Master Cylinder brake fluid leaks out fill caps

Rusty Davenport · 07-31-2009, 11:56 AM

Wildwood master cylinder has splashed/leaked out brake fluid around both fill caps........really looks good on custom paint job at firewall.......is this a freak thing or has anyone ever heard of this ?????

Tom Turner · 07-31-2009, 04:10 PM

Not a freak thing at all. If it's the Mopar style master, that's a common deal. I cured mine by running the level down about an inch. I think the problem is the splash shield on the bottom of the caps; poor design. TT

gmonde · 07-31-2009, 05:00 PM

i have the same deal with seapage out of the caps,run the fluid lower ,,one thing that seams to contribute the problem is the the amount of brake presure applied,,when i stage my car i have about 900-1050 psi and letting off the brake rushes the fluid back to the master and splashes back ,,i have to wipe off the master every now and then gmonde

TOP GUN · 07-31-2009, 08:38 PM

Seen it a lot with my strange mopar mc. File top ofthreads with aflat file to git rid of casting flaw. Add 1 or 2 layers of duct tape between rubber gasket and lids to titen twist on pressure.

Ronald Urquhart · 07-31-2009, 11:35 PM

Try taking and old plastic antifreeze jug or oil bottle, take the cap from your master cyl pop out the rubber gasket use it as a template cut out a couple of circles use them as shims between the rubber gasket and cap. I did this a couple of years ago hasn't leaked since.

Moparteacher · 08-05-2009, 12:22 AM

The seal on the caps must seal the fluid from the atmosphere. The vent in the cap directs atmospheric pressure to the top side of the seal.

Brake fluid is extremely hydroscopic in that it obsorbs moisture from the air, hence the seal.

If the fluid is pushing past the seal, and the seal is good, then the fluid may be contaminated. Moisture and oxygen in the fluid will expand with heat and push past the seal. Contamination will also lower the boiling point of the fluid.

Consider flushing the system and replacing with new fluid from a previously unopened container.

Gary Tackett · 08-05-2009, 05:37 AM

I have a Lamb and have never had an issue. Take a look at the rubber boots in the cap. If they are protruding out, you have air in your system. That rubber nipple in the cap will take up space in the master and force the fluid out.

Good Luck

lgvoiles · 08-05-2009, 09:52 AM

Same leaking problem with mine also, I re-bleed my capilers then filled
the level about 3/4" lower than before, seems not to be leaking now.

07-31-2009, 11:56 AM	#1
Rusty Davenport Senior Member Join Date: Jun 2005 Location: Nashville N.C. Posts: 506 Likes: 4 Liked 101 Times in 27 Posts	Master Cylinder brake fluid leaks out fill caps Wildwood master cylinder has splashed/leaked out brake fluid around both fill caps........really looks good on custom paint job at firewall.......is this a freak thing or has anyone ever heard of this ?????

07-31-2009, 04:10 PM	#2
Tom Turner Member Join Date: Jan 2005 Location: Lake Tapps, Washington Posts: 137 Likes: 0 Liked 0 Times in 0 Posts	Re: Master Cylinder brake fluid leaks out fill caps Not a freak thing at all. If it's the Mopar style master, that's a common deal. I cured mine by running the level down about an inch. I think the problem is the splash shield on the bottom of the caps; poor design. TT

07-31-2009, 05:00 PM	#3
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 165 Times in 59 Posts	Re: Master Cylinder brake fluid leaks out fill caps i have the same deal with seapage out of the caps,run the fluid lower ,,one thing that seams to contribute the problem is the the amount of brake presure applied,,when i stage my car i have about 900-1050 psi and letting off the brake rushes the fluid back to the master and splashes back ,,i have to wipe off the master every now and then gmonde

07-31-2009, 08:38 PM	#4
TOP GUN Member Join Date: Dec 2004 Location: wake forest , n.c. Posts: 162 Likes: 2 Liked 0 Times in 0 Posts	Re: Master Cylinder brake fluid leaks out fill caps Seen it a lot with my strange mopar mc. File top ofthreads with aflat file to git rid of casting flaw. Add 1 or 2 layers of duct tape between rubber gasket and lids to titen twist on pressure. __________________ nitro joes TOP GUN 3 years straight mark young

07-31-2009, 11:35 PM	#5
Ronald Urquhart Member Join Date: Apr 2002 Location: Chesterfield, Va Posts: 160 Likes: 240 Liked 77 Times in 39 Posts	Re: Master Cylinder brake fluid leaks out fill caps Try taking and old plastic antifreeze jug or oil bottle, take the cap from your master cyl pop out the rubber gasket use it as a template cut out a couple of circles use them as shims between the rubber gasket and cap. I did this a couple of years ago hasn't leaked since.

08-05-2009, 12:22 AM	#6
Moparteacher Junior Member Join Date: Nov 2007 Location: Boise Posts: 49 Likes: 0 Liked 0 Times in 0 Posts	Re: Master Cylinder brake fluid leaks out fill caps The seal on the caps must seal the fluid from the atmosphere. The vent in the cap directs atmospheric pressure to the top side of the seal. Brake fluid is extremely hydroscopic in that it obsorbs moisture from the air, hence the seal. If the fluid is pushing past the seal, and the seal is good, then the fluid may be contaminated. Moisture and oxygen in the fluid will expand with heat and push past the seal. Contamination will also lower the boiling point of the fluid. Consider flushing the system and replacing with new fluid from a previously unopened container. __________________ Gary Weaver Moparteacher@yahoo.com

08-05-2009, 05:37 AM	#7
Gary Tackett Junior Member Join Date: May 2007 Location: Corona Ca. Posts: 16 Likes: 0 Liked 13 Times in 3 Posts	Re: Master Cylinder brake fluid leaks out fill caps I have a Lamb and have never had an issue. Take a look at the rubber boots in the cap. If they are protruding out, you have air in your system. That rubber nipple in the cap will take up space in the master and force the fluid out. Good Luck

08-05-2009, 09:52 AM	#8
lgvoiles Junior Member Join Date: Jan 2006 Location: Xenia, Ohio Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	Re: Master Cylinder brake fluid leaks out fill caps Same leaking problem with mine also, I re-bleed my capilers then filled the level about 3/4" lower than before, seems not to be leaking now.