09 3v power loss "cured" with 5w40

[max78]

This adventure has really been something. Is there any chance the rubber seal in the master cylinder is loose or dislodged? Something is not releasing as you noted.

Ya it's been rough, and I keep stopping diagnosing and buying parts thinking that surly that's the issue, but then I realize it's not.

There is only 1 seal on the master that I can see and it's intact and sitting properly. If I manually pump the master by hand it works and releases every time as intended. Only when I mount it to the booster does it lock up. I bet if I put washers on the master to space it off it would have the proper push rod gap and work. I might try that for fun, but no way I would ever let anyone drive it that way.

I watched some videos on how a brake booster works and from what I gather an internal seal failure could absolutely lead to inconsistent and sticking brakes like I have been experiencing.

From what I gather, through YouTube certification. The engine pulls a constant vacuum on the whole booster, both sides of the diaphragm. Once you press the pedal you close a valve on one side that then bleeds off to atmosphere allowing the other to remain under vacuum giving you that boosted assist. If the rubber part that seals the vacuum chamber is damaged it could seal, or partially seal causing vacuum to apply the brakes, but not enough to be super obvious. A good but dangerous way to test this is to remove the vacuum line and see if your dragging brakes stop. Mine is broken to the point where it's just not working at all. . .

I found a low ish milleage one on an ebay salvage yard because there are no replacements or alternatives. no close by salvage yards have anything worth entertaining. The dealers and a boat load of parts stores all came back negative. Advanced Auto did have a place they send these to for rebuild, estimate was $500 all said and done.

Once I get a new one in hand and verify it works I will tear down the old one to try and dertmine what the issue was. I will be sure to follow up with all the pictures and findings.

I'm going to kick myself in the butt for a long time if this turns out to be the issue causing my low power this whole time. . . .

 

[whtbronco]

There should be 2 seals inside the master cylinder. One for the front brakes and one for the rear. Since it seems to work without boost pressure it's likely not the issue as you determined.

I had considered the booster as well, then talked myself out of it. I'm good at talking myself out of an accurate diagnosis. It does make sense though with both brake issues and engine performance issues.

Another option might be to take your booster to a parts store and start comparing. On my 78 Bronco I had a 78 F-350 Dual Diaphragm Booster and a 94 Mustang SVO master cylinder and talk about a massive increase in brake power. Anyway, you might find that one from an F-150 would fit, I dunno.

I hope this is the fix for you. Don't get down on yourself, this stuff can be tough to diagnose and each of us has failed at troubleshooting at some point. I've been chasing vibrations for 8 months and I think I might have finally resolved the last of it today.

 

[max78]

Thanks for the help and kind words.

I scoured the internet to see if I could use a different but close enough booster that would bolt up. What I found is for 2009 and 2009 only the brake booster is a unicorn and specific to that year.

2008 the booster is physically different and probably wouldn't not bolt up.

2010 is physically the same I would bet it would bolt up and work perfectly, however. . .

The 2009 has all the electrical switches and components internally to the booster. There is an electrical plug on the booster itself. This is for the brake lights and shifter interlock and everything. . . That's cool and all, bit it was for only 2009 . . .

2010 this plug is missing, it would more than likely work mechanically, but I would have no brakes or electronics.

 

[whtbronco]

Jeesh what a mess. No brakes would be an issue, haha.

Oh I see, the electronics in the booster might be part of the roll stability control, hmm.

I am no fan of all the electronics in modern vehicles.

 

[max78]

So. . . .

I purchased a second hand low millage (125k) brake booster off of ebay. installed it and used my newly purchased power brake bleeder to bleed the brakes. I connected via full version of Forscan and cleared all adaptive tables for everything. After putting everything back together and bleeding the brakes its finally working! No more locked up brakes. They pump up good and feel the way they did when we first got the truck. Braking is great again and no no more sticking that I can tell of.

Power across the board seems to be back up for the time being.

I took the driver side fender liner out and noticed that the rubber piece the airbox snorkel pokes through and it was tore up and flapping around. I wonder if maybe some of that was occasionally blocking the intake. Not sure.

I haven't driven it much but it was due for an oil change and I went back to 5w-30.

Hopefully it will stay good but once again, only time will tell. . .

 

[max78]

Updated:

It been a while with some really good mileage on the truck since I replaced both front calipers and the brake booster. So far the truck is driving really good. The truck rolls easier and will coast now, before it would slow down rapidly when letting off the throttle.

I still have the occasional issue with low power but that generally only happens when its 105° plus outside. Once it cools off it drives a lot better. Putting some 91 in the tan and it seems to have helped with that.