Help fixing a front brake bias problem

[ERA Chas]

Originally Posted by Jerry Clayton

The dot 4 fluid will not flush out dot 5 even if you pumped 50 gallons thru it----

So what does? Are you telling him to replace all seals/o-rings and lines in his system?

[Jerry Clayton]

Usually on a brake system with adjustable bias front/rear---if you have a obvious problem with a wheel---the fault is at the other end of the car---in this case, the rears aren't doing there job and the driver just pushes down on the pedal to stop the car and the brake that is working correctly will lock up and get the blame for something wrong with it-- in this application, the bias is too much toward the front, the rears aren't contributing there portion of the stop force and because of a heavy left front weight causes the right front to lock up.

[Jerry Clayton]

I see also that this is a Back Draft????
have you changed the brake system or is it stock??? Vacume booster??? How big is your cam and how much vacume does the engine pull with your induction system????

[Rwillia4]

I think there maybe some confusion on the problem. The problem is the front right will lock up before the left. If I push hard enough the left will also lock up. If I really jam on it I could probably get the rears to lock up also. There is no bias system installed F/R or L/R. It is a stock system. There is plenty of vacuum for the booster.

Here is the cam:

[Jerry Clayton]

OK---I have tried to lead/guide you thru some brake basics---in this day and age of anti skid/traction control equipped cars, people lose track of basic principals---in your car you have a simple vacume boosted master cylinder---which is affected by engine vacume---your comment about it has plenty of vacume does not put a number on how much vacume that it does have, which is a valuable piece of info toward solving a brake problem on a high performance car.

But moving on--you haven't come up with pressure numbers at the calipers, sizes of the calipers, or corner weights of the vehicle.

You want to ignore the Dot 5/ dot 4 issues-----

You want to ignore if the calipers are the correct size and same side/side

You want to argue about the rears doing there portion of the braking by saying its the front locking up---

Now, a couple of basics for you----hydraulic pressure MUST be equal side to side
Calipers must be equal side to side

The front do more braking than the rear, so if the rears are weak, the fronts lock up first---
A brake system should be set up where the rears will start to lock before the fronts

Rob--sorry if this came across a little rude, but it is important basics about solving your problem, I got yelled at for taking a maple frosted donut, spilled my coffee, and we're out of treats for the dog, sky is dull, cold and looks like rain(maybe snow around the corner)

[Tommy]

Let me see if I can add to the confusion a little. If the brake line pressure, the brake components, wheels and tires are the same on all four corners, the thing most likely to cause one wheel to lock up before others is the amount of weight on it. Tires with less weight will lock up before tires with more weight. So, on a normal car the rear tires will tend to lock up before the fronts due to "weight transfer" during braking. Manufacturers routinely account for this by using different components in the rear to reduce its braking effectiveness. ... If the brake components are the same and one front tire locks up before the other, it is likely because there is less weight on that tire than the other (e.g., the engine is offset to one side a little).

Jerry has been suggesting actions to first confirm that your brake components (i.e., line pressure, caliper alignment, etc.) are as they should be. After you confirm they are right, the next logical step would be to get corner weights and adjust your springs if required to balance them.

[ERA Chas]

Originally Posted by Jerry Clayton

OK---

You want to ignore the Dot 5/ dot 4 issues-----

Jerry,
I asked you this question in post #21 where you tell him that '50 gallons' of DOT 4 will not flush out of his system:

"So what does? Are you telling him to replace all seals/o-rings and lines in his system?"

-and you ignored the question! It's a legit question and I never heard or experienced that it can't be flushed. I have flushed silicone fluid with DOT 3 with no ill effects.

Helping a guy is fine but just making empirical statements with no superior or alternative methods is not helping. It's talking down to a guy.

[Jerry Clayton]

Well Chas----

I'm sorry if you think I was talking down to him------He obviously doesn't have a handle on the workings of brakes as probably a good percentage of modern day drivers don't.

The Cobra is a high performance car with very basic systems----the obvious thing seen or asked about in these threads are probably 180* from the root cause of the problem.

