how to kill the twitch?

[mk1matt]

Ok I was doing some reading last night on the suspension of the aw11. I read a couple of articles saying to use semi metalics on the front and just normal pads on the rears (organic?) to keep the car level during breaking, and to drop the conpression of the front struts to induce more nosedive?

Dose any of this really work, or what can I do to reduce this? What I have read about the rear end coming out kinda makes me a little scared about pushing my 2 to the limit.

[CpuZapper]

I've never *knock on wood* had the rear of my MK1 come out during braking. Mine is an '86 but I've got '88 brakes on it. I've never had the rears lock up on pavement even under panic braking - only the fronts. Toyota has the brake proportioning valve setup to really keep all the braking to the front anyway. Getting less grippy pads in the rear will just increase your stopping distances and cause your rear brakes to overheat quickly. I wouldn't reccomend normal Semi-Metallics either as they just chew up your rotor. Porterfield R4S or Hawk HPS are about the best street pads you can get that will last a while. While you're down there upgrade to DOT4 brake fluid (I use Castrol GT LMA) for street use as it will reduce pedal fade under hard braking conditions. Also, don't use those slotted or drilled rotors as they don't really offer any performance gains.

Most of the "Twitch" comes from the amount of weight sitting over the mid/rear of the car. During hard cornering, bump steer will cause the back end to step out, and once the back end comes around, the bulk of the mass is there and wants to keep moving sideways. Also, having a stiff swaybar (or even just having a swaybar) in the rear or rear wheel toe out makes the rear more jumpy.

[Dumbscout]

What is the reasoning behind slotted and cross drilled rotors not offering any performance gains? If they weren't better, why would cars like porche, and Mercedes have them on their higher end cars? Every AMG car comes with slotted cross drilled rotors from the factory.

[CpuZapper]

There was a lot of discussion on this over on the other board - most of those sedans/sports sedan's rotors are the size of the mk1s wheels!!! And they also have more weight to stop, and a lot more horsepower. Mercedes/BMW/Porsche are all cars designed for the autobahn too, and need to routinely stop from 150+ mph, whereas I've never had my mk1 NA over 130 in extreme cases. Also, most of their rotors are also thicker, and designed to be drilled.

If you consider that our mk1 rotors will warp just by having one wheel lug tighter than the others, removing material just makes them more prone to cracking, especially if you get them really hot, such as in track racing. I have found fine cracks in my stock Raybestos rotors after a good spirited... well, more than spirited... run over a closed forest service road with Porterfield R4 Race pads. Besides the speed and weight, we don't really have any kind of brake ducting to make the drlled rotors effective at cooling anyway. Also, the front rotor is already designed to move air through the core. Venting/slotting on the other hand can work, but compared to the thickness of porsche performance rotors our rotors are like a potato chip; if you take too much material out, you're going to severly weaken the structure of the rotor. Imagine just slotting 1/16" into a rotor face that is only around 1/4" thick - you just gave it a nice score line to break on. The brakes on many of the cars you mentioned are also designed to drilled/slotted rotors, and cost thousands of dollars. Ever hear how much a full brake job on a Porsche GT3 w/the race brake package costs?? Last I heard pads alone were $400...

Back to the question on hand. On the mk1, the rears are solid, so drilling really offers no gain for venting (if the pad is engaged over one side, the gas cannot escape between the two halves - it only hits the other pad). The slotting can work if you have pads that actually need to be vented such as Porterfields, and you actually use your brakes hard enough to warrant their use. Ask most people who track race their mk1s though. Considering that after one good race, the rotors are most likely going to be warped, you could spend $250 for decent quality slot/drilled rotors, or $60 for stock Napa rotors. I'd be willing to bet that Matt will never ever push his mk1 hard enough to warrant drilled or slotted rotors regardless of whether they were stock rotors, or a full custom brake package.

