Need help diagnosing a leak

[Cobradavid]

For the past several months, I have noticed an occasional drip of slippery fluid on my vinyl floor mat in the driver side foot box. The drip is right under the brake pedal. Today I stuck my head down there to investigate, and it appears that there's fluid leaking around the rod going from the brake pedal into the master cylinder. The fluid does not look or smell like ATF/power steering fluid (I'm running the donor hydroboost system), or motor oil or grease. I think it's brake fluid.

Pertinent specs:
Donor was a 2001 GT with 46,000 miles. Since completing it 2 years ago, I've put 3700 miles on the roadster. I've had no brake issues and never had to re-fill the fluid reservoir. The brake fluid level has dropped a very small amount. Brake pedal is firm with no fade.

Is it possible that a seal has gone bad and I'm leaking brake fluid out the back of the master cylinder?

Thanks in advance for any suggestions.
David

[charles roybal]

If you take small amount of Ajax in you palm of your hand and blow it up into the area of the leak... it should stick & identify where it's leaking from. My .2 cents on finding oil leaks.
charles

[3kcarbon]

If its brake fluid be carefull the stuff is the best paint remover ever...

[canuck1]

It's most likely your hydrobooster. Unfortunately the seals in these units can break down leading to a drip inside the footbox and/or a drip from the small breather hole underneath the booster itself. If you have 4 into 4 headers, you will often see this external drip as white smoke in the engine bay as it drips on to hot header tube.

While I have managed to staunch my own leak with Lucas Power Steering stop leak, I don't know the long term success rate just yet:

http://www.ffcars.com/forums/17-factory-five-roadsters/271001-quick-fix-leaky-hydroboosters.html

The only recommended course of action is replacement of the hydrobooster. There are a few hydraulic repair shops that can rebuild these units, but the replacement cost from Max at Chapman Ford will probably sway you towards a new one.

Sean

[AC Bill]

I have read of instances of the m/cylinder leaking at the rear, due to the angle the push rod sits at. Apparently this misalignment can cause issues, as the piston is being forced in at an angle, rather than straight on.

I just can't remember if the walls of the cylinder were getting scored, or if it was the uneven pressure on the seal, that eventually caused the leak..You may want to do a search on FFCars for more info re this issue, as there were several posts about it over the years.

[canuck1]

I have read of instances of the m/cylinder leaking at the rear, due to the angle the push rod sits at. Apparently this misalignment can cause issues, as the piston is being forced in at an angle, rather than straight on.

In the case of hydroboost power brakes, the connection to the pedal (the brake pushrod) goes into the hydrobooster, not the master cylinder. The hydrobooster is bolted directly to the master cylinder (uses a separate, hydraulically controlled pushrod to push MC). There is no opportunity for misalignment at that point and it would be unlikely for brake fluid to leak into the hydrobooster to find it's way back to the driver's footbox.

However, the same (severe angle) pushrod misalignment that can cause MC failure in manual brake setups CAN destroy the seal in a hydrobooster as well. With a hydrobooster, the fluid that escapes out of the brake pushrod opening is most likely power steering fluid, not brake fluid.

Run your hand under the bottom surface of the hydrobooster. There is a small breather hole on the bottom that may feel wet as well if the seals in your hydrobooster are failing.

Try Googling "hydroboost leak, Mustang" and you'll get an idea of the problem I'm describing.

Sean

[Cobradavid]

I think Sean diagnosed the problem. I did some more poking around in the footbox and the fluid is leaking out from around the brake pushrod. I didn't find any fluid or wetness under the HB unit (and no smoke from the headers!), so it's no leaking out of the weep hole. I used a clean rag to wipe the fluid off the brake pushrod, and it looks like it might have a pink tinge to it. Although it doesn't smell skunky like ATF (power steering/hydroboost fluid), I now suspect this is fluid from the hydroboost like Sean explained. Looks like I'll be getting some Lucas Oil stop leak soon!

Thanks for your help!

David