A Car Talk skeptic is converted

The Show
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Dear Tom and Ray,

I’m writing to tell you about my friend, a retired machinist and lifelong gearhead who didn’t think much of your show…until today.

But first, a little background. Last Saturday morning we were on a long drive together. When 11:00 rolled around, I tuned in faithfully, as I do every weekend. My friend began to disparage your show as lacking any useful information, but I defended you staunchly, and maintained that I had learned many useful things from your show over the years. When it came time for the puzzler, the puzzle was about a Land Rover (or some such vechicle) in Africa (or some such remote place) from which one of the brake calipers had fallen off. The bolts were missing, and thus the caliper could not be reattached. As I recall it, the problem was solved by a local native and a shoestring. Aha! I said to my friend. I bet that native clamped that brake assembly around a suspension part, such as a tie rod end, and tied it in place with the shoelace. Clamping the brake around a suspension part would prevent the caliper from falling out, and would provide the resistance necessary to allow the other brakes to function normally. My gearhead friend agreed that, yes, that’s probably what the native did, and he had to admit, that was a pretty clever solution to a serious problem.

Now, fast forward to today, as I helped my friend try to replace the brake pads on one of his rear wheels. When we got the brake caliper off, we were unable to push the piston back into its cylinder. It wouldn’t budge. No amount of force we could apply would budge the piston, and therefore we could not install the new brake pads. The dilemma was further compounded by the fact that the old brake pads were so worn that they had been chewing up the rotor. Therefore we did not want to install the old pads and put the caliper back on the wheel as it had been before. But we couldn’t just leave the brake caliper hanging there until my friend could buy a new caliper and complete the repair.

Or, could we!!! In a flash, we remembered the native man with the shoelace. Aha!..we said, let’s jam a pair of brake pads into the caliper to keep the piston from falling out, and tie the caliper onto the rear suspension. We found that one new brake pad plus one old worn one were the perfect thickness combined to jam into the brake caliper, which we accomplished with the aid of a hammer. And with some zip ties from my tool bag, we wired the caliper firmly onto the rear stabilizer (at least, that’s what I think it was!).

Now, granted, our solution was not EXACTLY the same as the native man’s. We used zip ties instead of our shoelaces, and we used a couple of brake pads to jam into the caliper, instead of clamping it directly onto a suspension component.

Nevertheless, my friend and formed Car Talk skeptic was forced to admit that HE ACTUALLY LEARNED SOMETHING USEFUL from your show, and I will never again be forced to tolerate another one of his anti-Car Talk rants, ever again!!!

Appreciatively,
Jesse S.
Norwood, MA

PS—attached is a cell phone picture of our makeshift repair, to prove that we actually did it!

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This isn’t a forum for Tom and Ray. It’s other car enthusiasts some amateur and some professional.

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Hi Mike, thanks I know. I emailed Tom and Ray directly, too. But their contact info suggests posting emails to them in the discussion forum, too for other people to enjoy (or not :-0)

Plus, I’m hoping that a little exposure on the forum might get my letter noticed by the staff and read on air. Or not.

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Funny how things happen like that. Was the caliper jammed, or was it one of those that has to be retracted by rotating something back in?

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Good Lord!
For anyone reading this…please don’t emulate this approach. Thhe brake line could easily have overstressed at one of its connections as the wheel moved up and down in its travels and the OP could have lost half his brake system in one big puddle. Call a towtruck. Or hitch a ride to the part store.

To the OP, I’m glad you lived to tell about it.

By the way, when you were trying to push the caliper piston back, did you have the bleeder opened? Does this system have ABS?

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That’s a spin-back caliper. No amount of force with a C-clamp or anything else will compress that piston. You needed one of these, and everything would have been okay: http://www.harborfreight.com/four-wheel-disc-brake-piston-tool-95713.html

Also available at any auto parts store. Too bad you apparently bought a new caliper over this…

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Man oh man, the advise you get on Car Talk!!

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mark907 — "That's a spin-back caliper. No amount of force with a C-clamp or anything else will compress that piston. You needed one of these ..."
... or one of these.
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That works, too, Mechaniker. Improvisation is good and can save money and frustration. I still have a tool I made years ago out of an exhaust hanger that is very useful for removing and installing brake shoes on older Ford trucks with the Dana 60 rear end.

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I’m just happy to hear that zip ties may serve a purpose. I might use them when a shoelace breaks.

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mark9207 — "Improvisation is good and can save money and frustration. I still have a tool I made years ago out of an exhaust hanger that is very useful for removing and installing brake shoes on older Ford trucks with the Dana 60 rear end."
Saving money is GOOD. A tool for installing brake shoes made from an old exhaust hanger? You must be the king of improvisers.
FWIW, the "screw"† type brake piston is used in rear brakes where the parking brake is mechanically applied through the piston to the pad. In essence, the brake piston can be pushed against the pad either by hydraulic pressure (normal operation) or by a rod that is pushed toward the inboard surface of the piston when the rod is actuated by the parking brake cable. Unless an adjusting mechanism is used between the rod and the piston, as the brake piston slowly moves outward in the normal course of pad wear, the distance the rod must travel to press against the piston would increase, thereby causing greater and greater slack in the application of the parking brake. To keep the parking brake from becoming too slack over time, a device similar in purpose to the threaded star-wheel used in drum brakes is required.

