Drum Brakes Question

[Duke W.]

Re: Drum Brakes Question

Yes, don't use DOT 5 unless you start with everything thoroughly cleaned/flushed with denatured alcohol, dried, and free of any DOT 3 or 4 glycol-ether based fluid.

In all my other cars I use DOT 4 and flush the systems every two years. DOT 4 has higher dry and wet boiling points than DOT 3, and there is also some evidence that DOT 4 has a better corrosion inhibitor package that DOT 3.

Duke

[David D.]

Re: Drum Brakes Question

Thanks Duke....finally, what would be the reason to replace vs. rebuilding wheel cylinders?

I would think they are the 1" bore and simply buying a rebuild kit and rebuilding would/should suffice?

David

[Duke W.]

Re: Drum Brakes Question

They may be too badly pitted to hone out, and a lot of honing can get them out of round. New wheel cylinders are relatively cheap, and all you need is a functional replacement since they cannot be seen during Flight judging or even Bow Tie - other than the brake line connection and bleed valve.

IIRC , I disassembled, cleaned and inspected my originals, then just decided to buy new for my SWC - disassembled and cleaned them with denatured alcohol, then assembled them with silicone fluid. Brake parts are always assembled with a little brake fluid, so they must "processed" as above if you choose to use DOT 5 silicone fluid, and in addition to wheel cylinders the list includes master cylinders, hoses, and new or original pipes.

Duke

[Stuart F.]

Re: Drum Brakes Question

David;

I was advised by a number of old time car collectors before I did my recent brake job on my 63 to go with the DOT 4. As Duke says, it is easier to make the upgrade to it w/o conflicts that might arise going with DOT 5 Silicone, and it has improved properties over DOT 3. Also, if I recall right, the silicone fluid has some negative characteristics, but I don't recall the specifics (don't have the photo memory anymore). It was something like a more spongy pedal. Perhaps Duke can weigh in on that as he may have been the source of my impression, what with his computer like memory.

Stu Fox

[David D.]

Re: Drum Brakes Question

Duke and Stu and all others, once again thanks....DOT 4 it is.

(don't have the photo memory anymore)

I still have enuff left, but only when I'm actually looking at the photo.

What was the question

David

[Duke W.]

Re: Drum Brakes Question

David;

Also, if I recall right, the silicone fluid has some negative characteristics, but I don't recall the specifics (don't have the photo memory anymore). It was something like a more spongy pedal. Perhaps Duke can weigh in on that as he may have been the source of my impression, what with his computer like memory.

Stu Fox

Apparently DOT 5 silicone has a greater tendency to entrain or dissolve air than conventional polyglycol-ether fluid as there are anecdotal stories of silicone fluid causing loss of pedal height when the vehicle was driven to high altitude. I never had any kind of problem with pedal firmness or pedal height, but care should be taken - don't shake silicone fluid and pour it slowly.

Also, silicone fluid is not recommended for modern ABS systems. Apparently the rapid pressure pulsations as the ABS valves open and close can cause cavitation.

One other note. Some ask whether they should use "synthetic" brake fluid. The fact is that all brake fluid is synthetic - whether or not is says so on the label - because the base chemicals don't occur in nature, but are "synthesized" in a petro-chemical process. "Synthetic" has become just another marketing buzzword like "green".

Duke