I hope this post makes sense - it's been an hour or so of occasionally writing while I'm at work

[Gairloch]

I don't know that much about the handling characteristics of a MkI. Would you mind spelling out what you mean by twitch?

[Dumbscout]

That's a good point on the rotor size, I've never looked into that before, I just know that I've seen a lot of High end cars with the slotted cross drilled rotors, but that's true, they are pretty big.

[mk1matt]

what I mean by twitch is that many mk1 owners report the rear end of there cars sort of "twitching" or losing traction thus causing a spin out.

[tgidavid]

I think you got the pads switched around. There are a lot of people who complain that the rear bias is not enough. I use to run hawks with a higher friction coefficient in the rears for a more balanced braking. You can acheive the same kind of bias with stock front pads and aftermarket rears (hawk, porterfield, MBC, etc.)

The other thing that helped me out at the tracks was slotted rotors. I didn't have any brake fade and a set of pads lasted much longer. I read that the slotting keeps the pad surface fresh and also aids in the bedding process.

Just my $.02

[willy swafford]

ihavent experianced the twitch much,but its there for sure.i use cr/dr rotors front an rear,but its give an take.they killed my brake fade,but in trade you take in consideration that theres no abs,an that they are more prone to damage under hard braking.if i had to do it again,i would have just gotten fronts an used brembo solid rotors for the rear.i ve just recently di weight redux to under a metric ton and i think the bite is to much for the car,so im prolly gonna change my rears for some solid soon

[Jackstand Queen]

I'd like to emphasize one of CPU Zapper's points as being uber important: Dot 4 Silicone Racing brake fluid. This stuff makes a world of difference in hard braking.

My next 2 cents worth is the Brake Lines. If you have stock 20 year old brake lines and are driving hard and fast on them . . . you should win a Darwin Award. Old brake lines blow out suddenly!

I stuck some Goodrich braided steel brake lines on a while back, those combined with Silicone Racing brake fluid and upgraded rear pads seem to be a good working combination for me.

Side by Side racing has rear tie rod sets that seem to have a pivoting ball joint at the inner end. I've heard that this is a mod that is supposed to reduce "Bump Steer", or the twitch. Has anyone got any experience to relate, or engineering level info to add on this Mod? I have them installed, but I haven't driven on them enough to notice the difference. My car is on jackstands again, hence the name "Jackstand Queen".

[tjmr2]

Twitch: Rear of car want's to pass front of car, usually much faster than occupant desires, most often on wet or icy roads when right foot has uncontrollably fallen to the floor and the TVIS opens up. Remember Murphy is alive and well and he hates nice shiny cars that go fast.

Remedy: almost 100% foolproof, when it's wet or icy out, drive like the Drivers License Examiner is sitting in the seat next to you. He has a tazer pointed at your lap and an evil gleam in his eye!

All kidding aside: physics dictate that a car will rotate and put more weight on the front wheels during braking. Asking the rears to do more than designed to by changing the stickiness of the pads on the front and rear will probably diminish the overall braking ability of the car. As in - it will take longer to stop at any given speed.

Drilling rotors lightens the rotor (reducing unsprung weight which is good) and gives the pad somewhere to squish water into when it rains. It also increases surface area of the rotor, thus increasing it's ability to shed heat. It can also lead to premature pad, failure, and an unbalanced rotor. If not drilled correctly can also lead to catastrophic failure.

After pondering this mod long and hard I decided that the Toyota Engineers went to school and then practiced with a lot of the factory's money to give us the best they could with the money they had available.

Bigger wheels, with bigger discs and bigger pad assemblies with more pads would probably help, but I've been flogging mine hard for years and only once have my tires failed to stop me in time, close enough that no damage was done. My point is the stock brakes are pretty awesome, the SS braided lines were an improvement over stock.

Spend your money on struts, springs, bushings, sway bars and SS braided brake lines. I guarantee it won't feel like the same car.

Keep the shiny side up and don't swap paint!

