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Grif
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Mar 29, 2009, 2:44 PM
Post #1 of 14
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Hey folks,
First of all, thanks to everybody who answers questions on here. You are all very helpful and it is appreciated.
I'm back to work on my 1975 Ford F-100 pickup. I toasted the inner wheel bearing on my front driver's side wheel and replaced all bearings over the weekend on both wheels. The brakes had become spongy at the exact same time the wheel bearing went out and I figured that the two problems were related. The hub had a lot of play in it and I was thinking the caliper piston wasn't working like it should because of this. That is not the problem, though. I'm having trouble figuring out what's causing the brakes to be soft. When I open up the the bleeder valves on the rear wheels, brake fluid pours out of the valves just like it should. When I open the bleeder valves on the front wheels, I get no fluid, even when the brakes are pumped. Any ideas? Bad master cylinder maybe? If I disconnect the hose where the line connects to the caliper, fluid is there but doesn't leak out unless the brake pedal is pushed. The truck has disc brakes on the front and drum brakes on the rear.
Here's another related (and dumb) question: How do I tell if this truck has power brakes?
Thanks in advance for your help, everybody!
Nick in Kalamazoo
(This post was edited by Grif on Mar 29, 2009, 2:59 PM)
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Tom Greenleaf
Ultimate Carjunky
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Mar 29, 2009, 5:08 PM
Post #2 of 14
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Re: Brake problems
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Hi again Nick,
Ok: Power or not: They near certainly are power brakes but there's a chance they are "Hydro-boost" which uses PS fluid pressure - more likely a plain large whoopie cushion behind master cylinder is a vacuum booster.
No fluid pumping out of calipers. Ok again, if they went soft and master is old too the pumping to the floor is a new area inside the master and may have torn up the pressure seals. Should be an easy and reasonable job on this to replace. Look for any leakage in the front lines and caliper. If you can "gravity" bleed the fronts that may help and you can take caliper off and point hose as upward as possible if the piston is out at all pushed back the air will back bleed to caliper that way. Bleeders themselves can be the issue. If they move at all you can clear them out with drill bits by hand. One 1/8" us size and a tiny one near the point where it seals when shut. Air should blow thru there.
I don't think this is amount the fussy to bleed vehicles but who knows. Once you get it started you should get a firm feel at the pedal. If all attempts stay soft then you could try plugging the master with a made up plug for the line closest to firewall which is for the fronts and regain a firm pedal or not without the front brakes involved at all for that test.
Sometimes and a maybe the proportioning valve will act up. There may be a button to push on that will recenter it if I recall - been a while for the vintage!
That's just a maybe that the valve is stuck all the way one way send all fluid to rears only and needs be centered to use both. It's supposed to recenter by itself but might not be. When out of balance a red brake light should also stay on.
Keep trying. It's common to blow (not a waste to replace either) the master that was good before another issue that required the bleeding of the system,
T
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Guest
Anonymous Poster
Mar 30, 2009, 4:12 AM
Post #3 of 14
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Re: Brake problems
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Grif
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Mar 30, 2009, 4:30 AM
Post #4 of 14
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Re: Brake problems
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Hi Tom,
Thanks for taking the time to help me out.
This truck does have a brake booster (big round thing behind the master cylinder).
I read in the Haynes manual about the proportioning valve. According to the manual, I'm supposed to hold a small rod in the pulled out position on the proportioning valve while bleeding the brakes. I did that with a pair of vice grips while bleeding. I'll have to double check how to recenter the valve. Maybe that is the problem.
If that doesn't help, I think I'll replace the master cylinder. It's cheap and not too much work. I don't think I've ever bench bled a new master cylinder before. It is pretty straight forward?
Thanks!
Nick
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Tom Greenleaf
Ultimate Carjunky
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Mar 30, 2009, 5:02 AM
Post #5 of 14
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Re: Brake problems
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Nick: Hope this pic shows.....
The one on the right should be yours. That button gets PUSHED not pulled TMK - been a while but I believe just one push usually did the trick. There's a slide in there that when off center will ground and brake warning will come on AND if far enough will block off the lesser pressured end. Seems like 95% of these just do that if you ignore them for a minute - it's old now so it may need some help. New fluid should be good for all items in system.
To balance system - hold brake pedal when you get some pressure WHEN brake warning light is on indicating an imbalance and release a minor amount of fluid under pedal pressure from the better working end (front or rear) and the thing should recenter by itself - light will go out indicating it's in operating mode. You are just letting some fluid out - not much and can use a line right at the master but close off as not to allow air back in.
I don't recall this "vise grip" trick and not sure that's good for this thing - haven't had to replace any ever but they certainly could cause a problem.
