4 replies to this topic

[blackhallr]

hi,i have a 1972 mini 1380 engine it has single line system with 7.5" front discs/ drum rear no servo the brakes have just been serviced/new cylinders, seals and larger master cylinder what fluid should i use i have read that silicon stops rubber functioning properly but i wanted something that wont attack paint just in case of spillage any one have any experience on matter.

[dklawson]

Silicone (DOT-5) fluid does not "stop rubber from functioning properly". There are issues with it that may or may not show up on your particular car.

1) Though some people flush out DOT-3/DOT-4 fluid to run DOT-5, it is better to start with a completely dry, new system. That includes the flexible hoses, cylinder seals, servo internals. The interaction of DOT-3/DOT-4 residue with DOT-5 can cause some rubber bits to sluff off a bit of their surface. The new fluid will become dark and some swelling of the old rubber may occur.
2) If your car has a hydraulic brake light switch, there are MANY anecdotal stories of that switch failing (even when new ones are installed) after the switch to DOT-5. The answer is to install a pedal box mounted mechanical brake light switch instead.
3) The reference you made to rubber not functioning properly typically involves the lubricating properties of DOT-5 compared to DOT-3/DOT-4. There are manufacturers studies that indicated that DOT-5 does not lubricate the seals as well as DOT-3/DOT4 when you are discussing new hydraulic cylinders. Ironically what this means is that if you have old brake cylinders without pitting, this is an instance where rebuilding what you have with new seals MAY give better results than buying new parts. However, your results with new parts may vary.
4) The two most common complaints about DOT-5 are pedal feel and difficulty bleeding the system. The pedal feel issue can be addressed by using stainless braided brake hoses instead of standard rubber hoses. The Mini is already hard to bleed so if you use DOT-5 be sure to add fluid to the reservoir carefully to avoid bubbles. To avoid bubbles when adding fluid, take a long screwdriver and wipe it completely clean. Place the bottom end in the reservoir and "pour" the fluid slowly onto the top of the screwdriver shank so that it runs down the shank slowly into the reservoir without drips or splashes that produce bubbles.

If your biggest concern is not ruining paint, DOT-5 is really your best option. With all new rubber in the system, and taking care while bleeding, you should not have any problems. However, during the first year of use pay attention to any drops in the level of the reservoir and if any occur, check the conditions of all the seals in the system. The lubricity issue may have surfaced on one or more cylinders. If that happens, repair or replacement is your only option. I personally have not had this issue and all three of my British cars use DOT-5 fluid.

[pdaykin]

I'd be interested to hear from people who have actually used DOT5.

For me, changing to braided brake lines didnt make any difference.

That said, neither did I think the pedal feel was 'bad' either.

But I have reverted to DOT4. Yes, it does need changing every few years. Yes, it is quite aggressive.

But it does its job. Gives a good pedal feel. And it cant be that bad if manufactururs are stil using it

[dklawson]

I DO use DOT-5. It is in all three of my British cars including the Mini. I have the braided lines on the Mini and rubber lines on the GT6. I did find the pedal firmer on the Mini with the braided lines.

There is nothing wrong with DOT-4 fluid or DOT-3 fluid. The main reason I use DOT-5 on my classic cars is that I don't want to risk any damage to the paint under the bonnet. I did not switch for performance reasons.

The choice of which fluid to use (today) is largely an owner decision. Back in the day when my Mini was new, it was DOT-4 or nothing. The seal composition back then was not at all compatible with DOT-3 and DOT-5 had not arrived yet.

[tiger99]

I always use silicone if I rebuild a brake system. I did a Cavalier, new rear cylinders, overhauled calipers and master cylinder, new braided hoses, and Kunifer pipes where needed. I blew through the remaining steel pipes with compressed air to get rid of the old fluid.

That car was doing a very high mileage, and the brake system needed no attention ever again, except for a set of front pads every so often. The car was already old, and accumulated another 110k miles before it was scrapped due to rust.

I also had no problems with a 1984 Mini.