Dave in Chicago

I will also vote toe, seems to affect these cars quite a bit under heavy braking.

TonyN

Hmmm, sounds very familiar. I've gone through all this my 968 Firehawk. Basically it's a rear bias issue, and you have to choose. If you want more overall brake power, then you have to put-up with some tail wag. You can eliminate the tail wag with the 18bar BB valve, but you will get less overall brake. However you may end up being able to brake harder because you will have more confidence without the rear dancing on you. I found that the BB is a pain in the ***, because when you come in too hot, and naturally press harder on the brake pedal, eventually you will speed up because the BB cuts pressure to the rear and you loose overall braking power. I've even had to let up on the brake a bit to get the rear to continue to provide useful brake (sort of like "restarting" the braking).

If you want to stay with the 33bar BB, then play with the pads. (BTW, Hawk Blue has more bite and torque than Pagid Orange, so that is why the problem got worse). If you like Pagid, go with Black in front and Orange in the rear. If you like Hawk, then go with Blue in front and Black in the rear. Both will give you much better brake balance and best compromise (power vs. F/R balance).

I like the Hawk HT-10 the best for the 968/944 with 33 bar BB, because they have less bite than the Blue and higher temp before fade, but slightly greater torque. However they require a significant warmup(therefore track only), while the Blue warms up quickly. So you may want to try HT-10 in front, and Hawk Black in the rear, but I found that HT-10 F+R works great because it has less bite than Blue. (Remember that the 944/968 applies the rear brake 1st). This may give you a smooth brake engagement and release, while giving you significant brake power. The HT-10 wears the rotors as does the Blue, but lets you brake lightly. Some tracks require very light braking, and the Hawk Blue does not let you do that when used in back. I could not use Pagid Orange in front on the 968 because they would crack badly and chunks would actually score the rotors, because they are too low top temp rating. Pagid Black is better but much more expensive that Hawk. Hawk never does this, they are much cheaper and last much longer(twice the life) than the Pagids.

As far as ABS goes, I try to not use it, because I feel that I can threshold brake "better" than engaging the ABS. But it does save you when you make a mistake or hit a slick spot. The 944/968 ABS is 3 channel, so both rear wheels are cycled together, if you have ABS.

Hope my experiences are helpful. Of course this was all on the track with 968 M030/928S4 brakes, rather than on the street. As others have commented, alignment needs to be correct. Regards,

RedlineMan

1) Alignment
2) Ride Height
3) Brake Pad Shuffle

If you brake hard in a straight line, does the rear end tramline? Meaning, wig wag back and forth? This is classic alignment symptomology. You do not have enough toe in, or it is not even side-to-side. Outside chance, it could be a worn or failed bushing.

Then, you can sometimes cure bias issues by resetting the ride height a little lower in the rear and/or higher in the front. This keeps more weight to the rear when you stand on the brakes, improving rear stability and its percentage of deceleration.

Only when these issues were addressed would I get into juggling brake pads. If you have one of the above abnormalities, musical brake pads is just a band aid.

M758

I agree compelelty with John on the ride height issue as well.

First aligment and second ride height.

Oddjob

I dont think my ride height is out of wack, but what about the corner balance being off?


Yes, thats the symptom. High entry speed, hard braking corners are the worst. I have in car video footage of the car doing the side to side slide right off the track during straight line braking for a corner that is about 125mph at the brake point down to maybe 55mph at turn-in (obviously after that, I changed my technique). And the car is difficult/impossible to trail brake, even though it is set up neutral to understeer.

A previous reply stated 1/8" rear toe-in, is that typical?

I had an old set of Hawk pads in a compound that no longer exists, HT-8 I think. They were impressive and had a lot better stopping power than the previous porterfields I was using. When buying replacements for those, I tried the Hawk Blue, which was disappointing compared with the older compound, and I really didnt notice much braking difference between the blues and the Porterfields. I looked at getting a different compound like the HT-10 or 14/15, but couldnt find them in stock and that they were about as expensive as the Pagid, so I went with the Orange when I bought my last set of pads.

RedlineMan

Hey Odd;

I am quite confident you have an alignment abnormality. The only thing that causes tramlining like that is a severely failed suspension pickup, or misalignment. Of course you should check for the former, but expect the latter.

