our brakes

PHIL O · 12-11-09, 06:38 AM

the brakes on the hdj81 is strong, but i have been observing the vacuum booster. repeated stomps on the brake pedal at panic stops feels like the booster runs out of vacuum on the second or third step. i was thinking of a vacuum leak but the dummy light doesnt indicate that. i was also wondering if vacuum is drawn back to the pump. do we need a check valve for the vacuum line? i dont see any chack valves on the hoses. any idea mudders?

Chang-kuao-lo · 12-11-09, 10:16 AM

Booster test:

With engine off, pump up the brake pedal untill it loses travel and gets "stiff". Hold it there and start the engine. if the pedal is slowly drawn in after the engine starts, your booster is working properly. Your rear brake self-adjusters might be stuck, and need a manual adjustment.

sandcruiser · 12-11-09, 11:29 AM

there is no check valve on the line from my vac pump to the booster
but I think that there should be

I also want to install a vacuum reservoir of some sort so that something fails on the vac pump, I've still got a little booster left. But it isn't a high priority.

cruiser_guy · 12-11-09, 12:21 PM

Quote:

Originally Posted by sandcruiser

I also want to install a vacuum reservoir of some sort so that something fails on the vac pump, I've still got a little booster left.

Doesn't the '80 series have a vacuum reservoir like the '60 series diesels?

sandcruiser · 12-11-09, 02:43 PM

probably it should have a reservoir, but mine is a swapped-in motor and there are a variety of bits that aren't necessarily as they "should" be.

cruiser_guy · 12-11-09, 03:09 PM

Quote:

Originally Posted by sandcruiser

probably it should have a reservoir, but mine is a swapped-in motor and there are a variety of bits that aren't necessarily as they "should" be.

Gotcha! I didn't forget that little tidbit with the '55 swap.

Was your swap done in Costa Rica? If so, I can imagine there are probably a few other things that didn't make it either.

Enigma · 12-11-09, 03:21 PM

Quote:

Originally Posted by PHIL O

the brakes on the hdj81 is strong, ?

This is the first time I've heard anyone voice that opinion, the general consensus seems to be they are mediocre at best.

PHIL O · 12-12-09, 06:06 AM

Quote:

Originally Posted by Enigma

This is the first time I've heard anyone voice that opinion, the general consensus seems to be they are mediocre at best.

i say strong because i could throw my passenger to the windshield when i stomp on the brakes.

but a series of pedal pumping (less than a second of an interval) almost makes it feel that the vacuum is not sufficiently replenished by the pump. i checked for booster vacuum leak, but turned out negative. my 80 has that vacuum reservoir. they say it is good for 6 pedal pumps before it runs out. could adding a check valve solve this? where should it be placed? in between vacuum pump and vacuum reservoir or between vacuum reservoir and booster?by the way, the brakes work great on single pedal pumps. did a 100% brake job recently
(changed rusted pistons, rebuilt caliper with oem kit, have oem pads, also opened LSPV for maintenance, adjusted LSPV rod height on axle end. also repadded the shoe of ebrakes...7 clicks and it hold rig on incline...no automatic adjusters on this since it is rear discs)
thanks for sharing your ideas fellow mudders

PHIL O · 12-12-09, 06:16 AM

by the way, it makes me wonder why our diesel rigs don't have a check valve on our brakes system. doesnt the pump draw in vacuum sometimes? is there a maintenance that mudders do on this pump? i dont know if the gassers have their vacuum drawn from the intake.

Chang-kuao-lo · 12-12-09, 03:48 PM

Did you put on a vacuum guage and check that the pump is giving specified vacuum? The root of your problem might be the pump itself, the vanes wear out but the rebuild kit is relatively inexpensive.