LUVTruck.com

So this is a 1979 Chevy LUV 2wd. I recently replaced the stock carb with a weber.

One day, the brakes seemed sloppy and the pedal went further than it normally would. I didn't pay much mind, just thought I'd add some fluid later.

Next day, no pedal + no brakes, and there lay a puddle of brake fluid underneath the left rear tire. I take off the drum and looks like the wheel cylinder blew. So I order a pair of wheel cylinders, brake shoes, and a hardware kit. Now with everything replaced, I try to bleed... and nothing comes out. A little spurt here and there, but nothing of note. I tried a lot of the suggestions from searching this site, such as bleeding the master cylinder, bleeding the brake lines, and bleeding with the engine running. Didn't fix the bleed issue, but now I notice that when the brake pedal is pressed, a puff of air comes up from the carb. When the engine is running and the brakes are pumped, the engine shutters and spurts.

So my question is... Do I have some vacuum lines crossed which is not allowing the booster to build up pressure? The weber replacement went less than swimmingly but I drove the truck for about a month before the brakes went out.

Any insight is appreciated.

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1979 Chevy Luv Mikado Stepside
1979 Chevy Luv
1980 Chevy Luv Mikado 4x4

Sounds like your brake booster may have a leak.

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Certified pilots, looking down on people since 1903.

There should only be one vacuum line to the brake booster. On a '78 it is rubber coming off the intake at the rear, switches to pre-formed hard line until just before the booster where it turns back to rubber where it connects to the check valve in the end of the booster. Air (or vacuum) will travel towards the intake but not the other way if the check valve is functioning.
(BTW without a proper check valve you will have brakes with the engine running but almost none without & the pedal will be very hard. The check valve retains the vacuum in the booster for a period to continue to assist the brakes after the engine is shut off & stops providing vacuum.)
I suspect when the wheel cylinder went & you used the brakes with low fluid you damaged the master cylinder or maybe pushed some of the trash in the bottom of the reservoir into someplace it didn't need to be. I would replace the master cylinder, make sure to bench bleed the new unit before installing. You can take an short piece of brake line (it's M10x1.00 or ask for "3/16 metric" at NAPA), cut it in two, attach the coupler ends to the outlet ports and bend the cut ends so that they are submerged in the reservoir fluid, activate the plunger until no bubbles. There is an adjustable rod sticking out of the end of the brake booster than may need not be the right length, it's easy to make a gauge to check for the proper length.
There is a pushrod seal that can be damaged by bleeding the brakes without the engine running. I did it with the engine off for years with no with no apparant damage because I didn't know better. Now that I know better I bleed with the engine running.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

Thanks for the help. OK, so I'm looking at a brake booster and a master cylinder? I'm moving and already packed my manuals, is there an online FSM that I can get somewhere?

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1979 Chevy Luv Mikado Stepside
1979 Chevy Luv
1980 Chevy Luv Mikado 4x4

Replace the master cylinder first, if the booster goes you still have brakes, just not power brakes.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

Master cylinder was it. Swapped it out, brakes bled, now it's good to go. Thanks for the help!

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1979 Chevy Luv Mikado Stepside
1979 Chevy Luv
1980 Chevy Luv Mikado 4x4

I am so glad you reported back with the results of your request for help.
Many times a question is asked, possible solutions are suggested, then nothing else is heard. With feedback as to whether the suggestions worked or not the next person with a similar question is way ahead, & might even find the answer with a simple search.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.