Rear Brake Problems

[cv2065]

Hey all. Just about at my wits end with these rear brakes. I thought it was the MC, as did FFR, so received a new one, installed it and have the same issue. So here’s what I know:

1. These are the stock Mustang calipers that come with the kit (Not Wilwoods)
2. Front brakes work great. Rears are not engaging enough to stop the rotor from turning by hand.
3. I’ve bench bled the MCs and pressure bled the lines multiple times. Both appear to be air free.
4. Rear MC collapses before the front MC when brake pedal is pushed with bar set in middle. Front MC is stiff with little movement when brake pedal is pushed. Same thing happens no matter where bias bar is set. Currently in middle. This is exactly what happened with old MC
5. Brake pedal is moderately spongy. Not hard, but not falling to the floor.
6. I tested new MC with finger over connection fitting and system is building pressure. Rubber gasket in reservoir also builds pressure.
7. I can hear something going on with the piston on passenger side caliper when brake pedal is pushed, but zero activity on the drivers side caliper.

Thoughts?

[TexasAviator]

Have you vacuumed the rears through the bleed ports on the rear calipers?

[Norm B]

Have you adjusted the rear callipers by repeatedly applying the parking brake? The rear callipers have an internal screw type adjusting mechanism. They self tighten with repeated applications of the parking brake.

HTH

Norm

[Fixit]

Couple of things to check/re-check:
- Ensure the caliper pistons aren't "jammed" on the internal adjuster mechanism... or, tightened all the way down/in tight.
- Check that the pistons are "clocked" to the pads. The nubs on the pads should register in the slots on the pistons.
- After the above, Actuate the E-brake lever (at the caliper) as far as possible about 30 times per side (yeah, 30)... this should take out any freeplay
- Is the fluid level in the reservoir the highest point of the system?

From your description it sounds like you're air-bound on the MC.
For S&G's, can you temporarily rig the rear MC reservoir on an "IV stand"... meaning get it at least a foot above the cylinder? Then you'll know for sure there's not some errant air bubble/pocket giving you grief.
With the reservoir way up high, you can then gravity, pressure, vacuum, or age-old pedal "pump it up" bleed the system (again...arhg).

[rich grsc]

Have you adjusted the rear callipers by repeatedly applying the parking brake? The rear callipers have an internal screw type adjusting mechanism. They self tighten with repeated applications of the parking brake.

HTH

Norm

This is my exact thought too.

[cv2065]

Thanks for the replies.

"Have you vacuumed the rears through the bleed ports on the rear calipers?"
I have not done this. Thought I'd stick with one form of bleeding, which is pressure. I can do another way (pedal push, gravity, or vacuum), but wanted to keep that a constant for right now.

"Have you adjusted the rear callipers by repeatedly applying the parking brake? The rear callipers have an internal screw type adjusting mechanism. They self tighten with repeated applications of the parking brake"
After reading one of Craig's posts a while back, I did actuate the parking brake about 15-20 times, but I didn't see any change to braking. I will tell you that the e-brake seems to be working as it should. I can definitely try this again, as I need to tighten it up a bit so full engagement is around the first 30-40% of the range. Right now, it falls in 80-90%.

"Check that the pistons are "clocked" to the pads. The nubs on the pads should register in the slots on the pistons"
I'll have to check this. Does this apply to all pads for these calipers? The pads looked all the same when I installed them and didn't see any pins, but I'll definitely be checking these again. Would this help address the MC issue as well?

"Is the fluid level in the reservoir the highest point of the system?"
Reservoir levels are well above the MC's (5-10 degrees)

"Ensure the caliper pistons aren't "jammed" on the internal adjuster mechanism... or, tightened all the way down/in tight."
Not sure about this one. If the pistons are too tight, whats the best way to get them to move?


Thanks for all the replies. Those are a few things I'll check tonight.

[scottiec]

This suggestion is not meant to be insulting - I made this mistake before. Do you have them on the correct sides so that the bleeder is pointed upwards?

[Norm B]

If your brake pads don’t have the pins to stop the piston from rotating then you won’t be able to get the calipers to adjust with the parking brake. Without the calipers properly adjusted the pistons will have to travel more. This requires more fluid from the master cylinder. Making it seem like a master cylinder or a bleeding issue.

Norm

[cv2065]

This suggestion is not meant to be insulting - I made this mistake before. Do you have them on the correct sides so that the bleeder is pointed upwards?

Not insulting at all Scotti...Yes, the calipers are on the correct sides with the bleeder pointed up. I saw that if you don't have them positioned on the correct side, the e-brake cable cannot be installed correctly.

[cv2065]

If your brake pads don’t have the pins to stop the piston from rotating then you won’t be able to get the calipers to adjust with the parking brake. Without the calipers properly adjusted the pistons will have to travel more. This requires more fluid from the master cylinder. Making it seem like a master cylinder or a bleeding issue.

Norm

Thanks Norm. This is what I need to check today, as I don't recall seeing any pins on the pads. These are the same StopTech pads that get sent with the kit.

[cv2065]

Hey guys. Was just reviewing the FFR instruction sheet for IRS 13" Brakes and all it says is to "Insert pads into the caliper" with no mention of pins. I just spoke with FFR and they are telling me that the rears have no pins to align up to?



Also, I spoke with Wilwood, and they are saying that they don't think a 5/8" MC for the rear is enough to move the correct amount of volume. I said that FFR sells a ton of these kits and if that were an issue, I'm sure it would be corrected by now. Spoke to FFR and they said the same thing. Tech from FFR wants to start at the beginning with trial and error by plugging off the MC to see if it builds pressure at the pedal. Have a plug on order...

