what i heard is that you need to take the check valve out of the master cylinder for the rears to work properly . any else ever here about this ?

 

Correction here - the pin isn't part of any safety mechanism, as fairlane68 has pointed out. The pin is used to bypass the metering valve when you bleed the front brakes. Pulling the pin out fully depresses the metering valve, so that fluid can flow right to the calipers instead of being delayed. This prevents air from being trapped in the proportioning valve when bleeding the fronts. You pull it out and hold it there prior to bleeding the fronts, then release it when you're done.

Also, fairlane68 - thank you for this information. I had some misconceptions about the proportioning valve - I was under the understanding that the proportioning valve also had a means to isolate the low-pressure side in the event of a failure, but the isolation actually starts in the master cylinder itself. This lets you maintain pressure in the "good" circuit even if there's no pressure in the "bad" circuit. You'd simply lose the fluid in the bad side. Thank you for this information; reps sent to you.

 

Lol...back atcha for the point you made in another thread!

 

Can you tell me about the hydroboost. I've been looking into it. For the used parts, I can convert for about the same $ as it would take to go the 78 booster/bracket route. It doesn't seem that complicated? You just use a unit out of a 2001 (or thereabouts) F250--550, and get the lines and pump too, right?

If I can find one around, I am going to go for it. I guess the main prob would be to make the s.pump fit in my 4.9 bracket.

What would you estimate the cost of parts for your installation?

 

I spoke to Wilwood, and they recommended using a master with a smaller diameter bore. Tomorrow I am installing the master from a 78, with a 1 1/16" bore. I decided not to spend the $ on the 78 F350 booster, since there is only .5" difference in the diameter, both duals.

If I am still not satisfied, I'll start moving in the direction of a hydroboost system. I am very surprised at how inexpensive they are to install, and how easy it is to do (according to other write-ups). A little more than $100 for the j.yard parts!! With everything complete, it should run about $130. I like that. The new 78 booster would run me about $100, and it wouldn't be nearly as powerful.

 

smaller master cylinders will move less fluid to the calipers , 1/2 ton trucks have smaller diameter master cylinders than 1 tons do . the calipers are bigger on 1 tons and there by need more fluid .

 

My hydro was off of my engine donor Dodge 2wd Cummins. Cost estimate is hard as all my parts were paid for with the price of the donor. I reused all of the parts that come into contact with fluid, including the steering box, so all the lines were unmodified. The hardest part was mounting the steering box and the brake booster/master and connecting them to the pedal, the only other mildly difficult part was having brake hard lines made up metric on one end and sae on the other.
Hope you can see pictures here, if not let me know.
Old Ford Crew Cab Community, Pre 1980 Ford Crew Cab owners community and information source.

 

That is what I thought before I spoke to the experts at Willwood. Case in point: In 78 Ford changed from a 1 1/4" master (on the F350) to a 1 1/16" master. The smaller bore delivers more pressure. And the 78-79 is the sought after ticket. Yes, the booster for those years was a tiny bit bigger (Ford went from a 8.80" to 9.125") but the surface area difference in diaphrams is nothing to rave about. The major difference is the bore diameter.

Disc brakes do not need to move a lot of fluid. In fact, once they are bled/adjusted, the piston in the caliper moves very little, unlike drums. The fluid is like a solid core cable from master to calipers.

 

Thanks for the info.

 

well good luck with the smaller cylinder hope it works for you and let us know !

 

I installed the new master (rebuilt) from a 78 F350 today. I like to refill the lines with a syringe device I have before I hook everything up. It makes it a lot less work to bleed them that way.

Anyway, I have loads of pedal, firm, until I start the truck, and then the pedal drops and is spongy. I rebled the system, and then heard that old familiar sound of air escaping when brakes are applied. So I'll have to dig through my records and see if I can find my receipt/warranty for the booster.

I will say one thing: Even with the low pedal the rears locked up, and I had the adj.prop. valve set to where the rears didn't lock with the previous mastr.

Note: The 78 style master will not bolt directly to a pre 78 booster without fabrication. The bolt holes on the 78 master are 3/16" further apart. Nothing a dremel couldn't help.