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Discussion Starter #1
2017 Bolt, 67000 miles, garaged in Maine. I just had it in to my mechanic for a new set of summer tires and the annual state "safety" inspection. He mentioned the rear pads were getting a bit low. I wondered aloud about it and he said the Prius's that he's seen tend to wear out the rears. He said they didn't need replacement right away though.

Yesterday my wife said one of the rears was hot and was acting strange. She drives the Bolt most days. This morning I left I jacked up the right rear and spun the tire. The pads rubbed just a little, but not much. There was plenty of pad though. I was confused, took a picture, and put the wheel back on. I drove to work in D and did a few N stops. When I got to work (about 12 miles) I touched all four wheels. They were cool, rotors were a little warm, but all the same.

On the way home I did the same, and when I got into the garage I felt the wheels and the left rear was quite warm. I jacked it up, pulled the wheel, and that side has zero pad left.

Anyone seen this before?

20200824_202239.jpg 20200824_080526.jpg
 

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Brand new Bolt, same issue!

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What efficiency (miles per kWh) were you getting? If you are seeing a change, it may be an indicator.
 

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Was the car mainly driven in L?
Just curious if actually we should consider driving in D from time to time...

All smaller cars are prone to rear calipers binding/rusting.
 
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Was the car mainly driven in L?
Just curious if actually we should consider driving in D from time to time...
The Bolt can regen just as much in D mode as in L, so D vs L won't make any difference unless you press the brake pedal so hard that it exceeds the car's regen capability. In other words, if you decelerate more rapidly than L mode with the regen paddle would give you.

That's stronger braking than you'd normally need in day to day use, so either way you'd want to do some extreme braking maybe once a month to make sure you're actually engaging the hydraulic brakes. Or put the car in N so that the brake pedal uses JUST the hydraulic brakes.
 

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The Bolt can regen just as much in D mode as in L,
I thought I had seen some actual braking tests for the Bolt using all possible combinations, but this is all I could find.


"Using the brakes, the Bolt will stop from 60 mph in 128 feet. Using only Low mode, it stops from 60 mph in 665 feet. Using both Low mode and the regen on-demand paddle, it stops from 60 mph in 528 feet."
 

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Discussion Starter #8
What efficiency (miles per kWh) were you getting? If you are seeing a change, it may be an indicator.
Hard to say. I don't personally drive it most days. I sort of looked on the infotainment system the last day I drove it but I remember not seeing anything that felt helpful. Both rear wheels and calipers are off it now so I can't check again. Boltstat unfortunately doesn't have efficiency data. my.chevrolet.com is clearly broken and useless:

Last 7 Days1 Kwh/100 mi (yesterday was 5 Kwh/100 mi)
Last 30 Days13 Kwh/100 mi
Last 12 Months734 Kwh/100 mi
Lifetime20 Kwh/100 mi


I'm also wondering if application/release of the e-brake (or lack of use) could cause something like this?
This morning before I pulled the calipers I applied the e-brake and confirmed both wheels were locked. When I released it, the "bad" side brakes were still pretty tight but I could now budge the wheel by hand. I did not try to manually unscrew the parking brake actuator on the caliper after I removed the parking brake motor.

The EPB does get some occasional use. The fact that the car sometimes engages it automatically (on steep inclines) contributes as well.

The Bolt can regen just as much in D mode as in L, so D vs L won't make any difference unless you press the brake pedal so hard that it exceeds the car's regen capability. In other words, if you decelerate more rapidly than L mode with the regen paddle would give you.

That's stronger braking than you'd normally need in day to day use, so either way you'd want to do some extreme braking maybe once a month to make sure you're actually engaging the hydraulic brakes. Or put the car in N so that the brake pedal uses JUST the hydraulic brakes.
Yes, mainly driven in L. The friction brakes don't get a lot of use.

I haven't read conclusive discussion either way as to if driving in reverse is ALWAYS friction braking or not, nor have I tried to determine this for myself yet. But backing out of the garage I've always thought I felt the friction brakes engage and I figured that was enough to take care of some "surface rust", although supposedly that's a by-gone thing with the GM FNC rotors anyway. But now my concern is ensuring the caliper piston gets truly exercised.

I ordered a new caliper from my parts counter at the local Chevrolet dealership. Fortunately I was a little prepared as they showed me a parts diagram for the caliper itself, and wanted to know which part I wanted, saying they only sold individual parts. I knew this wasn't true and gave him the part number for the caliper and he got it ordered for me. $135.82 all in. The online GM parts places were cheaper but I've had irregular success with shipping during the CORONA era. The local NAPA would have been cheaper by the cost of the core charge, but they didn't have anything in stock and given the vehicle age I decided to just go with OEM.

On a mechanical note, the caliper support brackets on newer GM vehicles, including the Bolt, are supposed to have single-use torque-to-yield (TTY) bolts. I don't personally care to debate if you can or should re-use them or not, but I've had a bit of a hard time nailing down the exact part number for that bolt. I found 11562022 but that says it is the lower bolt. The parts diagram on that page shows a different number for the top bolt, but I can't find that parts diagram on a page that lists all the parts on it. These bolts aren't shown on the parts diagrams for the brakes. NAPA lists the UB 82211, which just says "rear" but says it fits the car. I'm going to call to ask about that bolt and if it is a pack of one or two.
 

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I had to make a panic stop the other day at around 35 mph when some jerk cut across the other lanes leaving a mall and swung wide into my lane. I have total confidence in the Bolt鈥檚 brakes as they locked up the tires as I came to a screeching near stop. Maybe the tires can be better, but the brakes are just fine.
 

