Just changed my reservoir fluid pipe so need to top up. Ordered some dot-4 fluid which has just arrived. My existing fluid has a very light amber colour, the new looks to be clear. Can I mix these ok? I got dot-4 as I believe you can mix with dot-3. Any thoughts please before I top up.
Technical Brake fluid top up
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Technical Brake fluid top up
Hi, I would bleed the system until you see the new dot4 from all corners. Some fluids can be mixed, but I'm not a fan. If you flush out the old dot3 you are sure the better fluid is in place.
Ian.
Am I right in thinking to start from farthest and work in?
Brake fluid tends to darken as it ages.
The shade of colour can vary a little between brands but is usually a very light straw to amber colour when new.
I'd be surprised if what is in your system is DOT 3, this hasn't been used in a very, very long time. Iirc, the last time I saw DOT 3 it was Girling? brand and was iirc, red in colour...
Brake fluid absorbs moisture over time, this lowers the boiling point of the fluid, so it's usually recommended to renew it after 2 years.There are moisture testers available for brake fluid but it's cheaper to buy the requisite amount of brake fluid than the b/f tester
There is also DOT 5 brake fluid. This is silicone based and does not absorb moisture. It used to be recommended for classic cars that are infrequently used/stored to prevent corrosion occurring in the brake system. However, this fluid has several disadvantages - spongey pedal despite proper bleeding, can cause seals to shrink, can allow air to be drawn past seals as brakes cool down, can't be mixed with or even topped-up with other brake fluids. In short, best to stay away from this stuff. I actually experienced total brake failure at over 100mph - 1st couple of hard braking applications were fine, continued on, brakes cooled down, air was drawn in past the caliper seals, next brake application, pedal went to the floor, zero brakes I don't know what I was more worried about, me getting killed or writing-off a 5 ton Presidential armoured limousine worth £1m+ at the time. Once bitten...
There is also DOT 5.1. This is like a better version of DOT 4 fluid, mainly a higher boiling point. Totally unnecessary on something like a Fiat 500. Afaik, it's only used on some high-performance/racing cars.
In case you're wondering, DOT stands for the U.S. Dept. of Transportation, which drew up the original specifications that brake fluid should meet (or exceed).
The main problem with bleeding brakes on an old car is the possibility that the seals in the master cylinder can fail if you bleed the brakes manually (i.e. by pressing the brake pedal all the way to the floor) What happens is corrosion can build up in the end part of the master cylinder bore where the seals never travel in normal braking - if you bleed the brakes by pressing the brake pedal fully, the master cylinder seals are pushed over this rough corroded section and are then damaged. To avoid this happening, many people opt to use either pressure or vacuum brake bleeding equipment - this also means that the bleeding operation can be carried-out single-handedly.
Another problem that can occur is finding that one or more bleed screws on the wheel cylinders have seized. (this is usually much more of a problem with disc brake calipers). If this has happened, it's probably a good idea to apply some penetrating oil/WD40/diesel fuel/home heating oil and give this sufficient time to work before commencing the bleeding operation.
On old cars, if you find the brake fluid colour is grey /almost black, beware as this is usually a sign that the rubber cylinder seals are badly worn and shedding material.
A final word of advice and this is very important, don't shake the container of new brake fluid. If you do, you'll mix air from the space above the fluid with the fluid and waste a lot of time repeatedly bleeding brakes when you've been topping up the reservoir with aerated fluid. Even carrying the new container of brake fluid home from the store can mix some air into the fluid. I always leave new fluid to sit for a couple or 3 days to allow any air bubbles to rise to the surface. If you have accidentally or otherwise shaken the new fluid, do yourself a favour and let the fluid sit for a couple of days before attempting to bleed your brakes. It is, however, ok to use aerated fluid to just top up a low reservoir as any entrapped air will rise harmlessly inside the reservoir over time and not affect brake operation.
Al.
The shade of colour can vary a little between brands but is usually a very light straw to amber colour when new.
I'd be surprised if what is in your system is DOT 3, this hasn't been used in a very, very long time. Iirc, the last time I saw DOT 3 it was Girling? brand and was iirc, red in colour...
