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330 ->325xi brake swap and rear brake question

7K views 21 replies 9 participants last post by  redbull 325is 
#1 ·
after doing some reading and coinciding nicely with a preplanned brake job, I want to do the 330->325 brake swap.
I will be doing this in the front only.

My questions are as follows

1. can I use any 330 brake setup or does it hvae to be from an 330xi

2. in the rears, I wanted to replace the rotors, are they interchangeable among 325's or does the xi use a special rotor?

thanks!

Josh
 
#2 ·
You are going to need the calipers, carriers, rotors, and pad for the fronts. You will need rear hubs from a 330 in addition to the calipers, carriers, rotors, and pads or else the parking brake won't work anymore. If you don't use or need the parking brake then you just need the same 330 components as the fronts.

330i and xi brakes are the same unlike the 325i and xi.

Oh and you will need 17in or larger wheels to accommodate the larger brakes if you don't already have them.
 
#3 ·
I'm puzzled what the benefit is? Seems like lots -o- parts and $ to gain what? Not trying to make the OP defend himself obviously he knows the bonus but as this swap is not popular or 325's aren't exactly known having a weak brake system - just wondering. I switch cars all the time driving various company cars etc. I'm always amazed just how good my brakes are compared to other systems, never considered they could be better. In other words, as a DD is there a pay-off? You track guys don't count.
 
#4 ·
I'm puzzled what the benefit is? Seems like lots -o- parts and $ to gain what? Not trying to make the OP defend himself obviously he knows the bonus but as this swap is not popular or 325's aren't exactly known having a weak brake system - just wondering. I switch cars all the time driving various company cars etc. I'm always amazed just how good my brakes are compared to other systems, never considered they could be better. In other words, as a DD is there a pay-off? You track guys don't count.
No, there isn't. It's just to make them look cool. If you can lock the brakes up, you have more than enough stopping power. A larger rotor can shed heat faster but on the street, that won't matter. If you track, then go for it but if not then I wouldn't bother.
 
#5 ·
Thats a fair question, but I disagree with sam's assessment that their is no DD benefit. I only learned about this swap this morning, so based on what I have been able to ascertain, I have two schools of thought on it.

First, I want to clarify that I only plan on doing this to the front. I need to get new pads and rotors anyways, so I am only paying for new carriers and calipers. I can buy a set from NAPA (for example) for 200 for the pair, so this is only costing me a small amount of money.

Now as to the reasoning:

1. why did BMW put bigger brakes on the 330's? The car is not significantly 'sportier' (not in an xi trim anyways). Its not significantly heavier either. The only reason I can see is because it represents an 'upgrade'. Bigger is better in brakes, that shoudnt be in dispute. What is in dispute is if the 325 brakes are inadequate (they are not), but you could argue that about any number of modifications that people make to their vehicles (whats wrong with the stock clutch, oem tires, oem shifter, etc....)


that brings me to my reason:

2. I do mostly stop and go driving with the occasional rip out in the countryside. I had pretty bad brake fade the last time I did this, which is why I am doing new pads/rotors (regardless). I also am pretty hard on my brakes, when I learned to drive stick, I didnt really cotton to downshifting into stops, so I use my brakes quite a bit to stop the car, so again bigger is always better.

And my last reason, because I am pretty much dead set on turning my base level xi into a car its not. Upgraded to style 44's, gauge cluster rings, lip spoiler, etc... maybe it will get mistaken for a zhp some day :)
 
#8 ·
BMWs are German cars. They get driven at their top speed in Germany. A faster car needs bigger brakes plain and simple.

Bigger brakes weigh more also. You need more motor to make the payoff worth it.

If you have or have had brake fade I would *seriously* consider changing brake fluid asap. And get better pads.
 
#10 ·
BMWs are German cars. They get driven at their top speed in Germany. A faster car needs bigger brakes plain and simple.

Bigger brakes weigh more also. You need more motor to make the payoff worth it.

If you have or have had brake fade I would *seriously* consider changing brake fluid asap. And get better pads.
If I decide to do this I will weigh both setups for comparison. I can't imagine the weight difference is that great.

I have had some serious brake fade driving in the mountains (oh **** brake fade). This was more-hey, I am not slowing as quickly as I usually do fade. I have no clue what pads I have on now, so that's a no brainer....fluid probably needs to be flushed as well. I haven't done it in the year I have had the car.

Any recommendations for pads? Did I see to stay away from ceramic??

Also, how often do you need to change your ebrake shoes? As needed or regularly scheduled...
 
#7 ·
So given the cars are essentially the same weight (330/325 XI's), the larger front only setup would make for less fade when whipping and spurring in the twisty's as well less fade when hard braking under a panic stop. I thought ABS took over modulation under panic situations? Red, do you suggest pedal application or human modulation is applied as normal? Of course we don't generally mash the pedal on but when digging into them, it's normally progressive with slight on/off unless your performing winter techniques such as braking on ice staying out of ABS land.

Bigger sounds better if you can use it. I see guys putting on those "big brake kits" and always thought for the thousands they spend, the street pay-off was iffy?
 
#19 ·
I have thought about doing this upgrade, but the 330i rotors are 20 lbs each - 5 extra lbs of unsprung weight.
Unsprung wt would jump from about 75 to 80 lbs and make the 325xi feel slower.
While the 325xi can use the 330i and xi calipers on front and rear, this upgrade increases unsprung weight a lot and hurts handling in the end.
 
#20 ·
Yes, in theory a slight decrease in acceleration, but increase in stopping power and safety. Just like adding wider tires.

If you need bigger brakes, you probably already know it. Not necessary for a casually driven car. If you are glazing or burning up front pads at the track or want the extra weight transfer for autox, it's a no brainer.

There are lighter rotors available too.
 
#22 · (Edited)
I did this too, everything was plug and play. Only needed pads, rotors and calipers/brackets from the 330i F&R (rear parking brakes are the same between 325xi and 330i) Took the car for an aggressive drive in the mountains today and really enjoyed the increased braking power and the lack of fade when I got on them pretty hard.
 
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