His braking problem is not caused by the right front locking up, it is probably the only brake doing its job---lets see---he has changed pads, doesn't know for sure if the tires are the same, doesn't know his corner weights, doesn't know how much vacume he has, doesn't know the front/rear, right/left pressure at his calipers, doesn't know if the calipers are the same size right/left or mixed front/rear, hasn't mentioned the type/brand of calipers

what he does know is the tires are the same brand, he has replaced dot 5 with dot 4 fluid,he has ss lines(I assume here he means braided stainless lines to the wheels)

We don't know if this car has always done this( I assume he bought it used or he would be all over the dealer)

Your opinion of Dot 5 brake fluid isn't the same as mine----I would bet that his master cylinder and all the seals in the calipers are junk and need a complete overhaul or replacement.

YOU CANNOT MIX DOT 5 AND DOT 3 / 4 BRAKE FLUID-----YOU CANNOT JUST PUMP SOME OF EITHER THRU TO FLUSH OUT THE SYSTEM.

[Excaliber]

I don't think "ruining" the seals by switching from Dot 5 to Dot 3 or 4 is really that large a concern. Perhaps over time, maybe, but I wouldn't loose any sleep over it. Flush the 5 out with 4 and move on with your life, in my opinion.

[ERA Chas]

Jerry,
Thank you for replying. I understand your concerns and you raise some valid questions.

I don't wish to beat a dead horse about just the fluid when you rightly claim that he has other, bigger problems.

But what you claim about the fluid is counter to my experience and apparently Ernie's too. I am simply asking what is the correct method, in your view, of purging silicone fluid and are you saying that the entire system integrity must be rebuilt with new seals etc?

Please tell me your experience and methods in this procedure. Your answer may help not only Rwillia but the rest of us as well.

Thanks,

[Rwillia4]

wow, lost of writing since I last looked... …as far as the pissing contest, I don’t care. Everyone communicates different, some are better then others.

well,
The calipers are the same BMW E-36 M3, visual inspection they are installed the same and appear to be in good working order (no leaks, look symmetrical to each other).
Pads were replaced with Repco semi-metallic to minimize brake dust. Visual inspection they are wearing the same. The pads that were removed also looked to be wearing the same.
The BMW E-36 M3 front rotors (315mm X 28mm (12.4")) are the same and show no signs of overheating, warping, or inconsistent wear.
Front tires are the same brand, type, size, and have the same treadwear.
The flexible brake lines from the hard lines are stainless steel replacing the stock rubber lines.
The car was aligned and balanced at the same time. I did not ask what the value for each corner was or even the spread, I should have. I also don't know if there was dummy weight added for the driver. I am now living 3000 miles from that shop.
The vacuum is in the mid 20's and drops to about 0 depending on if the engine is under load. I can feel the brake booster "function" when the car is started, as in feel it in the brake pedal.
The car has always had this problem since day one independent of any of the changes made including: springs, pads, brake lines, alignment, balancing and brake fluid.
As of today, I have been unable to determine the pressure at the calipers due to the fact that today is monday and most buy-on-line places don't ship on sundays. When I do receive the two pressure gauges I will test both sides at the same time with the car running and off, to ensure the brake booster is function correctly and the pressures are the same.

I purchase the car as a new roller and installed the rest myself (not hard to do).

I am pretty knowledgeable in how my vehicle works and a number of other things: physics, fluid dynamics, structures, aerodynamics, and arrogance to name a few. How brakes function is a simple concept, even anti-lock systems. And I personally like the fronts to lock up before the rears so the rear doesn’t become the front under corner braking.

I will try to determine the corner weights and test the caliper pressures soon.
I'm just asking for ideas to fix the problem, that I haven't already tried.

Thanks for the help,
Rob

[Jerry Clayton]

Rob---thanks for understanding and your patience with the contest

Chas----over the years---I have seen dozens of times where a braking system break down was caused by the brake fluid and brake components being incompatible---always dot 5 was the fluid---it IS NOT friendly with most standard brake system seals, o-rings, etc, and causes inumerical problems----they need to be dis a ssembled, cleaned with solvent, dried/replaced, lubricated with proper fluid that is compatible and reassembled.

Further---Dot 5 was developed for the military for use in equipment parked on that island in the Indian Ocean ( Dago darcia????) it is not supposed to absorb/mix with water----which dot 3/4 does, and then dot 3/4 has its boiling temp lowered like from 600* to 500*f which as racers we know is a NO NO---Dot 5 doesn't mix with the water that collects in the brake system so the boiling point of the DOT 5 isn't lowered!!!!! good deal, right????HOWEVER, the water that is collected in the system does boil, and at 212*f-----which do you want????

