Power brake booster for Series IIA

[S11A]

I have the original RN disc brake kit with both fronts and rears, which I installed a few years back. Life intervened and I didn't have a chance to finish it off. I decided to get the truck going, paid a shop to do it, they in effect gave up, and basically I am finding I now have to redo everything they did since they didn't actually get things to work.

I suspect they they got the parts used off of fleabay since I have already had to junk the electric vacuum pump and the vacuum switch (this was the SSBC kit). (My truck is a 2.25 diesel.)

i replaced the vacuum pump with an AC Delco unit, and a different switch and that part of the system now appears to be working.

The check valve seems fine - when I pulled it off the servo, there was a loud vacuum being released sound like cracking open a cold one. Blowing through it does only work in one direction.

But the pedal is still rock hard. It does get harder when I pump the pedal but only by a minor amount - rock hard and rock harder. It also makes a bit of hissing noise when pumped, although over the agricultural notes of the diesel engine, it is hard to say how much. But the hissing and a firmer pedal when pumping are what I would usually look for to see if the booster is working. It is almost like it is working, but starts from such a hard state it does not have anywhere to go to from there.

The only other thing I can think to replace is the servo itself. I am not sure which one the ***clowns at the shop
installed but from measuring externally the case is about 7-1/2" diameter. I was set to spring for the Santana one from Paul at Heystee, but they have been out of stock for like months and he didn't have a date and sounded a bit frustrated with the factory.

In in the mean time, I was thinking about it some more and the fact that the servo seems to be holding vacuum (the vacuum releasing sound I mentioned), makes me wonder if the diaphragm is actually ok, and from my limited experience that is what I have seen usually fails. So maybe it is not bad? Any other way to test it?

I am am also not sure which MC was installed either. I am going to look for numbers cast into it over the weekend and see which one it is. I could see this making some difference in pedal effort if an incorrect model was installed, but it seems worse (harder pedal) than I would suspect for the wrong MC. In case I need to replace that too, would the right MC just be the standard Defender non-ABS one, since it is driving standard Defender calipers? Is the flaring on the lines different between Series MCs and Defender ones?

Any ideas on what else to check?

For example, misalignment of the valve rod (pedal side rod) with the pedal? The brake tower is an S3 tower. I would not think that would be an issue since the centerline of all of the parts should be directly in a straight line so which servo should not be an issue.

If Paul won't have the Santana units any time soon I may just go with the Type 50 servo. Has anyone done that one, and is anything required besides squeezing the forks on the valve rod together to fit the S3 pedal?

(Thanks for the great page on this, TerriAnn.).

[o2batsea]

I assume that they used a Series 3 brake pedal tower that is made to take the booster. Honestly I can't troubleshoot the problem from behind this keyboard. All I can tell you is that I used an early 110 tower with a type 50 booster and a 110 master. That gives you a two circuit system. The master that fits the 50 type booster is cast iron and has a plastic reservoir. That as opposed to the later 110 one that is a steel tube.
Rock hard pedal means that there's something wrong with the master. Either the linkage is wrong or the master is wrong or not working.
Can you open a bleed nipple and push the pedal easily?

[Ian]

Do you have the hole plugged in the bottom section of the booster? If it is not plugged you loose all of your vacuum through the hole and the servo does not work

[S11A]

Thanks Bill and Ian. I will check the bleed and see what that shows. Also, I didn't know there was a hole at the bottom of the booster, but the vacuum pump does shut off when pressure is reached but if is worth a look.

[pitchrollyaw]

You may also want to check the adjustment of the servo pushrod to the master cylinder. Too little or no clearance (too long pushrod) results in the brakes staying partially engaged, w/ too much clearance results in excessive pedal travel. The pushrod should be adjustable at the M/C end with a threaded end and locking collar.

The adjustment is not covered in the manuals I have. I learned this the hard way; I replaced the Type 80 servo on my diesel 90 w/ a new production one and the pushrod was set long and the brakes would drag, worsening w/ the heat from driving. I had to grind down the locking collar a bit to allow enough adjustment to get the brakes operating properly....the impact of dealing w/ new production parts intended to cover multiple applications.