front brakes-- DIY fiasco-- broken bolt /cut wires

Today, I went through a 6 hour odyssey trying to change my front pads and rotors. In theory, it is quite simple. And, I didnt' have any problems where I though I woudl-- trying to get bolts out and the rotors off. I'll save the gory detail for another post-- but for now my car is still on jackstands awaiting the resolution to the first problem below.
BTW, right now, i'm feeling like the $500 it would've cost to have this done by a delaer would be a great deal. I don't know how you guys who are abel to do this in 1 hour manage it. Even w/ experiene, I think it would stil take me 2-3 hours. IN theory, the job is quite simple- but in practice its a real PITA in a few ways.

Now for my problems (its always the small things...)
I got the driver side done and put back together-- everything went ok (took a looong time, but eventually everything seemed to go back together, and I torqued everything properly).

1. ON the passenger side, as I was tightening the top caliper bolt (the 7mm hex one) w/ my torque wrench set to 41 ft-lbs, I managed to snap the head off of it. I don't know how I managed to do that, but I did. Fortunatley, the remains of the bolt are stuck in the brake carrier, which is easy to remove (and has been removed).
Its not like the bolt is seized--it just has its head snapped off. There a few potruding threads, but not enought to get any sort of grip on. Any advice for removing it would be greatly appreciated. I've been reading about "EZ outs" and "left handed screws", but I wanted to get some practical advice here.

2. ON the driver's side, I couldn't figure out how to get the sensor wire out of the brake pad. I pulled and pried to no avail. I finally succeeded in damanging the wire to the point that I just decided to cut it w/ a scissors. I taped up the end w/ electrical tape since I didn't have a replacement sensor wire handy and all the dealers were closed by that point.

But, how do you replace the snesor wire?- it utlimately plugs into a black box that's mounted in the wheel well. I tried "unpluggiing" it but couldn't figure out hw to release it. And, given my track record, I decided to quit before I risked dmanaging more wires that are harder/more expensive to replace. When I do get a new sensor wire-- how do I replace it?

Originally Posted by robg

2. ON the driver's side, I couldn't figure out how to get the sensor wire out of the brake pad. I pulled and pried to no avail. I finally succeeded in damanging the wire to the point that I just decided to cut it w/ a scissors. I taped up the end w/ electrical tape since I didn't have a replacement sensor wire handy and all the dealers were closed by that point.

But, how do you replace the snesor wire?- it utlimately plugs into a black box that's mounted in the wheel well. I tried "unpluggiing" it but couldn't figure out hw to release it. And, given my track record, I decided to quit before I risked dmanaging more wires that are harder/more expensive to replace. When I do get a new sensor wire-- how do I replace it?

Sorry to hear about your ordeal Rob.

WRT the wire, the black box in the wheel well opens up. There should be 2-3 plastic tabs on the left side of the box, which you needs to gently pull on to release then top /outer part of the box and pivot it along the vertical axis - just like a little door. The end of the wire is connected inside the box, and it has a little tab which you need to press to release and disconnect the wire.

The caliper guide bolts are only torqued to something like 28 lbs-ft (maybe even 28 newton-meters, which is even less). These are the 7 mm hex head ones that hold the caliper in place on the mount and the caliper slides on. A short piece of threaded section, then a longer smooth pin.

I can do PADS only in about 45 minutes. Rotors add a bit of time.

WRT the sensor from the pad, you just pull it out. But it pulls striaght out radially to the rotor. ie straight away from the hub. As long as you have the wheels off every so often and take a look at the pads, the sensor isn't needed. It is for the brain dead who never have anything checked until a red light comes on.

The sensor wire should be very easy. As mentioned above, just open up that little black box like a door, and pull the wear sensor wire out.

I've never tried to remove a bolt that had the head snapped off. But I have used the drill bit things (sorry, I forget the name) from Sears to remove stripped screws. Maybe they have something similar for your problem.

Good luck.

I don't know how you guys who are abel to do this in 1 hour manage it.

Their car never sees road salt.

Originally Posted by robg

I've been reading about "EZ outs" and "left handed screws", but I wanted to get some practical advice here.

Do yourself a favor, run down to Sears and get a bolt extractor kit. They really do work.

This guy snapped off one of the lugs on his rims and the Sears extractor kit worked.

Originally Posted by Pinecone

The caliper guide bolts are only torqued to something like 28 lbs-ft (maybe even 28 newton-meters, which is even less). These are the 7 mm hex head ones that hold the caliper in place on the mount and the caliper slides on. A short piece of threaded section, then a longer smooth pin.

I can do PADS only in about 45 minutes. Rotors add a bit of time.

WRT the sensor from the pad, you just pull it out. But it pulls striaght out radially to the rotor. ie straight away from the hub. As long as you have the wheels off every so often and take a look at the pads, the sensor isn't needed. It is for the brain dead who never have anything checked until a red light comes on.