[CpuZapper]

^^^
I second tjmr2's statements regarding the better investment. No sense dumping a huge amount of money into brakes when they lock up just fine! Better gains will be found in suspension, and hydraulic efficiency.

Also tgidavid made a good point about using pads to adjust the brake bias. It works great, and I know many a racer who will put pads with a much higher coefficient in the rear to try and balance it out, however, I don't suggest this for a street car.

Since the pads will behave differently at varying temperatures, it's tough to predict how the car might respond in a daily driving scenario, especially considering things like rain, or even one wheel going through a puddle. If the rear pads don't have good cold initial bite, it can increase the distance required to stop, and you find yourself planted in that car than ran a red. If you're decelerating from a high rate of speed, you may have enough room for the pads to come up to temp, and suddenly your rear brakes really dig in. You may find the back of your car trying to race you through a corner. Racing is different. The pads usualy maintain a somewhat consistently high temp, and behave more consistently.

[efx]

Just wondering if you used the Two's R Us steel brake lines and if you did, did they go in fine without any special modifications? Any pictures? Thanks.

Originally Posted by Jackstand Queen

I'd like to emphasize one of CPU Zapper's points as being uber important: Dot 4 Silicone Racing brake fluid. This stuff makes a world of difference in hard braking.

My next 2 cents worth is the Brake Lines. If you have stock 20 year old brake lines and are driving hard and fast on them . . . you should win a Darwin Award. Old brake lines blow out suddenly!

I stuck some Goodrich braided steel brake lines on a while back, those combined with Silicone Racing brake fluid and upgraded rear pads seem to be a good working combination for me.

Side by Side racing has rear tie rod sets that seem to have a pivoting ball joint at the inner end. I've heard that this is a mod that is supposed to reduce "Bump Steer", or the twitch. Has anyone got any experience to relate, or engineering level info to add on this Mod? I have them installed, but I haven't driven on them enough to notice the difference. My car is on jackstands again, hence the name "Jackstand Queen".

[ebouwman]

Originally Posted by mk1matt

what I mean by twitch is that many mk1 owners report the rear end of there cars sort of "twitching" or losing traction thus causing a spin out.

Do you mean twitching from braking? Or from bumps? I've noticed that going over bumps in a corner makes the car skip to the side a bit, but never lost traction from it, and i've never had the rear end lock up from braking in my mr2, and i drove it though the winter. It's my understanding that with a stock setup that essentially doesn't happen when hard braking in a straight line, or is the twitch referring to braking causing a spin in a corner?

I did once have the rear end lock up while straight line braking in my brother's FJ40 (landcruiser) on snowy/icy roads. Something was f'ed up with that car, and when i went to brake hard to stop for a light that changed to red the rear locked up and it started to spin. Unfortunately on an FJ40, the wheelbase is short, the steering wheel is MASSIVE, there's no power steering, and the rack turns VERY slowly. So you can't turn the steering wheel fast because it's huge, and even if you could turn it fast the rack was slow so you need to turn it more to get the proper correction, and you're spinning really fast because it's so short. Ya, i spun right out...

But i did stop on the stopping line! But i was pointing the wrong way

[Timon]

Braking in the MKI is perfect stock with the 87+ brakes/rotors. I've never had the rear end slip out while braking. It's nice and smooth, and doesn't seem to be bias to the front or rear specifically.

I can vouch for the brakes locking up rather easily. I spun out at 65-70, and all 4 tires locked up when I punched the brakes. My rear passed my front end, and I slide backwards about 15 feet before coming to a stop completely unharmed. Not an experience I'd like to relive unless I'm on the track next time, but the brakes did a wonderful job.

[MR2 Drifter]

Slotted Drilled rotors do help,
the slotted design helps slow the car down faster (wearing out the pads faster than usual)
the drilled design helps cool down the rotors (also eats away your pads pretty fast)

Just as said earlier why would every expensive fast car have them if they didn't do anything?