Brakes Lock too easily

[Lauren]

Not driven a car with Celica brakes but I've also driven FEAM and found the brake balance to be similarly horrible (It had Hi-Specs at the time, not sure if these are brakes you've driven or if they were changed). Those brakes were stupidly over specced though considering there was nothing special on the back. I think the current owner has since fitted something else to make it a bit more driveable.

They probably were Hi-Specs Phil. It does however demonstrate the point that having whopping brakes on the front made the fronts lock up way too easily.

[PW@Woodsport]

So nobody knows why MK1s with over-sized brakes apparently defy the laws of physics?

Constructive as ever.

[Lauren]

So nobody knows why MK1s with over-sized brakes apparently defy the laws of physics?

Constructive as ever.

Well, why not Paul? I state something, you say it isn't so. Someone with a modicum of knowledge of physics comes along and illustrates my point. Then you and another affiliate clutch at straws to support your theory.

Brilliant.

[Keri-WMS]

So nobody knows why MK1s with over-sized brakes apparently defy the laws of physics?

Mine obey the laws of physics perfectly, they do exactly what I tell them to...

Paul's just sold his soul or something!!

[PW@Woodsport]

I'm not clutching at straws at all, all i can add is my own findings having driven many cars with various upgrades and i have never found this lock up.

I've offered reasons as to why this "might" be the case, including the extra weight of engine converted cars, but all you can say is the usual Lauren sarky comment , in this case cars defying laws of physics.

Hardly adding anything worthwhile to the discussion is it?

People are getting pretty fed up with your negative attitude on just about everything, add something constructive to the subject or say nothing at all.

[PW@Woodsport]

Yes i have to add Keri's brakes too suffer no lock up problems at all and we have used them as well quite a few times.

[Lauren]

People are getting pretty fed up with your negative attitude on just about everything, add something constructive to the subject or say nothing at all.

These people being you per chance? Stop throwing your teddies out of the pram. It's tiresome. Accept that actually it might be good to challenged once in a blue moon.

[aw11rally]

From experience of the following:

Mk1 with 320mm bremsport 4pot kit (standard mc) willwood polymatrix A pads (full race/wrc spec pad)
Mk1 with st165 two pots with ds2500 pads
Mk1.5 with st185 single pots and ebc yellow pads

Bigger brakes really don't mean more locking of the front wheels (unless you just stomp on the middle peddle).

The change in master cylinder to slave cylinder ratio gives a slightly longer peddle with a more progressive and adjustable feel under braking. All positive if you ask me.

What makes the front lock or fade is knackered rear brakes or crap rubber.

[PW@Woodsport]

LOL, let's take a poll shall we and see if it's just me?

I don't mind healthy debate at all, but i have enough intelligence to be able to offer more than "So nobody knows why MK1s with over-sized brakes apparently defy the laws of physics?"

Why not add to the debate with a reason it's happening rather than insinuate two affiliates are clutching at straws?

Or would you like me to ignore the years of roadtests and customer testimonies and just nod my head agreeingly?

[Moustachio]

Probably more down to sh1te pads and discs rather than anything else.

My st165's used to lock really badly... I put new discs on and some decent EBC pads... now I have no lock up at all.

both situations were on track.

[Tiamat]

Chris (LimeyMK1) has Hi-spec on the front of his MK1 and I have never known that to lock up. But won't all this depend on how hard you hit the pedal, speed, how you are entering a corner (if applicable) suspension, tyres, pads, discs, what gear you are in, which engine is in the car etc etc

[PW@Woodsport]

Completely agree, there are far too many variables going on, all within the laws of physics too, so it is definately not a case of Mk1's with bigger brakes will have a lock up problem, it's not a black and white situation as some would suggest.

There are far too many people with experience of no problems with lock up on big brake set ups (myself included) for it to be a simple case of unbiased brakes cause the problem, that's just not true, people get lock up with stock Mk1 brakes too because of crap pads/tyres etc.

Some of the upgrades out there are truly excellent and of course it all depends on tyres/pads/discs etc as well. My own experience of st205 brakes produced a car that would stop quicker than anything else i've ever driven in the Mr2 world and no lock up. My current 996 set up is pretty much the same, they will only lock if i absolutely murder the pedal.

There's certainly nobody defying the laws of physics or straw clutching, i find comments like that obtuse and not contributing anything to the actual reasons some people have a lock up issue.

Moustachio's experience is interesting, because he reports lock up with st165's but cured the problem with pads and discs, so perhaps it really is that simple and falls down to that along with tyre quality etc?

[Lauren]

Okay fair comment, sorry Paul.

