Triumph Spitfire Brake Fluid

By Craig Ranson
By Craig Ranson

Managing Director – Bridge Classic Cars

Classic car technician Jon has continued his investigations into the running issues that our 1977 Triumph Spitfire has been experiencing.

He bled the brakes of the car and noticed that two different types of brake fluid had been used.

Triumph Spitfire brake fluid is usually DOT5. However, when bleeding the brakes, both DOT5 and DOT4 were found.

DOT4 and DOT5 Brake Fluid

In very simple terms, brake fluid is responsible for moving the pressure from the brake lever to the brake pads. Brake fluid should lubricate the callipers, help prevent corrosion, and have a high boiling point. There are 4 different types of Brake fluid – DOT3, DOT4, DOT5, and DOT5.1

Each type of brake fluid has a different boiling point. If brake fluid boils, it forms air bubbles which increases how much it can be compressed resulting in poorer performance of your braking system.

DOT3 and DOT4 are the most common types of brake fluids used.

DOT4 brake fluid is glycol ether-based. It has a higher boiling point which is more stable than that of DOT3 brake fluid.

DOT5 is a silicon-based brake fluid and can withstand higher temperatures than DOT3 and DOT4.

As a general rule, it is usually a good idea to change the brake fluid in your car every two years. Obviously, this will depend on the amount of mileage you do but two years is a good timeframe to keep in mind. Brake fluid absorbs water over time so the longer you leave it between changes, the poorer your braking system will operate.

It’s worth noting that DOT3 and DOT4 brake fluid shouldn’t be mixed with DOT5. Doing so could result in brake failure. DOT5 is a silicone-based brake fluid so is not compatible with the glycol-based DOT3 and DOT4 fluids.

Our 1977 Triumph Spitfire Brake Fluid

When Jon bled the brakes of our Triumph Spitfire, it was clear that both DOT4 and DOT5 had been used. In the photo below, you can see that the DOT5 brake fluid has risen to the top while the DOT4 fluid fell to the bottom of the container.

Now the brake fluid issue has been resolved, investigations continue into this classic car’s running issues.

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