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A Brake in the Weather · 19 April 06
Good news! I’ve pretty much wrapped up the brake work on Eve. Yes, that means no more bad puns…at least about brakes.
This photo isn’t actually of Eve’s front disc brakes, but of our old VW Golf. The Golf is due for inspection but the front brakes have been pretty noisy so I figured I’d work on them while working on Eve’s brakes. Good thing I checked, the front rotors and pads were in pretty bad shape.
New England really needs to come up with a road de-icer that doesn’t eat cars…
That looks much better!
I’ve never worked on this car’s brakes before and was surprised at how easy it was. Once you get the wheel off the rotor is only only held on by a single screw (and the brake assembly).
The brakes are held on by two allen-headed bolts, nicely enclosed in rubber boots. Anyone who’s whacked the crap out of their knuckles and tools trying to free rusted bolts would certainly appreciate how nice these were to take off.
Bonus points for not having to mess with the bearings. Wish I could say the same for Eve.
While I was poking around I took this picture of the ABS sensor. The sensor is a little magnetic pick-up assembly positioned right next to a slotted steel plate mounted behind the rotor. The plate spins with the wheel, while the sensor sits in one place “watching” the world go by…
The ABS computer most likely gets regular pulses as the wheel spins which it turns into an RPM for each wheel. Should one of the wheels start sliding on ice, essentially zero RPM or much smaller RPM than the other wheels, the ABS computer can shut off the hydraulic pressure for that wheel until it starts spinning again.
Anyway, enough of that ol’ car, let’s get back to Eve.
Since I have an electric vacuum pump and plan to keep the vacuum assist braking I decided to examine and clean the vacuum booster.
First off it was obvious that the old master cylinder was leaking and for some reason the booster was rusting (you can see a pre-cleaning photo here). This is what they call foreshadowing.
As you can see I took it apart. Click the images for larger views. The right side shows the rod that the brake pedal pushes against. I’ve pulled off the rubber seal and the “filter” material. When you push the brakes the vacuum inside the booster sucks in air from this side. It’s essentially helping pull the brake pedal and making it easier on your foot.
On the other side of the booster, between it and the master cylinder, is a pusher rod. It goes through a flat rubber washer (shown in the front) and pushes/compresses the hydraulic fluid in the master cylinder.
The flat, thick disk area goes into a notch that is on the working end of the other rod. This way it can push without going too far off center or slipping.
I’m not quite done with the booster though. It has been painted, everything put back into place, but there’s a small vacuum leak around the seal. Maybe these seals aren’t really meant to be messed with?
Remember what I was saying about foreshadowing? I’m kind of wondering if the last owner didn’t get some water in the brake oil by accident or something.
This is the rear drum brake hydraulic wheel cylinder. When I popped off the rubber boots to inspect them I was surprised to find an oily, rusty mixture oozing out.
This is what a brand new set looks like. Nice. Well, they ought to be, probably the costliest part of the bunch.
I had been holding off on buying the rear brake parts for a while. After reading an article on replacing the entire rear drum brake assembly with disc brakes (from another Probe model) and seeing the shape of these I thought maybe I might just go the rear disc route. Calls to local junkyards came up empty, one old fella saaying, “Sure, had about 20 of them…last year. I crushed ‘em all!”
Rear drums it is…
Here’s the whole assembly put back together. Before I finish off the back-end completely I need to pick up new bearings and find someone to press them.
An EV is all about optimization and low rolling resistance is one of the big ones. One of the guys mentioned in the comments a while back that his EV was using more current on flat stretches than he thought it should. Turned out to be his brakes being stiff and not fully releasing when he let off on the pedal. While I’ve got Eve up on stands and all taken apart I figure I fix up whatever I can.
The front brake calipers weren’t as rusty as the rear, but they were pretty worn so I decided to replace them as well.
This photo, in case you are curious, is the little piston inside of the front caliper. Hydraulic oil pushes against the flat surface which in turn pushes and therefore squeezes the brake pads together. There’s a piston seal gasket inside the caliper and a rubber dust cover boot around the outer edge snapped onto the groove on the piston to keep hydraulics in and dirt and water out.
Unfortunately while putting the new assembly on the left front I noticed that the rotor assembly had play in it. Checked the right side, no play. The manual shows this elaborate measuring setup to precisely measure the amount of play allowed before the bearings need to be replaced. Suffice to say even the most insensitive among us could easily tell the bearings are shot.
Brakes are done, bearings are next. Back to the parts store.