'76 XJ6C Brake Fluid Top Up

[klass6]

I have seen the past discussions of need for care in matching "top-up" brake fluid to ensure compatibility. I need to top up; a sticker on the reservoir says "Dot 5".
The actual reservoir is EMPTY so I can't confirm which fluid it actually contains. Any way to check this easily?

 

[equiprx]

If the res. is empty, there is a high likely-hood you have a substantial leak and you'll just be pouring it on the floor eventually. The sticker was probably added long after the car was built, because I don't think they had DOT 5 in '76. It might be time for a rebuild anyway.

 

[klass6]

Thanks. I took a flyer and added some Dot 5 to the reservoir. No obvious leak on the concrete, either before or after adding the fluid. And the brakes are working just fine...had the car out for its spring initiation today, drove about 60 miles with no problem with brakes! I'll check the level over time. This vehicle has been defying gravity for some time.

 

[LarryK]

Watch for fluid in the footwell area under floormat, as a leak can be hidden from the rear of the master cylinder. Dot5 is a lot newer than the 76 and you cannot add anything else. Might try bleeding system a little from each brake caliper to let out dirt and moisture as Dot5 will not mix with the moisture.

 

[Exotexs]

Dot 5 is Silicone Brake Fluid, bad news in my opinion. My experience with it was "never again".

you might drain and then flush the system with alcohol several times, and go back to Dot 3.

just my opinion.

Ex

 

[emery]

It is my understanding that old british cars braking systems were designed for Mineral Brake Fluid to be compatible with Natural rubber seals, as opposed to DOT 3 Glycol-Ether Brake Fluid and synthetic rubber seals used in American vehicle of the same period. Using Glycol-Ether based fluid in a british car will ruin the seals and contaminate the fluid. It will become quite dark and rubber deposits will be floating around. Upon disassembling, the rubber seals will simply desintegrate. The same applys for the clutch hydraulic system. I have lived that situation years ago. I use LUCAS-GIRLING Mineral Brake fluid; GIRLING-LOCKHEED Mineral Brake Fluid. Four years ago, I tried CASTROL LMA (Low Moisture Absorbant)Brake Fluid with good results so far.
Pat

 

[Roger]

Back in the 60s British cars had 2 brake makers, Girling and Lockheed. Dire were the warnigs if you used the wrong fluid Castrol Girling (crimsone) Or Lockheed (amber) as appropriate.
Then in the early 70s, someone started selling a generic fluid. Gasp! Shock! Horror!
Personally, I think it's all Horlicks, but I do use LMA for preference, too.

In any case, by 1976 the old natural rubber stuff had long gone.