Brake info/ adivse. J-spec to uk?

Hi all

I know that one of my j-spec front calipers is starting to bind. So decided to change them but thinking of changing to uk fronts for the extra stopping capabilities.

So first diahlema is, is running uk fronts and j spec rears a good idea? or will it though out the balance and make in unpredictable?

Im not going to change the rears as they were brand new oems installed only a couple of years back, along with new pads and disks.

If this is ok to do, I seem to remember someone doing a template to print out to see if wheels clear uks, could someone point me in that direction please, as i keep hitting blanks.

I'm running UK fronts and J-Spec rears. Stops ok. What wheels have you got?

Currently running Volk racing Av's 3 piece split rims, but they are 17" not 18". Will be changed soon but if i go for uk brakes probably hold off on new wheels for an extra 6months or so.

Can be seen here

http://www.mkivsupra.net/vbb/showthread.php?305017-Gauging-interest-Volk-3-piece-wheels

I put big brembos on mine today. seem fine with the j spec rears.

The issue could well be with the clearance between the inner surface of the spokes

to the caliper face, arrowed in yellow rather than the inner diameter of the wheel

My Work Equips were very close to the back of the spokes

I have uk fronts and j spec rears and car stops fine aswell

I think it'll be mega close if they do fit over them.

I also have UK fronts and JSpec rears with no dramas.

Find someone local to you that has UK brakes, and test fit a wheel.

You'll probably find the rears start to fade, if you are pressing on hard but you'd have to be doing some silly speed, uk fronts, j-spec rears with chris wilson pads is a great combination

Most US owners fit jap rears (NA) with UK fronts (TT) to allow clearance for 15/16" drag wheels.

ok cheers guys, I know a couple of people with uk's so I will send some cheeky pm's If they fit im thinking I may aswell go for them.

Brake upgrades can set out to try to achieve several objectives.

The commonest are to increase resistance to fade and or increase

braking effort for a given pedal effort. IE, the pads are

pushed against the discs harder for a given pedal effort than

before the upgrade, or the brakes will stop the car from 100 MPH,

hard, for more times before fade sets in, than previously. The feel

from the pedal, that almost intangible quality, can also be addressed

and sometimes improved upon by brake size, or pad material changes, or

brake flexi hose upgrades to something less squashy than rubber.

It's easy to get carried away by the thought of brake upgrades.

The limitation in most cars as to how short a distance they can

stop in is tyre friction. Leaving aside pedal feedback, and fade,

it is almost certain that a Supra on stock Jap spec brakes will

stop in just as short a distance as one with an AP six pot kit on

it, a Brembo kit, Pauls KAD kit, or whatever. It may not feel to

the driver that it does, but usually such is the case if you just

nail the pedal as hard as you can. The fancy kits may *FEEL* to

stop the car faster, due to less pedal effort, and a better bite,

but in reality, if you hit the pedal as hard as you can with stock

Jap spec brakes, UK spec brakes, AP kit, KAD, whatever, the car

will stop in the same distance. Repeat this test 10 times and stock

Jap brakes may be on fire and long since faded, or the fluid boiled,

UK ones may be very hot and bothered, but the upgraded ones will

probably still be working within pad, disc and brake fluid temp

limits. Add in the intangible "feel" factor, and a desire to brake

as hard as possible, using as little skill as possible, but WITHOUT

relying on the ABS to take over, and for sure a well set up brake

upgrade may well allow more finesse.

Herein though lies the rub.

Upgrade only the fronts and the brake balance of the stock car may

well be compromised. Let's take stock brakes. You press smoothly on

the brake pedal with (say) 50 pounds force. The car stops fine. 70

pounds, the fronts are just beginning to lock (car makers ALWAYS aim

for the fronts to lock first, as rear wheel lock makes the car very

unstable and liable to swap ends). The rears are doing as much work

as the brake engineers deemed safe to prevent premature rear lock up.

The ABS cuts in, and maximum retardation has been reached. Now, take

a car with big front discs and calipers. Only 40 pounds pressure now

gives a smooth, lock free and powerful retardation. 50 pounds and the

new, more powerful, (for the same pedal pressure), fronts are locking.

The ABS cuts in. BUT, and this is the crux, those original rear

calipers and discs are still well below the caliper pressure where

they are able to achieve maximum retardation without fear of the

rears locking.

