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F750 chassis mount brake booster test


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mbavers
User

May 1, 2016, 8:28 PM

Post #1 of 28 (753 views)
  post locked   F750 chassis mount brake booster test  

1972 Ford F750. I have no power assist. All vacuum lines to the booster seem OK. Before I took everything apart the vacuum gauge read very low, maybe 5 or so. When I suck (by mouth) directly on the vacuum side of the booster I get air through it, with a little resistance. When I blow I can easily blow air through it. Is this normal, or is there a leaky diaphragm? I just bought this booster (rebuilt) FROM napa about 9 or 10 months ago and it worked fine last summer. It's been sitting all winter, but that shouldn't matter. I can't find any diagrams on this thing, and before I remove it and take it back to NAPA I want to be sure that it is bad.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 1, 2016, 11:09 PM

Post #2 of 28 (746 views)
  post locked   Re: F750 chassis mount brake booster test  

Yikes - do clue how big an F-750 is but same deal with vacuum boosters for ages. What's your vacuum available to this just for info meaning engine running, line plugged off?


If you can just draw air thru it it's probably bad if ever worked. Rule out check valve and grommet and maybe it's trying to work if pushrod is pushing on it from brake pedal but would think unless stuck that would have been a problem right away unless stuck somehow?


Probably just another bad booster,


T



Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 2, 2016, 4:32 AM

Post #3 of 28 (739 views)
  post locked   Re: F750 chassis mount brake booster test  

If it leaking that bad, you should hear a huge vacuum leak with the engine running. Most of the time if they are leaking, you hear a hissing noise up around the brake pedal where the shaft comes out.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


mbavers
User

May 2, 2016, 9:17 AM

Post #4 of 28 (728 views)
  post locked   Re: F750 chassis mount brake booster test  

No pushrod to booster; it is chassis mounted. Thanks.


mbavers
User

May 2, 2016, 9:18 AM

Post #5 of 28 (727 views)
  post locked   Re: F750 chassis mount brake booster test  

Thank you.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 2, 2016, 9:31 AM

Post #6 of 28 (717 views)
  post locked   Re: F750 chassis mount brake booster test  

Can't know a set up for this HD a truck. Still something pushes it somehow is all just ruling out slight chance it thinks you are riding the brake and are NOT.


It's likely the booster. As DS said also if your reading of 5 Hg if that's what you meant it would have side effects unless a pump creates vacuum or just a VERY tolerant engine not mentioned would about hear it.
It should be a warranty deal and would get it redone or exchange for another. I just haven't had to have one rebuilt and wait but rather new and not many ever needed for anything,


T



mbavers
User

May 2, 2016, 9:36 AM

Post #7 of 28 (713 views)
  post locked   Re: F750 chassis mount brake booster test  

Yes, the more I think about it the more convinced I am that I should NOT be able to suck air out of it with my mouth.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 2, 2016, 9:55 AM

Post #8 of 28 (708 views)
  post locked   Re: F750 chassis mount brake booster test  

Agree. Jeez - I should be able to recite how they work but so few failure just basics. They have vacuum at the ready, engine running or not up to days. You push brakes it consumes that and don't think it recharges the vacuum help till you let go such that if you could pump one fast enough you might lose boost or when an engine stalls you should get ONE more good boost.


The check valve doesn't allow vacuum from booster back out to source - most intake manifold vacuum but can allow more vacuum power as when you may use engine as a brake and when intake vacuum is higher vacuum is higher in booster
1972 seems early for belt driven vacuum pumps but if so same deal just constant with belt and pump as the source.
I'm not surprised at all such a heavy duty machine as this would have things available for almost forever. It's a work thing, must be at that load rating.


Good luck for a speedy fix or replacement unit. IDK - I favor keeping old cores till a new one proves itself then turn it in if they do it that way for this or can. Only because burn a couple times leaving some clip or part on one that was supposed to be put on the next which so far was still found at the parts outlet not sent back yet - assorted items that get rebuilt,


T



mbavers
User

May 2, 2016, 10:03 AM

Post #9 of 28 (703 views)
  post locked   Re: F750 chassis mount brake booster test  

Now that you mention it, it never held vacuum with the engine not running, so it was probably never leak free. I hope NAPA will exchange it; didn't get any warranty with it.
Good idea about keeping core for awhile!