In a disc parking brake, the parking brake rod does not actually push against the inner face of the piston, but rather is threaded into a sleeve nut which, in turn, pushes against the inside of the piston. The threaded rod does not rotate, but only moves toward or away from the piston as the parking brake is applied or released. The sleeve nut, on the other hand, is allowed to turn in one direction only (like the brake drum star-wheel), outward as the pad wears by a clutch spring anchored in the piston. This outward movement of the sleeve nut along the parking brake rod effectively increases the length of the parking brake rod and takes up the slack in the parking brake mechanism as the pad wears.

To push the piston back for pad renewal, the piston (which anchors the clutch spring) must be rotated to rotate the sleeve nut back along the parking brake rod.

There may be better explanations on google, but I have not found any. The following diagram comes from a Lexus technical manual.

Note †: The piston itself does not rotate in braking — there are no threads on the piston itself. However the piston must be rotated when pushing it back into the caliper because it needs to move the threaded sleeve nut, to which it is attached by the clutch spring, back along the parking brake rod (or bolt). Just wanted to make that clear.

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To add to Mechaniker’s explanation as to how this type of caliper works, this is also why the parking brake should be actuated repeatedly once the new pads are installed. I’m honestly not sure if this is necessarily a requirement to servicing these calipers, but it always gave me peace of mind in the work and seemed to give better pedal feel once the job was done if this was part of the job. I would usually just actuate the lever at the calipers individually until the caliper would cause the pads to grip the rotor rather than use the parking brake lever or pedal.

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The hold down spring tool I mentioned that I made from an exhaust hanger was made from a hanger like that shown below. I cut off the short end of the hook to make it shaped more like an “L” and welded the piece I cut off about 5/8" below the short end of the “L” to make a tool to deal with the hold down springs on those Dana brakes. Stick the bottom of the “L” into the rolled part of the spring and use the welded on nub to push the spring towards the backing plate and hook it into the hold down pins. Here is a link showing the Dana brakes I am referring to. http://www.boyandjeep.com/wp-content/uploads/2008/11/d60-drums-27.jpg In this image, the installer is using a C clamp and screwdriver to do the job of my little exhaust hanger tool.

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mark9207 — "The hold down spring tool I mentioned that I made from an exhaust hanger was made from a hanger like that shown below above. I cut off the short end ..."
Now I understand what you did. That was clever.
Rear drum brakes on front-wheel drive cars are non-servo; they lack the center anchor pin that causes the rearward facing brake shoe to "wrap into" the drum to increase brake pressure when the brakes are applied. (The forward facing shoe also wraps into the drum to some extent on servo brakes.) Non-servo brakes, lacking a center anchor pin, apply less brake pressure than servo brakes, as is required by front-wheel drive cars with their lighter rear-ends.† But the difference in spring arrangement between servo and non-servo brakes makes most of the older spring removal/installation tools obsolete.

I have a curious-looking brake spring tool sold by Honda for use on their non-servo rear drum brakes. It consists of a T-handle at the bottom of which is a small “foot” about an inch long with three “toes.” Projecting from the bottom of the heel is a small nubbin of a rod about 3/16" long and 1/8" in diameter.

When the tool is used for brake spring removal or installation, the nubbin below the heel is inserted into a hole in the brake shoe, the spring loop is positioned between the big center toe and one of the two side toes (which side toe depends upon whether the left or right wheel is being worked on), the tool is rotated in the hole using the T-handle, and the spring easily pops out or in.

I know the main brake spring can be removed and replaced with more conventional tools, but the Honda spring tool makes the job faster and less dangerous. I had a friend who almost lost an eye when the screwdriver he was using to stretch a brake spring slipped out of his hand and flipped backwards into his forehead. He went to a hospital emergency room where he required multiple stitches just above his eye socket.

I have retired the Honda spring tool to a curio case in my living room, where it sits with no written explanation of its purpose. When I eventually buy the farm and my wife does the inevitable estate sale, I’d like some folks to be scratching their heads and guessing what it is.

Nice corresponding with you, Mark.

Note †: I’m also aware of the different sized front and rear pistons in the master cylinder, for anyone who finds nits to pick.

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I agree with all who expressed horror about this approach, and I will no longer ride in my friend’s car until he gets the brakes fixed. He has an admirable sense of thrift and ingenuity when it comes to (not) repairing his cars, and he has owned a series of remarkable junkboxes, none of which I was thrilled about riding in, but this was the last straw. I was pleased that the above brake repair forced him to acknowledge that he actually did learn something from Car Talk, but I agree that what we actually did was not safe. It was supposed to be a VERY temporary fix just so he could get the car to the shop, and until he does, I won’t touch it with a yardstick.