Rear brakes upgrade discussion

There have been quite a few discussions on upgrading the rear brakes.

While the AR fronts are 4-pots and perfectly adequate, the small rear calipers don't look up to the job, even when they are painted red! (as a few were).

The options have included adding 4-pots to the rear or the slightly cheaper 2-pot ARs from the late Chinese TFs, but there seems to be more-or-less agreement that in fact more stopping-power is not really necessary - as the ideal balance of 70/30, front/back is adequately handled by the standard calipers.

I must admit that in terms of appearance the smart AR 2-pots on the rear would look the part, but I noticed that the Alfa 4c, which has 240bhp from a 1747cc engine - with turbo - has similar feeble-looking rear calipers to the F/TF:




If, for a 'new' car, only a couple of years old, the Alfa engineers reckoned those calipers were adequate, then I reckon I can give up on the idea of going for something hairier and just put decent pads and decent drilled/slotted disks on the back? Both together are about the same price as the separate caliper for the hand-brake otherwise needed!

Drilled/slotted discs make absolutely no difference to braking force. They just help with heat dissipation. :dry:

Better pads/higher friction coeficient pads do help with the braking force and if you are sure you are sticking with the original size callipers and discs then getting better pads is a less expensive way of improving braking at the rear, :yesnod: although you will find that the cost does increase significantly from standard pads. They will also wear out the discs faster too, requiring replacement more frequently.


Personally having gone through most of the combinations of standard discs/better pads right through to 304mm discs all around.
I would place the various options in the order.
Standard 240 discs and pads.
+Better pads fitted.(better braking)
+304mm fronts fitted.(Better but lots of front brake lockups)
+Bigger rear discs and blocked out callipers(Not tried this one personally, but have seen warping issues. Better braking balance_)
+brake balance adjuster fitted (Better again reducing front lockups)
+304mm discs all around. (stunning braking, with no lockups)

All are straight upgrades except the 304mm discs all around. This requires a separate handbrake spot calliper and manufactured brackets,re routing the handbrake cables plus some work on the rear hub to get the callipers to fit. The braking is stunning though. Plus I haven't tried better pads in the 4 pots yet

I was thinking drilled/slotted variants of discs help maintain braking effect rather than increase it, as you say due to heat dispersal.

Did you find yourself that 304s - standard on TF160s for example - caused lock-up - not something I have come across?

Bigger rear discs - why would that cause a better brake balance if 70/30 is ideal anyway?

Is it not the case that TFs don't need a balance adjuster as it's built in?

You have tried 304s all round and it feels great, but is it just subjective as it exceeds the 70/30 ideal?

304s all round look the coolest, but most performance cars, eg Porsche (6 pots at the front, merely 4 at the rear), and the Alfa 4c (looks like 4 pots at the front and f/TF type at the back, have bigger fronts than rears - if Alfa make a new car with 240bhp and £60k to buy with 'standard' rear calipers - could they be wrong?!

Heat dissipation only comes into useful effect if you are using the car on track. The only time I have seen a need for better heat dissipation on the road was a very spirited drive down Hartside pass resulted in all cars with standard brakes having smoking rear brakes! Interestingly the cars with 304 fronts didn't experience overheated rears mainly because that configuration means most of the braking is done by the fronts.

If you consider that the original configuration was 240 discs all around, then 304 all around makes more sense than 304/240 setup. Most cars with 304/ 240 were made that way by MGR and they either have ABS and/or the proportioning valve altered/removed.

Front wheel locking occurs when you upgrade the fronts to 304 on a 240 all around car. By adding the adjustable bias valve you remove the standard proportioning valve and can then get a better balance front to rear 304/240.

The 70/30 balance is usually for a front engined car, ours are rear/mid engined which does have an effect. Slightly more rear force is effective for our cars.

An important point is that the adjustable valve/proportioning valve is only in the rear brake line, so only affects the rear force. The front force is unaffected, So without any proportioning/adjusting the balance would be 50/50.

I have found that reducing the rear to 60% of max gives a very good balance on my car.
In effect this is a balance of 62.5/ 37.5 front to rear.

All standard braked cars have the proportioning valve in the rear line. I believe this reduces the rear force to about 45%. so that would give a standard balance of 68-69/31-32
More or less 70/30.
By changing to 304s you are increasing the front braking force substantially, so the original proportioning valve will be allowing more overall percentage force to the front, hence the front locking.

An additional point is that the bigger front discs mean less force is required on the brake pedal, all this means that the rear brakes are under utilised. This has led to seizing of the rear callipers and subsequent handbrake failures in many cases.

So a TF160 has a different proportioning valve to a standard tf???

My TF160 has ABS, no proportioning valve .

mgbv8mike wrote: My TF160 has ABS, no proportioning valve .

Yeah, that makes sense. :yesnod: I am uncertain what the position is for any 160 TFs that don't have ABS(if there are any). Whether they have a different proportioning valve or none at all.:shrug: Anyone out there have one?

For example, the early Trophy 160s didn't have ABS, but as I say, I don't know whether they had a proportioning valve or not.

I thought all the VVC cars had ABS and I thought the proportioning valve was in the ABS pump.

Yes all the 160s have ABS it was one of the upgrades to make the 160 stand out [ with leather seats ] but the later TFs also got abs
I also think the F vvc had abs with leather seats and different wheels

What about the 135 with 304mm discs did they have a proportioning valve?Or were they all abs equipped?
Only ask because a 135 without abs is getting a pair of 304mm or 280mm in the near future and I assume it has a valve fitted

I presume that any F/TF with factory fitted 304s would be equipped either with ABS or with a setup giving decent balance front to rear. Whether this involved a different proportioning valve or no proportioning valve :shrug:

Someone needs to take a gander at the pipework on a 304mm factory equipped car without ABS, to see if there is a proportioning valve in place.
You just need to remove the black plastic shroud under the bonnet and take a look.
Here is a photo showing the valve in position.



And the adjustable valve in its place.