In other words the FRONT brakes are doing TOO MUCH work, albeit without

breaking into a sweat, and the rears are, to exaggerate a bit,

just along for the ride. The BEST scenario is to upgrade front AND

rear brakes, carefully ensuring the original balance of effort at any

given brake pedal pressure remains as designed, but that the more efficient

front AND rear brakes stay cooler for more hard stops, and that old

intangible "feel" from the brake pedal is improved, at lower rates of

driver effort on the pedal. The latter may or may not be good or

desirable, and can be engineered out by changing BOTH front and rear

caliper piston sizes, or pad areas. In a race car the balance would

be adjustable via 2 brake master cylinders, with a driver selectable

change in mechanical leverage effort between front and rear brake circuits,

one cylinder operating the front brake calipers, the other the rear. This

can also be achieved on road cars, but to do so is usually complex and

expensive, especially if ABS and brake circuit failure safeguards are to be

maintained. It is far easier to calculate the caliper and disc sizes, along with

pad area and compound to achieve this, as near as available off the

shelf equipment will allow.

Caveat. I said before makers engineer more effort on the front brakes to

encourage straight line stopping if the tyres are locked up . They err on

the excessive side, as, in the wet, the rear tyres can take a lot more

braking effort than in the dry, due to less weight transfer onto the front

tyres, as they will lock before as much weight is transferred when the grip

of the road surface is reduced. So adding yet more front brake effort worsens

this existing imbalance, especially in the wet. If it were not for the

ABS the front wheels would be locking up very early. On the Supra a

relatively sophisticated ABS allows some effort to be taken off JUST

the fronts, and an artificial and very inefficient balance is returned.

On cars with lesser (1 or 2 channel) ABS, or no ABS at all, a brake

upgrade on just one end of the car can be lethal.

Thank you for the in depth right up Chris that's the type of information I was looking for. And having read that maybe I would be better off just swapping for a new set of j-spec fronts with oem disks and a decent set of pads then, as I already have relatively new rears this would make the most logical sense.

I will price up the comparison of the jspec fronts against at whole set of UK's and make the decision from there.

Out of interest do you sell Brake set ups Chris? I know you do your pad setups, but do you supply callipers and disks.

Whilst UK fronts with J-Spec rears work safely, they are not optimal, the rears are not doing their potential. I sell OE disks, and race discs, and race calipers. I do not sell OE calipers, but do seal kits, when I find stock, and do my own stainless steel pistons for Supra and any other caliper that needs refurbishing that uses "normal" piston designs.

What sort of price do you charge then for a rebuild on jspec front brakes, if I did both for piece of mind along with new pads and disks and a fluid change. The car is not raced and its only an NA so something that would suit those needs would be great. If I brought the car to you how long would it take also? Ben nice to have the brakes and everything looked over properly as these cars are getting old these days.

So long as you don't want fancy powder coating or anything (I only offer satin black Kephos coating on a basic bead blasted caliper), and assuming you wanted my stainless pistons and new seals fitted, the front calipers would cost about £160 each, with the slider pin bores reamed and correctly greased with new seals. It's impossible to give a totally firm price without looking at the calipers and sliders. OE discs would be whatever Toyota are currently charging, but I have TUV pattern ones for less. A fluid flush and change wouldn't be much at all with the above work, perhaps an additional £20

Brilliant thankyou that gives me some ball park figures to work with and compare against OEM new ones etc.

If I was to get the car to you first thing in a morning is it a job that is do-able in a day or would you need the car for an extended amount of time?

I'd need it a few days, no point in you buying stainless pistons if not needed as the old ones are still fine, these jobs take time unless I were to just throw all new parts at it, which is a half day's work or so.

If your not going for power, there's not point in going for UK brakes.

Only problem I ever had when first NA-t with 373hp was on a track. Never ever had a problem on the road with stock jspec fronts pads/discs.

Save yourself some cash.

If I had the smaller brakes fitted and they needed completely overhauling (calipers refurbed, new discs & pads etc.), I'd personally take the opportunity to upgrade to the larger brakes front and rear. I'd price up the 2 options and then make a decision.

I'd need it a few days, no point in you buying stainless pistons if not needed as the old ones are still fine, these jobs take time unless I were to just throw all new parts at it, which is a half day's work or so.

Right ok Thankyou for the information, I will price up the comparison against brand new oem j-specs and a full set of uk specs.

If your not going for power, there's not point in going for UK brakes.

 

Only problem I ever had when first NA-t with 373hp was on a track. Never ever had a problem on the road with stock jspec fronts pads/discs.

 

Save yourself some cash.

It will have more power one day, but I ruled out the idea for now but the car is going to stay now and will probably go na-t in the future so I like the car to be setup ready to go. Its never going to be a big power car but small single power would probably be where it stops. I've been spending the cash on making sure everything is new and ready to go, rather than chucking a snail on and hoping.

If I had the smaller brakes fitted and they needed completely overhauling (calipers refurbed, new discs & pads etc.), I'd personally take the opportunity to upgrade to the larger brakes front and rear. I'd price up the 2 options and then make a decision.

This is the thing Nic if the rear where had it too I would just go for a full new uk set-up but alas the rears are only a 1 and 1/2 years old. This is the only thing holding me back.