If you do replace the master - do bench (in a vice) bleed the thing first leaving temp lines to reservoir playing bar tender while carrying it over to the truck to install while filled - laugh. Leave hose clipped to reservoir and quickly be ready to install lines.
Trick - After install, push back a caliper piston (just a tad with screwdriver) which should pop back the last little bubble at front brake line. If parking brake is applied BEFORE you do this - pump up before, set parking brake - press brakes again. When you release parking brake the wheel cylinders will push that last bubble back up to master also for the rear line. Again - Front line is closest to firewall or larger reservoir end.
All suggestions would be for a complete re bleeding of brakes.
Good luck. It's mostly crude plumbing except when rust cause problems with lines and I/WE can talk you thru making up new ones as needed if needed at all,
T
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Grif
User
Mar 30, 2009, 5:32 AM
Post #6 of 14
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Re: Brake problems
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Thanks Tom - very helpful.
I don't have the Haynes manual in front of me right now, but I'm sure the procedure for bleeding the brakes was to PULL the rod on the end of the proportioning valve and keep it pulled out completely through the entire bleeding process. Haynes even suggested using vice grips or a fabricated spring-like tool to keep the rod pulled out. If the weight rating for the truck is under something like 6500 pounds, the rod is supposed to be pulled (and held) out during bleeding. If the weight rating is over 6500 pounds, the rod should be pushed in (and held in) during bleeding. My rating is around 5700 pounds as I recall.
I will try to recenter the proportioning valve. My brake warning light is not on when I start the engine, though. I think it should be if the system is out of balance, right?
Thanks for the help, Tom.
Nick
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Tom Greenleaf
Ultimate Carjunky
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Mar 30, 2009, 5:49 AM
Post #7 of 14
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Re: Brake problems
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Nick,
Just know that I don't know some things that the trucks did as well as the cars. An F-100? Whatever - should be the least of the ratings for a truck so brakes are more likely to be very similar to the monster Fords of the era that actually had similar GVW = Gross Vehicle Weight car/truck with full load is what that means.
One difference with trucks is some are designed for rear brakes to apply first vs cars the fronts begin first and will work harder vs trucks with an unknown load in the bed. That would be involving the proportioning valve so I'll mostly shut up on what your directions say.
Basic cheapo manuals aren't always so informative on specifics as you may have found out. The best books of the time were VERY costly and you shouldn't need them for this.
Warning Light: Same light bulb should light for leaving parking brake on or a fluid imbalance. It can be out of balance and the light not on as some only come on with the full extreme.
I have a busy day so may be slow if you are actively working on this. Just hang in there - I check in as much as I can,
T
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Grif
User
Mar 30, 2009, 6:18 AM
Post #8 of 14
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Re: Brake problems
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Tom,
I won't be actually working on this again until later tonight. Your responses have been very quick and I appreciate it.
It looks like a replacement proportioning valve for this truck is difficult to find. I hope I won't need to replace it.
I'll try a few things tonight and hopefully it will be an easy fix. I'd hate to start replacing things that don't need to be replaced. That gets expensive.
Nick
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Tom Greenleaf
Ultimate Carjunky
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Mar 30, 2009, 7:31 AM
Post #9 of 14
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Re: Brake problems
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Uk - ebay had millions for 99 cents on up and hard to figure out. Here's one that might work just for the view,
  View larger picture  price: US $69.95 Buy It Now Get low monthly payments
End time: Apr-05-09 15:00:08 PDT (6 days 6 hours) Shipping: US $7.95
US Postal Service Priority Mail®
Service to United States Ships to: United States Item location: Horsepower Sales-LLC , United States
That pic and info will expire no doubt and it's easier than you think.
It's local to me but a phone call to a local HUGE supplier of brake parts for Eastern Mass that doesn't usually do a big on line biz and doesn't need to would be a wealth of info for you.
They are,
Automotive Brake Warehouse
120 Central St.
Hudson, MA 01749
978-562-7004
Ask for Jim or Bear tell them I sent you. They do the homework and will mail one if you need to get one at all. You may not need this - can't say just yet. If you do need this get the exact right one. Tons of universals are available but it will cause you to become a brake line making expert and I doubt you had that in mind!
Used is only legal in some states but worth asking locally. Generally I don't choose used for brake anything but might make an exception for this part as they rarely are toast but again - could be.
Either way - do yourself a favor and put some PB (power blaster brand) penetrating oil on the flare nuts and lines where they stick inside the nuts now - better chance of no problems when and if you go there.
This item may or may not be pricey depending on how and where you find it. I'll let you do the searching for super bargains if you wish.
