Front wheels won't turn after driving. - Ford Truck Enthusiasts Forums

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Front wheels won't turn after driving.

  #1  
Old 10-13-2018, 03:48 PM
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Front wheels won't turn after driving.

Recently installed a new Master cylinder and brake calipers and pads on my 2WD 1991 F250. After a few days I started smelling burning brakes. Jacked it up and the front wheels were locked up. After cooling off they start turning again.

Checked my Master cylinder info and I had bought the one for under 7K lbs.GVW. I bought the correct one and bench bled it and all wheels and it still was locking up the wheels when hot..

This morning I exchanged my calipers and brake pads and put on two new front brake hoses and bled the ABS and front brakes. Just took it out and when back jacked it up and wheels were almost locked again. Took a lot of force to move them.

The only symptom that happens other than the locking wheels is that when I start the drive the pedal is good but not firm. Seems that after driving the pedal gets more firm and I assume the pads are not releasing from the rotors. So could the issue be a proportion valve or possibly a bad brake line blocking flow or something else? I am at a loss for now and could use some help. Sandy
 
  #2  
Old 10-13-2018, 04:05 PM
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It's possible that it's down at the rotors, but more likely it's up at the master. Sounds like the booster rod is just a tad too long for this new master.
I'm assuming this is vacuum boosted (aren't they all?) on your truck? When you installed the new master, do you remember it seating all the way up against the booster, or was there a bit of a gap that you had to either push it hard up against the face of the booster, or use the nuts to pull it up tight?

Even if you don't remember, it would be worth it at this point to loosen the master and check again. There is a specification for an air gap between the back of the piston and the tip of the rod, but I'm not sure what it is for your truck.
Could be as little as a few thousandths, or as big as 1/64th of an inch I suppose. Just as long as there is some gap before the pedal is pushed.

The other possibility is a failing booster. Even if it did not do it before the brake change, our beloved trucks are hell-bent on shooting us in the foot with "coincidental carnage" by which I mean that if you replace one thing, it's almost guaranteed that another item will choose just that time to fail.
And often that item is one that requires that to install it you remove the item you just installed!
Yes, I'm being cynical and negative. But it does happen a lot!

Check for the gap spec and see what yours has.
The good news is you don't need to remove the brake lines and bleed it again usually. Just pull it far enough forward to let you check, and adjust the rod if needed.

Paul
 
  #3  
Old 10-13-2018, 04:21 PM
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Thank you Paul. Rather than go into everything in my post, I did turn the booster rod IN 1 1/4 turn yesterday. Same results with wheels and ABS light came on when I started it. Today before I drove it and had put all new parts in I moved the rod back OUT to where it was. Glad I marked it. My bro in law said to try a quarter turn and see what happens. Master sits flush with the booster. Personally I think it is the booster like you said but ? How do I check the booster for this particular issue. I will see if I can find the free length of the rod in the meantime. Please respond if any of the above gives you a clue. Sandy BTW the rod has some front to back play in it.
 
  #4  
Old 10-13-2018, 04:33 PM
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What happens to boosters is that the relief valve in the back starts to fail and remain slightly open when it warms up, letting air into the back of the diaphragm and essentially applying the brakes without your input from the pedal.
Sometimes you can trick it into releasing by pulling up on the pedal, but not very often. However, since yours is just now giving you this trouble, if it is the valve then maybe you can fiddle with it to see.

Did you try pulling up on the pedal at all when this was happening?
Also, I would think a valid test would be when you stop and can't spin the wheels, disconnect the vacuum hose from the booster. If it's the booster then this should release the brakes.
In theory...

Never had this happen to me, so I don't know if that test is valid. But it seems like it would be.
The other thing that can lock up brakes is the proportioning valve. In my case they always failed to let full braking take place. But I do know of some modern aftermarket ones that have been defective and caused the front brakes to drag.

Paul
 
  #5  
Old 10-13-2018, 05:29 PM
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Thanks again Paul. I like the disconnecting of the brake vac line if the theory works. I am going to try that tomorrow. I'm done for today but will be back on it tomorrow. If you are anyone else can offer suggestions as always they will be appreciated. I did do a booster test I read about and that consisted of pumping the brake pedal with motor off and then holding it down. Start truck and the pedal should go down some if booster is ok. My pedal got more firm as I pumped it and when I started it, it went down indicating the booster is ok. ACCORDING to the test. Have yet had time to find the suggested length of the rod but I will tonight and check it tomorrow also. Sandy
 
  #6  
Old 10-13-2018, 06:57 PM
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Had to try it tonight. Got it hot and parked and wheels were locked. Jacked it up and pulled the brake booster vac and wheels still locked up. Started it up and checked vac on the line and it was strong as motor almost died. Front brakes just takes a very slight touch to start stopping truck. Good indication pads are against the rotor and not releasing. Will check the rod etc tonight and work on it tomorrow. Sandy
 
  #7  
Old 10-14-2018, 12:24 AM
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Ok, good test. I can relate to not waiting 'till tomorrow too!
Next test you could do as well, would be to get them to bind up like that again, then loosen the master from the booster. If they release at that point, then you know it's either the adjustment, or still the booster.

I think the test you performed is legit, but only to tell you that the booster is "working" as in, it's offering assist. But I don't believe the pedal-while-you-start-the-engine will tell you of a slightly failing valve.
I could be wrong on that though. There was a big long thread here, or on another forum in the past few months that detailed one guy's long drawn out testing of his. I think it was doing the same thing (but would have to find the thread to make sure) and finally after much prodding and poking, changing the booster fixed the issue.

