Why do my front wheels lock up under fairly heavy braking?

[Station]

I've had this problem for a while in my MR2 - brakes work fine, but as soon as any heavy pressure is applied to the pedal, the front wheels lock up.

I know there's not much weight on the front wheels, but it's a bit embarassing when you're braking in traffic and the person in front can hear the shriek of tyres behind him. In the rain it's worse - tonight I braked at a roundabout, I was miles off but they locked up when a car going round decided to change lanes - I've got so used to it now I'm more efficient than any ABS system on the planet. (there's no ABS on the car by the way)

 

Is this inferior brake pads or something else like brake bias?

[twosmoke300]

Shit tyres

[HH-R]

Tyres were my first thought too.

 

My brother's old Orion used to lock up and he said it was traced to a brake hose that had broken down and kinked inside, but neither of us are mechanics!

 

I usually have the opposite problem, I don't think any of the shite I've driven in the past few years could muster up enough braking effort to invoke ABS.

[mrcitroen]

Shit tyres

Or old hard tyres. When I got he GS it came with 37 YO Michelins. I could lock them on my damp driveway at just over walking speed. I kid you not!

[twosmoke300]

Lowered stiffened suspension ? No weight transfer to the front under braking ?

[stripped fred]

Get some Uniroyal Rainexpert 3's on, cheap from Tyreleader. Excellent grip wet or dry.

[forddeliveryboy]

Rear calipers which aren't working as well as the fronts. And all the above.

 

If you stamp on the brakes suddenly, not allowing the load transfer onto the front axle with a mid-engined car, then especially with tired suspension/cheap tyres it can lock the fronts up a bit easily. 

[chodweaver]

Are the front and back calipers stock items? There's a lot of molestation of brakes by caliper 'upgrades' that's gone on in Mr2 land. And the same goes for the front/rear brake pressure distribution, which should be set correctly by the stock master cylinder and pipework. It'll most likely be out if the calipers have been upgraded.

But first, check for good rubber, pads, discs and new fluid. Then engage a tame Mot man for the use of his brake tester

 

Sent from my GT-S5830i using Tapatalk 2

[steveo3002]

all of the above and check the tyre pressures ....had this drama on another forum and it turns out the guy was making up the tyre pressures , dropped it to what it should be and all good 

[Supernaut]

Get some Uniroyal Rainexpert 3's on, cheap from Tyreleader. Excellent grip wet or dry.

 

Bloody hell, at that price I might just get a set of them for the new car!

[gordonbennet]

Brakes are not too good at the front, its the rears either not getting enough pressure or providing effort for some reason or the rear shoes/pads might be different material.

 

I had the latter on a Golf 2 donkeys years ago, twas the ex Mil's car, low mileage when she bought it and i noticed the front discs were wearing but the bloody OE pads showed no wear at all and it required one hell of a shove to stop the bugger and then it was all or nothing, far too heavy for her.

 

So got some Ferodo pads for the front from the local factor, big improvement controllable progressive and much less pedal pressure required...however obviously the rear shoes were the correct material to balance the OE set up, hence easy lock up of the fronts...another trip to factor, Ferodo rear shoes fitted, brakes superb all round.

 

Good points about tyres, oh and don't suppose it has a load sensing/proportioning valve for the rears?...had one of those on an old Landcruiser i had, that was prone to locking the fronts but a bit of gentle adjusting of the rod was able to get that much better.

 

They're designed to lock the front first anyway, be a right bloody handful if the rears locked first.

[M'coli]

Brake bias can be adjusted manually and on the fly by pulling on the handbrake as you're applying the brakes - this will give you an idea as to how much work the back brakes are doing.- it worked on my Imp, which had similar locking-up issues with the front brakes. The real problem with the imp was that the tyres were old and shit because the front ones don't wear out, so I'd be tempted to get them changed.

[Asimo]

My MR2 worked much better all round with two 25kg bags of sand in the front boot ("frunk"as the MR2 community insists on calling it.)

 

Noticeably improved braking and steering for £2.

 

All of the rear engined/ mid engined cars that I have driven have locked fronts first - ABS worth the trouble here!

 

As above, get some good tyres; the fronts don't wear fast so may be ancient. These cars are set up to understeer in order to protect the driver from over-exciting oversteer. I expect that rear grip bias affects braking as much as it does steering.

 

Edit - playing with the handbrake won't tell you anything on an MR2 as their handbrakes are almost completely useless, especially at MOT time.