld & remachine to get them right. Sometimes they bolt on close enough and everything is fine.

Obviously if you can't get them on with calipers retracted & without fudging every bit of slop with loose bolts there's a problem.
There's a few different thickness of rotors and pads- there could be a mismatch there as well. There's supposed to be at least 1/8" clearance when that stuff goes together.

 

Thanks, I presented this problem to Speedway with the same photos and a detailed explanation. They said that it's normal and they don't see any issues and the pads just need to wear in and to go ahead and bleed the system and put some miles on it.

The caliper goes on a bit tight but it's totally doable, especially with the caliper bracket bolts loosened. I was mainly concerned with the gap on one side of the pad when I tighten the caliper bracket back up.

 

The gap on one end of the pad is disconcerting, but probably won't cause any issues. Being tight, otoh, might cause issues.

 

The caliper bracket loosened lets the center of the caliper shift over the center of the rotor.
Then bolting the caliper bracket tight applies the outer pad into the rotor, does it not?

Youre an engineer right?
Dust off the calculator and measure up the problem.
Dollars to doughnut if you install the parts without the pads that you will see the problem. You'll need to measure to find the area that needs corrected.

You could grind the pad to compensate for where there is lack of room, but that's not correcting the problem, it's chasing the symptom

 

Yes those are good points. My intuition pointed to a warped bracket from manufacturing or maybe the roid was welded off just a bit. I'll take the pads off and put it back together and see if I can see any obvious issues. I also coincidentally have another set of caliper brackets from another kit I didn't use that are the same size and made by a different manufacturer. I might give those a try too.

I didn't like the Speedway advice of just putting miles on it and not troubleshooting further.

 

By the way here's what Speedway had said:

"In regards to the pads, what you are experiencing is normal. Sometimes, they just won’t sit flat against the rotor from the get go.

Brake pads need to go through almost a break in period, called bedding in. What I would suggest is just to get everything tightened up as needed and then just go run around town doing some light driving. Stop and go traffic is what we are after, so that those pads can get worn in nice.


From what I can see in your pictures, it doesn’t look like anything is out of the norm, just need to go put some miles on."

 

Here's a normal bedding procedure:

After installing new pads make 6 to 10 stops from approximately 35 mph with moderate pressure. Make an additional two to three hard stops from approximately 40 to 45 mph. Do not allow the vehicle to come to a complete stop.When completed with this process, park the vehicle and allow the brakes to cool completely before driving on them again. Do not engage the parking brake until after this cooling process is compete.

I don't see any where it says to drag a pad on the rotor till it wears off. There's no way to say for sure till its over but I'd bet that one side of the rotor and the pad gets burnt. The wheel should spin nearly freely with just a slight drag when properly set up.

 

I am in agreement. I'm going to have find out why there is no gap between the rotor and both pads on the left side. As I showed before in the photos above, the right side shows a parallel gap and the wheel definitely spins by hand.

The left side does spin by hand but tighter. I will take the pads off and do more inspecting and report back. Thank you for your advice.

 

Sounds like you got your car up safely . as per your other thread. Glad it is working out.

 

Thanks! I fell asleep under the car for an hour on Saturday and hit my head on a shelf but other than that I've been able to work out of that garage fine actually!

 

I would bet on the roid to bracket having been welded slightly off from the manufacturing process. The bottom of the brake pad has a gap once the bracket is tightened. The top does not. If the welded roid was off it would pull that bracket (and caliper) in and no gap would be present. The driver side has a gap on the top and bottom.

I'm going to make measurements and also bolt up the other spare bracket I have to see if anything changes.

 

pads should not go in tight. they should be able to move freely or they will stick and wear prematurely or uneven. it seams every set of pads i get lately i have to take a file to the contact edges to get them to slide properly.

 

Thanks. The right side looks correct and they don't go in tight. The left side doesn't behave the same so I'm going to look at whether the caliper bracket is manufactured incorrectly.

 

check the pads like i wrote. they stamp them out of steel and the dies are ****py and the edges are not cut clean. file out the little "forks " so they can lay flat.

 

Thanks I will do that as well.

 

With regard to your post #10, I would consider trying the second set of caliper brackets in your possession. As suggested, you might want to mount your calipers (first) without the pads in place. That will allow you to take measurements to insure that everything is going to fit properly and the caliper is truly centered over the disc.
Good Luck and let us know the answer to this one.................. Jeff

 

Thanks I will do that. I will also try taking off the caliper bracket and just installing the caliper and pads to see if there is an even gap between the rotor like on the driver side.

 

I did a little more inspection. When I took the caliper bracket off the driver side, and put the pads and caliper on the rotor and held it by hand, everything is flush but no real gap at all but the rotor can spin.

Next I took the p***enger side caliper off. I measured the thickness of all the brake pads. The inner (piston facing) are 0.627" total thickness from where it rides on the piston to the surface that rides on the rotor. I checked edges, etc and found very little deviation in both the driver and p***enger sides. I repeated the same for the outer pads and both measure 0.537' total with no irregularity or funny corners/edges.

