I have a '78 F-150 4x4 super cab that was upgraded to F-250 D60 axles and suspension components. Braking has always been terrible. I think I goofed and used the F-150 brake booster instead of the F-250 brake booster when doing the swap.

Now that my master cylinder has died, I guess it's a good time to make sure I'm running the correct booster. However, I'm curious about some of the talk I've seen about guys going to a hydroboost system.

I'm going to put in a 460 that has an R/V cam, so I guess there could be a vacuum issue with the booster.

Question 1: If I get the correct booster installed, will I see a huge improvement in braking power?

Question 2: If I go to hydroboost, how is the braking when the engine is off? I ask because I do haul some heavy loads in my bed and don't want to get in a bad situation if the engine cuts out. Also, my wife sometimes drives the truck and I don't want her to get put in a bad situation either where braking takes a lot of muscle and is only good for two pumps.

 

I ended up going hydroboost. It's nearly done. I'll post a write-up with pics when I'm all done and tested.

 

If you put a dual diaphragm booster & mc off a 2wd f350 you will see a big improvement.
With the engine shut off the hydro boost will still have manual brakes, not very good.

 

Too late. The hydroboost is all in. I'm finishing up bleeding the brakes tonight. I'm currently setup with a hydroboost from an '88 F-450 and my old MC. If anything, it's an interesting expirement....

 

Man, it's just too cold tonight. Maybe I'll get them bled by Saturday when it warms up a little.

 

Let us know how they work out.

 

Well. I power bled the brakes today. I held the pin 'in' on my proportioning valve since my truck is over the 6800 weight rating (see post # 8 at https://www.ford-trucks.com/forums/7...ing-valve.html). It was odd that the right side front caliper bled freely, but the left side needed someone to work the pedal to get things moving. I guess the line must have been clogged.

I did have to rebuild my hydroboost unit since it leaked terribly from around the accumilator. The rebuild kit I purchased included a recharged accumilator. I noticed that the recharged accumilator was a lot harder to compress than the old one. Maybe that's just how worn out the old one was .

I'm reusing my old master cylinder thinking it still good since there didn't appear to be any leaking spots.

I am so far dissappointed with the results of this project. I'm going to have one more round on the bleeding to see if there is still some air in the line. To see if it makes a difference, I might switch back to the old accumilator if the second round of bleeding doesn't do anything.

One question I've had open for a while: Does the front line out of the master cylinder go to the rear line in of the proportioning valve (rear brakes)? I'm wondering if I've had my lines reversed and didn't realize it.

 

Yes, the front one (small reservoir) is the rear.

 

I bled the brakes again doing the right rear, left rear, right front, and then left front (holding the pin in while doing the fronts). Some bubbles came out again and then it ran clear for a while.

My problem is the same as when I had the old vacuum booster...if I do a quick press down on the pedal, the pedal is tight and brakes are good. However, if I do a slow press on the pedal, the pedal slowly goes to the floor and the brakes are nearly nothing.

I have no idea what's up. Maybe I'll try the F-350 master cylinder that Mark A. recommended. I'm guessing my rebuilt hydroboost didn't go well. If the new master cylinder doesn't get me there, then I'll have to go back to the dual diaphram booster.

I am starting to hate spending money without results.....

 

So I saw a thread a week or two ago that had some guy look to see if, when he pressed down on the brake pedal, did the brake fluid squirt up out the top of the master cylinder. Mine squirts big time. I'll try to locate that thread again, but that's a hard feat sometimes. Does the squirting mean a bad master cylinder?

 

Sorry to hear your brake job is turning into a nightmare.
First off virtually no sinking pedal problem is due to the booster, either vacuum or hydraulic. So rule that out. Also I have had fluid shooting up out of the resevoir many times with good master cylinders so that will not tell you good or bad.
Your problem sounds to me like one of these, still air in system, bad master cylinder with incorrectly adjusted pedal to master cylinder actuating rod.
Hope this helps.

 

I'll probably get a new F-350 master cylinder. Prior to putting the old one on, I checked for any difference between the F-450 master cylinder and mine to be sure the rod length (or depth that the rod went into the master cylinder) was still the same, which it was. I'm tempted to throw on the F-450 master cylinder, but it might be a bit much for the F-250 parts and could blow out the rear slave cylinders.

 

Does the bore of the F450 M/C look very much bigger than the F350 one? It is only bore diameter that will affect line pressure.

 

I didn't do any measuring, but I don't think so. IIRC, it seems to be pretty much the same size on the end where the booster rod goes in.

 

Then, if you believe it to be good, I would be inclined to fit it.