76 F100 2WD 302 3spd

Back story: Owned the truck for years and sold it. Bought it back. New owner changed old manual brakes to a brake booster. Added new lines. Truck has disc up front and drums in rear. Unsure if it had disk up front when I sold it.

Problem: Very little brake pressure. Mash it to floor to barely stop. Very spongy. Noticed brake pedal does not pull back fully. As if the rod is too short.

Troubleshooting: adjusted rod length to increase pressure and now just stops suddenly so adjusted back.

Any advice: Do I need to supply numbers from pedal, brake booster and so on? Any advice on rundown of troubleshooting?

 

The MC bore needs to be +/- 0.005'' deeper than the length of the booster rod. Did you measure it accurately ?

Air in system ?

Rear shoes adjusted correctly ?

Is the pedal ratio at +/- 4 : 1 ?

 

1973/79 F100 2WD: Manual disc brakes were standard equipment, power disc brakes were optional.

Previous owner swapped in the wrong booster as it didn't match the brake pedal, a common problem because people are unaware of...

1973/79 F100/350: TWENTY TWO different brake pedals, NINETEEN different P/B boosters, SEVENTEEN different master cylinders, SEVEN different clutch pedals, I kid you not.

Whatever booster is installed, it has to match the brake pedal. The pedal has an ID number stamped on it.

1973/76 brake pedals are different than 1977/79 and then there are some odd ***** used in 1979 only.

 

What were they doing? Buying from the local union chapters cousin and using till gone then repeat with a different relitave? That is absolutely with out a dought one the dumbest things I have ever heard of.

 

I knew as soon as this was posted you would be flying numbers at me!!!

After much reading and searching I'm afraid the wrong booster was installed and I'm hoping that's all... my quick fix if possible is to just remove the booster and go back to manual brakes for the time being?? Of course I'll have to get numbers and be sure they match I assume?

 

@ND

I've been meaning to ask you for a while now.

Have you any idea what the type of differences are ? (E.G. Hole in pedal bar for rod connection at different heights.)

I ask because my F350 with an F350 booster has a pedal ratio of 5.7 : 1, and I'd expect a ratio closer to 4 : 1.

The pedal travel was more than I liked, and it was a tad spongy because of the extra leverage.

Even when I removed the brackets and placed the booster directly against the firewall, the rod connecting the booster and pedal remained 100% straight.

A 2002 F150 master cylinder corrected the travel and spongy feel due to its bigger 1 1/4 '' bore.

 

That's interesting. I'm clueless to everything else you are saying. As far as air in lines I am checking today. But the pedal when not depressed sits about an inch away from the stop and no way near the brake pedal light switch. As if the connecting rod is too short.

 

A couple photos. I will get under the dash tonight. I also notice the booster seems to be upside down. But I dont see that being an issue?

Booster looks upside down. Unsure about anything else.

Booster #s

 

Haha, I'm also a bit clueless, hence my question to ND.

I just want to clarify the rod we're talking about coz there's 2 of them.

There's a rod that comes from the firewall side of the booster (rear) that attaches to the brake pedal arm.

Then there's a rod that comes from the front of the booster directly into the MC, and that's the one I was referring to earlier.

Make sure that the front one has a gap between the rod tip and MC bore face.

I set my brake pedal to the same height as the gas pedal, and I think I was able to adjust the rear rod to set the height. (It was quite a while ago.)

The rear rod should move in a horizontal straight line, and not at an angle, when the pedal is depressed. (Can't remember the specifics.)

Pedal ratio FWIW :

https://www.onallcylinders.com/2016/...e-pedal-ratio/

I don't think the booster being upside down is detrimental, assuming that all bolts etc are dead centre.

I have no idea what ND means when he says that the pedal must match the booster, but I'd like to know.

 

Have a look at the videos in post 37 to see what I mean about the front booster rod :

https://www.ford-trucks.com/forums/1...-refurb-2.html

 

Brake pedal numbers

This is the gap im referring to. This is as far as the pedal will come back after depressed down. Brake switch is adjusted all the way out. Thats about a 2"gap. Can this be adjusted?

 

D3TZ-2455-B .. Brake Pedal - Use without Power Brakes / Marked: D3TA-CA / Obsolete

1973/76 F100 2WD

You cannot use a P/B booster on a truck with manual brakes, you have to install the correct P/B brake pedal:

D3TZ-2455-A .. Brake Pedal - Use with Power Brakes / Marked: D3TA-AA / Obsolete

1973/76 F100 2WD & 1975/76 F150 except 1975/76 F100/150 with Speed Control // 1973/76 F250 2WD with single piston caliper disc brakes, except 1975/76 without Speed Control.

 

I see what you mean now, and the pedal probably sits closer to the floor than you'd like.

Seems I'm not as clueless about 'matching' as I thought.

Your system mismatches because the rear rod is too short, and the pedal ratio is too high.

Removing the booster and reverting back to manual brakes, with the OE rear rod, takes care of the rod length, and the pedal ratio would be correct.

It would be a shame to lose the power brakes.

Or, you could retain the booster and make up an extension for the rod.

I've seen rod extensions for sale, but have no idea if they would fit your setup.

Assuming you extend the rod and keep the booster, the brake pedal position would be correct, but you'd experience a slight spongy feeling due to the large pedal ratio. Not a big deal.

You might have to make up a bracket to reposition the brake light switch.

Or just find a matching pedal at a JY for the booster.

The picture below shows two F350 boosters with different length rods.

The one on the left was on my truck when I bought it, and I'll assume it's for an F350.

The rod end has a flat face which I believe is for cruise control.

The one on the right is what I fitted, but removed the booster brackets first.

It fits perfectly flush against the firewall.

Had the brackets not been removed, the rod would be too short, and there'd be a mismatch.

I wasn't able to adjust the rear rod to get the desired pedal height as I had said earlier. I lengthened the rod attaching hole by 1/8'', moved the bolt forward and closed the gap behind it.

I still have a 5.7 : 1 ratio manual brake pedal, which in theory is not suitable for a 4 : 1 booster assisted ratio, but it works just fine.

The extra ratio simply gives free additional leverage.



One can now see that fitting a booster upside down would have no detrimental effect.

If you have a combination valve fitted, make sure it is for a disc/drum setup.

 

Ok that's what I was afraid of. I believe he added a booster and didnt change the pedals. Am I able to convert it back to manual??

 

More than likely I'll convert back to manual for the time being somehow...