And the DOT 5 has a compressibility problem that 3/4 doesn't have, and dot 5 in a vehicle at sea level taken to higher altitude ( Bonneville, Denver, Salt Lake) will bubble and act just like the system is full of air!!!!

So--- if you like DOT 5---use it--but don't mix it, change it, flush it with 3/4, or really expect the brakes to be there everytime you need them.

One other thing---read on here how many BDR's have ongoing and re occurring clutch problems----DOT 5

[Argess]

er....just how bad is this problem? I think you stated that when you really brake hard, both wheels lock up.

I'm going to think out loud.....

Assume for a second, there is nothing wrong with your brakes. It leaves an explanation of uneven weight from right to left. So you measure the tire contact patches with scales. OK....a static system. Now what happens when you brake? Weight transfers forward. The R/L % weight ratio can now change. So what do you do?

First I'd adjust the two front springs independantly to get the exact same frame to ground height on each side. Now the car is level, but the spring pre-load may be different. But it's level. Funny thing is, the scales still read as before. So the problem is still there.

But hold it....isn't friction proportional to the downward force x the Co-efficeint of friction? hmmm......the tires are the same. It's got to be the weight....

How much do you weigh? 200 lbs maybe? Quite a bit more downforce on the driver's side, so the passenger side should lock up first.

Why not put sandbags equal to yhour weight in the passenger seat and try the brakes. (even more accurate by taking the scale reading into consdieration)

If they both now lock up at more or less the same time, you'll know what the problem is. You just need a 200 lb passenger to go with you. Start taking your wife to McDonald's a lot........

[Richard Hudgins]

Rob,

I would suspect the calipers and their mounting on your car.

If they are the BMW E-36 units they are floating calipers.

These can bind on the stud mounts etc. due to wear or even a loose stud mount.

In other words the mount geometry can get wrong and cause problems

The mounting is where I would first look.


Pressure differential in a closed hydraulic system is only true until the system stabilizes, then pressures are equal. (This time is measured in milliseconds)

Therefore you must look to mechanical problems such binding, alignment, etc.

Your corner weights would have to be way out to cause this problem.

And fluid is not the problem either.

You will get there, just look at the mechanical basics carefully and the answer will be there.

[ERA Chas]

Originally Posted by Jerry Clayton

So--- if you like DOT 5---use it--but don't mix it, change it, flush it with 3/4, or really expect the brakes to be there everytime you need them.

Now I see the problem-you think I'm using and defending DOT5. I never said that.

When I built my car in the 80's it was the thing to use. After one season I knew it wasn't and flushed it out of my system with DOT3, with no ill effects. Been using Castrol LMA ever since. Combined street and track use.

Back to the regularly scheduled program.

[Jerry Clayton]

Chas

My date with the lovely Dot 5 was in the 80s also on a 200mph Pro Stock
wouldn't stop, mushy pedal---new seals for masters and calipers and LMA also
stopped fine after that

as time went on heard many other horror stories and also helped fix many of them at races

today---most karting brake problems are dot 5 and I feel the clutch issues on the BDRs are from Dot 5

And all because Dot 5 won't hurt the paint!!!

[Argess]

I have to admit, I used DOT 5 (as per the manual) back around 1994. It's still in the car. I am a bit worried abotu changing due to potential seal damage.

On the OPs problem. If Master cylinder seals are going, he still gets same pressure to both front brakes, just not as much. If he has one caliper seal going, he will have unequal braking, BUT he will also have a brake fluid leak. Should see some on the floor I would think.

Does the car pull to one side when you use the brakes "light to moderate"? If there is something wrong with the brakes, one side compared to the other, it should pull to one side with light to moderate braking.

[Rwillia4]

the car tracks straight under braking and only pulls once the front has locked up. Even then it is not a major pull.

[Argess]

Well, I am certainly no brake expert, but a 200 lb driver in a 2500 lb car puts 16% more weight on the driver's side. A rough approximation, I know, but it does seem likely that the passenger side would lock up first under a "particular amount" of pedal pressure.

If this happens over a narrow range, in other words, if a little bit more foot presssure causes both wheels to lock up and a little bit less won't cause either wheel to lock up, I can't help but wonder if it's normal.

Odd, but i have never braked hard enough to lock up any wheels on mine.