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BMW and MINI – Warped Brake Rotors, Short Pad Life or Uneven Pad Wear

Aug 12 14

This answer is applicable for many BMWs and MINIs in addition to the one listed below.

Q
Dear Otto:
I have a 2007 328i.  I started to get a vibration through the steering wheel when braking, so I figured the brake rotors were warped.  I went to your online store and purchased the Meyle Platinum brake rotors and the Cool Carbon brake pads.  I installed them a couple weeks ago and everything seemed fine.  The vibration under braking was gone … in fact, it seemed like the braking felt better than ever.  However, after a few days, the shake started to come back.

I  did some more searching on your blog and found that another possible source for front vibration or shake could be the control arm bushings and/or ball-joints.  I did replace the complete control arms about four months ago and, while the front is now much smoother while driving along,  they had no affect on the vibration while braking.  After replacing the control arms, I also did the testing that you described in a couple of  the blog posts on front-end shake and warped rotors (http://blog.bavauto.com/3478 – Otto) and the car does surge when coming to a stop.  What could be going on?  I’ve got brand new brake rotors and pads, and the warp testing still shows surging as I stop .  Is there something else that could be causing this?

A
You are correct in noting that a front-end vibration could be worn control arm bushings and ball-joints, as well as warped or otherwise damaged brake rotors.  Since you have already replaced the control arms, we will assume that these are not the problem.  You also noted that the replacement of the pads and rotors initially eliminated the braking shake.  Therefore, it’s a good assumption that the replacement initially took care of the shake problem.  If the vibration/shake and the surging while stopping have indeed returned (after the initial period of smoothness, with the new parts), the problem is likely with the brakes and the new rotors may be warped again.

Sooo …. why would the shake return?

Here are some thoughts and possible root causes for the “brake shake”:

*  Brake pad material transfer - Unrelated to the original braking vibration issues, you may have a bit of pad material transfer.  In other words, you may have spots on the rotors where the pads transferred a very light layer of material onto the rotor surface.  This can happen if the pads and rotors are very hot and then the vehicle is stopped before the pads and rotors can cool down a bit.  Pad material transfer can usually be eliminated by re-bedding the pads to the rotors.  With the brakes fully warmed up, from 60-mph, use the brakes to slow the vehicle in a moderately aggressive manner, down to about 20-mph (no need to “throw the anchor out”, but more aggressive that your normal braking).  Accellerate back to 60-mph and repeat.  Do this 3 to 4 times, then drive at about 60-mph for a minimum of 1-mile to cool the pads and rotors.  Be sure to ONLY perform this procedure in a safe place and a safe manner, with no other traffic.

*  Sticking brake caliper pistons - The caliper pistons (both sides or just one side) may be sticking in the bores.  In this case, the piston does not fully retract when braking pressure is released and it keeps some amount of pressure on the brake pads, pushing them against the rotor. This creates extra heat and overheats the rotor, causing it to warp (and likely also transfer pad material, as noted above).  A quick test can be performed as follows;  1) Lift the wheels off the ground (jack and jack-stands), 2) Apply the brakes firmly, 3) Spin the wheels, they should spin freely.  If one or both show noticeable drag, the caliper piston is likely sticking.  Note that the rear drive wheels, or the front on 4wd vehicles, will not just freely spin due to the drag of the axles and drivetrain.  However, if one side has more drag than the other, it may be a sticking caliper.  In this case, the cure is to rebuild or replace the sticking caliper(s).

Click below for Brake Calipers:

*  Sticking caliper guide pins - Most BMWs and MINIs use a single-piston brake caliper.  In these designs, the caliper floats (or slides) on cylindrical rods (guide pins) so that the force of the piston extending from the bore causes both sides of the caliper (and the brake pads) to press against, or pinch, the brake rotor.  The guide pins are actually bolts with polished shanks (these are the Allen-head bolts that you remove in order to replace the pads).  The caliper has rubber bushings pressed into it.  The guide pins fit through these bushings.  The caliper then floats, or moves side to side, on the guide pins via the rubber bushings.  With age, the bushings can begin to stick on the guide pins.  This causes the outer brake pads to remain in contact with the brake rotor after the brakes are released, overheating the pad and the rotor and potentially warping the rotor or causing pad material transfer.  Performing the wheel spin test, as noted above, may show a dragging brake in this case.  Additionally, the outer brake pad will typically show more wear than the inner pad.  Finally, if only one of the two guide pin bushings is sticking, the brake pads may show a tapered wear.  In other words, one end of the brake pad is worn more than the other end.  The cure for sticking guide pins is to either remove the pins and clean all rubber off them, lubricate with the Sta-Lube synthetic brake grease and re-install …. or …. install new rubber bushings and new guide pins (with the Sta-Lube lubricant).  We typically prefer to replace the bushings and the pins, as the bushings do soften with age (allowing excessive caliper movement and tapered pad wear) and the inner bores of the bushings may be rough and torn up (due to the transfer of the material to the guide pins).

