Dual vs single diaphragm booster

[abyars111]

Now I see that I have the option of changing my brake booster to the dual diaphragm F350 version which also fits 73-76 F250/F350. Will I see any advantages by switching from a single diaphragm to a dual diaphragm booster?

My 70 crew cab has factory dual piston front disc brakes already and the 12x21/2 rear drums.

[papabug71]

A dual diaphragm booster simply applies more braking force with less pressure on the pedal. Unless you're having to stomp the brake pedal with your single diaphragm booster, I don't think you'll see much improvement swapping to the dual unit. Prolly not worth the time & money doing the swap unless your current setup is in need of repair.

Let others chime in before you make a decision tho. That's the great thing about this site, lots of guys with lots of good advice!

[abyars111]

I have to replace my booster anyway so I was just thinking this might be an upgrade. My booster seems a little stiff to me, now it's whoosing everytime I press the brakes and the idle changes on the engine denoting a vacuum leak.

The boosters listed at the parts store both have the same diameter one is just dual one single which doesn't make sense to me as usally the single are larger diameter than the dual.

Here are the units. Autozone lists the size, I looked them up on Amazon and they list the same size. I can't find any specs on anyone else's site.

single:
http://www.autozone.com/autozone/parts/ ... 44611_0_0_

dual:
http://www.autozone.com/autozone/parts/ ... 44554_0_0_

[abyars111]

I just figured out Ford used the dual diaphragm booster on the dentside trucks when it had disc brakes with dual piston calipers and the single on single piston calipers. That may be why my booster seems stiff, I have the dual piston calipers and I have the 12 x 2 1/2 shoes out back.

[papabug71]

Yup, sounds like your booster is on its way out.

Since your truck has the dual piston brakes, you might as well go for the dual diaphragm booster.

One thing to look out for: If the dual diaphragm booster is physically longer than the single, will your brake lines have enough slack in them to still reach the master cylinder? I went from manual drum brakes to power drum brakes a couple of years ago & my lines barely had the slack. I had to undo the bracket that held the lines on the top of the steering box in order to make it work.

[abyars111]

I changed over to the dual diaphram booster this weekend. My lines reached with no problems. I installed the booster without disconnecting the brake lines. One thing I had to modify was the plastic sleeve between the firewall and the booster. I had to shorten the sleeve by 5/8" to clear the back of the booster. The rubber belllows would not fit inside this sleeve so I cut it to fit over the sleeve so it will be sealed.

Thanks for everyone's help.

[papabug71]

Good deal.

How does the dual compair to the single booster? Any difference?

[abyars111]

It's not the huge improvement I was hoping for but it is easier to stop. The biggest improvement is at stoplights it's easy to keep the truck still now.

[Fake Name]

Hello, all- been away for a while, and jumped on to ask a nearly identical question for the same reasons. Hissing inside the cab on brake application, etc. Also, I recently ran out of brake fluid without indication of leaks on any wheels, so I assume the master cylinder is leaking into the booster. I overfilled the res- that's why it's wet.

The PO of my truck ('70 F250 2wd) claims to have installed the front disc setup from an F350- and it looks like it. At least I know they're discs and very large. He also put on some sort of odd valve devices, claiming some advantage it towing. I'm tempted to remove them- keep it simple.

So- what master cylinder will be the correct choice for this setup? I don't know if he changed it during the front swap or not.

Thanks.

Currently:




I also don't appear to have a lot of clearance between the booster and my fancy-pants valve cover.