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1986 F350 IDI brake issue (among other thing but lets start with what could kill me first)

Discussion in '6.9L IH & 7.3L IDI Diesels' started by matthew mcelhaney, Sep 22, 2019.

  1. matthew mcelhaney

    matthew mcelhaney Registered User

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    First time joining a forum so I hope I am posting this correctly. I have always searched and found good info using these things but have finally ran into an issue I cant seem to find anything about. I have a 1986 F350 6.9 IDI SRW LWB. I have had this truck for a little over a year. Since I bought it It has had braking issues. Seems like the front disc brakes are not engaging properly. Early on it was intermittent and for the first few stops they worked just fine. after stopping 3 or 4 times they would stop working and I am stuck with just the rear drums. After a few months they stopped engaging all together and only rear brakes seem to be working. To date I have changed in order vacuum pump, vacuum line, brake booster/master cylinder, brake hoses. The weird thing is every time I changed out a part it would work again briefly. I thought maybe there is a piece of trash floating around in the proportional valve? So I pulled that off and apart and cleaned it. Very hard to get to by the way unless you take the time to pull the fender well, which I didnt. I didnt see anything abnormal except for maybe a worn out O-ring. With out a new one to compare it to I put it back together with the assumption it was ok. After bleeding all the brakes again it worked! or so I thought. they worked for about 10 times then quite again same as always. I have a new proportional valve sitting on my work bench to be installed next chance I get. Is there anyone out there that has experienced a similar issue, or has some input and would be willing to share some words of wisdom? I have been chasing this gremlin for a while and am ready to have it resolved.
     
  2. Garbage_Mechan

    Garbage_Mechan Garbage Mechanic

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    I would check and be sure there is clearance between the master cylinder piston and the pushrod coming out of the booster. If the master cylinder piston cannot completely return it blocks the fill port in the reservoir and odd things like this happen.
     
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  3. matthew mcelhaney

    matthew mcelhaney Registered User

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    Garbage_Mechan, Great suggestion I will try that and see.
     
  4. matthew mcelhaney

    matthew mcelhaney Registered User

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    Garbage_Mechan, I had some extra time at lunch today so I gave it a go. Unfortunately it did not seem to help. for the sake of time I made a drastic adjustment with the hopes I would see some kind of difference good or bad. I should have time this week to change out the proportional valve and I may go ahead and break down and buy all new brake lines and replace those to while I am at it. If The valve doesn't fix the issue that was going to be my next move anyways.
     
  5. riphip

    riphip Supporting Member Supporting Member

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    What kind of shape are your calipers in since you had the problem before replacing those parts?
     
  6. matthew mcelhaney

    matthew mcelhaney Registered User

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    They should be ok. I bought the truck from a guy I work with and he is a good mechanic. He did allot of work to the truck before he sold it to me and rebuilding the calipers was one of the things he did. That being said we are all human and capable of making mistakes no matter how good we are. If the new brake lines and proportional valve don’t work tearing the calipers back down are my next move.
     
  7. frankenwrench

    frankenwrench overkill is under rated!

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    Did you bleed the perportioning valve? Rab's? It has to be blead as well and I didn't see you mention that.
     
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  8. matthew mcelhaney

    matthew mcelhaney Registered User

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    I did not bleed the proportional valve. I just assumed it would bleed out when I bleed the brakes like normal. Would I just need to crack open the one side with the piston and spring assembly and allow it to bleed that way or is there a more proper way to do it? Really appreciate all the good info here guys.
     
  9. riphip

    riphip Supporting Member Supporting Member

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    I have never had to bleed the proportioning valve of any of my 80+ model trucks
     
  10. frankenwrench

    frankenwrench overkill is under rated!

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    I have had to bleed mine any time I mess with the braking system. My 91 has a bleeder on the porportioning valve as well as my 85 and even on my 89 that's a gasser as well as my other 91 gasser. Just did my sister's breaks on her 89 idi and hers has a bleeder as well. Just assumed that they all had bleeders even in the gassers.
     
  11. matthew mcelhaney

    matthew mcelhaney Registered User

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    Well I successfully swapped out the proportional valve and replaced one line that rung off as I removed it. Same results. I am now certain though that all the brakes are working and am now leaning toward not obtaining the power assist from the booster. I am going to be really pissed if what I end up finding is an issue with my new booster or master cylinder. Either way I am tired of bleeding brakes ha. I am going to make up an in-line vacuum gauge at work Monday and see what I’m working with. I had already ruled out a vacuum leak early on by running a line from the new pump straight to the booster. I did the same thing again today to double check myself. I highly recommend pulling out the fender well. It is amazing the ease of access you have to that whole side of the engine.

    image.jpg

    image.jpg
     
  12. riphip

    riphip Supporting Member Supporting Member

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    Did you replace the check valve in the booster where vacuum line connects? I don't remember if replacement boosters come with a new one.
     
  13. matthew mcelhaney

    matthew mcelhaney Registered User

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    The new booster came with a new check valve
     

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