Brake Bleeding/ Pressure Problem C5 Brakes

[epeterson]

Hi guys, having a real frustrating problem with the recent brake conversion on my 1986 Monte Carlo. I have upgraded the front brakes to a complete C5 front setup. It has C5 calipers, rotors, pads, umi conversion brackets, wilwood hubs, and stainless flynbye lines. The rear brakes are stock drums (will upgrade after getting new rearend). Ive tried beeding my brakes the manual method with someone in the car pumping and me at the bleeder opening and closing. This method worked great for the rear drums and fluid flow was great and all the air came out of the rear lines. Moving to the frront, after the pumping and hold method I open the bleeder on the C5 caliper and little to no fluod dribbles out...I did some research and discovered that I had th calipers on the wrong sides of the car (bleeder screw down instead of up) and switched sides with the calipers and assembled everything again. Tried bleeding the brakes again after this swap and still little to no fluid dribbles out. I was getting some air bubbles flowing out very slowly but there is still little to no pressure coming out. I have a brand new wilwood master cylinder on the shelf so I bench bled that master thoroughly and installed it onto the car. I wanted to verify that the master was not the issue s thats why I swapped this on. It bench bled perfectly and connected the car just fine with no leaks. But i am getting the same issue, the drums bleed just fine but the fronts still have very little pressurre. Im stumped and would like to know if you guys have any insights. Thanks guys.

[ClosNova805]

If the master cylinder bled properly off of the car, put the master cylinder on the car and bleed it again using the same clear bleeder tubes. If the master cylinder bled off of the car but does not once it is installed on the car, then there has to be a problem with the linkage between the pedal and the master cylinder. The most common issue is the rod that comes out of the front of the brake booster and pushes the piston of the master cylinder. (NOT the booster rod that goes to the pedal, the opposite side.) This rod is often slightly too long and causes a pre load on the master cylinder. This pre load generally prevents fluid from flowing properly out of one of the master cylinder ports. This booster rod should be almost touching the piston of the master cylinder, but not actually making contact. This is often a very small preload of about a 1/4". If you are unsure if this is your issue, try putting a pair of 3/8" thick horseshoe washers between the booster and master (temporarily) and see if the master cylinder starts to bleed properly. Make sure you bleeder screws aren't clogged

[epeterson]

Okay I will try bleeding the master on the car today and see how that results. My bleeder screws are brand new for the calipers so I can't imagine there is a clog but you never know. Being both sides of the car having the same low pressure issue makes me think there's a problem distributing the fluid to the front brakes..but I don't know for sure. I will bleed the master on car today and post again in the thread, thanks for the response!

[ClosNova805]

I was also going to say fill up your master cylinder open up your bleeder screws and just let them self gravity bleed them selfs for about a hour and see if that helps.

[epeterson]

Just bench bled the master on the car, I got a few more air bubbles to come out of the master and the pedal has a nice feel and motion all the way to the end of pedal extension. Connect the hard lines back up to the master and I've got a pedal the goes down about halfway then gets very hard and difficult to step down. I'm not sure if this is normal or not but I just thought I'd share if it does share info to help out. I have the calipers some small taps with a rubber mallet as I had the bleeders open and some air bubbles popped out as well. Stupid question about gravity bleeding though. I made sure the master cylinder was topped up full and then opened the bleeders and got no fluid to dribble out of the calipers, the bleeder screw faces up so I'm wondering how fluid would travel up and out of the bleeder...I had them open for about an hour and saw no evidence of fluid flowing out of the bleeder so I shut them at this point. Maybe I'm just not understanding gravity bleeding fully and any insight would be gravely appreciate!

[epeterson]

Update: Ran to the parts store and picked up speed bleeders for my c5 calipers. Installed them on the car and at first little no pressure still but slowly pressure built up and by about 30 pumps the pressure was shooting out of the bleeder, I pumped about another twenty times (continuously checking the master to make sure it never ran low) and then closed up the bleeders. Turned the car on to see if any progress was made and the pedal still goes right to the floor, very spongy. Do you guys think I have to just keep bleeding? Maybe there is an air pocket somewhere that needs to be worked out? I appreciate the help in trying to figure this out!

[Dark Pursuit]

are you using a disc / disc master cylinder

[epeterson]

I will check the part number for the master when I get home and double check on Wildwood's site. The front resivor is much larger than the rear. Probably a 70/30 split between the two sizes. The only reason I changed masters from original is because I was having this issue so I wanted to verify that the issue wasn't with my master. I'm getting the same conditions with this Wildwood unit that I was with the factory unit but can certainly switch back to the original as it is certainly disc/drum

[ctcz28]

Erik,
Sounds like there is still a problem with air in the MC. While you said you bled it, I wonder if there is still air in it. I don't know what type of MC you have, but if it's a stepped bore type, when stroking the piston to bleed it you need to wait at least 15 seconds or so between strokes to avoid aerating the fluid. I've always done this with the looped tubes into the reservoir and manually stroking the piston, but recently I bought an A-1 Cardone brake bleeder tool (very inexpensive). This is thing is great. Looks like a large syringe and only takes a couple of cycles (injections) and you're done, no more air in the MC. Additionally, I gave up on the manual push the brake pedal bleed years ago and got a Motive Power Bleeder. They aren't too expensive, and really work great, makes it an easy one person task.