Doesn't sound right though, if he's doing the rotors the caliper CARRIER has to come out and the torque spec on those things are significantly higher.

It's hard to imagine how a caliper guide bolt can break, since most hex keys will bend and hex key attached to a driver will strip before the guide bolt should break. The caliper carrier bolt, on the other hand, CAN break off if you apply too much torque.

Try this next time you need to fasten something that's more than 50 ft lbs...Tighten it to 2/3rd it's rated value first, then 3/4, then 1:1...i.e. if you need to tighten a suspension bolt at 70ft lbs, I'd first tighten to about 40ft-lbs, then 65, then 70. It's time consuming but it prevents you from over-tightening and breaking off a bolt. But since you were far away from actually achieving the torque spec and sounds like you had a few threads still showing, I would say you may have cross threaded the bolt and was physically forcing the bolt in and that's why the head snapped, Robg. You will need to have that bolt drilled out and the king-pin tapped.

Usually I use a small screw driver to pry out the sensor from the base of the pad/tip of the sensor, to avoid damaging the wire.

He said CALIPER BOLT, 7mm HEX. That sounds like the caliper guide pin. And trust me, my Snap On hex socket will generate more than the required torque. And they do snap off, not that I have done that, yet.

You are right, the caliper bracket bolts are a higher torque, but they are more like a 17mm hex head bolt. But yes, you can snap those off.

I torque the 7mm hex guide pins to tight with an 8" ratchet.

Originally Posted by Pinecone

He said CALIPER BOLT, 7mm HEX. That sounds like the caliper guide pin. And trust me, my Snap On hex socket will generate more than the required torque. And they do snap off, not that I have done that, yet.

You are right, the caliper bracket bolts are a higher torque, but they are more like a 17mm hex head bolt. But yes, you can snap those off.

Then his torque specs are WAY off. The 7mm Hex caliper bolts only require ~30ft-lbs, at 41 it is almost 30% higher than the rated torque spec.

Actually...Even the caliper carrier bolt requires much higher torque too...Something in the order of ~72ft-lbs. Where did the 41 ft-lbs # come from? Did he mistake Nm for ft-lbs from the instructions?

Rob...

What's the outcome??

I'm travelling for work this week-- so I won't be able to deal w/ till tihs weekend. But, I'm going to buy the Sears "drill out" bits and try ot get the remains of the bolt out of hte brake carrier.

Hack-- it was the caliper guide bolts -- and yes, you're right, I was using the wrong torque spec (too high)--although it wasn't a problem on the other caliper. Even so, I'm sort of surprised that bolt snapped at less than 40 ft-lbs. Maybe it was defective, and I did myself a favor by discovering it. (yeah, that's it)

I was using a 3/8 torque wrench with a 7mm hex socket to tighten, not an allen wrench.

Does this bonehead move officially make me a "Hack mechanic"?

Well, the guide pins show 22lbft (30Nm) so 41 breaking the sucker isn't surprising. SergioK and I did something similar with the carrier bolts on the rear of his car once, so it happens.

Originally Posted by Kaz

Well, the guide pins show 22lbft (30Nm) so 41 breaking the sucker isn't surprising. SergioK and I did something similar with the carrier bolts on the rear of his car once, so it happens.

Holy cow, sorry to hear about your ordeal Rob. I just did my front brake pads and discs last weekend and I tightened the 7mm guide pins firmly tight using a 3/8 ratchet with a hex head, probably more than 30 Nm.

If the stated torque for the 7mm guide pins is 30Nm, what is the torque of the 2 16mm bolts that hold the brake carrier?

Thanks

Originally Posted by robg

I was using the wrong torque spec (too high)--although it wasn't a problem on the other caliper.

I would replace those (overtorqued) guide pins on the other side asap.

Originally Posted by Scott_H

I would replace those (overtorqued) guide pins on the other side asap.

Originally Posted by robg

I'm travelling for work this week-- so I won't be able to deal w/ till tihs weekend. But, I'm going to buy the Sears "drill out" bits and try ot get the remains of the bolt out of hte brake carrier.

Hack-- it was the caliper guide bolts -- and yes, you're right, I was using the wrong torque spec (too high)--although it wasn't a problem on the other caliper. Even so, I'm sort of surprised that bolt snapped at less than 40 ft-lbs. Maybe it was defective, and I did myself a favor by discovering it. (yeah, that's it)

I was using a 3/8 torque wrench with a 7mm hex socket to tighten, not an allen wrench.

Does this bonehead move officially make me a "Hack mechanic"?

Change your user name to The HACK 2 now.

I've found that MOST fasteners on the BMWs are rather torque sensitive. The drain bolt, for example, snaps at slightly over 25Nm. The bolts holding on the king pin/rear shock will snap at ~120ft-lbs, and the torque spec is something like 80 ft-lbs.

