Brake Bleeding Issue <> Problem Solved

[GoDadGo]

Hey Gang,

I'm helping my buddy Heath with some car maintenance, since he is recovering from a procedure, and we ran into a dilemma.
While trying to bleed his brakes the fronts bled with no issue but the rears seem to be air locked.
The car has 14,000 miles on it and doing a fluid flush is what we are trying to do.

We tried the following methods:
1. Pump It, Hold It, Bleed It
2. Basic Gravity Bleed
3. Vacuum Bleed

My questions are the following:
1. What could be causing this air lock situation?
2. Could the Rear MC be bad?
3. Could the Rear MC not be moving back to the neutral position thus causing the reservoir to be blocked by the piston?

Mr. H's MK-4 and mine use the same Wilwood Pedal assembly, have the same front brakes, with similar single piston rear calipers.
My car has separate reservoirs for the front and rear MC's while his uses only one reservoir for the front and rear.
Any recommendations from some Brake Bleeding Savvy Family Members would be greatly appreciated.

Steve

[Matt P]

I too am bleeding some neglected Wildwood brakes this weekend and it sounds like I have the same setup as your friend.
First off, are his rear calipers clocked at the 7pm position, with the bleeders facing down? If so, you need to unbolt the calipers and prop them upwards so the bleeders are facing up.
I too had an issue with what I presume was significant air in the rear passenger side. After I gave up for the night and came back the next day, I tried the pump/hold/bleed approach and it started working after about 7-10 iterations. Perhaps sitting overnight helped work the air towards the end a bit, or perhaps I was just 7 or so away.

Anyways, I am still not confident I have everything flushed and bled properly, so I'll be going back for more. Here is a video that Wilwood provided that recommends a 3-person 'purge' bleed.
https://www.youtube.com/watch?v=jELllXdtjdc

[Matt P]

After fighting bleeding the brakes for a few nights, I finally came across this older information. If anyone reading this has a similar older setup, following the below approach rather than the above (which was directly from Wilwood) worked for me.

https://www.factoryfive.com/wp-content/uploads/2012/08/Wilwood-rear-solid-axle-brakes.pdf

Key Excerpts:
Rear calipers must be clocked at the 3 or 9 position, so the bleeders are pointing directly horizontal. Bleed using only the upper bleed screw when at this position.

Start form the furthest from the master cylinder first. For rears, as above, only bleed the top screw. For fronts, bleed the outside (outboard) first then the inboard (inside) screw second.

[ggunter]

Not sure if this has been already stated or not. Do you have the dual Willwood master cyl's with a balance bar? If so, are you opening one front and one rear bleeder on the same side at the same time when you bleed? If not they will not bleed correctly. Also make sure there is at least 1/16" of play in the pushrods going into the MC's so they are able to fully retract and not have pressure on them from a pushrod being too long. Good luck, sometimes bleeding goes really well sometimes not.

[GoDadGo]

Not sure if this has been already stated or not. Do you have the dual Willwood master cyl's with a balance bar? If so, are you opening one front and one rear bleeder on the same side at the same time when you bleed? If not they will not bleed correctly. Also make sure there is at least 1/16" of play in the pushrods going into the MC's so they are able to fully retract and not have pressure on them from a pushrod being too long. Good luck, sometimes bleeding goes really well sometimes not.

Thanks for the tip and we'll let you know how it goes.

[GoDadGo]

I wanted to let you all know that we got the brakes properly bled and here is how we did it.

1a. We adjusted the balance bar so that it had an Extreme Rear Bias.
2a. We did the Pump It, Hold It method with Heath in the car and me bleeding the brakes starting with the longest run.
3a. Once we were getting good clean / non-bubble fluid we did a gravity bleed.
4a. The entire time we had a tube going to a cup full of brake fluid so air could not come back in.
5a. We then repeated the process for the shortest rear run.

1b. We adjusted the balance bar so that it had an Extreme Front Bias.
2b. We did the Pump It, Hold It method with Heath in the car and me bleeding the brakes starting with the longest run.
3b. Once we were getting good clean / non-bubble fluid we did a gravity bleed.
4b. The entire time we had a tube going to a cup full of brake fluid so air could not come back in.
5b. We then repeated the process for the shortest rear run.

Once this process was complete we readjusted the balance bar so that it was in a neutral bias position.