It's an expensive "test" though, to just replace one. So I'm all about checking and re-checking things.
If you readjust it and still have the issue though, I would think it's the booster for sure.
Unfortunately we can't just ignore sticking calipers, or failing proportioning valves either. Just that the booster seems to come up more often as the culprit in these things.

Paul
 
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Old 10-14-2018, 12:46 AM
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[QUOTE=1TonBasecamp;18248466]Ok, good test. I can relate to not waiting 'till tomorrow too!
Next test you could do as well, would be to get them to bind up like that again, then loosen the master from the booster. If they release at that point, then you know it's either the adjustment, or still the booster.


I like this test and I can test it your way and if that doesn't work, I can do another test I read about after just as easy. I'll let you know what happens. Thanks Sandy
 
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Old 10-14-2018, 12:53 AM
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Don't rule out collapsed hoses Sandy.. just a thought ,it's a possibility. I hafta get around to changing my 93's hoses out. Luckily I have a new set here waiting should I have issues.
 
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Old 10-14-2018, 02:49 PM
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[QUOTE=1TonBasecamp;18248466]Ok, good test. I can relate to not waiting 'till tomorrow too!
Next test you could do as well, would be to get them to bind up like that again, then loosen the master from the booster. If they release at that point, then you know it's either the adjustment, or still the booster.


I tried the above test and wheels stayed locked. Then I tried my test.


After watching a 50 minute video that could have taken 5 minutes here is what I discovered about the booster rod length. Measure the depth of the hole in the master cylinder to the area that mates with the booster. I used a caliper as suggested and the depth was 39.41mm. Then measure the rod length to the back where it recesses into the hole. That was 48.21mm. The video said there should only be about one mm difference in clearance.

After adjusting the rod clockwise I finally bottomed it out at about 43.5mm. Checked brakes and took it for a drive. Pedal was a little low on braking but all worked well. I braked a lot and brought it home. The wheel turned but not very freely. Better than it has been. After letting it cool for about 10min it is easier to turn now. Like I said I worked them hard while driving and my pads are new . Also my RABS light didn't come on like it did with a 1 1/4 turn. When I adjusted the rod I turned it many times to get to bottom out at 43.5mm.

So now the wheels will turn after driving albeit not totally freely. Before they were locking pretty tight. My brakes work fine. The recommended rod clearance from the video could not be accomplished because it bottomed out. Not sure where I stand at this point. Any ideas? Sandy
 
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Old 10-14-2018, 03:50 PM
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Something does not sound quite right. Not sure how you can have a rod that is literally almost a centimeter too long and not have the master bottom out on it before it touches down on the booster.
Are you using some kind of a straight-edge to measure the rod as it sticks out of the booster?
The fact that your pedal was lower this time tells me that you did indeed adjust the rod inward far enough that it's not not touching the piston at all until you start to push the pedal. The extra gap between the piston and rod is now being taken up first, which causes the additional travel at the pedal.

But it's not much out of tune at this point, because you have to remember that the pedal ratio is probably something between 6:1 and 8:1 or thereabouts. This means that for every 1/8" gap between the piston and rod, you could have a full inch of pedal travel before anything starts to happen at the brakes.

Not sure what else you need to do yet, but if the amount of pedal travel is troubling/bothersome to you, I would turn the rod out slightly as you take up the slack. Obviously not as much as it was before, but maybe half-way?
Because the brakes still drag when they get hot though, means there may be more than one issue at work here. Hopefully others will have some insight or experience with the issue.
I'm guessing most all of the fluid is new at this point? Since you've bled the brakes for a new master AND calipers, it should be almost 100% new if not the full 100%, correct?
Did the pads seem super thick and you could just barely get the calipers over the rotors the first time?

What about any sliding surfaces? Did you smooth and clean them, then add brake grease on all sliding surfaces?

At least you're not having them lock up now. That's an improvement! But if you want to get rid of some of that extra pedal travel, creep back up on the rod clearance a tiny bit and play with that.

Paul
 
  #12  
Old 10-14-2018, 04:35 PM
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Paul here are a the answers to your questions. 1. I am using a vernier caliper with a feature for measuring length. 2.Fluid is brand new and has been bled several times and all of it should be totally new and fresh off the shelf. 3. Pads slipped over rotor without compression pistons. 4 Cleaned and lubed all sliding points on calipers and pads.

I just removed a wheel and could barely turn the rotor by hand. I had tap the caliper off with a hammer as the pads were pretty stuck. When I got it off there was an imprint of the pad. Rotor turned freely without caliper.

Bottom line as I see it is there is an issue somewhere. Brake pads are not releasing fully. About all that is left is the booster itself. I don't think having to adjust the rod length as much as I did is correct. Could brake lines other than the front ones I replaced cause this to happen to the front wheels? What do you think with this info? Sandy
 
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Old 10-14-2018, 07:41 PM
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Had the same thing happen on my 89 F250.



Make sure there is no junk between the rod and master cylinder piston. The "reman" new MC I got had something stuck inside where the push rod hits the piston of the MC. Drive me nuts till I found it!
 
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Old 10-14-2018, 08:05 PM
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Check your proportion valve. Try loosening your bleeder screws when your brakes are locked.
 
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Old 10-14-2018, 08:16 PM
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Originally Posted by Eddiec1564 View Post
Had the same thing happen on my 89 F250.



Make sure there is no junk between the rod and master cylinder piston. The "reman" new MC I got had something stuck inside where the push rod hits the piston of the MC. Drive me nuts till I found it!
Thanks. Nice diagram. My Booster rod has some in and out free play. Rod pushed in it is 0.922 to the tip. My measurement from the booster to the rod tip extended is 0.996. My Master cylinder is still connected with the lines so I couldn't see in there but feeling for anything obstructing the rod is not noticeable. Any ideas? Sandy
 

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