[Moel]

Hello all

I've got to get my 235i back into shape. I'd like some advice on what is likely to be the problem.

So I replaced the pads on my car, and ever since then the braking hasn't been particularly right.

I replaced the pads, but I didn't grease the edges to allow them to float freely in the calipers, as a result as I slow down, under gentle braking you can feel the pedal modulate underneath your foot. Under hard consistent pushed braking, the modulated feel is very much reduced

Slowing from 70'ish (officer) to 5, (rapidly, for instance approaching a roundabout) when brakes are warm results in a sound akin to running over cobbles.

Essentially I want to know my options, I'm aware that I should probably bin my current rotor and pad assembly and start again, equally i'm aware that will probably cost me around £500+ to do that.

Could it just be that the pads are stuck in the calipers and therefore not applying releasing evenly? When i swapped over my rear pads a few weeks ago, that was a complete and utter pig as again they refused to come out without some severe wangling.

Thanks in Advance

Alex

[H2O_Doc]

There is a lot of myth and folklore around rotors being warped. This might be worth a read particularly in light of what you've described: https://alconkits.com/technical-info...ed-brake-discs

[Moel]

And that's my precise problem... i don't want to replace everything, if it's not the problem.

Whats the best way to test? I'm guessing I need a gauge of some sort.

That said i've found Apec discs on ebay that i'd be happy to fit (never had a problem with them on other cars i've owned)

[Pray for Mojo]

I'd pull it apart again and regrease the pad backing and pins before throwing more parts at it.

[Maynard]

if the pads were stuck in the calipers, you might have the wrong pads; or perhaps not OEM and they are defective? If the piston wouldn't retract it may be frozen. But most likely is disc contamination or poor bedding; clean rotors and re-bed first before buying parts.

[Moel]

Ok, I'll do that.. whats the best way to clean the rotors, and how do I re-bed the pads?

One more thing to note, as I was just driving home, there's a nice bit of straight downhill road.

I applied the brakes, there was literally no steering wheel wobble, would that add credence to the fact it's just rotors that need cleaning?

[aerobod]

Originally Posted by Moel

Ok, I'll do that.. whats the best way to clean the rotors, and how do I re-bed the pads?

One more thing to note, as I was just driving home, there's a nice bit of straight downhill road.

I applied the brakes, there was literally no steering wheel wobble, would that add credence to the fact it's just rotors that need cleaning?

Use brake cleaner (available from any motor factors) to clean the rotor surface.

This is the sort of bedding procedure I would use: https://www.brakes-shop.com/brakeped...k-in-procedure

Bear in mind that this procedure isn't inline with the recommended BMW "drive gently for the first xxxx miles on new pads and rotors", so is carried out at ones own risk.

[Moel]

Ok, so it doesn't matter about reusing the same pads, i'm literally just using brake cleaner. I was kind of under the impression that as it's just a solvent it won't take away any pad material thats transferred unevenly?

[aerobod]

Originally Posted by Moel

Ok, so it doesn't matter about reusing the same pads, i'm literally just using brake cleaner. I was kind of under the impression that as it's just a solvent it won't take away any pad material thats transferred unevenly?

That's what the bedding procedure will do - transfer an even pad deposit to the rotor.

[HP Autosport]

Originally Posted by Moel

Hello all

I've got to get my 235i back into shape. I'd like some advice on what is likely to be the problem.

So I replaced the pads on my car, and ever since then the braking hasn't been particularly right.

I replaced the pads, but I didn't grease the edges to allow them to float freely in the calipers, as a result as I slow down, under gentle braking you can feel the pedal modulate underneath your foot. Under hard consistent pushed braking, the modulated feel is very much reduced

Slowing from 70'ish (officer) to 5, (rapidly, for instance approaching a roundabout) when brakes are warm results in a sound akin to running over cobbles.

Essentially I want to know my options, I'm aware that I should probably bin my current rotor and pad assembly and start again, equally i'm aware that will probably cost me around £500+ to do that.

Could it just be that the pads are stuck in the calipers and therefore not applying releasing evenly? When i swapped over my rear pads a few weeks ago, that was a complete and utter pig as again they refused to come out without some severe wangling.

Thanks in Advance

Alex

You could try to borrow a dial indicator and measure rotor runout first.

[Moel]

Sadly i don't know anyone that owns a dial indicator :-( My plan is (weather dependent) clean the discs this weekend with brake cleaner and a spot of wire wool.

then go thru the bed in procedure again, and see what happens.

[Maynard]

I'd use a clean towel rather than wire wool - you are aiming to clean off any grease or contamination, not the pad material (and given what you posted above, an unlikely source of the problem); bedding in takes care of the pad material. As another noted above, if there is any rotor runout it will also cause this, so if you had the rotors off you may want to clean under them for a perfect flat seating to the hub (even tiny bits of grime or sand can set it off enough to cause problems).

