135i brakes on 128i; softer pedal feel issue?

[M-A]

hey guys,

i just installed bmw performance brakes on my 128i (135i brake setup). the pedal feels slightly softer... its blead properly with no air in bud the pedal feels somewhat a little softer... mind you, bedding isn't finished; freshly installed.

anyone felt the same feeling?

[juld0zer]

With the engine on, foot firmly on brake pedal does it sink or stay firm at the same height? Is there any mush or springyness if you try to press further?

They can be a pain to bleed those calipers especially the fronts with only one bleeder for both banks. Try thump the caliper with a mallet as you pressure bleed them. Did you wedge the brake pedal down before disconnecting calipers or let the master drain completely?

[MightyMouseTech]

Originally Posted by juld0zer

With the engine on, foot firmly on brake pedal does it sink or stay firm at the same height? Is there any mush or springyness if you try to press further?

They can be a pain to bleed those calipers especially the fronts with only one bleeder for both banks. Try thump the caliper with a mallet as you pressure bleed them. Did you wedge the brake pedal down before disconnecting calipers or let the master drain completely?

There are two bleeders on each front caliper.

[M-A]

Originally Posted by MightyMouseTech

There are two bleeders on each front caliper.

i didn't see more than one bleeder? im 100% sure...

[M-A]

Originally Posted by juld0zer

With the engine on, foot firmly on brake pedal does it sink or stay firm at the same height? Is there any mush or springyness if you try to press further?

They can be a pain to bleed those calipers especially the fronts with only one bleeder for both banks. Try thump the caliper with a mallet as you pressure bleed them. Did you wedge the brake pedal down before disconnecting calipers or let the master drain completely?

pressure is stable but smooshier... master cylinder never got bwlow minimum either.

it just feels so much different when i brake. has ifi didn't have enough braking power. but no air bubble since i still have brakes...

mind you, it may be the pads bedding time...

[juld0zer]

Genuine pads and discs?

The F car Brembos have two nipples on the fronts.

How did you bleed the system?

[M-A]

Originally Posted by juld0zer

Genuine pads and discs?

The F car Brembos have two nipples on the fronts.

How did you bleed the system?

mine only have one one "nipple" foe bleeding.

for budget purpose i went with zimmermann discs and trw pads. i believe the pads are just missing initial bite.

also, the pedding time is now also complete since i hadquite a drive to do yesterday. they feel much better now.

[MightyMouseTech]

Originally Posted by M-A

i didn't see more than one bleeder? im 100% sure...

Hmm, now WTF am I thinking of. I think you are right. My bad.



To OP, going to a caliper with a larger piston area will have softer brakes unless the master cylinder is also upsized.

[asbrr]

To OP:

I put on 135i brakes on my 128i about 18months ago, with Stoptech street performance pads. They were very lightly used so bedding had already occurred. Compared to stock brakes....there was no comparison. Great bite, and it scared the crap out of me the first time I had to really hammer on them.

So - yea likely just bedding time, but after they are bedded go to an empty stretch of road and stomp on the pedal, it should be quite noticeable

[M-A]

thanks for all your answers guys! they're now bedded-in and they're great!

[juld0zer]

TRW pads have heaps of bite for a cheap aftermarket pad, not as much as genuine BMW pads but close. Zimmermann paints their rotors, which fouls the pads and extends the 'bedding' (ie until normal performance is achieved) time.

[M-A]

Originally Posted by juld0zer

TRW pads have heaps of bite for a cheap aftermarket pad, not as much as genuine BMW pads but close. Zimmermann paints their rotors, which fouls the pads and extends the 'bedding' (ie until normal performance is achieved) time.

i concur 100% to this statement. True and tested in the past few days! Acceptable street pads but there's better for sure.

[Stewy_604]

Originally Posted by MightyMouseTech

To OP, going to a caliper with a larger piston area will have softer brakes unless the master cylinder is also upsized.

^^^ This. Your master cylinder needs to move a lot more fluid to give the same pedal feel and response from the brakes. I know in the case of my F15, when I put the MPBK on, I had to code it for the Sports brakes kit (there's a vacuum accumulator which helps pedal feel). Before and after coding, it was night and day. Not sure if that's the case here or not?

[juld0zer]

Master cylinder is same across all non-M E8x models. Yes, for all models except 135i you will need to code the car for Sport Brake. I actually find stock 125i/128i brakes to be far sharper than stock 135i brakes.

First i've heard of a vacuum accumulator for F15 models, not even the M models have one. The software changes are mainly to adjust the DSC threshoulds to update the vehicle order.

FWIW i have coded my 135i to have sport brakes even though they come with them from the factory. There was a slight change in pedal feel but you quickly get used to it and forget it has evem changed. You cannot reverse this once it has been done unless you alter it using software other than ISTA/P. Maybe BMW technical might be able to reverse it on request also. Even coding a new DSC control unit did not delete the sport brake

[M-A]

Originally Posted by juld0zer

Master cylinder is same across all non-M E8x models. Yes, for all models except 135i you will need to code the car for Sport Brake. I actually find stock 125i/128i brakes to be far sharper than stock 135i brakes.

