Rear disk convertion questions...

NeX

NeX

You're after my robot bee
Club Member
hi ya,

has anyone done a rear disk convertion?

i'm going for the upgrade from my drums but i have been told that the disks need less pressure to activate than the drums meaning that the disks will lock the wheels before the front ones engage.

will this happen?

does anyone know how or what adjusts the pressure between the fornt and the back brakes?

i've heard that some cars get round this by having two master pistons....


any help would be great :)

thanks loads guys n girls,
 
ok, so i can sort it without having to get extra bits?

the super s doesn't have some extra bit that solves the problem it's just set up differently?

thanks loads mate :)
 
if your doing the rear disks purly for stopping poewr there is no need. If your doing it for looks then cool :)
 
hehe well it's mainly for looks because the pulsar ones can stop a shuttle!

but also the drums aren't as sharp as disks so i want a shape hand brake as well as a foot brake...
 
Usually drums when working as they should are infact sharper than disks. ITs much easier to apply a force to a drum than disks. Just drums seem much more unrelaible...
 
really? i though drums were reliable but weak...

that's why the hand brake operates the drums so that the car is held in place...

anyway i want really good brakes because i'm going 1.6 turbo...

i might be able to get hold of an ABS system are these hard to install?


thanks loads people
 
ABS is not too hard to install if you have all the bits.
People have said that rear disks make the car 'flatter' under braking whis is a benefit
 
cool well i'm getting the guy who has the ABS to see how difficult it is to take out....

and i want all the stopping power i can get, i'm getting EBC brake pads and everything :)
 
drums are sharper, but they never stay as they should. On a disk/pad setup, when the pad has bedded in, it will work at 100% all the way until its getting to the very end of the material. Whereas a drum/shoe setup takesa heck of a long time to bed in. When it is finally beded in as it should, which sometimes never happens, yo ucan lock the back wheels at 2 click. BUt they normally need attention. The adjusters rarely work and as they wear, they become less efficient.
 

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disk brakes are more powerful than drums,far more...heres the maths

the average woman can exert 265N of force from there foot, u get a mechanical advantage from your pedal, as its a lever, the average dimension is 76.2mm by 25.4mm, using this formula

A=76.2
B=25.4

Mechanical advantage= (A+B)/B=(76.2+25.4/25.4=4/1

your breaking force at the master cylinder is 1060N

going off the average master cylinder cross sectional areas because there are obviously variations you get 2551K Pa of pressure out, i will show the maths for that if you want

so 2551K Pa at disk using 38mm pads u get 5787 N of total clamping force

-- pressure*area=force, i.e 2551x 10^6 x [(3.142x.38x.38)/4] m^2 x 2=5787 N

if you take your 5787 an x that by the coefficient of friction for a brake pad

--5787x0.45=2604 N
so your get 2604 of actual braking force at the disk on disk brakes

you also get 407Nm of torque, i can do the maths if you request

on drum brakes
force on brake shoes x coeff of friction x no of brake shoes

2551 becomes 2586 when taking into account the size of the brake shoes as aposed to pads

2586 x 0.45 x 2=1164 N

so a braking force at the wheel is 1164 N with a torque of 149 N

These are only figures for average brakes but they show you get nearly 4 times more torque an twice the force using disk brakes, so who ever said 'drums are sharper' need to look at the figures, the coeficent of friction is taken from the brake pad/show material
 
that's why the hand brake operates the drums so that the car is held in place...
Click to expand...
problem with rear discs and the hand brake is if you have done alot of braking and the pads and disc is hot, you come to stop, say park on a hill and leave your car for a while, you may find it wont be there when you get out.

it's because the heat expands it then it retracts when cooling down so it doesn't apply as much pressure.

i know on scoobies and some other cars you have a mini drum inside the rear disc for the hand brake to stop this.


sorry if you already knew this :)
 
ricardo_swarez interesting post, but how did you arrive at those assumptions? They are way to oversimplified to actually mean anything.

There are many areas in which drums have advantages over disks. And one is stopping capability - hence why they are the norm on busses trains and lorrys. The fact is on a micra drums are actually fine when they work as they should, but disks are more fashionable.

Wilsonian points out that disks shrink, which is true, but the real reason for differnet systems is that its required by the construction and use regulations to have two totally different break systems on a car. One mehanical such as cable systems. Its easier to make drums into a break disk I would imagine than it is to make special brake calipers that could be cable as well as hydrolic.
 
ricardo_swarez said:
disk brakes are more powerful than drums,far more...heres the maths
<cut some really bad maths>
These are only figures for average brakes but they show you get nearly 4 times more torque an twice the force using disk brakes, so who ever said 'drums are sharper' need to look at the figures, the coeficent of friction is taken from the brake pad/show material
Click to expand...

