Wheels and brake fluid

[theboyfold]

Couple of questions, as I'm trying to get my car (306 Rallye, so FWD) sorted for some track related fun!

At the moment, the steering wheel has a vibration at high speed and a slight pull to the left. So I'm going to get this fixed with 4 wheel alignment. However, I have another set of wheels for the track (which are exactly the same type of alloys), so when is it best to get the alignment done, with the road or track wheels on? What part does the alignment work on? Is it, the wheel or 'bits' behind the wheels (Please forgive my technical ignorance!)

Also, I'm looking to upgrade the brake fluid to try and resist brake fade. I've been told that dot 5.1 fluid can rust the system and it needs to be changed every month or so. Is this true? What are the bad points to using 5.1 over the standard fluid?

Thanks!

[Trooper2]

theboyfold said:

Couple of questions, as I'm trying to get my car (306 Rallye, so FWD) sorted for some track related fun! At the moment, the steering wheel has a vibration at high speed and a slight pull to the left. So I'm going to get this fixed with 4 wheel alignment. However, I have another set of wheels for the track (which are exactly the same type of alloys), so when is it best to get the alignment done, with the road or track wheels on? What part does the alignment work on? Is it, the wheel or 'bits' behind the wheels (Please forgive my technical ignorance!) Also, I'm looking to upgrade the brake fluid to try and resist brake fade. I've been told that dot 5.1 fluid can rust the system and it needs to be changed every month or so. Is this true? What are the bad points to using 5.1 over the standard fluid? Thanks!

Alignment deals with the bits behind the wheels, the steering and suspension components. It is a series of adjustments (camber, caster and toe) that are meant to ensure that the vehicle goes down the road straight, turns properly including the steering wheel wanting to recenter after a turn and doesn't do anything weird when you hit a bump. Since you are going to drive more on the road and the 2 sets of wheels are the same (especially the off-set), I would recommend that you have the aliment done with the road wheels and tires in place (less likely to prematurely wear out any tires).

5.1 Brake fluid should be allot less corrosive to the brake system (keep it away from your paint) as it doesn't absorb water like dot3 or dot4 do, you can go as long as 60 months without changing it, 12 months is recommended for dot3 and 4, but as you will be pushing the car at track days I would change it more often than 60 months.

The down side to 5.1 is thats it's not as easy to find as dot 3 or 4 and it's more expensive.

[GreenV8S]

Trooper2 said:

5.1 Brake fluid should be allot less corrosive to the brake system (keep it away from your paint) as it doesn't absorb water like dot3 or dot4 do, you can go as long as 60 months without changing it, 12 months is recommended for dot3 and 4, but as you will be pushing the car at track days I would change it more often than 60 months. The down side to 5.1 is thats it's not as easy to find as dot 3 or 4 and it's more expensive.

I think you're confusing DOT5 and DOT5.1 fluid. Despite the similarity in the name, they're completely different and incompatible with each other.

DOT5.1 is basically similar to DOT3 and DOT4, but with a higher temperature rating. This is the stuff you want. In a road car it will last two or three years without any problem, but on a track car you would be advised to put fresh fluid in after each track day. All these fluids are highly corrosive and will damage anything they touch, they are a highly effective paint stripper, and highly flamable. Basically nasty stuff. But the insides of the brake system are designed for this stuff and will cope indefinitely.

DOT5 is quite different. It has a significantly higher temperature rating than any of the other fluids. It is far less corrosive. It doesn't absorb water, which sounds like an advantage but is actually a disadvantage, because water will inevitably get into the braking system and if it isn't absorbed by the fluid it will collect in droplets. The water droplets are very bad for seals and moving surfaces, and have a very low boiling point, so you need to flush the fluid every six months or so. This might be tolerable if the car is only ever used for track days. The really bad news is that DOT5 is completely incompatible with the other fluids and if you change to/from DOT5 you need to replace every seal in the system and flush the pipes through.

>> Edited by GreenV8S on Tuesday 4th April 23:44

[Trooper2]

Damn and I only had that brakes class 8 months ago, thanks for the corrections GreenV8S.

[theboyfold]

GreenV8S said:

DOT5.1 is basically similar to DOT3 and DOT4, but with a higher temperature rating. This is the stuff you want. In a road car it will last two or three years without any problem, but on a track car you would be advised to put fresh fluid in after each track day. All these fluids are highly corrosive and will damage anything they touch, they are a highly effective paint stripper, and highly flamable. Basically nasty stuff. But the insides of the brake system are designed for this stuff and will cope indefinitely.

Hmmm, thanks for that. Is there a solution where I won't have to flush my system after every track day? Or is this just something you would suggest doing to mantain the best performance from the brake fluid?

[GreenV8S]

theboyfold said:

Hmmm, thanks for that. Is there a solution where I won't have to flush my system after every track day? Or is this just something you would suggest doing to mantain the best performance from the brake fluid?

The reason for replacing the fluid after each track day is that the fluid degrades when it gets really hot. If you upgrade the brakes to the point that they never get really hot then in theory the fluid would last for years. Or just drive really gently, but that rather defeats the object I've seen (but not tried) fluid recirculating systems which circulate fluid through the caliper each time you apply the brakes. This ought to mean that the fluid doesn't get cooked as easily. If you don't mind plumbing a new set of brake lines in then this wouldn't be hard or expensive to do. But in the scheme of things, replacing the brake fluid isn't much of a job, you'll be going round anyway to check/replace pads/discs, check suspension and tyres etc.

[leorest]

GreenV8S said:

... you'll be going round anyway to check/replace pads/discs, check suspension and tyres etc.