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Superfin Mini Alloy Brake Drums


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#1 JDImini

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Posted 13 January 2020 - 10:44 PM

Hi

 

looking to adjust the rear brake drums as the handbrake doesn't hold the car. While trying to tighten them I can see that the drums, when they spin, the face nearest the backplate are not flush. The gap between the shock absorber being used as a datum and the back edge of the drum varies by about 6-7 mm in one revolution. Is that normal?

 

I hope the photo better describes what I was measuring

 

Attached File  IMG_5079.jpg   41.82K   3 downloads

 

Thanks

Darren



#2 nicklouse

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Posted 13 January 2020 - 10:47 PM

Depends on the quality of the casting.

 

it may or many not be an issue. 
 

depends on how the braking surface is moving.



#3 Ethel

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Posted 14 January 2020 - 01:52 AM

It sounds a lot.

 

The question is why - To investigate you could bolt the drum on to the hub inside out and rig up a pointer on a floor stand so you can inspect hub to drum; drum to wheel and friction surface are all true & concentric with the rotation.



#4 JDImini

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Posted 14 January 2020 - 09:52 PM

Depends on the quality of the casting.

 

it may or many not be an issue. 
 

depends on how the braking surface is moving.

 

Hi Nicklouse, thank you, they have minisport superfins as part of the casting. I bought them many years ago and i'm certain i wouldn't have knowingly bought some cheap knock off copies as i'd read about what poor quality the can be. In saying that while trying to adjust the drums I can feel that the shoes have a tight area and a looser area in one revolution of the wheel so the implication is they are not properly centred. by the way the car has only done about 1,000 miles so they should be OK

Thanks

Darren



#5 JDImini

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Posted 14 January 2020 - 10:19 PM

It sounds a lot.

 

The question is why - To investigate you could bolt the drum on to the hub inside out and rig up a pointer on a floor stand so you can inspect hub to drum; drum to wheel and friction surface are all true & concentric with the rotation.

 

Hi Ethal, thank you, I can see what I'm doing this weekend. 

Thanks

Darren



#6 JDImini

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Posted 14 January 2020 - 10:26 PM

Is there a good quality superfin? As I could spend a few hours measuring what I have only to find they are out of true and then buying a new set anyway

 

I'm prepping the mini for a track day so want the brakes to be as good as they can be.

 

Thanks

Darren



#7 nicklouse

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Posted 14 January 2020 - 10:29 PM

 

Depends on the quality of the casting.

 

it may or many not be an issue. 
 

depends on how the braking surface is moving.

 

Hi Nicklouse, thank you, they have minisport superfins as part of the casting. I bought them many years ago and i'm certain i wouldn't have knowingly bought some cheap knock off copies as i'd read about what poor quality the can be. In saying that while trying to adjust the drums I can feel that the shoes have a tight area and a looser area in one revolution of the wheel so the implication is they are not properly centred. by the way the car has only done about 1,000 miles so they should be OK

Thanks

Darren

 

Ahhh you have bought cheap knock off versions. 
 

unless you mean you bought some SuperfFns from MiniSport?

 

very few things that can cause the edge to move. Poor casting but has no bearing on anything if the brake surface runs true.

 

miss fitted drums. IE. parts between the mating surfaces. But should not give that much movement.

 

poor bearings causing the hub to rotate poorly.

 

my old genuine SuperFines do not have as much movement as you describe. But do feel to bind slightly but I think that is more to do with the pads working correctly and pulling onto the braking surface as it is not the same point.



#8 DeadSquare

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Posted 14 January 2020 - 11:11 PM

Is there a good quality superfin?

 

I'm prepping the mini for a track day so want the brakes to be as good as they can be.

 

Thanks

Darren

When motor racing, many Mini drivers disabled the rear brakes, as the little braking that they do, is not worth the occasions when they work too well and loose the rear end.



#9 Ethel

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Posted 15 January 2020 - 01:12 AM

Not sure if you got my point from the reply. There's no need for a specification, if they're true they'll rotate without any wobble anywhere. The bits that really matter are the bits that contact other components.Such as the brake shoes and hub & wheel so that the wheel doesn't wobble either.

I'd suspect something fouling the fit of the drum to the hub rather than the drum itself.

#10 JDImini

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Posted 17 January 2020 - 09:45 PM

thanks all for the comments, I'll get some photos and measurements tomorrow and post an update



#11 JDImini

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Posted 18 January 2020 - 11:59 PM

so...

 

setup the DTI and there was only 0.35mm difference on the braking surface of the drum in one revolution so i assume that small amount means the drum is running true. When the shoes are adjusted and the wheel is rotated the wheel gets very difficult to turn through about 90 degrees. After some further investigation it is only where the hub fixing screw get to about 12 o'clock and only if the screw is properly tight, if I loosen the screw by about a turn the wheel doesn't bind in one place, the force required to turn one revolution is consistent

 

hope this makes sense 

Thanks

Darren 



#12 dyshipfakta

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Posted 19 January 2020 - 08:09 AM

Is there something underneath the drum that is pulling it off square when the screw is tightened. Is the hub straight?

#13 Dusky

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Posted 19 January 2020 - 09:07 AM

Do you do that with the wheelnuts torqued?
If so, the screw you have is too long and catching on something.

#14 nicklouse

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Posted 19 January 2020 - 09:16 AM

Look for where the screw is catching. It will leave witnesses marks.

 

i have never used the screws ever on any car.



#15 JDImini

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Posted 19 January 2020 - 06:49 PM

Look for where the screw is catching. It will leave witnesses marks.

 

i have never used the screws ever on any car.

 

Hi Nicklouse,

 

It doesn't look like the screw is fouling anything and I did wonder what the point of the screw was as the wheel nuts via the wheels clamp the drum to the hub.  

 

The weather was nice today so with wheels torqued up my son and I found a nice quiet straight bit of road and tested the brakes, clearly had the rears adjusted too tights as they locked up very easily as the weight transferred to the front of the car, so back home wound the adjuster off a bit and much better this time and the hand brake still holds the car which it didn't before we started, which was the main reason for adjusting the brakes in the first place and just to check all was OK before a track day - I Know that DeadSquare said about racers disabling the rear brakes but as this is to be mainly a road car I think it does need some rear braking force and a more importantly a working handbrake.

 

When we do the track day we'll take some tools with us so we can adjust the brakes if we need to.

 

Thanks to everyone that contributed to this thread.






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