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Brake booster question


mustrmrk

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Hi everyone.  It's been a few years since I've posted here - we sold our '87 Escaper in 2018, tried a few other rigs, and missed it so much we just bought it back yesterday.  On our way home,  I had some brake issues I thought I'd run by the list and see if anyone has any suggestions. 

 

New rear brakes, drums turned, cleaned front brakes, plenty of pad left, everything bled. 

 

Leaving the campground this morning I had to stand on the brake pedal to get stopped. After a short downhill, the brakes worked much better, but the pedal went almost to the floor.  For the rest of the ride home they were pretty much okay except for being spongier than I'd like.  BTW - there is no sponginess with the engine off - the pedal stops firmly near the top of it's travel, giving me no indication of poor adjustment or air in the lines.  I thought it might be the booster or the check valve, so about 4 hours after we got home and shut it down,  I pulled the booster side of hose off the check valve and heard a bunch of vacuum suck in.  So it hadn't leaked down in 4 hours, suggesting (to me, anyway) a decent check valve and booster diaphragm.  I have to take it in for a Virginia safety inspection and am afraid it'll fail the way it is.  Not to mention that I'd prefer not to die or kill anyone else on these mountain roads <g>.  I guess the next step might be to attach a vacuum gauge and get some real numbers to report.  At any rate, any suggestions as to where to look next appreciated.

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13 minutes ago, mustrmrk said:

Hi everyone.  It's been a few years since I've posted here - we sold our '87 Escaper in 2018, tried a few other rigs, and missed it so much we just bought it back yesterday.  On our way home,  I had some brake issues I thought I'd run by the list and see if anyone has any suggestions. 

 

New rear brakes, drums turned, cleaned front brakes, plenty of pad left, everything bled. 

 

Leaving the campground this morning I had to stand on the brake pedal to get stopped. After a short downhill, the brakes worked much better, but the pedal went almost to the floor.  For the rest of the ride home they were pretty much okay except for being spongier than I'd like.  BTW - there is no sponginess with the engine off - the pedal stops firmly near the top of it's travel, giving me no indication of poor adjustment or air in the lines.  I thought it might be the booster or the check valve, so about 4 hours after we got home and shut it down,  I pulled the booster side of hose off the check valve and heard a bunch of vacuum suck in.  So it hadn't leaked down in 4 hours, suggesting (to me, anyway) a decent check valve and booster diaphragm.  I have to take it in for a Virginia safety inspection and am afraid it'll fail the way it is.  Not to mention that I'd prefer not to die or kill anyone else on these mountain roads <g>.  I guess the next step might be to attach a vacuum gauge and get some real numbers to report.  At any rate, any suggestions as to where to look next appreciated.

Sounds like you have some air trapped in the lines or contaminated brake fluid. Do a complete line flush using new brake fluid. Gravity will do the work. Open your bleeders same sequence as for normal bleeding, but allow the fluid to run out until only new brake fluid is seen. Keep an eye on your master cylinder. Keep it topped off. Don’t let it run dry. When all bleeders show clear fluid you should be good.

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Fred,

 

Thanks for your input. I considered bleeding them again, but the PO assured me that he'd done a full fluid replacement and bleed. The brakes are totally firm, no pumping needed to be near the top. He's a plane

mechanic for the Marines and seems to know his stuff. Mechanically, the Escaper is in great shape, cosmetically, well....

 

At any rate, you could very well be right. I'll give the passenger rear a quick bleed and see how the fluid looks.

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  • 4 weeks later...

For what it's worth I pulled the booster a few days ago. It was full of brake fluid. Now I'm just waiting for new dual diaphragm one I ordered to arrive so I can see if it will fit.  

 

I also have a new 1" bore master cylinder to replace the leaking one. Hopefully these take care of my issue.

Edited by mustrmrk
Added MC paragraph.
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It probably did no damage to the booster that's kind of expected any cylinder leak will be increased because of the vacuum in the booster so the guts are pretty hardened to brake fluid. That used to be common decades ago.

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Maineh,

 

That's really interesting. I thought brake fluid in the booster was a death knell for the diaphragm. It's an old, rusty Bendix, not sure how old.  Symptoms are press brakes slowly, get assist, pedal may or may not reach floor. Press fast, no boost, rock hard pedal, brakes that work if I stand on em, pedal stays high.  Seems to me that intermittent boost with good vacuum (18 inHG at idle) points to booster. Maybe I'm totally wrong?

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Brake booster, bad quite possibly. Master cylinder bad, most definitely.

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If you are going to replace the booster get a check valve too or try that first. Any thing above an idle the vacuum drops fast. The ideal with the check valve is to have at least one good boosted stop no matter what.

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Check valve tested and seems fine. Flow in one direction and not the other. It even held vacuum for  several hours after I turned off the engine. Which begs the question maybe the diaphragm is still intact?

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Check valve tested and seems fine. Flow in one direction and not the other. It even held vacuum for  several hours after I turned off the engine. Which begs the question maybe the diaphragm is still intact?

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Linda,

Here are the parts. The jury is still out on how they fit - delivery scheduled for tomorrow, so I should know This or Fri. I'll let you know how it goes.

 

Booster Cardone reman 53-2776 

MC Dorman new M39996

 

I got both numbers from https://www.roundforge.com/articles/toyota-4x4-brake-master-cylinder-and-brake-booster-specs/

 

It looks like I have room for the larger booster. Fingers crossed.

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10 minutes ago, mustrmrk said:

Check valve tested and seems fine. Flow in one direction and not the other. It even held vacuum for  several hours after I turned off the engine. Which begs the question maybe the diaphragm is still intact?

Short answer yes. The parts are resistant to brake fluid because it is a safety factor rubber parts swell if they are not fluid resistant and it's possible you would not be able to depress the peddle. Years ago it was kind of normal to find brake fluid in boosters a lot of it was burned up in the engine but yeah.

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The new booster arrived today so I started test fitting it. The old one had a 3/8 spacer built in and is smaller in diameter. The new one wouldn't quite seat without touching the steering shaft. So I fabricated a spacer out of 5/16 flat aluminum stock and made the appropriate adjustment to the pedal clevis.  That seems to have done the trick - I'll know for sure once I get it bolted in, hopefully tomorrow.

 

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Linda,

 

I bought a Cardone 53-2776. According to Summit Racing (https://www.summitracing.com/parts/aaz-53-2776) and some other places I checked, it is a dual diaphragm booster.  It's supposed to fit 89-95 4wd truck and 4runner.  So far, with the addition of a 5/16 spacer, it fits my 87 Escaper. I'll update as I progress...

 

I think Yotamasters sells one like it, too, but they're pretty spendy - like twice as much. Forgot to mention that Yoramasters lists two boosters that cover 79-95 if you're looking for one that will fit the older models. In the notes, however, they say the steering shaft might interfere with installation on some trucks - sounds familiar...

Edited by mustrmrk
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  • 3 weeks later...

To finish this up, the Cardone 53-2776 booster fit well. I only had to fab a 3/8 spacer to hold it off the steering shaft a bit and adjust the pedal  rod clevis accordingly. 

 

The Dorman M3996 master cylinder bolted right in.  I had to slightly bend both brake lines because of the new position caused by the new booster.  And the float switch connector didn't match my harness so I swapped ends with the old one.

 

All in all it was a pretty easy job and I'm happy with the results. 

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