Hello guys!

Quote: "I’m willing to bet that 80% of the 914’s on the road have inoperative rear calipers."

Is that true?

Well, I've been in the 80% league lately with some struggles adjusting the rear brake calipers. I found they're almost locked hard on the rotors. I first noticed this from a bad gas mileage. The calipers are from PMB so they must be perfect. I just don't get the adjustment right or something else might be wrong.

What's happening is after I set the venting clearances at our favorite spec, it feels great only for the 1st few runs. After that it just gets tighter. It's as tight as you can't turn the rotors by hand. Emergency brake handle's range of movement gets smaller too.

The result of my 2nd try seems to be better than the 1st but I've already noticed the venting clearance's gotten smaller than yesterday.

The rubber brake hoses are not more than 3 years old and the fluid is just bled but the MC might be more than 20 years old.

I will check on the MC push rod to see if it's out of adjustment.

What do you all think?

Thanks in advance,

kkid

If the push rod is out of adjustment the front brakes would be the first to drag. Is it possible the ebrake cables are sticking and holding the pads slightly engaged?

Hey zambezi, you're right!
I will raise the front to see if they're draggin' too.

As for the rears, the pads are still tight on the rotor even after the cable is disconnected. Cables(e-brake handle) are very loose in the beginning then it gets tighter and tighter. But I still have about 8 clicks total in the motion range.

Where do the cables drag at normally???

If the cables are old and rusty inside, you can apply the e-brake and when you release the e-brake, the cable will not return because of the internal rust and it will keep the brakes applied. It doesn't sound like that is your case though because yours are still dragging even with the cables disconnected.

Just got back from my garage. The front rotor turns freely.
So I guess my MC is still good.

I don't think I have fresh rotors though. I bought them used from one of a member here cheap and have them turned within the spec prior to the installation. I see they aren't really true.

How about the brake proportioning valve? How does it fail?

Check if your rotors are warped. I had a similar thing happen on one of my motorcycles years ago, the rear rotor was warped and it acted as if you were pumping up the brakes until the rear brake would lock. I would crack the bleeder and release the pressure and I could go a couple more miles. replaced the warped rotor and that fixed it.
Maybe not the same thing but something to look at.

edit: I see you said you checked the rotors.

Hey Olympic,

I see the pads are touching the rotors unevenly. Does this mean I have warped rotors? So they must have overheated at some point then.

BTW, I have seen an Olympic Blue 914 somewhere near Giant Eagle on the Shady Ave awhile ago. Is that yours?

I will check onto my rotors again,

Thanks,

kkid

Do the pads float in the calipers or are they jammed in there? First thing I do with any disc brake job is make sure that the pads fit in the caliper with little resistance. If they don't, I buzz the edges with an angle die grinder.

I've had customers bring me their vehicles with a brake job less than 10k miles on it and pads worn down to metal because the ignorant mechanic forced pads into the caliper with a hammer. The root cause being that manufacturers foreign and domestic aren't doing dimensional checks of the mass produced backing plates. Stamping dies get out of tolerance which results in oversized, out of spec parts.

**rant on** The typical production minded shop wants vehicles in and out in a certain amount of time to make top dollar. The typical customer doesn't know any better returning to have their brakes replaced. It's a money making machine. **rant off**

Thanks for the heads-up, tomeric914.

Since the rotors are out of spec(too thin and warped), I installed new rotors and pads. Took the calipers off the trailing arms and cleaned well then checked the pads if they're not sticking in the calipers. I smoothed out the pads to not get jammed. Then adjusted the clearance at 0.008" .

So the car is still on the jack stands and has not seen the roads since. Because the venting clearance still gets tighter as I keep pumping the brake pedal.
Click to view attachment

Strange!!

Is there anything wrong with the MC? Front tire rotates freely when the rears are locked. Could MC only work properly on the front but not on the rears?

Just bled the fluid and it has newer rubber lines so all I can think of is a bad MC or a crazy proportioning valve.

What do you all think?

Thanks in advance,

kkid

I've yet to dive into the rear brakes. Does the e-brake act on the caliper? Could this be the cause of the dragging?

I have a Vette and the rear brake actually has a drum brake inside the disk for the e-brake.

The venting clearance should be eliminated when you step on the brake pedal. Here is a tip I got from The Cap'n a while back: remove the two Phillips screws that hold the rotor to the mounting flange. Put a few of the lug nuts on and tighten them down so the rotor is tight on the flange. Then put the phillips screws back on. Adjust the outer to .004", then the inner. Yes .004"

"Yes, .004" "

That's right. Adjust the clearance with the rotor clamped down to the hub with the lug bolts, and turn the rotor to find the high spots while dragging the feeler gauge. Lock the adjusters as appropriate and recheck it. Make sure the pads move freely in the calipers.

The Cap'n

Thanks for the tip, kreiger and capt'n!!

Off to my garage now.

kkid

OK, so I put 2 lug nuts on the rotor then set the clearance at .004". Got in the car and pumped the pedal 10 times, then 20, finally 30 times and checked the venting clearance every 10 counts. I was not able to insert the feeler gauge when I counted 20.

The fronts are fine. The car still has the proportioning valve that I've never touched before.

There is a concern about my MC though. It is missing a dust cover at the pedal side. Wondering if it is sticking with some dirt in it. But again, the front calipers seem to be working without a drag.

Any thoughts would be appreciated.

Happy Holidays!

kkid

Where's Eric?

OK, a little update here!

So no matter how many times and how hard I adjust the venting clearances, it just gets tighter as I pump. I am tired of adjusting it forever.

Next, I removed the floor board and checked the push rod clearance that goes on the MC. It's a little rod into the dark hole that I barely see so I just backed it off a little further and tired to pump the pedal but brakes are still tight.

Next I took the front wheels off to double check if they're tight.
Yep, they're both tight especially the driver side is as tight as rear calipers and passenger side is fairly tight as well. I don't know why the front R/L are not equally tight though.

Anyways, I now assume the MC is bad.

Does any body know how to test to see if the MC is bad?

Thanks in advance,

kkid

with the car in the air, pump up the brakes and see if all is still tight. If they are tight like thay have been, then quickly crack a bleeder screw at each wheel (one at a time) and see if that wheel now becomes easier to turn. If not then the problem lies right there at that caliper (do the same to check each caliper). If the wheel is easier to turn then you have to find where in the system it is holding pressure. Either the rubber hoses or the master cylinder (if the return port is plugged). The master cylinders can be pulled apart and cleaned or just replace it.

Thanks Zambezi for the idea! I will give it a try tomorrow.

can't wait to see the result!

kkid