This analysis is so far off from the truth, I don't even know where to start.

1. You can't compare a standard front disc with a standard rear drum. The rear drum is intentionally designed to apply less braking torque than the front disc, because otherwise the rear wheels will lock up and you will lose control.

2. Pad area has nothing whatsoever to do with force applied, it is down to the area of the piston. Frictional force is independant of area, at least if you are talking about static friction.

3. For a given pressure in the hydraulic system, and assuming the same area of piston, a drum brake will exert more braking torque than a disc brake. Look in any automotive engineering book.

4. The issue was about "sharpness", which I think most people would assume isn't the same braking torque. Disc brakes have a nice linear relationship between braking torque and applied force, whereas drum brakes, because of the self-energizing effect, aren't linear at all - they'll snap on in an instant.

I'm not saying drums are better. They suffer from brake fade more. They are harder to maintain. They don't self adjust or wear evenly. But discs are not better for the reasons you state.
 
hmmm, some interesting posts

so why do the super s's have quad disks? is that just to look good?

and why are there disks on the front where all the braking is needed?
could it be to do with heat because drums can do lots of breaking and don't get too hot but disks heat up really quickly or am i just wrong :)

also the hand brake problem wouldn't that be the same on drums? or would the drum contract making the braking harder?


one problem i know with drums (cos i got it on my bike) is the drums filling with water when its wet....


ok anyway back to the origanal question, if i chuck disks on the back of my car will they work or will i have to change the biast??

and what part of the super s controls the biast? because i'll need to get it...

thanks loads guys,

i didn't think this would be such a debate
 
hard to say if you will need to or not. most micras are different in the way they handle and brake. after you have done the conversion take it for test drive and find out where the braking is. then adjust bias to suit. although its a bit trial and error. you may have to adjust it more than once. the bias is not controlled by the super s but the valve all micras have. as in the haynes. the abs setup has a control system for the brakes which is setup for the rear discs, but it seems likes its not needed, but i dont have experience of this conversion 1st hand.
 
Discs are much better brakes, primarily because they are better ventilated and have a large swept area than drums, so cool better and hence you don't get brake fade. They also throw off water and dirt, unlike drums, like you say.

The brakes stop the wheels turning, and the tyres stop the car. Ultimately, the rate at which you slow down under braking is determined by the contact between the tyre and the road, not the braking torque in the brakes. As long as the wheels can be locked up, you have sufficient braking torque. Both drums and discs are totally adequate to do this.

I don't know if you'll have to adjust the bias, as I don't know about the K11 braking system in particular. I should imagine the rear cylinders to be smaller, so wouldn't need as much work. But, getting it right is very important. Having the rear wheels lock hard before the fronts have even thought about stopping would result in a nasty spin unless you quickly controlled the skid - it's also very hard to detect this happening.
 
why is it hard to detect this? i havent had a problem telling difference from fronts and rears locking up.
 
Since were looking at why the K11 had rear disks in the first place the answer for this is actually very simple!

ABS

Nissan had not designed a system before using rear drums with an ABS system, so at the time of the K11s release the only way for them to give the K11 ABS was to fit disks all round. This soon changed however as a couple of years later the Micra was developed with rear drums and ABS. Since then the Micra never saw rear disks again.

Ed
 
which means for the micra either drums are better or are cheaper to manufacture and fit than calipers/discs. wouldnt mind betting its cheaper though. in fact i know its cheaper. look at the cost of calipers and discs and pads compared to drums/shoes/cyliders. drums are so much cheaper. budget city car you see.
 
ok so the super s rear disks were more of an experimental thing..

and the bias control is standard on all micras and if i'd bothered to look ing the haynes i'd have found it :)

i'm not doing the convertion myself i'm getting a pro because as many people have mentioned its quite dangerous if i get it wrong... so everything will probably be done on a rolling road or someting.

I'm sure disk design has come along way, and disks have all the advantages of being open air... its very interesting :)

i think i'll do the read disk convertion just because i'll be using the super s ABS system, and for the wank factor ;)
 
Beachboy said:
which means for the micra either drums are better or are cheaper to manufacture and fit than calipers/discs. wouldnt mind betting its cheaper though. in fact i know its cheaper. look at the cost of calipers and discs and pads compared to drums/shoes/cyliders. drums are so much cheaper. budget city car you see.
Click to expand...