[Fixit]

Don't quote me, but most of the rear disc setups I've seen (that use the mechanical E-brake) have the nubs/pins on the pad insert, and either a dedicated notch/slot in the piston, or the pad registers into the slot you'd use to crank the piston back inward.
Now it throw a monkey in the wrench... sometimes a bean-counter gets involved, and says "we can save .03 per backing plate by not putting pins on 1/2 of a set". Read this as you may have two inboard, and two outboard pads. The inboards (piston side) have pins, the outboards do not - and they don't mention this. It was up to you to pay attention removing the old pads on disassembly... which you're not doing as it's a new install.

"Pistons Jammed" - Make sure the pistons aren't cranked all the way in/down hard against the mechanical limit of the assembly. Crank them in until they (gently) stop, then back them out whatever's needed to clock them to the pads.

Bleeding method... there's no "one" method that's a sure thing for every install, and especially on a brand new totally dry system. It is surprising the amount of fluid that's needed to fill a bunch of 1/8" lines. The secret is to go at nearly a glacial pace. Trapped air will get forced and hide into the smallest void, and become a spring.
A few tips that have served me well:
- give the bleeder screw threads a liberal coating of chassis grease. It's amazing how much air can be sucked/pulled around the threads.
- when the lines are under pressure or vacuum, give them a smack with a screwdriver handle. Dislodge any bubbles/air pockets.
- on a dry system I'll pull at least a quart of fluid through each leg. Just keep transferring it back into the reservoir.

Hope this helps!

[TexasAviator]

I hope you were able to work on the car some, Mondays are horrible with school and family stuff to do. If you get a chance, pull a vacuum (I literally used a shop vac and a piece of rubber hose) to bleed air into a little cheap reservoir from the auto parts store. It pulled out tons of air and it took a long time. I feel you are not going to get a good bleed from the pedal pump alone. Good luck, with all the great help here I am sure you will get it figured out.

Brandon

[cv2065]

I hope you were able to work on the car some, Mondays are horrible with school and family stuff to do. If you get a chance, pull a vacuum (I literally used a shop vac and a piece of rubber hose) to bleed air into a little cheap reservoir from the auto parts store. It pulled out tons of air and it took a long time. I feel you are not going to get a good bleed from the pedal pump alone. Good luck, with all the great help here I am sure you will get it figured out.

Brandon

Thanks John/Brandon! Ran into a little snag. I was adjusting the tension screw on the e brake spring and the head snapped off. Strange as I was barely turning it. Now I need to replace the top half of the caliper. Good thing the parts are relatively inexpensive. Should have one by Wednesday and I’ll report back as soon as it’s painted and installed.

[CraigS]

Can you provide a picture of one of your rear calipers please? I just want to make sure we are thinking of the correct part because the local guys I know w/ MkIVs all have different calipers due to IRS etc. Here is a pic of the common caliper where you can see the notch in the piston
Rear caliper by craig stuard, on Flickr
There is a small stub on the back of the pad that must fit into the notch. What happens is that, as you pull the park brake, an internal threaded rod screws out of the back side of the piston pushing it out against the pad and tightening it's fit to the rotor. If the piston spins because the notch isn't engaged by the pin, then the adjustment doesn't happen. Also, the pad is in the caliper at an angle since it is sitting against the top of the pin rather than the pin fitting into the notch.

[RJD]

Hey all. Just about at my wits end with these rear brakes. I thought it was the MC, as did FFR, so received a new one, installed it and have the same issue.

Don't rule out that it's not another bad MC. I had a bad one right out of the box. Perhaps there's a quality control issue at the manufacturer causing a bad batch.

[cv2065]

Can you provide a picture of one of your rear calipers please? I just want to make sure we are thinking of the correct part because the local guys I know w/ MkIVs all have different calipers due to IRS etc. Here is a pic of the common caliper where you can see the notch in the piston
Rear caliper by craig stuard, on Flickr
There is a small stub on the back of the pad that must fit into the notch. What happens is that, as you pull the park brake, an internal threaded rod screws out of the back side of the piston pushing it out against the pad and tightening it's fit to the rotor. If the piston spins because the notch isn't engaged by the pin, then the adjustment doesn't happen. Also, the pad is in the caliper at an angle since it is sitting against the top of the pin rather than the pin fitting into the notch.

That’s exactly the one I have Craig and the pad does indeed have a pin that fits into that groove and it was aligned properly. The manual leaves that out so probably why I missed it. Interesting that FFR tech didn’t know about it either.

[Boydster]

Can you confirm that the parking brake is locking up the wheel? I looked over your posts and didnt see that anywhere. Perhaps a caliper issue. Just trying to help... I dont have this setup.

[cv2065]

Can you confirm that the parking brake is locking up the wheel? I looked over your posts and didnt see that anywhere. Perhaps a caliper issue. Just trying to help... I dont have this setup.

Hey Boyd. Yes, the e brake was seizing up the rotor when pulled. Just needed to adjust the range a bit.

[rich grsc]

Bleed the brakes with the parking brake engaged.

[Norm B]

In addition to the advice above try repeatedly applying the park brake with the brakes applied. I don't know why or how but this seems to do the trick occasionally.

[cv2065]

Thanks Rich and Norm. As soon as I get this caliper reinstalled, I’ll give it a go. I’m sure we’ll get this worked out in short order. Ned to get my tires on and engine installed!