First i've heard of a vacuum accumulator for F15 models, not even the M models have one. The software changes are mainly to adjust the DSC threshoulds to update the vehicle order.

FWIW i have coded my 135i to have sport brakes even though they come with them from the factory. There was a slight change in pedal feel but you quickly get used to it and forget it has evem changed. You cannot reverse this once it has been done unless you alter it using software other than ISTA/P. Maybe BMW technical might be able to reverse it on request also. Even coding a new DSC control unit did not delete the sport brake

thank you for those precisions!

[MightyMouseTech]

Originally Posted by juld0zer

First i've heard of a vacuum accumulator for F15 models, not even the M models have one.

All the N55 and newer cars have one, as in all engines with Valvetronic. The engines no longer produce vacuum, as there is no real throttle body, so there is a mechanical pump inside the head to supply vacuum to the booster.

On the 1ers, this started in 2011.

[juld0zer]

Correct, but it's not an accumulator. The only vac accumulator on an N55 is in the rocker cover on early engines with pneumatic wastegates.

[gjm120]

Originally Posted by asbrr

To OP:

I put on 135i brakes on my 128i about 18months ago, with Stoptech street performance pads. They were very lightly used so bedding had already occurred. Compared to stock brakes....there was no comparison. Great bite, and it scared the crap out of me the first time I had to really hammer on them.

So - yea likely just bedding time, but after they are bedded go to an empty stretch of road and stomp on the pedal, it should be quite noticeable

Did you upsize the master cylinder or did it work fine with the 128i master?

[asbrr]

Originally Posted by gjm120

Did you upsize the master cylinder or did it work fine with the 128i master?

I did not, using the stock 128i master cylinder. Of note, I have not added the rear matching calipers for the BMW performance system on the 128i, these are larger 42mm single piston vs the stock 40mm single piston, but not the same as the 135i rears. Not sure if adding that small increase in piston size in the rear would push the brake feel over the edge, but as it is right now I noted no negative side effects of the front caliper install, in fact it was a huge improvement.

Lastly - I have also not done the "coding" for the BMWP brakes...I've had the car on the track a couple of times with no complaints so far so not sure if I will get to that...

[gjm120]

Originally Posted by asbrr

I did not, using the stock 128i master cylinder. Of note, I have not added the rear matching calipers for the BMW performance system on the 128i, these are larger 42mm single piston vs the stock 40mm single piston, but not the same as the 135i rears. Not sure if adding that small increase in piston size in the rear would push the brake feel over the edge, but as it is right now I noted no negative side effects of the front caliper install, in fact it was a huge improvement.

Lastly - I have also not done the "coding" for the BMWP brakes...I've had the car on the track a couple of times with no complaints so far so not sure if I will get to that...

So you're running 135i front calipers and 128i rears and obviously happy with the feel and balance.

The 135i rear calipers are 2 piston? I guess that could over tax the m/cylinder.

[asbrr]

Originally Posted by gjm120

So you're running 135i front calipers and 128i rears and obviously happy with the feel and balance.

The 135i rear calipers are 2 piston? I guess that could over tax the m/cylinder.

Yes correct - the feel and balance is just fine. Now mind you I go to 3 or 4 causal lapping days a year, I'm not hammering on the car for an ultimate track time. My driving style is generally easy on the brakes. But in daily driving no problems with feel, and they have been a good upgrade.

Yes the 135i rears are 2 piston and would probably have a larger combined volume than the stock 40mm rear single piston (can't seem to find the rear piston sizes for a 135i caliper easily). So I guess they would be worse for feel and would require a larger master cylinder, not sure how to really quantify the worse feel as there are a few people that have run them on their 128i. You do lose the e-brake if you just swap them onto your 128i rear, keeping the e-brake involves changing out the wheel carrier IIRC.

[gjm120]

Originally Posted by asbrr

Yes correct - the feel and balance is just fine. Now mind you I go to 3 or 4 causal lapping days a year, I'm not hammering on the car for an ultimate track time. My driving style is generally easy on the brakes. But in daily driving no problems with feel, and they have been a good upgrade.

Yes the 135i rears are 2 piston and would probably have a larger combined volume than the stock 40mm rear single piston (can't seem to find the rear piston sizes for a 135i caliper easily). So I guess they would be worse for feel and would require a larger master cylinder, not sure how to really quantify the worse feel as there are a few people that have run them on their 128i. You do lose the e-brake if you just swap them onto your 128i rear, keeping the e-brake involves changing out the wheel carrier IIRC.

Didn't think about the e-brake. For my driving, what you did would be more than enough. Adding this to my wish list. Doesl the 135i front caliper fit with 17" wheels?