Drums are infact more complex and have more moving parts than a caliper which the only moving part is the piston and pads!

The thing is and it makes no difference how many think otherwise, from a technical point of view the micra does NOT need rear disks. I can say this by having the March ST which even with around 150bhp and fully loaded the GTIR front calipers and disks would fade way before the rear drums would. You have to understand that the rear drums do their job on a K11 with no problems at all and when totally disregarding the fact that disks are more fashionable there are absoutely no advantages to fitting rear disks at all!
 
except when you want to upgrade to an ABS system that will only except rear disks :)
 
Beachboy said:
why is it hard to detect this? i havent had a problem telling difference from fronts and rears locking up.
Click to expand...

It's much easier telling when the front wheels have locked - you will lose all steering straight away. When the rears lock, the rear will tend to follow the front until it feels like breaking away, and by that point you will have gone into a very bad skid. This is especially bad when you have little braking torque on the front wheels, and loads on the back. You want them closely matched, so that the when the driver detects any wheel locking, he can assume that all the wheels are close to locking.

Look at it this way. You are driving along, a hazard occurs directly in front which causes you to do an emergency stop. You slam the brakes on, the rears lock entirely, the fronts don't at all. You keep on going forwards, in a straight line. The steering still feels like it works, so you decide to turn away from the hazard. The front moves, sending the back flying out, and you go into a spin.

If the fronts were near to locking up when the backs locked up, you would notice ineffective steering, and hence release the brakes somewhat. The turn could then be performed with much more control
 
Unless you use the later design that still had drums!! :) haha If it helps you NeX, Dave S who occasionally uses this forum did the drum to disk conversion himself on his car. (Straight ABS rear swap) Brake balence is fine, you have nothing to worry about there, the only problem has has if any is the rear disks dont do alot of work so they never really seem to bite properly looking at the surface of the disks. Sometimes also the calipers stick slightly.
 
Andrew said:
Beachboy said:
why is it hard to detect this? i havent had a problem telling difference from fronts and rears locking up.
Click to expand...

It's much easier telling when the front wheels have locked - you will lose all steering straight away. When the rears lock, the rear will tend to follow the front until it feels like breaking away, and by that point you will have gone into a very bad skid. This is especially bad when you have little braking torque on the front wheels, and loads on the back. You want them closely matched, so that the when the driver detects any wheel locking, he can assume that all the wheels are close to locking.
Click to expand...

Just too ad that the rear bias is always set for worst case sinero i.e. snow and water and Ice. so that the rear never breaks away before the front. Some cars have rear break bias load compensation such as 106 and Saxo VTS/VTR. Which alters the rear bias depending on rear load. Lots have come unstuck when lowering their car tricking the system into thinking it has lots of rear load when it doesnt, resulting in rather scary driving conditions!
 
RE: RE: Rear disk convertion questions...

Ed said:
Unless you use the later design that still had drums!! :) haha If it helps you NeX, Dave S who occasionally uses this forum did the drum to disk conversion himself on his car. (Straight ABS rear swap) Brake balence is fine, you have nothing to worry about there, the only problem has has if any is the rear disks dont do alot of work so they never really seem to bite properly looking at the surface of the disks. Sometimes also the calipers stick slightly.
Click to expand...

thanks mate :)

so what had ABS and drums... the SR or is it all those 2000+ models?

the only reson i'm getting this ABS system is because it off a car that i'm getting a load of other stuff off as well so i thought i'd get the ABS as well.

So the quality of the rear calipers is a bit lame if they stick and don't bite proplerly,

so back to some of the first questions is it possible to put the old front calipers on the back :)

Well thank you everyone. still alittle confused and it's starting to sound like this convertion is a bit of a waste of time but then it's all about the wank factor :p
 
Andrew said:
quickdraw said:
we also have andrew and ED disagreeing o_O

hmm.. i wanna hear more on this debate. regarding these 2
Click to expand...

What have we disagreed on? I can't see anything...
Click to expand...


your saying discs are better ED saying drums are.

all im saying is...

i wanna see both side points as up to know the only ones with real info on why this is so.

since i was gonn ad discs to the rear of mine. but on convinced me otherwise against this. now your sayign the iscs are better. im getting 2 sides of the story so very interesting read as to why each side thinks so.,
 

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Better isn't sharper or more powerful.

The limit to how fast a car can stop is the tire/road contact, not the brakes.

Both drums and discs are perfectly capable of exerting enough force to stop a car.

