77' FJ40 - Two successive new OEM brake MC failures, or...? (1 Viewer)

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I've read through all the brake bleeding/adjustment threads multiple times and am still scratching my head here.

About three weeks ago I lost pedal pressure and the brake warning light began lighting up with every depression of the pedal. Bled the system, checked all the lines and connections as well as the aftermarket MC that looked to have been on the 40 for many years. No obvious leaks to be found but the rear wheels weren't getting any pressure. After removing the MC, the seal at the back where it meets the booster appeared to be worn out.

The front rotors and pads are new as of a few months ago however the rear drums hadn't been touched, so I ordered an Advics/Aisin MC and 4 Japanese wheel cylinders for the rear axle. My mechanic and I installed everything and followed the proper bleeding and rear adjustment procedure repeatedly. Despite this, the new MC would not hold pressure and we concluded it was an internal defect.

So, I ordered a second Advics/Aisin MC and we tried again. This time the procedure worked as hoped - pedal firmed up nicely, system was holding pressure and the 40 was stopping beautifully. About 75 miles of happy stopping power later, I started the truck after sitting for a few hours, drove a few feet, slowed down, pedal went to the floor and back came the warning light. Again we bled and adjusted - rears bled properly, but the front would not. No leaks at any of the connections, but with a finger over the front brake line connection at the MC no pressure could be felt.

SO.... is it possible I'm having terrible MC karma and have received two successive bad OEM parts? Its worth noting these have come from city racer and cruiser outfitters - not some fly by night supplier. Or, am I/we screwing up or missing some other obvious issue?

Any insight would be greatly appreciated - apologies for the rambling post!

Luke
 
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I should add - pumping the pedal does not result in its firming up and I don't think this is a shoe-seating issue. There is very minimal stopping power at all times.
 

JohnnyC

Long ago TLCA# 2231
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I do not read anywhere that you bench bleed the mc

If it were me I’d disassemble and see what’s what in the mc ... then bench bleed
 
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Well there’s the problem with MC #1...How does that even happen?
416B6AD4-CC59-4392-A398-D1C490BF8770.jpeg
 
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That is very possible and concerning. Guess I’ll find out after I remove and open the one that’s on the 40 now..I’ll report back.

For reference, what is the function of that bolt?
 

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