[epeterson]

This is the Wilwood master cylinder I have on the car now


I haven't found the info if it is a stepped bore or not but at this point I'm considering put the stock master back on and trying to bleed them. Because the calipers are not on the correct sides that might have just been my issue and my stock master will work just fine for this application as it sits (disc/drum). I can try bleeding this wilwood unit again by waiting 15 seconds in between pumps but if I'm still having an issue I think I'll try the factory master one more time. Thanks guys!

[epeterson]

I don't know why Wilwoods site came out so tiny..the part number is 260-8555 for the master cylinder

[ctcz28]

Erik,
I feel your pain as I recently converted my '69 Camaro to C5 front discs. I hate bleeding brakes. So here are some random thoughts and feedback to your earlier questions:
(1) Gravity bleeding works based on Bernoulli's principle (or equation). I'll spare you the details, you can look it up, but basically the elevation differential between the outlet lines of the MC and the bleeder valves on the calipers/wheel cylinders drive the fluid from the MC to the bleeder.
(2) I don't know which model of the 260-8555 you got, but going to the C5 4 piston system, I downsized my OEM MC with the 1 1/8" bore to a 1" bore cylinder to improve brake feel and to generate more pressure and move more fluid per unit area of piston.
(3) I don't believe your Wilwood MC is stepped. I'd give Wilwood a call and as for their input on this problem, they've probably heard it all.
(4) Another source is Tobin over at Kore3 Industries. He is a wealth of info and even though you didn't buy any of your stuff from him he may be willing to give you some ideas.
(5) I installed a proportioning valve in my system to allow me to regulate the operation of the rear brakes so they do not lock up prior to the front brakes. Wilwood makes a really slick prop valve and a set of pre-bent lines that are set up as a direct connect to your new Wilwood MC. I used something else since I don't have a Wilwood MC.
(6) I put in a Wilwood 10# residual pressure valve in the line to my rear brakes since my new MC did not have one built in. You might look into this if you're going to retain your rear drums like I have.
(7) One of the respondents above mentioned the length of the push rod between your MC and the power booster. That was a good catch and something you need to verify is correct. Measure your original setup and make sure this is correctly duplicated with your Wilwood MC.
(8) Since you've bled the MC so many times and feel it's ok, there must be something else. Are your rear brake shoes properly adjusted and not too far away from the drum thus causing too much pedal travel?
(9) Check the flex line and its connections at your differential.
(10) Does your car's brake lines go into any type of hold-off valve the retards the pressure to the front brakes to allow pressure to build in the rear brakes first (primarily for being stopped on a slippery surface like snow so the rear wheels don't creep)? My Camaro does and it has a button that has to be depressed and held in order to bleed the front brakes properly which is why I ask about this. If your car has this it may not allow the new C5 calipers to correctly bleed.
(11) Down to checking obvious stuff - all connections correctly threaded, not cross threaded? I typically need too connect the brake lines to the MC prior to connecting the MC to the PB to make sure the brake line flare is firmly and correctly seated and the nuts fully tight. It's easy to get a tube flare ****-eyed in the bore and it will leak even though the nut is tight.

[epeterson]

Thank you for the very detailed response ctcz28! Last night I bench bled the stock master cylinder and put it on the car, opened up the speed bleeders up front and ended up getting a whole bunch of air out of the system. After bleeding the front brakes a couple of times I tested the brake pedal and I actually had brake feel! The pedal was much tighter than before and the 'brake warning light' was no longer lit. I've gotten most of the large air pockets out of the system at this point and I'll be getting a helper to do a final bleed on the entire system this evening. Looks like my stock master cylinder was just fine and it was the calipers being mounted on the wrong sides. After the calipers got switched it seems to have cleared up the bleeding issue I was having and he stock master displaces more than enough pressure to work these brakes. Thank you guys for all the responses and I will update this thread after tonight to update you guys on how the 'final bleeding' went! The only unfortunate thing is that it snowed some over night here north of Chicago and they've heavily salted all the roads around me again. So looks like I won't be able to road test these until the next heavy rain to wash the salt away :(

[epeterson]

Finally got the girlfriend in the garage to help with the final brake bleeding, the brakes bled great and this thing stops on a dime! Fantastic pedal feel and stops very quickly. Very happy with the outcome! Thank you for the help guys I appreciated all the answers!

[ctcz28]

Congratulations, well done!



Chris