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 2, 2016, 10:21 AM

Post #10 of 28 (700 views)
  post locked   Re: F750 chassis mount brake booster test  

Warranty and NAPA by name. I've had such wild help from my local NAPA dealer it's nuts. Even if explicit no warranty they made things work out because it was the right thing to do.
I'm mostly done but the place was like that and not just for me, an account holder but anyone. Prices could be higher but the cost of cheap has no limits most of the time.
Trust me, they know parts fail and benefit long term in knowing which ones sometimes so can correct that or always used to.
They should have some record that one was sold even if not in your name if you can't even produce a receipt. Maybe they aren't all the same but mine does and I deal with slow selling not stocked items all the time. Good luck but you were dealing with the best chance for proper biz antics I know of for parts,


Tom



mbavers
User

May 2, 2016, 10:29 AM

Post #11 of 28 (695 views)
  post locked   Re: F750 chassis mount brake booster test  

I've got the receipt. I'll let you know what happens. It might be a week or two.


mbavers
User

May 6, 2016, 9:48 AM

Post #12 of 28 (646 views)
  post locked   Re: F750 chassis mount brake booster test  

I'm not sure if this is the correct way to update my own post.
I hooked up a vacuum line directly from the engine intake manifold to the brake booster and the brakes work this way, so I am replacing all the hoses and tubing in the system.
Thank you all for your interest and comments.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 6, 2016, 12:51 PM

Post #13 of 28 (643 views)
  post locked   Re: F750 chassis mount brake booster test  

What are you saying? You hooked up a different vacuum hose and it now works or what?
Boosters are usually hooked up only to their own vacuum source very commonly for general 1972 and more right under the carb for any gasoline engine the most secure source for fast and ready vacuum.
Please explain what you did, if that changed the show with a hose or new source used or what the heck it's doing now,


T
(edit in) Upon re-read it seems brakes now have boost - right? If you didn't have to plug off the original hose or plug off the port it was going to there should be a wild vacuum leak and engine shouldn't really be able to run at all even the largest gasoline one could only be the 460 Cubic Inch engine. If a diesel I personally don't know what would be used so let's clear that up I didn't see what engine or type.
The massive size of that engine might run but has run poorly with the size hose to a vacuum booster wide open. Super tolerant engine but not that much - owned in cars (same cubes) 1969 and a 1977 personally so have a clue. Can run almost without notice with a plug wire hanging off, wild vacuum leaks too. You first said they all were or looked fine.
Before replying if you catch this, is this all VERY sludged up at the port where vacuum hose should go? That's the problem if so about only cause by serious neglect of plain oil changing. Need to know more.........



(This post was edited by Tom Greenleaf on May 6, 2016, 1:02 PM)


mbavers
User

May 6, 2016, 1:18 PM

Post #14 of 28 (636 views)
  post locked   Re: F750 chassis mount brake booster test  

OK, here's the complete story.
Brake booster is remote mounted on truck chassis. Originally I had no power brake (after truck sat all winter). I suspected a leak somewhere in the hose/tubing system between the intake manifold and the booster. I circumvented the hoses and steel tube by running a new hose directly from the intake manifold to the booster and I now have brakes. Therefore, I guess there must have been a leak somewhere in the hose/tube system and the many connections incorporated therein. I am now going to replace the original hoses and tube with new vacuum hose (the old hoses were heater hose, not really approved for vacuum systems).


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 6, 2016, 2:05 PM

Post #15 of 28 (635 views)
  post locked   Re: F750 chassis mount brake booster test  

I can still operate on the concept of how vacuum boosted brakes work however they are placed. Vacuum source is (you say so) intake manifold and finding another spot to tap into makes the brakes work - right?
If that's right then what did you do with the original hose combo of rubber and metal is fine but can't be wide open. If left wide open and this ran OK even it must be clogged up at engine end now still or at least hissing away like nuts when running.
Anything low on base of carb is a great spot for dependable vacuum. Hose should be large diameter like perhaps 3/8th I.D. or 10mm about same if new now marked for PCV and Fuel rated on the hose or regular hose would collapse.


Its being old isn't bothering me if you can tell. These hoses from new should or have to have been replace several times already in fact new on a roll about now still in a store wouldn't be much good from 1972.


Jeez, I'm doing all this guessing at two threads right now and will guess again like a fool: The port is clogged, bent or something all wrong probably clogged. It should be so direct you could clear that out with mechanics wire or that product is much like a more bendable coat hanger wire can twist and go around curves for assorted purposes or use. I don't see it sold anymore or named that. Then however cleared out follow up with carb cleaner or take all this stuff off the truck and clean it up off the thing if really clogged all the cleaning will throw junk down it and make other problems if this bad.