So go put some penetrating oil on anything flared that you might need to remove for now and take a brEAk from this for the day,
Tom
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Grif
User
Mar 30, 2009, 8:27 AM
Post #10 of 14
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Re: Brake problems
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Hey Tom,
Thanks for looking for the proportioning valve for me. It's good to know that they are available and not ridiculously expensive.
Can you tell me the signs of a malfunctioning proportioning valve? I'll be happy to replace it, but I want to make sure it really is shot before I tear it out and order a new one. Maybe I should replace the master cylinder first since it's cheap and easy. That is, hopefully easy. You never know what can happen when you start a project on these old-timers.
Thanks,
Nick
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Tom Greenleaf
Ultimate Carjunky
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Mar 30, 2009, 1:29 PM
Post #11 of 14
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Re: Brake problems
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Hmmm? What would be faulty?
Leaks, light can't go out, locked in one end (that's the maybe) or so rusted you can't get lines out without damage to replace lines usually. Since the early 70s I've had to mess with like THREE and NONE were failures completely for braking purposes.
So far you haven't been able to bleed the fronts - right? That means there's no real fluid in new calipers to push back and watch it go back to master or see bubbles in master,\.
We need to isolate why and the two reasons are the master itself or this P valve. You need to try to see if fluid will blow out with some force with a line for the fronts right at the master, then if good the next fitting is that valve and the next is the caliper itself. With that you would know where the pressure stops. If line from larger reservoir can work all the way to the proportioning valve then master might still be good and then if nothing or VERY little on its outet that's the stopper.
I simply don't know if pulling on the thing could make it stick. It really just floats with springs I think to want to be on center but the slightest resistance could stop that so they put a button there. That button is also to release a wanted residual pressure for rear wheel cylinders as the cups of that style seal like pressure to stay in contact and the return springs way overcome the little residual pressure.
Another guess: If the lines drained the master cyl dry while replacing the caliper for any length of time the master itself may need to be "bench bled" again. If it's fairly level as installed you could probably do it while on vehicle and you make up lines and curve them to go back to their respective reservoirs until no air is seen. If that didn't squirt a good flow with no resistance from brakes that master needs one last test in the vice and declare it junk.
"Bench Bleeding" Have nothing to copy so I'll just write a bit on that and what you do. In a vise holding the body shaft of a master cyl you fill the reservoir and have either plastic temp fittings or make up real brake line with proper flare nuts to be return lines back to reservoir. Slow, with cover off and fluid mostly full you push as the pushrod for the braked would until it bottoms. Slowly release and repeat watching for bubbles if you can nicely rig those temp lines back under brake fluid. Several full pushes to bottom then a few quick short pushes make the last little hiding bubbles come out and you carry this mess back over to the waiting vehicle - cover still off OR temp lines removed and plugs put in holes. New ones frequently come with stuff to do this and would print better directions then I just did I think
With that known done, the system will usually just gravity bleed with maybe a quick prompt from brake pedal when all is back together. Some are fussy and I start one by applying vacuum to a bleeder with a hand held pistol type vacuum pump and use clear line till I see fluid then remove as you don't want fluid in those pumps.
Hey - everyone's on a budget for a certain job and neither you nor I want to waste money on parts but if the master isn't expensive locally for you (might be $20) consider throwing it - would be nice to know it's done. I don't hesitate to toss those - as said if older the rubber seals in the tear easily when the first time in years the pedal goes to the floor as the bore isn't squeaky clean there from lack of use.
Last note for this post: Don't reuse brake fluid except the bench bleeding with new to start with is ok. Otherwise it shouldn't ever be reused,
T
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Grif
User
Mar 31, 2009, 4:16 AM
Post #12 of 14
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Re: Brake problems
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FIXED (and driven to work today)!
Thanks, Tom, for all your help. It is great to see that there are still people out there who will spend some time helping complete strangers.
The proportioning valve needed to be recentered. I followed your advice and bled the fronts without pulling the rod in the control valve out. So we got lucky on this one - I didn't have to replace the master cylinder or proportioning valve.
All is well on this truck for now. I'm sure it's just a matter of time before something else pops up on this 34 year old Ford, and I'll be right back on here asking for more help.
Thank you Tom!
Nick
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Tom Greenleaf
Ultimate Carjunky
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Mar 31, 2009, 5:47 AM
Post #13 of 14
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Re: Brake problems
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Great news Nick and thanks for letting us all know of the success!
Turned out to be quite a thread and helped me refresh my understanding of the bleeding issues that can come up. Most just behave and you can get complacent after a while.
YOU fixed it - we can only suggest possibilities from here.
Thanks for the kind words,
T
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way2old
Veteran
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Mar 31, 2009, 3:04 PM
Post #14 of 14
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Re: Brake problems
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For you Mr. Greenleaf.
Being way2old is why I need help from younger minds
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