Like you and others have said that are a hell of a lot of variables to consider. Whilst I experienced horrible lock up on a car with big front brakes there are doubltless lots of other variables to consider. I guess my concern was that the rears are far more important on a mid/rear engined car than they are on a front engined car. I wonder what would happen if only the rears were upgraded, if it'd shift the bias backwards and help prevent front lock up?

[PW@Woodsport]

I guess my concern was that the rears are far more important on a mid/rear engined car than they are on a front engined car

Totally agree, there's not enough importance placed on that fact, they are extremely important on Mr2's.

The Americans swear by gutting the bias valve on a Mk1 to make it a perfect 50/50 split, over the stock 45/55 split, i can see what they are doing there, perhaps this is a worthwhile mod?

[Jim-SR]

personally i think the weak link is the driver, on a couple of counts...

if big front brakes are reducing (or at least not increasing) the lock up situation some people experience with stock brakes, then "driver feel" could well be a factor. you cant account for this in any form of physics equation, it is entirely on the driver. if bigger brakes in some way offer an improvement in brake feel, then the driver is going to be a lot more sensitive to lock up, and more easily able to avoid it. it might not be the case, but its certainly a possibility.

also, with regards moving the brake bias rearwards, this may be best for outright performance, but bringing driver error into the equation it can also be a lot more dangerous. locking fronts is normally going to send you straight on, locking rears can quite likely send you spinning. it can also make the car a lot more sensitive when braking mid-corner. which is often something which you have to do in a road car, if for example you encounter an obstruction around a blind bend (e.g. traffic jam). you dont really want to jump on the brakes and end up spinning out of control.

i find that the stock brakes arent too bad for locking up if they are well maintained and the pads and discs are in good condition. the only time i really get my brakes to lock up is when i first use the car and the brakes are cold, and they are very snatchy at lower speeds. thats on OEM pads and discs. otherwise they are no worse than any other car ive owned without ABS. in fact ive owned far worse cars for locking up!!

[Keri-WMS]

Tyre width comes into it as well, wider rear tyres will make the rear less likely to lock up than the front in normal conditions.

Interestingly we have a customer with a Mk2 race car (Nippon / Super GT AFAIK) who's opting for 300mm F+R with an increase in bias to the rear so we'll see how that works once it's all fitted. The change in bias "at the hub" F/R is from 58/42 to 55/45, a 6% shift of the total braking to the rear.

EDIT - Jim's point about road car vs race car is extremely relevant, a race car that's set up to brake pefectly in a straight line (more rear bias) is also a real pain on the road.

The sad truth is that locking the front wheels a bit early is very easy to control for the average driver, which is why car mfrs set their cars up that way.

[aw11rally]

Moving the bias towards the rear hugely improves the stopping power of the Mk1.

The rally car has 320mm Bremsport 4 pots on the front and mk1a fronts on the rear. There are adjustable proportioning valves in both the front and rear circuit which can be controlled from the drivers seat.

Once the system was serviced and working correctly we experimented with the adjustment.

Starting with full front but the rear dialed down by 33%. This gave good stopping power (as expected from the huge fronts) but with the tendency to snatch on changable surfaces and when trailing the brakes into a corner, in the wet this was a nightmare as it made initial turn in a bit unpredictable.

As I got used to the car I added more and more rear, this transforms the situation. With full front and full rear in the dry (on R888s) the stopping power is actually painfull. When in the co-drivers seat it becomes hard to keep hold of the notes and pencil!

I have even gone as far as dialing the fronts out slightly on dry tarmac. This gives me a lot more confidence when braking late into a corner or chicane. I know if I do lock up I can still steer the car then get back on the power through the corner to bring the rear under control.

Probably not quite the best setup for the road but it did show me how important the rear brakes are on a mid engined car.

Ever driven an MR2 with ceased rears? it gets very scary. Hence me suggesting that the OP checked his rears before he did anything else!

[tonigmr2]

Interesting discussion, I've got APs up front and stock MK1b rears - at the moment. I've gone and acquired some rev3 turbo rears as I thought it might help a bit.

What I'd found (with very limited driving so far ) is I didn't lock up, but the pedal travel and feel was very, very different. Indeed, I'm not sure I liked it, they felt almost under-assisted. Bit worried about it, but I'm looking forward to using them in anger though.

[aw11rally]

I agree with the under assisted feeling Toni. Once you get chance to use them properly you will then hate every modern car you get into due to the over assistance and complete lack of feedback. Especially with anything from VAG.

I'm sure car manufacturers have started over servoing their systems to make buyers think that the brakes are better than they actually are.

[Keri-WMS]

It's partly due to the simple fact that average cars weigh about twice what they used to in the good old days while the average human leg didn't get any stronger - easy solution is whacking up the servo.