Originally Posted by WAM

Holy cow, sorry to hear about your ordeal Rob. I just did my front brake pads and discs last weekend and I tightened the 7mm guide pins firmly tight using a 3/8 ratchet with a hex head, probably more than 30 Nm.

If the stated torque for the 7mm guide pins is 30Nm, what is the torque of the 2 16mm bolts that hold the brake carrier?

Thanks

Off the top of my head...~72 ft-lbs for the front ones, and ~50 ft-lbs for the rear.

Although my head is a little hazy right now.

Originally Posted by The HACK

The drain bolt, for example, snaps at slightly over 25Nm.

Is this right? (Or, did you mean "25 ft-lbs"?)

IIRC, the drain bolt spec is around 18ft-lbs, or about 25N-m (I think the spec is 25N-m). It would be surprising if it broke off just an hair above this.

robg-

Sorry you're having such troubles.

However I couldn't help but laugh aloud while reading your post. This is exactly how I find working on my cars to be. I'll read about how someone here changed, oh say, their clutch in like 20 minutes. Using a hair pin borrowed from the wife along with a spatula and fork taken from the barbeque.

And it takes me 3 solid hours to change brake pads and fluid on all 4 wheels. So fear not, there are others like you out here who also are not great (dare I say HACK?) mechanics.

Here's an old post of mine that might make you feel better:
http://www.bimmerfest.com/forums/sho...light=stripped

Good luck with it all. These things do get easier with experience.

Originally Posted by JonW

However I couldn't help but laugh aloud while reading your post. This is exactly how I find working on my cars to be. I'll read about how someone here changed, oh say, their clutch in like 20 minutes. Using a hair pin borrowed from the wife along with a spatula and fork taken from the barbeque.

Glad someone else feels that way too. Some people here seem to pull amazing "MacGyver" moves to fix a problem, or they just happen to whip out all sorts of fancy terms and equpment. I'm starting w/ 0-- I can't even assume that I'll have the right flathead screwdriver to pry off a clip, let alone some of the esoterica that gets bandied about here. :

"I lifted the car using my in-ground 2 post lift, then I selected the correct snap-on torque wrench, and used a gold-plated, non-stick socket to prevent marring the bolts. Then I applied some aerospace quality thread lubricant to the bolts, and while i was at it, I decided to re-thread all the bolt holes. I looked up the correct torques on my personal BMW DIS machine that I have in my garage. My friend, a professional machinist, did it for a few beers. I was able to completely re-build the engine in under 2 hours-- I can't believe dealers charge 10 hours for this simple task. Next weekend, I plan to install a custom differntial that I built from scratch (I make my own steel)"

My version:
"I lifted the car using my sears jack, and supported it on some jackstands that don't fit into the BMW provided jackpoints. I laid on my side on a dirty garage floor, got brake dust all over myself, used the wrong toruqe, broke a bolt and have been walking with a limp ever since from somehow pulling my butt muscles while attempting this job".

Originally Posted by robg

Glad someone else feels that way too. Some people here seem to pull amazing "MacGyver" moves to fix a problem, or they just happen to whip out all sorts of fancy terms and equpment. I'm starting w/ 0-- I can't even assume that I'll have the right flathead screwdriver to pry off a clip, let alone some of the esoterica that gets bandied about here. :

"I lifted the car using my in-ground 2 post lift, then I selected the correct snap-on torque wrench, and used a gold-plated, non-stick socket to prevent marring the bolts. Then I applied some aerospace quality thread lubricant to the bolts, and while i was at it, I decided to re-thread all the bolt holes. I looked up the correct torques on my personal BMW DIS machine that I have in my garage. My friend, a professional machinist, did it for a few beers. I was able to completely re-build the engine in under 2 hours-- I can't believe dealers charge 10 hours for this simple task. Next weekend, I plan to install a custom differntial that I built from scratch (I make my own steel)"

My version:
"I lifted the car using my sears jack, and supported it on some jackstands that don't fit into the BMW provided jackpoints. I laid on my side on a dirty garage floor, got brake dust all over myself, used the wrong toruqe, broke a bolt and have been walking with a limp ever since from somehow pulling my butt muscles while attempting this job".

I have yet to change my own oil. If you've done that, you're a step up on me.

Originally Posted by Kaz

Well, the guide pins show 22lbft (30Nm) so 41 breaking the sucker isn't surprising. SergioK and I did something similar with the carrier bolts on the rear of his car once, so it happens.

Yeah, that wasn't good. I had to drive to two different dealers to get that bolt.

Originally Posted by swchang

I have yet to change my own oil. If you've done that, you're a step up on me.

Well get a move on! Otherwise why did you buy all those new tools and that new fangled earl eggstraktar fer

Originally Posted by swchang

I have yet to change my own oil. If you've done that, you're a step up on me.

car_for_mom has changed her own oil...