another brake issue

[swampercj]

My son came home from school with his 86 f-250 diesel truck and he was complaining about how hard his brakes were to press and get the truck stopped. We checked both the front/back brakes and found everythin in good condition. So I believe it going to be either the booster or the mastercylinder thats bad. Anybody got an easy way to figure out which one is bad. I've got to get him rolling on his own in the next week so he can go up to Virginia so I don't need to be playing with this thing.

[ddm6685]

I have the same exact problem as swamper , If I start to apply the brakes and do not reapply the truck stops just ok, however if I reapply the brakes after initial It will hardly stop. Scary while pulling a trailer.

[swampercj]

After doing a bunch of reading and since the mastercylinder isn't leaking I'm thinking its gonna be a booster, since the pedal is rock hard. I'll let you know of my findings in the next couple of days.

[ddm6685]

I appreciate that swampercj, all research I can find also points to a bad booster. Seems like a straight forward replacement.

[twbhd04]

sounds like the booster to me had the same thing happen to me on a firebird one time it should be a lot easier to replace on a truck than it was for me on that damn car.

[Ross01]

You said it was an 1986? Sounds like the vacuum pump to me.

[swampercj]

The brakes on an 86 are powered by pump and not off engine vaccum?

[Ross01]

Yes. Since diesels have no throttle plate, they create no engine vacuum. Brakes have to be ran off of either hydroboost or vacuum pump. The old IDI's run off a vacuum pump and I would almost bet money that's what's wrong with it.

[Ross01]

The vacuum pump is mounted below the alternator, and runs off of it's own belt. I would check the belt, the vacuum line from the pump to the booster for holes, and if it's neither of those it's probably the pump.

[swampercj]

I didn't think about the vaccum pump, however everything I'm reading states I should be getting a light if the pump was faulty. I'm not getting any lights just have a really hard pedal.

I took a look at the pump belt its a little loose, I'll look into it tomorrow. @ how much vacuum should the pump be pulling at the booster, I can't find any specs for the pump anywhere.

Thanks for the help, I don't need to be tossing $ at it,