Not my truck but a friend's '04 DII. Today we replaced the master cylinder for the second time in two weeks. All was normal until the bleed. We can't get any bleeding on the RF/LR circuit. Nothing. No air nor fluid comes out. Any ideas?

A couple of weeks ago we swapped out his leaking master cylinder and bled the system. All went fine with the bleed then, although it was more dramatic than most with A LOT of air on the left front. Did it just like any other bleed I've done over the last 40 years. His daughter had essentially let the system go dry before asking about that pesky red light on the dash that read BRAKE.

Unfortunately the used MC he bought from a well-known parts reseller with a professional looking web site leaked far more than the one we replaced. It literally dumped the entire reservoir within 24 hours.

The seller sent another MC and we installed it today. Used the RAVE bleed sequence. Just a little fluid out of the RF bleed screw. No bubbles. Not much fluid either, but I thought that perhaps air elsewhere was taking the pressure and keeping the action minimal on the right front.

Lots of air and fluid from the LF. Feeling good. RR gave very little air if any and fluid flowed freely.

On to LR. Nothing. Pump. Open. Close. Release. Repeat. Over and over. Nothing. Huh?

Went back to RF. Same as LR. Scratched head and thought about it. Tried again. Same result. Packed up and came home to write this post.

Any ideas? If the RF/LR circuit is dry does it need something more than a conventional bleed to get fluid through the ABS modulator? Should we try a power bleeder? Motive? (Never used one but I'm expect it's not difficult. There's YouTube, of course.) Or TestBook? Any ideas? Thanks.

 

Did you bench bleed it first? If so, did fluid come out then?

 

the master cylinder has two pistons. one front, and one rear. i forget which is which but one feeds the rf, and lr, and one feeds lf and rr.

i bet your brake pedal is soft for the first hald of the stroke and then hard?

try bleeding the master cylinder itself first ( i did mine where the brake line screws into the abs mod).

if you can bleed both the front and rear of the master itself, then try bleeding your whole system again.

if you have trouble with the front or rear of the master, the problem lies within the master itself.

 

If there's that much air in then lines, it might be worth having them power or vacuum bled. Or, try gravity bleeding them. Just open the valves and leave them for a few hours, topping off as needed.

 

Final update (I hope),

Well, all's well that ends well.

We waited until my friend got back from an out of town business trip. I went over to his house and first checked fluid at the modulator and got a strong stream. Reconnected that and went to the RF. Bled normally. LR, same thing. The other circuit hadn't been touched so we left it alone. Road tested it, working up to a lockup, hard stop from 60 MPH. All seems good.

My assessment is that sitting six days, albeit with the system closed, had much the same affect as a gravity bleed.

Thanks for your input. Thankfully the basics of braking systems are pretty straightforward and largely unchanged since they were first used nearly a hundred years ago.

 

99 years to be exact I had to look up who actually invented them (Duesenberg) I was thinking Lockheed but they came in second.