Incidentally, I am assuming no mechanical defects here. To cause this sort of ugliness in attitude, they would have to be so obvious as to already have been known.

The factory spec is for 5/64 total rear toe. This does indeed work well. Some people like zero, some like more than 5/64. I think you will be safest using the factory spec. If your rear bushings are healthy, or spherical even, it will maintain toe-in - and therefore stability - throughout cornering stress. If you sense that you may have more than average bushing deflection, a little more toe-in will not hurt.

As to ride height, mine was not a reference to yours being "out of whack" but specifically setting it to be more conducive to your goals.

If you have an early 944 with the tail in the air as delivered, simply leveling it can dramatically increase braking effectiveness and stability. If you have a car that is locking front brakes, a small increase in rear ride height can offer more braking grip through increased forward weight shift, and vice-versa. True, you should look to other directly related areas to effect larger changes, but ride height tweaks can play a vital role in finalizing a handling package.

Corner balance would likely not be the culprit here. If you had a corner far enough off to cause something like tramlining, the ride height descrepancy of that corner would be quite visable.

Get that thing aligned and your problem will be gone, methinks. If you don't remember when it was done, there's the proof! Race teams would not align their cars every day if they didn't change!

JCP911S

Is the brake locking up or just the tail wagging?

If your problem is with the brakes, you should see some signs of tiresmoke... even if it is just some chirping.... if you are not, then problem would be more likly a suspension problem, i would think.

Also check your wheel bearings, hubs, rotors.... that can cause the rotor to **** in the caliper, causing premature lock-up

Oddjob

Its a little hard to tell if there is much locking/chirping going on. I first assumed, because it is wagging, that it must be locking. But after thinking about it now, I dont believe it is locking the rears.

Last alignment done was -0.04 deg front toe and +0.08 deg rear toe per side. Historically over the past 10 alignments Ive had, the range has been -0.05 to +0.17 deg front toe and +0.05 to +0.23 deg rear toe (per side).

When you say 5/64th, is that of a degree or of an inch?

With the other reply that talked about 1/4" front and 1/8" rear, how are you measuring in inches? With the toe plates and tape measures?

RedlineMan

Hey;

I work in inches, not degrees. That is as measured any way you choose. I use an alignment rack.

I would run 0 toe max in front for track cars. Slight toe in for dual use. At least spec for the rear toe in.

Oddjob

So, for example, 0.10 deg toe in equates to how many inches?

When using inches, what is the measurement relative to? What is 5/64" from what? The leading lip of the wheel/tire relative to the center of the wheel, the leading lip from the trailing lip?

I have seen guys using plates where you set the plates against the wheels on each side of the car, and use two tape measures placed in slots on the plates, one in front of the wheels the other behind. The difference in distance between the measurement in front of the wheel and behind the wheel will give some toe-in or out in inches, but that would only be relative to the length of the plate. If the wheel alignment is at an angle of 0.10 deg, that equates to approx 1/64" at 1 ft from centerline, 3/64" at 2', 1/16" at 3', 5/64" at 4', etc.

RedlineMan

Hey;

Get some math geek to figrue out how they correspond to each other. What do I know from inches to and from degrees?

Total toe is obviously the total amount of each side. 5/64 is the factory spec. Toe for each wheel is its deviation from parallel to the chassis. They give a total spec because hitting 64ths of an inch on both sides equally is pretty challenging, especially in the rear, and doesn't really matter in reality. A 64th of an inch won't ever matter on a street car, and really not on ANY car for that matter. I do try to get them withing a 64th though.

You start with a spec, and then an allowable deviation. When you are within the deviation range, the numbers turn green on the screen, red when out of spec. Green is Green as I like to say. When you hit it, you've hit it. Tighten it and move on!

When stringing or taping a car, you are approximating. If the wheel is straight, and you measure total difference between in front and behind the wheels, you are close. Obviously it is not as accurate as racking it, but if the car works fine, that tells you how critical the work is.

Not as critical as most people think as to 64ths of an inch deviation. More, it is critical that you have toe in or out on BOTH sides, and not any huge deviation therein.