Rear disc brakes

[cliftyhanger]

You wont be able to fit 256mm discs inside Sprint wheels 13 inch you would need 14 or 15 inch wheels, im using 260mm disc but im using 14 inch wheels

Dave

Fret not, 14" wheels already on the car.
256mm VW discs in the garage, just need to borrow some lathe time.

[TrustNo1]

whats the beneift in fitting rear discs apart from the lkleyhood of the rears locking up easer which personally I don't see as a benefit, if your brakes are not good enough this is down to one of two things, you're too used to a modern car with better brake balance etc OR there is actaully something wrong with your brakes such as old pads, weak fluid, sticky caliper or poor adjustment all of which can by sorted in a few hours

The problem is people assume that disks are automatically better than drums, so fitting them will improve things. Whereas in reality, you need to understand how something works before you can successfully upgrade it.

It is a bit like people who think they can get more power out of an engine by bolting on a bigger carb and randomly hacking bits off their cylinder head with a dremel. Who are then shocked when they put their car on a rolling road and find it makes no difference or has made the situation worse.

Thats aways going to happen when people push the boundary, there must be a few heads that have been ported badly, but unless you make mistakes how you learn what works

if you make a mistake porting a head the worse thats going to happen is you need a new head, if you make a mistake fitting brakes that were never designed for that car the worse that will hapen is is you kill a group of nuns and all the litte children they re taking out for a fun day.

[Carledo]

............... if you make a mistake fitting brakes that were never designed for that car the worse that will happen is is you kill a group of nuns and all the little children they're taking out for a fun day.

You forgot the kittens!

Steve

[TrustNo1]

............... if you make a mistake fitting brakes that were never designed for that car the worse that will happen is is you kill a group of nuns and all the little children they're taking out for a fun day.

You forgot the kittens!

Steve

they we're ran over years ago when someone fitted lowerd suspension and banded wheels

[jikovron]

Just to be a devil's advocate, rear discs aren't necessarily more powerfull than drums, however they have a more predictable response, recover faster from damp and fade, which is less likely in the first place, and don't harmonically resonate like a drum does at really high speeds, I loved the feel of discs all round on my dolomite progressive, smooth barely any fade and would never hint at locking the rears up unless on snow, far better than a massive heavy drum brake severely limited by an LSV, I will admit though that often but not always caliper handbrakes do deteriorate quite badly.

[GrahamFountain]

Oddly enough, it should be less likely that the rear wheels will lock first when the surface that both the front and rear wheels are on is more slippery. And, arguably, it's the order in which the two sets lock that matters more than anything.

Even though the back wheels are, overall, more likely to lock for a given pedal pressure on a slippery surface, they are less likely to lock first. That's because the grip a wheel has, so how much braking it can apply before it locks, is in proportion to the weight pressing down on it (among other things), and under breaking, one effect of the deceleration is that some weight is transferred off the back wheels and onto the front ones. And how much weight is transferred is in proportion to how hard you break (and how high the centre of gravity of the car is above the road), which is why the front end dives more when you break harder.

So, on a more slippery surface, you get less deceleration before the front wheels lock and so less weight is transferred off the back wheels before that happens. So when the front wheels lock, the back wheels have a big fraction of what little grip there is in total, and are therefore less likely to lock first. Whereas, if the surface is less slippery, the front wheels won't lock until there's much more deceleration and so much more weight is transferred off the back wheels. So, when that happens, the back wheels have a smaller proportion of the total grip and so are more likely to lock first.

So that, in part, is why fitting tires with more grip, e.g. wider or softer compound, can make it more likely that the back wheels will lock first. Why that effect of more grip making the rear wheels more likely to lock firsts is made worse if you fit bigger front brakes at the same time, is more complicated.

[GlenM]

Just to be a devil's advocate, rear discs aren't necessarily more powerfull than drums, however they have a more predictable response, recover faster from damp and fade, which is less likely in the first place, and don't harmonically resonate like a drum does at really high speeds, I loved the feel of discs all round on my dolomite progressive, smooth barely any fade and would never hint at locking the rears up unless on snow, far better than a massive heavy drum brake severely limited by an LSV, I will admit though that often but not always caliper handbrakes do deteriorate quite badly.

That sounds promising for those of us going with discs. Did you have a brake bias valve fitted with your set-up?

[jikovron]

Just to be a devil's advocate, rear discs aren't necessarily more powerfull than drums, however they have a more predictable response, recover faster from damp and fade, which is less likely in the first place, and don't harmonically resonate like a drum does at really high speeds, I loved the feel of discs all round on my dolomite progressive, smooth barely any fade and would never hint at locking the rears up unless on snow, far better than a massive heavy drum brake severely limited by an LSV, I will admit though that often but not always caliper handbrakes do deteriorate quite badly.

That sounds promising for those of us going with discs. Did you have a brake bias valve fitted with your set-up?

I didn't fit the lsv, I used the calipers from a rover 45 which arguably being of similar weight with likely more front bias seemed a great match as it had smaller rear pistons than mgf calipers unsurprisingly.
My feeling is that had I used mgf calipers that the lsv would have been a good idea, with all the other benefits withstanding.

[bazyerma]

Hi

I used Ford Ka callipers at the front with the tracker jack kit, and MGF callipers at the rear with no LSV, other than a longer travel of the brake pedal I think it was a worthwhile upgrade to my 1500TC
and no nuns or kittens have been killed!

Regards

Barry

[GlenM]

[/quote]
I didn't fit the lsv, I used the calipers from a rover 45 which arguably being of similar weight with likely more front bias seemed a great match as it had smaller rear pistons than mgf calipers unsurprisingly.
My feeling is that had I used mgf calipers that the lsv would have been a good idea, with all the other benefits withstanding.
[/quote]

I meant a brake bias valve rather than the LSV. I will probably fit one, then I can adjust the balance, if necessary. What front discs did you have?