Brake Booster Hose

[jetmech]

Trying to find the correct vac. hose for power brake booster for my '86 350 SWB. The local auto parts are trying to sell me fuel hose saying that is what everybody uses. I don't know if I agree that it is safe to use fuel hose. It is made to hold up under low pressure but what about vacuum? Do you guys use anything other than fuel hose and if so what?

[bd]

Your skepticism is valid!  Brake booster vacuum hose is stiff-wall 11/32" flexible hose specific to vacuum booster systems and is constructed to meet DOT regulations; see Gates 27232.  Fuel hose will collapse!  It was irresponsible of your local parts house to tell you to use fuel hose, because that's "what everybody uses."  People substitute the wrong materials for lack of knowledge - in this case it is a dangerous substitution!

[Irish_Alley]

bd, when i need to replace a vacuum line i use fuel injection hose. much more ridged than fuel line, never used it on the brake booster but other parts and haven't noticed a problem that i can think of. would injection line work?

[bd]

It's pretty simple, really.  Booster vacuum hose is specifically constructed to satisfy DOT requirements.  Unless the hose you use meets/exceeds the specification and fulfills the requirements, you risk brake failure.  Look at it this way, pressure hose is designed to contain "interior" pressure to prevent ballooning and rupture.  Vacuum hose is designed to resist "exterior" pressure to prevent collapse.  They have different purposes.

[Irish_Alley]

i do understand they are made for different purposes, i would like to put a injection line on vacuum and see what it does both new and used.

[jetmech]

Thanks bd for your help. Had O'reilly's order the correct hose. The manager still insisted fuel hose is all he ever used as a previous mechanic. Gates lists vac. (and pressure) specs for their hoses and the 27332 does out perform fuel hose (duh). This must be common mis-knowledge as no surrounding O'reilly stores had the vac hose in stock. It came in a 3 foot section for less than 4 bucks. Thanks again.

[Irish_Alley]

it may out perform it. but whats the max vacuum your engine will reach? dont get me wrong it was cheap and wasnt a rip off, but its not needed imo.

[bd]

Thanks bd for your help. Had O'reilly's order the correct hose. The manager still insisted fuel hose is all he ever used as a previous mechanic. Gates lists vac. (and pressure) specs for their hoses and the 27332 does out perform fuel hose (duh). This must be common mis-knowledge as no surrounding O'reilly stores had the vac hose in stock. It came in a 3 foot section for less than 4 bucks. Thanks again.

You're welcome!

[jetmech]

You bring up a good point, what is the maximum vacuum your engine will reach? Also, for how long? Could a fuel hose collapse and you not even know it? It could be my years of being an aircraft mechanic kicking in telling me to be a mechanic and not an engineer. Being a hot rodder is being both and even more at times. There is a wealth of knowledge and experience here and I'm always ready to listen and learn.

[bd]

A normally aspirated engine will generate a maximum of ~28" Hg vacuum.  It can also generate upwards of 80 PSI of transient pressure during an intake backfire.

I’ve modified, hotrodded and professionally repaired vehicles as my livelihood since 1970... that's more than four decades to date... performed my share of substitutions and upgrades, and redesigned various systems with excellent, consistent success.  I always focused my attention on specific circumstances with respect to proper function and the intended result, giving extra attention to safety concerns.  My opinions are tempered by professional experience and augmented with vocational, OEM and aftermarket training.  I consider all substitutions and alterations thoroughly before I implement them.  I don’t cobble something together with whatever is available just so it will roll down the road.

I share this because I am amazed at how insistent people are to hold onto false data as fixed opinions (the parts guys you referenced are a case in point).  IMO, to use something incorrectly based on, “that’s what everybody uses,” is ridiculous reasoning!  Under the right circumstances it's also deadly! 

The negative focus of my original post concerned the soft 3/8" fuel/vacuum hose used on carbureted engines, since that's what I thought you were referring to.  But, I later added, if the hose one uses meets or exceeds all of the requirements of the application, it will function.  Well, DOT approved booster hose fulfills the requirements for effectively evacuating a power brake vacuum booster.  Other hoses may meet or even surpass those requirements.  The soft 3/8 fuel/vacuum hose does not.

Here’s the history behind that statement:  During my professional career I replaced ~85% of the 3/8" fuel/vacuum hose that I encountered, that had been substituted for 11/32" booster hose, to correct actual, observable hose collapse and loss of power brake assist.  Some of the 3/8" vacuum hoses were collapsed to the point of perforation, creating significant engine vacuum leaks.  That same 3/8" fuel/vacuum hose is routinely and correctly used to plumb PCV valves.  Significantly, I've replaced many collapsed PCV hoses for similar reason.

In comparison, I've replaced fewer than 1% of the 11/32" DOT booster hose - but, never for wall collapse - instead, OE booster hose needed replacement because of age hardening or carbon coking.  The 3/8" hose rarely survived sufficiently long to become brittle or restrict with carbon.  That in itself should tell you something.

[Irish_Alley]

rich you defiantly have more experience and knowledge of this stuff. and i see what your saying, just because it has worked for me doesnt mean its right. its kind of like the truck you see on the road with a rusted out frame to the point the bed touches the cab, it may work for them but it just might be flirting with disaster.

 but the standard fuel line that has no  reinforcement i wouldnt use even on a pcv valve. but something i learned about the reinforced hose is that its not made to be submerged in fuel and depending on the age of the hose its not formulated to hold up to the e10.
on a side not the brake booster hose is rated for 30 and the fuel line is rated for 24 (whats the proper name for the reinforced line?)