1986 F250 brake questions
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1986 F250 brake questions
I have recently picked up a 1986 F250 2wd. It has the 7700 GVW rating. The truck needed many things and brakes are one of them. I have already put new rotors, calipers, pads, etc on the front and shoes and wheel cylinders on the back. The brake pedal is very inconsistent. Sometimes the brakes feel great, other times the feel a little spongy. I have bleed the lines numerous times and I'm confident I got all the air out.
I'm going to replace the master cylinder. I notice that there are two available, over/under 8500 GVW. The only difference I can find is the under 8500 has 2.5" wide shoes and the over has 3" wide shoes.
I plan on upgrading the booster also, which is also different between the two.
Anyways, my questions...
1. Are the drum and shoe size the only difference, besides the MC and booster?
2. Is the proportioning valve different?
3. Has anyone done this swap?
4. Do all F250/350 have that rear brake line valve that regulates brake pressure based on the load?
Sorry for all the questions...just researching my options.
Thanks
I'm going to replace the master cylinder. I notice that there are two available, over/under 8500 GVW. The only difference I can find is the under 8500 has 2.5" wide shoes and the over has 3" wide shoes.
I plan on upgrading the booster also, which is also different between the two.
Anyways, my questions...
1. Are the drum and shoe size the only difference, besides the MC and booster?
2. Is the proportioning valve different?
3. Has anyone done this swap?
4. Do all F250/350 have that rear brake line valve that regulates brake pressure based on the load?
Sorry for all the questions...just researching my options.
Thanks
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From: Virginia
Do some more research, and see if the over 8500 GVW are f450's. If they are, they may have had a hydroboost system, which I believe takes a different master cylinder. I know all this happened in the late 80's and 90's, but don't know if the hydroboost was available in 86.
For your inconsistent pedal, make sure you have the rear shoes adjusted all the way out. The way I do it is jack the wheel up and manually adjust the brakes till I can't turn the tire. Then I manually back it off till I can turn the tire, but there is still a little bit of rubbing going on. This will bring the shoes out to the drums, keeping the springs from pulling them back too far and giving you a low pedal sometimes.
For your inconsistent pedal, make sure you have the rear shoes adjusted all the way out. The way I do it is jack the wheel up and manually adjust the brakes till I can't turn the tire. Then I manually back it off till I can turn the tire, but there is still a little bit of rubbing going on. This will bring the shoes out to the drums, keeping the springs from pulling them back too far and giving you a low pedal sometimes.
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Thanks for the replies. The LMC catalogue shows different part numbers for the over/under 8500 gvw proportioning valve.
I'll recheck the rear brake shoe adjustments, if that doesn't work, I'll try a new MC.
I'll recheck the rear brake shoe adjustments, if that doesn't work, I'll try a new MC.
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Thanks for the info. I wonder what determines what truck got the rear brake load sensing brake valve?
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Year of assembly?
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Cargo Master
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From: NJ
My '86 F-250 Supercab 8800 lbs rating had a load valve in the back. My previous truck, an '86 F-250 standard cab 8800 lbs rating had one as well. I remove them when running new brake lines as they get rusty and don't work properly. Never had a problem locking the rear wheels.
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From: Virginia
My '86 F-250 Supercab 8800 lbs rating had a load valve in the back. My previous truck, an '86 F-250 standard cab 8800 lbs rating had one as well. I remove them when running new brake lines as they get rusty and don't work properly. Never had a problem locking the rear wheels.
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From: Virginia
That's the whole idea. Trucks have been a problem in the braking and handling department ever since they were invented.
The rear of the truck is either extremely light, or extremely heavy, or anything inbetween. You need heavy duty large brakes when the truck is loaded, but when it's unloaded, these lock the rear tires up too easily. This has the same affect as someone playing around pulling the e-brake doing 180's. When the rear tires lock up the rearend tends to change positions with the frontend of the truck.
The factory has always been looking for a solution to this, some of their solutions had their good points and bad ones. The load sensing valve was one, and then they went to the RABS system. I am sure they have some sort of fancy computerized system on the new trucks.
All that being said, it's no secret that the brakes on Ford pickups are one of their weak points, especially the heavier f250-up trucks.
The rear of the truck is either extremely light, or extremely heavy, or anything inbetween. You need heavy duty large brakes when the truck is loaded, but when it's unloaded, these lock the rear tires up too easily. This has the same affect as someone playing around pulling the e-brake doing 180's. When the rear tires lock up the rearend tends to change positions with the frontend of the truck.
The factory has always been looking for a solution to this, some of their solutions had their good points and bad ones. The load sensing valve was one, and then they went to the RABS system. I am sure they have some sort of fancy computerized system on the new trucks.
All that being said, it's no secret that the brakes on Ford pickups are one of their weak points, especially the heavier f250-up trucks.
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From: Denver Metro Area, CO
That was my guess at an answer - year of assembly. 
My 1981 doesn't have one, I don't
think I've EVER seen a 1981 with one in the junk yards nor have I run across it in the factory
shop manual (but maybe I just haven't seen it there yet). I've seen 'em in the yards but never
looked closely at the years or models or anything, about all I know is I've seen 'em on
*some* trucks of this vintage.
My 1981 doesn't have one, I don'tthink I've EVER seen a 1981 with one in the junk yards nor have I run across it in the factory
shop manual (but maybe I just haven't seen it there yet). I've seen 'em in the yards but never
looked closely at the years or models or anything, about all I know is I've seen 'em on
*some* trucks of this vintage.