After installing my new front calipers (Wilwood D8-4) I used my Motive power bleeder to bleed the system. My plan was to run a couple bottles of fluid through to also flush the system of any old fluid. Prior to doing this I used a hand sunction gun (just a little hand pump) to draw out the fluid from the M/C to limit how much old fluid would have to be flushed out. I left about 1/8-1/4" of fluid in the M/C and then topped it up with fresh fluid before beginning the bleeding. I bled everything like I have in the past. I got good flow from the front and actually very little air. The rears seemed to flow a little slower than I would usually expect, but no air. Got out to test drive and I have low/soft pedal. The brakes stop good, but the pedal drops lower than it should...definitely feels like air. I re-bled all 4 wheels and test drove with no change.

My question is, could air have gotten into the M/C when I siphoned out the old fluid? I was under the impression that as long as no bleeders were open, and I wasn't hitting the brake pedal, no air would get drawn in.

I'm going to try rebleeding all 4 again, and this time make sure I give the calipers some good taps with a rubber mallet. If I need to I'll bleed the M/C on the car, but I don't want to do it if I don't have to, which is why I'm curious if it would've been possible for air to get in there.

I appreciate any advice

 

Park the car on a fairly steep hill, nose down to get the front of the master cylinder slightly downhill. On the level you will notice that it's high in the front. Now with the back of the master higher than the front, remove the cap and place a clean rag over the open mastercylinder. Now go inside the car and proceed to "Snap" the air out of the master. Pump the pedal a couple times and just let it go from the depressed position. Letting the pedal fly back to the stop as it were. Do this a few times. Should get trapped air out of the master.

 

If you never exposed the bottom of the MC to air you dont have air in the master. You don't state whether you let the master run dry?

 

I definitely didn't let the master run dry, I had the motive bleeder hooked up and it had plenty of fluid in it. The only thing I did was siphon out old fluid from the master and fill it with fresh fluid prior to bleeding/flushing the system. When I siphoned I left about 1/8-1/4" of old fluid in the master, enough to keep the ports in the bottom covered with fluid.

 

Try gravity bleeding the RF and then the LF using the mallet.

 

My first try with the Motive I had similar results. I did it again, and took care to tap the junctions and calipers with a wrench, and that got the bubbles out. I also used a tiny bit of loctite on the bleeder threads (not the sealing face) to keep air from getting back into the system (likely redundant with the Motive).

As long as the MC was not run dry, I'd start by just trying again.

 

With the Wilwoods you need to bleed the rears in a vertical position as the mounting position leaves room for air to be trapped above the piston.

 

That is most likely what is wrong here.

 

I shouldve mentioned, the rears are still stock. Well, they're stock replacement from VBP (Oring and SS sleeved) and about 5yrs old. I didn't do anything with the rears recently other than bleed them.

The front Wilwoods are the D8-4, the stock style that mount in the factory location.

 

As long as it is safe, driving the car and getting the brakes warm will dislodge any trapped air in the caliper and push it up to the bleeder.
Then just give it another bleeding.

 

Thanks for the advice. I notice they get a little better as I drive, pedal stays low but it brakes better. My plan was to drive to get everything warmed up, and then pull it right in and bleed. If that doesn't work, I'll pull the M/C and bleed it.

 

Pushing the pads back into the caliper will force fluid back into the master.
If there is a bubble there, it could push it out the compensation port.

 

question for you...…….when you installed the calipers did you have them loaded with the pads or did you bolt them up and hook up the brake lines letting fluid into the calipers and then have to fiddle with the pistons to get the pads in ? The pistons should really be depressed without brake fluid in the calipers. I think you will get away with bleeding again as long as an oring did not get compromised. If it does come down to bleeding the master cylinder do what 4-vettes described but I do it just a little different. Put a level on the master cylinder with the cap removed. Jack up the rear of the car until the level is centered. Now do what 4-vettes said...….this will get any trapped air in the master cylinder out...….you don't have to take the mater cylinder off. Good luck bud...….stay at it you'll get it.

 

I installed the calipers with the pistons fully compressed as they came, installed the pads, and then installed the brake lines... Then disconnected and reinstalled the brake lines because I forgot Wilwood uses NPT fittings going into the caliper and I needed to apply some sealant lol.

​​​​​

 

I installed the calipers with the pistons fully compressed as they came, installed the pads, and then installed the brake lines... Then disconnected and reinstalled the brake lines because I forgot Wilwood uses NPT fittings going into the caliper and I needed to apply some sealant lol.

I got very little air out of any of the calipers, pretty good fluid flow right away.
​​​​​
​​​​​

 

It may just be the difference in the front and rear calipers. Mixing brake part is never a good idea, but if it stops good just drive it.