[Moel]

Ok, so plans are delayed, my socket rounded off as i tried to remove one of the nuts...agggghh...got another one on order.

I'm now beginning to suspect the rotors have had it to be honest...the lip between the edge of the rotor and the actual surface, is noticeable when running my fingers around it.

Unfortunately won't be able to do any more till I can get the actual wheel off.

Maynard, why don't you think it's pad material causing the issue?

[Maynard]

Originally Posted by Moel

Maynard, why don't you think it's pad material causing the issue?

You misunderstood me; I meant that cleaning the disc w/ brake cleaner was unlikely to fix this. It would only fix it if you had contaminated a section of the disc, but then it would be happening all the time, and probably wearing itself out as the grease was burned off and spread about.

I think quite possibly it is incomplete bedding (and the easiest to check/fix) - try the rebedding procedure. That instruction sheet linked above doesn't say this, but you want to be stopping hard enough to nearly activate ABS, but NOT using any ABS, especially for the later stops - you should smell the hot brakes; and no parking brake or full stop until after a 10 minute cool down, at least.

Another option for cause would be that, a while ago, the discs were mounted slightly ajar - this will gradually produce uneven wear that gives the pulsing pedal feel. Knowing that there is a noticeable edge ridge means the rotors are well worn, so replacing them isn't a bad idea. The suggestion to check with a micrometer is a good one - if they differ in thickness at different points around the circle (inside the wear area, same distance from edge all around) then you have to dig in and figure out if the hubs are off of true, or if the rotor was installed a little off. A really good repair shop will be able to check this for you on the car, but they'll probably only do that if they did the install too.

And if you had a sticking caliper piston, that is your culprit (they should move freely, but slowly). It will produce both the uneven rotor, and often a chukking sound.

[Moel]

Well chaps i've bit the bullet. Thank you for all your advice so far. As the cars done 56k it just seems sensible to stop faffing around and replace the front pads and the rotors.

While i've been reading around the subject, certain other xAddicts forums have been suggesting that the pads and rotors are effectively designed to both be changed at the same time. Which is new and unusual in comparison to any other car i've owned. (Apparently once you've changed the pads the discs are pretty much at minimum thickness) Is there any truth to that rumour?

I mean I did think the fact i'd gone several years without new pads was pretty impressive to be honest. Love your thoughts.

[aerobod]

Originally Posted by Moel

While i've been reading around the subject, certain other xAddicts forums have been suggesting that the pads and rotors are effectively designed to both be changed at the same time. Which is new and unusual in comparison to any other car i've owned. (Apparently once you've changed the pads the discs are pretty much at minimum thickness) Is there any truth to that rumour?

This is very much dependent on the specific BMW, in my experience. On my E46 it was definitely the case, on my E82 I got 3 sets of pads to a rotor. The minimum spec is embossed in the rotor (normally 1.6mm less than the thickness new). You can put a new set of pads on if the rotor is above minimum thickness, but if it is close it is best just to replace thr rotors.

[Texan2er]

Myself and another M235 owner here in Houston have both had our rotors at minimum by the time it was time to do the pads so I'd say you're seeing the same. I have had multiple shops recommending doing pads and rotors together on these cars so that's what I've done. Makes the bullet cost more, but it's the one you've gotta bite.

[Moel]

Texan I suspect you were right...the lips on the outer and the inner of the disc were erm...fairly pronounced.

But it was a successful weekend, a new set of apec discs turned up, as did Mintex pads (within 10 minutes of each other) on Saturday morning, so on Sunday did the usual get so far, hop in spare car to get tools, on multiple occasions!

Can't say how glad i am that I didn't get a set of hex keys, and instead opted for hex bits for a ratchet (made it easier to shock the caliper retaining bolts out without stripping the head)

Have done about 40 miles so far, gave them a good bedding in yesterday (not super harsh, but 60-30 a fair few times, allowing them to cool and then being very gentle on the way home so they were nearly stone cold when i got back on the drive.)

So yes, between that and a big rubber mallet that i invested in to smack the rotors off...oh and the fact that I was shitting myself, using a 12 point socket (to the point i visited every motor factors near me to see if they had a 6 point 18mm socket, but it's an 'odd size') to remove the caliper bolts (but thankfully my torque wrench was just long enough to apply the sufficient amount of pressure to undo them)

So lesson learnt.

Also very happy that i effectively got the whole job done for £125 in parts and £30 in tools, I'm guessing at a main dealer i'd be looking at more like £800 (update: £553.02)