Next I looked at the ****py speedway organic pads that I didn't use since they had chunks missing. These measure 0.576" total thickness for inner pad, and 0.519" thickness for outer pad. The pads I got may just be a little too thick, they are Napa ultra premium semi-metallic. 0.070" difference between Speedway and Napa pads when inner and outer difference is totaled.

I still can't explain two things:
1. Why the p***enger side has a little gap still when I put the pads/calipers on but not the driver side. This is without the caliper brackets on. I'm not sure if maybe the driver side piston doesn't go in as far, an irregular caliper, or irregular rotor.

2. Why I get a funny space on the bottom of the outer pad (driver side) but not on the top as I showed in the photos above. Maybe a piston closes in uneven or the caliper bracket is off from manufacturing.

I could reduce the thickness of the pads and call it a day if I ignore points 1 and 2. Anyone have thoughts? I will measure the rotor thickness on both sides when I get home. I didn't have a chance to measure the caliper mounted to the bracket without pads yet.

 

Why don't you take those ****py pads and mount them up and see if
that changes anything, might just be the Napa pads are wonky.

 

I just measured the distance between the caliper bracket to the rotor at the bottom and top with the bolts tightened.
For the p***enger side I get 0.630" top 0.650" bottom. Note 0.020" difference
For the driver side I get 0.652" top 0.656" bottom.

Both Rotors measure 1.05" thick and do not seem warped.

Next I measured the caliper piston surface to outside edge (I couldn't measure the inside geometry with my digital calipers).
For the p***enger side I get 2.39"
For the driver side I get 2.43"

My conclusions: I don't think the caliper bracket is causing the issue on the driver side unless the caliper pin bolt holes were tapped at an angle or if the top is supposed to have a difference like on the p***enger side (difference of 0.020" but I may need to measure again to double check)). I would think the caliper bracket should be parallel to the rotor. I also don't see the bracket flaring out or looking warped. The threaded holes look perpendicular to the surface they were drilled into.

The piston on the p***enger side is further in than the driver side by 0.040". That could be the difference between spinning the p***enger side but not driver side. I had already cracked the bleed valve open and used a c-clamp to push the piston in on the driver side caliper but this is where it returns to.

Perhaps the slots and grooves for the outer pad in the caliper are not produced accurately and the brake pad sits in it funny and the gap is created on bottom but not the top. Hmmm.....

 

Thanks. I ran out of time but I will try that next. I already know they will fit on there and the rotor will spin since they are a little less thick. I think that will only allow me to see if the gap is parallel or if I have a difference between the bottom and top of the pad like I had shown above.

 

Those caliper brackets are just 3/8 flat plate correct? They appear to be Plasma or flame cut.

They could be slightly tweaked or a small amount of filing on the spindle to square up the mounts to the rotor

 

Thanks. Yep they appear to be 3/8" material. The p***enger side is not perfectly parallel to the rotor (0.020" off from the distance measured at the top and bottom), however that side isn't giving any trouble with spinning the wheel.

The driver side which is giving the problem looks very parallel with distance measurement from bracket to rotor.. 0.652" top 0.656" bottom.

Maybe the driver side piston doesn't go in as far and since it's being jammed a little maybe it forces the pad to sit at an angle. I can try the ****py speedway brake pads which are thinner and see if they sit parallel when not jammed in. Also it doesn't take a tremendous amount of force to get everything together. The rotor spins but I have to use a little bit of force but as you said, that could overheat the rotor.

 

Ok so this morning I put the ****py organic Speedway pads on the driver side caliper. The rotor definitely spins. The inner pad sits flush but there is a gap on the outer pad during this check. I didn't notice any uneven gap on the top and bottom of the pad but this was a check done by eye and no measurements made. Here are some photos:



Here are some photos of the organic pads that had chunks missing and hence I had bought the ultra premium semi-metallic pads from Napa.



At this point I could do the following:

1. Put the semi-metallic pads on again and inspect further to see what causes the outer pad to be flush at the top but have a gap on the bottom. Maybe the caliper bracket flexes or the grooves in the caliper for the outer pads have issues.

2. File the semi-metallics down and check to see if the pad is flush on the top and bottom when someone steps on the pedal and call it a done deal. Maybe the uneven gap is created because the piston is already all the way in when the caliper pin bolts and caliper bracket are being tightened up.

I could also use the Speedway pads but the fact they have chunks missing made me think they are low quality. Does anyone agree? I don't know that Napa would take the semi-metallic pads back if I cleaned them up and told them they didn't fit my application.

 

have you considered that speedway may have those pads cut down to fit your application and thats how they got chewed up?
you are using parts from different cars to make up that kit, it could be the speedway pads give you the clearance needed
in any case the pad needs to be in the same plane as the rotor when brakes are applied or the pads will wear at an angle and start dragging as they wear