Fluids and Brake Seals: TEST

[Scud]

Several months ago, I used WD-40 to clean my brake calipers and we had some discussion about the risks involved in that. For reference, the discussion is interspersed with other stuff in pages of 2 through 4 of this thread:  http://www.v11lemans.com/forums/index.php?showtopic=18967&page=4

 

GStallons suggested I do a test. Being curious myself, I said I would do so at the next opportunity, which has arrived. Here is the experiment:

 

One brake piston seal in four different fluids: I'm going to let them soak while I am away next week. The used seals are Brembo, from a BMW K75s. They are from inside the cylinder, the ones that the pistons slide against.

 

 

The fluids are:

1. DOT 3 brake fluid (our control subject)
2. 20w-50 petroleum oil
3. Brake cleaner
4. WD-40

What's going to happen? Step right up and place your bets....

[Gottagetone]

My bet is on the brake cleaner but for fun I would suggest trying another seal in blue Dawn with just a bit of water, that stuff works wonders!  

[czakky]

I honestly believe not much will happen. Ten years from now.... maybe something.

[gstallons]

By the time you get back , the engine oil will destroy the rubber brake part the most , the WD-40 I think will come in second , continuous Brake- Kleen third & the brake fluid last .

[Scud]

I'm rebuilding a pair of two-pistons calipers, so only four seals are available for this experiment. Apologies to blue Dawn.

• I expect no change to the one soaking in brake fluid, because the seal is what keeps the fluid from escaping the cylinder - it's soaking in brake fluid all the time.
• I chose petroleum oil because everyone seems to agree that petroleum products are bad for these seals. We'll see how bad it is.
• I'm most curious to see the affect of the brake cleaner and WD-40.

Other than a visual and manual inspection after the soak, what sort of test should I apply? Perhaps hang weights off them till they break?

[gstallons]

The affect of petroleum or petroleum distillates on hydraulic brake rubber parts is not good. They will swell .

[Scud]

This turned into a two-week test, because I was away on business travel and snuck in a little adventure, which involves a diesel truck and a snowstorm on a mountain pass in Idaho. So today (finally) the results are in.

• Brake fluid - seal has 44mm OD
• Engine oil - seal has 52mm OD - this is an 18% increase in the OD.
• Brakleen - seal has 44mm OD - it should be noted that the Brakleen evaporated, even though I had covered the jar with plastic wrap. Therefore, I have no idea how long the seal soaked in the fluid.
• WD-40 - seal has 59mm OD - this is a 35% increase in the OD.

The measuring caliper on the engine oil seal is set to 59mm so you can see how much more the WD-40 caused the seal to swell - compared to swelling caused by the engine oil.

 

Conclusions:

1. Cleaning calipers with WD-40 is even worse than cleaning with engine oil.
2. Despite the WD-40 "secret recipe" and some mystery about whether WD-40 includes any petroleum, it seems reasonable to assume that WD-40 does, in fact, contain petroleum distillates.
3. If brake cleaner has any negative effect on seals, it probably won't stick around long enough to do any damage.

[czakky]

So cool! Thanks for the experiment. What was original size?

[Scud]

Original size was 44mm - no change from soaking in brake fluid or brake cleaner.

 

I've been thinking about the implications of this. Even a little swelling of the seals would cause the pistons to get sticky - which might require more force to activate the brake, but more importantly (I think) it could make it very difficult for the pistons to retract, which in turn means overheating, excessive wear, or maybe worse.

[czakky]

Best thing I ever did to my brakes was clean the Pistons with some simple green and a toothbrush working each one individually. Unless you do this every once in a while you'll be lucky to use three Pistons.