What to do right now: Pull hose off if not already from where it belongs on engine/carb base and see if it will leak like crazy then look for the sludge if so. If not must or could be a hose totally collapsed (the old one(s) and stayed collapsed somehow and could even if proper hose and old enough.


In short it didn't seem to be getting any vacuum before this new trick with another hose so you need to find out why the old failed and fix it the way it was intended which really shouldn't be that hard but if sludge highly likely you will have to take care of and if so let's start another thread on cleaning up a sludged up engine if this does still run well at all you have a good chance for more time with it,


T



Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 7, 2016, 9:04 AM

Post #16 of 28 (619 views)
  post locked   Re: F750 chassis mount brake booster test  

The engine must have been running like crap if you had a booster vacuum supply hose leak unless a hose is restricted for some reason. Is the check valve on the booster or in the hose? Gotta make sure you have a check valve and it is installed correctly or you won't have back up vacuum in the booster if the engine were to stall out while you were stopping. I'm sure stopping a 10,000 lbs truck is fun with no power brake assist.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 7, 2016, 9:43 AM)


mbavers
User

May 7, 2016, 9:44 AM

Post #17 of 28 (610 views)
  post locked   Re: F750 chassis mount brake booster test  

I installed a new check valve, and it's on the hose. The truck is well over 26,000 lbs fully loaded (dump truck).


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 7, 2016, 9:46 AM

Post #18 of 28 (608 views)
  post locked   Re: F750 chassis mount brake booster test  

Is this on the new hose or the old one you installed the valve? I believe if it is installed backwards vacuum won't get to the booster. Maybe the old check valve failed and caused the hose to be restricted??





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 7, 2016, 9:50 AM)


mbavers
User

May 7, 2016, 9:52 AM

Post #19 of 28 (601 views)
  post locked   Re: F750 chassis mount brake booster test  

It is installed correctly. I test everything I do. And, as I said in a previous post, the brakes now function properly. The only question is, was the original problem in the vacuum line or a temporary malfunction in the booster.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 7, 2016, 9:53 AM

Post #20 of 28 (600 views)
  post locked   Re: F750 chassis mount brake booster test  

Time will tell eh? Its not often you see a hose fail, but could have been an iffy check valve in the hose causing the issue. That is if you had no vacuum at the booster.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 7, 2016, 9:55 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 7, 2016, 10:02 AM

Post #21 of 28 (597 views)
  post locked   Re: F750 chassis mount brake booster test  

Still a lot of questions in my last VERBOSE post unanswered. Is there vacuum at the dang port you are NOT using at all? Said it wouldn't run for crap or hiss like nuts.


For the sake of a check valve if in any question with the HD of a thing just toss it for new but better have a new grommet known available or on hand as it can tear up a good one just removing it. NAPA will find one - I know it for sure still only about $2-3 bucks,


T


mbavers
User

May 7, 2016, 10:13 AM

Post #22 of 28 (591 views)
  post locked   Re: F750 chassis mount brake booster test  

There is no port that I am not using. There is one port on the intake manifold. It is clean and unobstructed; no sludge. The engine is clean, as it was just rebuilt about 1,000 miles ago. I checked for suction with my finger with the engine running and it felt good. As soon as I get my permanent hoses hooked up I will have a pressure gauge in the line and will then have verification of vacuum.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 7, 2016, 10:16 AM

Post #23 of 28 (589 views)
  post locked   Re: F750 chassis mount brake booster test  

Be sure to attach your vacuum gauge between the valve and booster. It should hold vacuum after you shut the engine off unless you foot is on the brake of course.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 7, 2016, 10:18 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 7, 2016, 10:22 AM

Post #24 of 28 (582 views)
  post locked   Re: F750 chassis mount brake booster test  

OK. Now knowing it has full manifold vacuum with a gauge to know if that's just the wrong spot or what. Should read at least 18Hg at idle using nothing else for vacuum unless at very high altitude. Just know if the wrong port was chosen by mistake it could be air speed or AKA Venturi vacuum which isn't for brakes at all and near impossible as sizes should be all different,


T


mbavers
User

May 7, 2016, 10:28 AM

Post #25 of 28 (581 views)
  post locked   Re: F750 chassis mount brake booster test  

Yes, the gauge goes between check valve and booster. As I think back, it never held vacuum with the engine off, but I didn't know that it was supposed to. I now know. This indicates to me that I have had some suction leak all along. I will advise of results after I get all new hoses installed.






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