RABS dump valve bypass. oem part.

KZF250

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@towcat

I'm trying to track down a union so I can bypass the RABS on the shuttle bus and was wondering if you could confirm the fitting sizes?

7/16"-24 SAE inverted flare (brake line coming from the MC to the RABS)
3/8"-24 SAE inverted flare (brake line going to the rear)

Thanks
 

franklin2

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@towcat

I'm trying to track down a union so I can bypass the RABS on the shuttle bus and was wondering if you could confirm the fitting sizes?

7/16"-24 SAE inverted flare (brake line coming from the MC to the RABS)
3/8"-24 SAE inverted flare (brake line going to the rear)

Thanks

Both of mine were the standard 3/16" line with the 3/8"-24 thread. I just put a standard coupler from the store in there. But my lines have been replaced also from rusting through.

I didn't read this whole thread, but realize this puts your brake system one step above a 60's style brake system. You still have two brake circuits, one front and one rear, but that's it. They didn't use a proportioning valve when they used the RABS, so it will be straight shot to the rear, straight shot to the front from the master cylinder. Works ok, but you will get rear lock-up if you mash the brake pedal to the floor in a panic stop.
 

KZF250

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Both of mine were the standard 3/16" line with the 3/8"-24 thread. I just put a standard coupler from the store in there. But my lines have been replaced also from rusting through.

I didn't read this whole thread, but realize this puts your brake system one step above a 60's style brake system. You still have two brake circuits, one front and one rear, but that's it. They didn't use a proportioning valve when they used the RABS, so it will be straight shot to the rear, straight shot to the front from the master cylinder. Works ok, but you will get rear lock-up if you mash the brake pedal to the floor in a panic stop.

Thanks for the info. Front line going to the MC is definitely bigger...just wasn't sure if it was 7/16 or 1/2. Tracing the brake lines yesterday I did realize there was no proportioning valve and was wondering the consequences with a bypass. Never have had ABS and mostly drive RWD vans/trucks so I am used to pumping the brakes when it's slick.
 

IDIoit

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ive deleted all this jazz in the 87.
im running a adjustable prop valve, adjusted for 4 wheel lock up. I havnt had one issue with my brakes, it stops great!
hydro with rear disc
 

riotwarrior

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ive deleted all this jazz in the 87.
im running a adjustable prop valve, adjusted for 4 wheel lock up. I havnt had one issue with my brakes, it stops great!
hydro with rear disc

Caddilac calipers correct? I have contemplated doijg this as I have a set of those calipers..
 

Blind Driver2

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Btt...it seems to me that if the RABS sticks open, then adding a bypass line would give full fluid flow and the rears would still lock up....unless a proportioning valve was used.

My rears are locking up. I'm not sure if I want to bypass the valve or replace it.
 

79jasper

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That would be correct. Is post #39 Brian linked the proportioning valve he's using.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 

Jason McDowell

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It does exist. commonly found on F450 superduties 88-97.
will post the p/n later.
just look at the pics in the meantime.
It does exist. commonly found on F450 superduties 88-97.
will post the p/n later.
just look at the pics in the meantime.

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