Brakes exhibit something called brake fade, caused by heating. Discs are much better at cooling down, and hence don't suffer from brake fade as much. Brake fade doesn't just happen during hard driving, motorway driving can just as easily cause it.

Disc brakes aren't as sharp, which means you can control the force better. They are smooth and linear, whereas drums are more on/off. You don't really want sharpness in brakes, as it means it's very hard to control how much you are braking.

When a car stops, the weight distribution puts as much as 90% of the weight onto the front wheels. You need 90% of the braking torque to be there, so you need more powerful brakes at the front than at the rear. This braking effort will also mean 90% kinetic energy of the car is converted into heat at the front, so you need to be able to get rid of heat at the front better. Hence you use discs.

Although a disc and drum brake with the same sized cylinder will exert the same braking torque, it's easier to make a disc with a very large piston area - hence 4 pot brakes. You just can't do this with drums, there isn't the room.

Drums are much easier to activate using a secondary mechanical system than discs, and as has already been said, the drums contracting increases braking, whereas discs contracting will release them. So they are used for handbrakes.

Just take a look at something like the Carrera GT and it's brakes. The front rotors are immense, bigger than the wheels on most Micras. The rear ones are tiny, pretty much like the fronts on a Micra. Even when you reach that level of performance, there is still no need to have great brakes at the rear - they just aren't used.

So better is a matter of viewpoint. Ed and me agree on the same stuff about this, just it's such a complicated set of factors, that it might not seem like it.
 
but withyt he ratio on the micras being at roughly 70%-75% front to the 30-25% rear brake ratio should this not be an issue really.

as the rears wont lock up before the front surely o_O

if so then sumthing i wrong.

so speaking of engine conversions. as ED says the tyre to road contact therefor with a bigger weight behind the vehicle to slow would drums not be better?

or if the more power being put through the drive then which would be betetr as power increases.

when looking from between 150bhp-200bhp froma micra k10-k11.
would discs not be better?
due the the gradual decrease rather than the on.off lock up system the drum implies.

o_O

these are the mnay questionws i think people wanna know.
me included.

as Ed says. lorries etc all use a rear drum system on there brakes. and with a mass weight difference on them and the power torque they push through the drive. does this not prove that rear drums would be better?
but then am i right in sayingt he F1 type vehicalkes use a rear disc setup. sao then does this mean due to the less weight but higher power band (less powertorque thatn the heavier load. more torque to move the heavier load etc) that discs would be better.?

just a little confusion as to which IS actually better for what we are neeeded not in general.

question beign for the higher power transition the k10-k11 at 150-200bhp would discs or drums be better?
 
RE: RE: Rear disk convertion questions...

Andrew said:
Beachboy said:
why is it hard to detect this? i havent had a problem telling difference from fronts and rears locking up.
Click to expand...

It's much easier telling when the front wheels have locked - you will lose all steering straight away. When the rears lock, the rear will tend to follow the front until it feels like breaking away, and by that point you will have gone into a very bad skid. This is especially bad when you have little braking torque on the front wheels, and loads on the back. You want them closely matched, so that the when the driver detects any wheel locking, he can assume that all the wheels are close to locking.

Look at it this way. You are driving along, a hazard occurs directly in front which causes you to do an emergency stop. You slam the brakes on, the rears lock entirely, the fronts don't at all. You keep on going forwards, in a straight line. The steering still feels like it works, so you decide to turn away from the hazard. The front moves, sending the back flying out, and you go into a spin.

If the fronts were near to locking up when the backs locked up, you would notice ineffective steering, and hence release the brakes somewhat. The turn could then be performed with much more control
Click to expand...

from experience i found it instantly recognisable when the rears lock up. i can feel it, i can hear it. due to how my car is it gives me lots of feedback from the chassis and the steering wheel.
 
Beachboy said:
from experience i found it instantly recognisable when the rears lock up. i can feel it, i can hear it. due to how my car is it gives me lots of feedback from the chassis and the steering wheel.
Click to expand...

There is the key difference - "from experience". Very, very few drivers have experienced this. The car manufacturers don't want the average driver to wreck their car because of this behaviour. I would also think, when it came to the crunch, and you stop thinking and just acting, as you do when something really bad is happening, you too would prefer a car where the front wheels lock first, and you can intuitively deal with the situation.
 
RE: RE: Rear disk convertion questions...

Ed said:
Beachboy said:
which means for the micra either drums are better or are cheaper to manufacture and fit than calipers/discs. wouldnt mind betting its cheaper though. in fact i know its cheaper. look at the cost of calipers and discs and pads compared to drums/shoes/cyliders. drums are so much cheaper. budget city car you see.
Click to expand...