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The Bolt can regen just as much in D mode as in L, so D vs L won't make any difference unless you press the brake pedal so hard that it exceeds the car's regen capability. In other words, if you decelerate more rapidly than L mode with the regen paddle would give you.

That's stronger braking than you'd normally need in day to day use, so either way you'd want to do some extreme braking maybe once a month to make sure you're actually engaging the hydraulic brakes. Or put the car in N so that the brake pedal uses JUST the hydraulic brakes.
You are partially correct.
In gentle enough pedal application hydraulic brakes will not be activated when slowing down in D.
However, when below 5 mph or so, to get the car to a complete stop, the hydraulic brakes will be activated and pull the car to a halt.
In D you mimic driving AT with torque converter.
In L - the car stops using regen.

Therefore, I stated by driving in D you will engage pads from time to time. Especially in lower speeds.


To comment on the panic braking - yes, I had about 2 or 3 times sudden stops and the car slowed down very well.
 

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Out of curiosity - how is the rotor itself? I mean, the surface. Clean, smooth? Or rusty, channeled?

EDIT.
Just something I remembered about 500e I had.
I did the brakes inspection at about 45k miles (2014 YM, summer of 2019).
The fronts OK. The rears - plenty of meat, but slightly rusty and uneven wear.
They still would slide OK, but I could see they were not being used at all.
 

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when below 5 mph or so, to get the car to a complete stop, the hydraulic brakes will be activated and pull the car to a halt.
That's very true, but it takes so little energy to slow from 5MPH that I'm not convinced how viable it would be as a means of keeping the brakes 'broken in'. Mind you, I drive in L mode exclusively and pretty much ignore my brakes altogether, so who am I to speak?
 

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I did a multi legged trip yesterday, so at every stop I touched my brake rotors, every time each was cool to the touch. Hope that helps.
 

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btm is in Maine. The salt on the roads combined with the humidity in the upper midwest and New England does terrible things to the undercarriage exposed. It's possible those Bolts in that area may see occasional brake trouble and those in dry climes may not.

jack vines
 

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Discussion Starter #17
Still waiting on the caliper to arrive, found some more information on bolts.

Brake Caliper Bolts

GM does state in it's service manuals the caliper bracket bolts are single use bolts and must be replaced. They are the only single-use fasteners listed for the brakes (at least on my 2017 Bolt). Opinions vary on ignoring that guidance on replacement. I found a helpful parts counter person and combined with what else I found, I've assembled this:


Part #DimensionTorque SpecificationsList PriceReusable
Front Brake Caliper Bracket Bolt11562022m14 x 42mm160 Nm / 118 lb ft$24.62No
Rear Brake Caliper Bracket Bolt11516330m12 x 40mm100 Nm / 74 lb ft$6.02No
Rear Wheel Hub Bolt11588743m10 x 55mm58 Nm / 43 lb ft$5.57Yes


I need to double-check the dimensions on the rear brake caliper bolt when I get home. I can't seem to verify them online right now. Everything else I double-checked in online data. The "Rear Wheel Hub Bolt" I listed here just because the parts diagrams show it in a way that makes it seem like you need two different bolts for the caliper bracket, but the other bolt is the hub bolt (4 per side). This bolt is used in many other places and is usually listed online as a "compressor bolt." But you don't need to touch it for any brake work. The front hub takes different bolts (3 per side) and has different torque specifications. Fortunately these bolts are easier to get from the dealer as they're more common.


Parking Brake Service Mode + Calibration

The service manual says to put the vehicle in service mode for brake bleeding (vehicle off, do not touch brake pedal, hold power button for 5 seconds), but for most other brake tasks it only says to put the electric parking brake in service mode with a scan tool or:

1) power on
2) accelerator pressed halfway
3) hold parking brake switch in release (down) for 10 seconds, release
4) within 5 seconds, push switch down once and release.

To exit, apply the parking brakes.

You're supposed to calibrate the parking brake after changing the pads, rotors, calipers, or the EPB actuator. Can only be done with a scan tool. I'll report back on that.
 

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I try to remember to "exercise" the brake pistons: every week or two, at a stop light, try pressing the brake pedal hard to the floor (like for a panic stop); once it's as far down as it will go, hold for 5 seconds; briefly lift your foot up, then stomp down and hold again; repeat a 3rd time. This hopefully builds some good pressure in the brake lines, and if you have a stuck caliper piston, it may pop loose. Then, work the brakes harder than usual (e.g. when getting off the freeway with nobody behind you, shift to neutral, and slow aggressively using the friction brakes).

You can also just look at the rotors, and only do the above when a rotor looks suspiciously "not shiny." I have had to do this with VWs: their rear brake pistons have a "corkscrew" motion as they slide in/out, and this adds enough drag for them to get stuck after being parked for just a week or two. Before I did this, I had to rebuild a caliper and replace a pair of rotors (twice in two summers).

Let us know what requirements you find for the scan tool; I use a CRP129, but it probably needs a firmware update to speak to a Bolt. Reminds me of Volvo, where you need a PC plus $150 VIDA DICE + proprietary factory software, just to retract the parking brake and change brake pads :(
 

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FYI, re: those single-use bolts: in some cases, it's because the bolts are made to deform/stretch. In many cases, it's because the bolts come with a threadlocker compound which is not weakened by high heat, so the mfr. has a special part # for it.
 

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You're supposed to calibrate the parking brake after changing the pads, rotors, calipers, or the EPB actuator. Can only be done with a scan tool. I'll report back on that.
It looks like it's this process (the vid is for an Equinox, but likely the same for the Bolt).
 
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