Brake fluid absorbs moisture over time, this lowers the boiling point of the fluid, so it's usually recommended to renew it after 2 years.There are moisture testers available for brake fluid but it's cheaper to buy the requisite amount of brake fluid than the b/f tester
There is also DOT 5 brake fluid. This is silicone based and does not absorb moisture. It used to be recommended for classic cars that are infrequently used/stored to prevent corrosion occurring in the brake system. However, this fluid has several disadvantages - spongey pedal despite proper bleeding, can cause seals to shrink, can allow air to be drawn past seals as brakes cool down, can't be mixed with or even topped-up with other brake fluids. In short, best to stay away from this stuff. I actually experienced total brake failure at over 100mph - 1st couple of hard braking applications were fine, continued on, brakes cooled down, air was drawn in past the caliper seals, next brake application, pedal went to the floor, zero brakes
I don't know what I was more worried about, me getting killed or writing-off a 5 ton Presidential armoured limousine worth £1m+ at the time. Once bitten...There is also DOT 5.1. This is like a better version of DOT 4 fluid, mainly a higher boiling point. Totally unnecessary on something like a Fiat 500. Afaik, it's only used on some high-performance/racing cars.
In case you're wondering, DOT stands for the U.S. Dept. of Transportation, which drew up the original specifications that brake fluid should meet (or exceed).
The main problem with bleeding brakes on an old car is the possibility that the seals in the master cylinder can fail if you bleed the brakes manually (i.e. by pressing the brake pedal all the way to the floor) What happens is corrosion can build up in the end part of the master cylinder bore where the seals never travel in normal braking - if you bleed the brakes by pressing the brake pedal fully, the master cylinder seals are pushed over this rough corroded section and are then damaged. To avoid this happening, many people opt to use either pressure or vacuum brake bleeding equipment - this also means that the bleeding operation can be carried-out single-handedly.
Another problem that can occur is finding that one or more bleed screws on the wheel cylinders have seized. (this is usually much more of a problem with disc brake calipers). If this has happened, it's probably a good idea to apply some penetrating oil/WD40/diesel fuel/home heating oil and give this sufficient time to work before commencing the bleeding operation.
On old cars, if you find the brake fluid colour is grey /almost black, beware as this is usually a sign that the rubber cylinder seals are badly worn and shedding material.
A final word of advice and this is very important, don't shake the container of new brake fluid. If you do, you'll mix air from the space above the fluid with the fluid and waste a lot of time repeatedly bleeding brakes when you've been topping up the reservoir with aerated fluid. Even carrying the new container of brake fluid home from the store can mix some air into the fluid. I always leave new fluid to sit for a couple or 3 days to allow any air bubbles to rise to the surface. If you have accidentally or otherwise shaken the new fluid, do yourself a favour and let the fluid sit for a couple of days before attempting to bleed your brakes. It is, however, ok to use aerated fluid to just top up a low reservoir as any entrapped air will rise harmlessly inside the reservoir over time and not affect brake operation.
Al.
Last edited:
Thanks
Don't know what's in but very clean. The car has had a nut and bolt resto within last couple of years so should be ok. I've ordered a bleed kit so I can do it by myself and not involve the missus. I have bad memories of my dad screaming at me when I was a kid and wasn't pushing on the brakes right, down, hold, up, hold. ?
Don't know what's in but very clean. The car has had a nut and bolt resto within last couple of years so should be ok. I've ordered a bleed kit so I can do it by myself and not involve the missus. I have bad memories of my dad screaming at me when I was a kid and wasn't pushing on the brakes right, down, hold, up, hold. ?
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Had this scenario at the weekend with Mrs W...….Ironically I have a self bleed kit too but thought it would be easier to bleed the new calipers (on the motor home) by getting her to stand on the brakes...…..should have known better...….
It's not worth not bleeding it through to be fair, the amount of fluid it will take and the time involved makes it a no brainer...….I could mention the water content of the fluid if the vehicle is not used often etc but lets not start a massive debate