Drums are infact more complex and have more moving parts than a caliper which the only moving part is the piston and pads!

The thing is and it makes no difference how many think otherwise, from a technical point of view the micra does NOT need rear disks. I can say this by having the March ST which even with around 150bhp and fully loaded the GTIR front calipers and disks would fade way before the rear drums would. You have to understand that the rear drums do their job on a K11 with no problems at all and when totally disregarding the fact that disks are more fashionable there are absoutely no advantages to fitting rear disks at all!
Click to expand...
what i'm saying is drums are cheaper when it comes down to it.
you cant just say micras dont need rear discs, the rally micras convert to rear discs. they require the rear discs for more brake use at the rear wheels.

after my micra was lowered in all conditions the rear wheels locked up. if anyone has lowered there micra/has taken weight out of the back i recomend thinking about the brake bias.
 
Beachboy this wasn't when you put incredibly dangerous and thin tyres on the back to stop understeer was it ?! lol
 
Lorries aren't a great example. They try to keep as constant a speed as possible, and any speed changes are done using the engine, and not the brakes. Some newer tractors actually have a system that alters valve timing to use this "compression braking" to stop better.

When a lorry does want to stop however, it normally really wants to stop. Hence you have drum brakes, as ultimately, they can provide more torque. Lorry brakes are pneumatically operated as well, and discs don't lend themselves well to working like this.

Just look at it as brake fade, reliability, water shedding. Discs are better at this. Brake fade dominates braking performance when driving hard. When driving for economy, as in a lorry, you won't heat the brakes up enough to notice.
 
Busses use drum brakes. (the drums are almost to heavy for one person to carry apparently) and they do stop all the time, although I do agree with the engine breaking and other systems used, a bus is definately a stop start form or transport same as trains!
 
what about the hand brake then, because i don't want my car to roll away, will this be much of an issue or only if i've just done a 20 mile trip with the hand brake on...

oh and by the way people its Disk not disc, we're no American :p
 
the maths is simplified as i do maths as a minor in my degree and i can understand that if i put all the maths in then some ppl wouldnt be able to follow, those are simplified versions that miss out some steps but arrive at the same conclusion, they are taken from my thesis, a case study on braking systems, that i got 98% for, an the maths was totaly sound, so ED in this case your obvious superiority complex believeing your opinion overides all other is.....wrong, i would believe the teachers at uni, the one who takes me for mechanical systems actualy designed brakes for 20years, over some guy, who never has a good opinion of anythin an runs some site on the internet... i'll start my stop watch now........i'd say 10mins till im banned and my post is removed, because unlike other micra sites like micra holics an cisco's site, if you post any opinion that says the self titled god of micras disagrees (ED) u get banned and your post is removed...and your about to prove it when you ban me an remove this post...
 
Andrew

2. Pad area has nothing whatsoever to do with force applied, it is down to the area of the piston. Frictional force is independant of area, at least if you are talking about static friction.

since the braking force is dependant on the pressure being delivered........how can u say that the brake pad size doesnt matter!? pressure if force/area.........so if the pad was bigger then there would be a larger area, but less pressure, an if there was a tiny pad then there would be all the pressure accros a small area, so there has to be a ballanced striked between getting the rite amount of pressure and the right amount of friction, you my friend are a grade A retard
 
Was waiting for this thread to get out of hand and context...

Didn't take long i see, suppose it never does.

But on the same level - go for it ricardo. I belive you may have a point...
 
alittle harsh mate, but you seem to have some good qualifications,

is it all braking systems you studdied or just car systems?


one thing i'd like to know, does thermal expantion have any effect on the pad itself or is it designed not to change size due to heat? what are they made off, aspestos?
 
Titch, just because one poster chooses to bring it down doesnt mean the end of the world. If they wish to publically make a scene its upto them!
 
Ed said:
Titch, just because one poster chooses to bring it down doesnt mean the end of the world. If they wish to publically make a scene its upto them!
Click to expand...

Yea - and i wasn't saying it was either. What i was meaning was that since there seems to be so many diffrent views on this, it will no doubt end up in a argument, then get locked.

But now we're just going off of topic, so lets just leave it at that shall we?
 
No asbestos is used in cars any more its been totally outlawed for a while now. Also everyhing does change size due to heat, you cannot avoid that however clearences will be designed to accomdate this (one of the resons shims etc are used)
 

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