Click below for caliper guide pin and bushing kits (search guide bolt or bushing, after clicking link):

Sta-Lube synthetic brake grease:

Bavarian Autosport
BavAuto
www.bavauto.com
bavauto.com

BMW and MINI – Battery Still Going Dead After Replacing Alternator

Aug 5 14

This answer is applicable for many BMWs in addition to the one listed below.

Q
Dear Otto,
I’ve been having some issues with my 98 328i.  A while ago, it started missing and chugging once in a while, then would be fine for a while.  Oddly enough, this seemed to happen more at night.  Then a couple weeks ago, the battery went dead.  I got a jump and it ran fine.  Now, it may run fine for who knows how long or it may just not start right after shutting it off, but it will always take a jump and then seem to run fine …. with the exception that the missing and chugging seems more common.

Since the CHARGE (or BATTERY, Otto) light has never come on, my mechanic suggested that the battery was weak and I should replace it, and I did.  All seemed to be fixed (both the missing and the dying), but after a week or so, the same problems started to return.  This time, he checked the output of the alternator and said it was putting out, but seemed to be a little low.  He said that this could be why the battery was sometimes charged and sometimes dead, depending on how much electrical power I was using (lights at night, blower motor, etc.).  He also said that the engine missing may be due to low battery voltage, due to the alternator not charging enough.

Well, he replaced the alternator and the problems returned almost immediately.  I need some help!  I have a new battery and a new alternator, that still shows borderline low on output ….. and all of the same original problems.

A
All of your symptoms tend to point to a possible common issue on older models.

*  Intermittent engine missing

*  Intermittent dead battery

*  Engine missing and dead battery more common when electrical accessories are being used (lights, blower motor, radio, etc.)

*  Charging warning light does not come on

*  Alternator tests OK, but maybe a bit low, in car, but tests fine on a test bench.

These symptoms tend to point to a possible engine and/or battery ground problem.  If the grounding cable/strap that runs from the engine to the chassis, or the ground cable from the battery to the chassis is corroded and does not have full electrical conductivity, the alternator will not be able to deliver its full output to the electrical system and the battery.

Test the engine ground as follows:

With the engine running; use a set of jumper cables to ground the engine to the chassis, by using just one of the cables to connect from a bare metal part on the engine (alternator housing or mounting bracket, oil filter housing, motor mount, etc.) to a proper chassis ground (the provided ground jumper terminal or a strut tower nut or other clean and bare metal point).  If there is a spark when connecting the jumper cable, the engine ground cable is likely corroded (or missing) and needs to be replaced (and the terminal points cleaned).  You can double check this by testing the alternator output voltage with the jumper connected (vs. without the jumper).  If the output voltage is higher with the jumper connected, again, the engine ground is at fault.  Note that the cable may look visually fine at first glance, but may have internal corrosion.

On most BMWs, the engine ground cable runs from the left side of the engine (often the metal motor mount arm, alternator mount, alternator housing, or oil pan) to a point on the engine bay chassis.  In replacing the ground cable, clean the mounting points to bright metal and apply the DeoxIT compound to prevent future oxidation.

Please call your BavAuto Advisor at 800-535-2002 to order the proper engine ground cable for your model.

Click below for DeoxIT contact enhancer:

Bavarian Autosport
BavAuto
Bavauto.com

BMW and MINI – Engine Will Not Start After Running Out of Fuel (Gas)

Jul 31 14

This answer is applicable for many BMWs in addition to the one listed below.

Q
Dear Otto,

I ran out of gas in my 2004 330ci.  After getting a couple gallons of gas and pouring it into the tank, the engine would not start.  I went and got two more gallons and added it, but the engine will still not start.  How much gas do I need to put in to get it started?  This seems really odd, since I can normally run it for 10, 20 or 30 miles after the reserve warning light comes on, before the “range” shows 0-miles.

A
We suspect that you may now have a failed fuel pump.  The fuel pump on later model BMWs and MINIs (as well as most other cars) is mounted inside the fuel tank and actually uses the fuel to cool and lubricate the pump.  Consistently running the fuel very low, will limit the amount of fresh cool fuel to keep the pump cool and lubricated …… accelerating the wear and shortening the life of the pump (this also applies to earlier models that have external in-line fuel pumps).  It’s likely that this last episode of running out of fuel was the “straw that broke the camel’s back”.  This ends up being fairly common, especially if the pump has a lot of miles of use or is often run with less than 1/4 fuel level.

We recommend replacing the fuel pump and this will likely cure your no-start issues.  Remember to replace the pump seal ring and have fresh hose clamps available to replace the original factory crimp clamps or rotten old hose clamps.  The Bentley Publishing repair manual (for the applicable BMW or MINI model), will cover the fuel pump replacement.

Fuel pump:

Hose clamps (search “hose clamp” after clicking link):

Bentley Publishing repair manuals:

 

BavAuto

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Bavarian Autosport