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Restoring - General discussions that span across many different groups of years and models => Processes, Products & Techniques => Topic started by: V8_bloke_28 on April 09, 2015, 06:16:54 AM

Title: Brake bleeding problem
Post by: V8_bloke_28 on April 09, 2015, 06:16:54 AM
Hi.
I have a 69 mach 1 with discs and drums.
I've just rebuild the distribution block and prop valve and I'm struggling to bleed the front brakes. I get oil and air coming out of the bleeders on front only. Rear brakes are good. There are no oil leaks anywhere.
When I press the pedal down I see that little squirt but when I release the pedal bubbles come out of the oil in the reservoir. It's like air is getting into the system somehow.
Could the master cylinder be faulty?
Cheers
Title: Re: Brake bleeding problem
Post by: 67gtasanjose on April 09, 2015, 08:02:36 AM
If you haven't already looked, you might wish to see if the master is seaping from where it connects to the booster. You may need to remove it (lines attached if possible) and get a mirror down there to look.

When bleeding brakes, when you RELEASE the pedal, the system goes into a brief moment of vacuum. ANY place open to the outside air is suspect of drawing air into the system. Do not rule out the proportioning valve and the likes. USUALLY, the item at fault is also seaping fluid but when it is under pressure, the leak might not actually spray or drip fluid, thus making it harder to spot it. Clean and dry up all of your components, this will help to spot any potential small leak. Wipe everything down and clean with either brake cleaner or water and an air nozzle (using rags etc to keep from damaging your painted surfaces) BRAKE FLUID EATS PAINT so be careful! Use goggles too! Sometimes, walking away after a full cleaning and inspecting again the next day you will find your "wet spot"...THAT wet spot is likely your seap! Clean it again and wait again, if it keeps getting wet...there it is!
Title: Re: Brake bleeding problem
Post by: V8_bloke_28 on April 09, 2015, 08:14:09 AM
It looks dry everywhere
Title: Re: Brake bleeding problem
Post by: Brian Conway on April 09, 2015, 11:12:31 AM
V8 Bloke;  this seems to be a common problem for a lot of folks.  This is the most recent posting, I followed, and it does have a happy ending.  Brian  http://1969stang.com/forum/index.php?/topic/53249-bad-master-cylinder/
Title: Re: Brake bleeding problem
Post by: 67gtasanjose on April 09, 2015, 11:40:50 AM
 +1 on the vacuum method.

Yep, if no leaks and starting off with a correctly bench-bleed master cylinder, vacuum bleeding or pressure bleeding will always get the rest of the air out.

On the old cast iron masters like our old Mustangs have, I like pressure bleeding best, problem is the pressure bleeder itself has been obsolete for about 30 years or so,  vacuum bleeders have replaced them because they are more universal. In the 80's, they began selling master cylinder adapters for the new wave of plastic resevoirs coming onto the market allowing us to continue using the old-school pressure bleeders...Very cost prohibitive let alone the countless adapters you needed, not to mention you had to keep all of these things clean. (all nice & effective, yet all too complicated)

Hopefully you get it figured out quickly. 
Title: Re: Brake bleeding problem
Post by: suskeenwiske on April 09, 2015, 07:11:56 PM
If you haven't already, check the Caliper Pistons and Seals also, they sometimes will not show any leaks but may still draw air.

Not likely but wouldn't hurt to have a look.

Good Luck!

Ray
Title: Re: Brake bleeding problem
Post by: 1970shelbyguy on April 14, 2015, 01:56:52 AM
just went thru this with my 70 gt500  -  i put in the new seal kit for the dist block and proportioning valve.  everything looked ok but the stinking proportioning valve leaked thru the outside weep hole.  when i took the little guy apart the spring had moved down and scuffed up the little sealing ring. so i ordered a new one from fineline.  69.00 incl shipping   no problem now.  and also ensure those  front brake line to caliper bolts have new copper crush washers and bolts are "tight" . good luck
Title: Re: Brake bleeding problem
Post by: Smokey 15 on April 14, 2015, 03:06:38 AM
 Some very good answers here. Are you using silicone fluid?  It will not hurt paint.