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

matthew mcelhaney

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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.
 

Garbage_Mechan

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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.
 

matthew mcelhaney

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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.
 

riphip

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

matthew mcelhaney

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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.
 

matthew mcelhaney

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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.
 

riphip

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

frankenwrench

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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.
 

matthew mcelhaney

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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.

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riphip

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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.
 

matthew mcelhaney

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Ok! So haven’t posted anything on this topic recently due to my extreme frustration on the subject. Still seeing poor braking after replacing booster master cylinder proportional valve all hoses and checking the distance from the booster piston to the master cylinder. Really not sure what to do next other than replace all the brake lines which I really don’t feel are bad. I have bled the brakes 3 different times now with the changing of parts and have great flow every time. From there I suppose I will move on to replacing the calipers and drums even though they had been recently replaced before I bought the truck. One thing I haven’t tried and for some reason has just come to me is leaving off the vacuum line to see if it’s worse or the same which should tell me if I am getting my vacuum assist or not. Any thoughts out there?
 

DaveBen

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Matt, what year and model is your truck? Please put this information in your signature by going to your name, in the TOP BLACK LINE, above, and clicking on it and then click on "Signature". Fill out the details of your truck and you are GTG.

Do you have a vacuum assist or a Power Steering assist on your brakes? OK, now I see it - vacuum assist. Let us know how this goes.
 

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