1998 Dodge Durango

  • V8
  • 4WD
  • 130,000 MILES
I accidentally put brake fluid in my automatic transmission.
I drove it about 50 miles.
Is the transmission probably damaged?
Do you
have the same problem?
Thursday, March 26th, 2009 AT 1:48 PM

1 Reply

Probably not damaged but have the transmission flushed to be safe. A lot of the speedy lube places offer this service now. How much did you put in? Transmission fluid is a petroleum product. Brake fluid is glycol-based, and brake system rubber parts will be destroyed by petroleum products.

You are one lucky son of a gun! Transmission fluid in the brake system is a major repair expense, especially if you have anti-lock brakes. Here's a copy / paste partial reply to someone else who had a different problem:

.... Another cause of locking brakes is fluid contamination. Any petroleum product such as power steering fluid, engine oil, or transmission fluid will cause the rubber components to swell. Pull off the caps on the master cylinder. If the rubber seals under the caps are soft and mushy, and blow up so big you can't get the caps back on, the fluid is contaminated. In this case, all steel lines must be flushed and dried, and, ... This is critical;... ALL RUBBER PARTS MUST BE REPLACED. That means all front and rear rubber brake hoses, all calipers and wheel cylinders, the master cylinder, the combination valve on the frame rail by the master cylinder, the height-sensing proportioning valve, if you have one, near the left rear wheel or back axle, and the anti-lock brake hydraulic assembly if you have anti-lock brakes. The master cylinder and valve assemblies have rubber seals that become damaged from petroleum products. This repair can easily cost one to two thousand dollars; a very costly mistake. (Some unscrupulous sellers will add a little transmission fluid to the brake fluid to hide a defective master cylinder. Internal leakage will cause the brake pedal to slowly sink to the floor as you hold steady pressure on it. The transmission fluid causes seals to swell causing better braking, ... At first. After a few days, "you got junk")!

Fluid contamination will eventually cause more wheels to lock up. More importantly, as the seals swell in the master cylinder, they grow past a port and block it off just like if you held the brake pedal down an inch or two. Brake fluid is trapped and has just enough pressure to lightly apply the brakes. The heating of the brakes causes the fluid to expand. Since the fluid is trapped by the seals in the master cylinder, the pressure builds some more so the brakes apply harder and more heat is generated. It's a vicious circle, but the good news in your case is you are only having the problem with one brake, not all four. For this reason, I'm hoping fluid contamination is not your problem.

By the way, brake fluid can be contaminated by filling the fluid with a funnel that was wiped out after using it to fill engine oil. The residue in the funnel is enough to cause problems. Plus, the placement of some master cylinders necessitates the use of a funnel to fill the fluid.

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Saturday, March 28th, 2009 AT 6:38 AM

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