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Street Rodder - - Contents - Ron Ceri­dono

QI like to think of my­self as one of those street rod­ders who keeps his car in ex­cel­lent con­di­tion. I do all the pre­ven­tive main­te­nance nec­es­sary each win­ter and have had the car in­spected by the NSRA safety team at the Street Rod Na­tion­als and ev­ery­thing was good ex­cept for the park­ing brake, which I’ve since re­paired.

My car is a ’37 Ford, it has disc brakes up front, a Ford 8-inch rear with drum brakes in the rear, and a Ford dual cham­ber disc/drum mas­ter cylin­der with a dual-di­aphragm booster. The brake lines are 3/16-inch stain­less with braided stain­less flex lines front and rear, with a 10-pound resid­ual pres­sure valve in the front line.

While the brakes work per­fectly, when I did my win­ter main­te­nance, I dis­cov­ered the brake fluid was ex­tremely murky, al­most muddy look­ing. I don’t re­mem­ber it look­ing that way the last time I checked it, but since the mas­ter cylin­der is un­der the floor it does not get checked as often as it should.

Ob­vi­ously the brake fluid in my car needs to be changed, but what is the life ex­pectancy of brake fluid and what’s the best way to know if it needs to be changed?

Kyle Kraft ViatheIn­ter­net

ABrake fluid is one of those things that ev­ery­one more or less ig­nores. How­ever, due to con­tam­i­na­tion from mois­ture it should be changed when nec­es­sary.

Ac­cord­ing to the brake ex­perts at Wil­wood there are many ways for mois­ture to en­ter a brake sys­tem, in­clud­ing con­den­sa­tion from reg­u­lar use, wash­ing the ve­hi­cle, and hu­mid­ity, and there is not much that can be done about it.

DOT 3 is the most com­mon type of brake fluid used in do­mes­tic cars and trucks. Ac­cord­ing to the So­ci­ety of Au­to­mo­tive En­gi­neers (SAE), DOT 3 can ab­sorb 2 per­cent of its vol­ume in wa­ter ev­ery year. Over enough time ex­ces­sive mois­ture will cause cor­ro­sion in the brake sys­tem and can lead to is­sues like va­por­lock or a spongy pedal.

DOT 4 is for­mu­lated for use by all ve­hi­cles, it has a higher boil­ing point than DOT 3, and it does not ab­sorb mois­ture as fast. DOT 4 and DOT 3 are in­ter­change­able, how­ever it’s best to avoid adding DOT 3 fluid to a sys­tem that al­ready uses DOT 4. (It’s the pre­ferred type of fluid used for street and high-per­for­mance ap­pli­ca­tions.)

DOT 5 (often re­ferred to as syn­thetic brake fluid) is sil­i­cone-based, which means it does not ab­sorb any mois­ture. Many street rod­ders use syn­thetic be­cause it’s not cor­ro­sive to paint or other brake com­po­nents, which makes it great for pre­serv­ing clas­sic cars for long pe­ri­ods of time. But there are a few draw­backs to sil­i­conebased flu­ids. They ex­pand more when com­pressed, which can make the pedal feel spongy, also DOT 5 flu­ids can­not be mixed with any other type of brake fluid. DOT 5 will usu­ally have a vi­o­let tint in color to dis­tin­guish it from DOT 3. Wil­wood does not recommend us­ing DOT 5 fluid in any rac­ing ap­pli­ca­tions. Ad­di­tion­ally, DOT 5 fluid is highly com­press­ible due to aer­a­tion and foam­ing un­der nor­mal brak­ing con­di­tions, pro­vid­ing a spongy brake feel.

DOT 5.1 is a non-sil­i­conebased polyg­ly­col that has a boil­ing point over 500 de­grees. Un­like DOT 5, DOT 5.1 can be mixed with DOT 3 or DOT 4. Also, DOT 5.1 will usu­ally have the high­est rated boil­ing point, which is best rec­om­mended for se­vere-duty and high-per­for­mance ap­pli­ca­tions. AFCO rac­ing of­fers the Ul­tra

HTX that ex­ceeds DOT

5.1 re­quire­ments with a boil­ing point rated over 600 de­grees.

Due to the ex­treme op­er­at­ing tem­per­a­tures of a high-per­for­mance brake sys­tem, stan­dard, off-theshelf brake flu­ids are not rec­om­mended. Of crit­i­cal im­por­tance in de­ter­min­ing a fluid’s abil­ity to han­dle high-tem­per­a­ture ap­pli­ca­tions is the

Dry Boil­ing Point and com­press­ibil­ity.

The Dry Boil­ing Point is the tem­per­a­ture a brake fluid will boil in its vir­gin non-con­tam­i­nated state. The high­est tem­per­a­ture Dry Boil­ing Point avail­able in a DOT 3

fluid is 572 de­grees F. The Wet Boil­ing Point is the tem­per­a­ture a brake fluid will boil af­ter it has been fully sat­u­rated with mois­ture. The DOT 3 re­quire­ment for wet boil­ing point is a min­i­mum tem­per­a­ture of 284 de­grees F.

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