Booster troubles

H

Hillbilly38

Member
I have a 1978 traveler 345 727 Dana 44's ive replaced the booster from another used vehicle and neither one has any boost. Feels like manual brakes. Do I buy a new one at 110.00 or need to look for other possible problems. It stops but you have to be hercules to press the pedal down. Thanks
 
Let's start with the simple stuff and work through this.

First off, if it's a traveler, then it should have disc brakes on the front.

Make sure the booster/master cylinder combo that you are using is the "large" one like in the pic attached. The earlier sii with drum fronts used a much "thinner" booster that simply can't generate enuff "push" to energize the disc brake system. I only bring this up because many times these old rigs have been boneyarded to death and a new owner simply doesn't know what is correct stuff and what is not.

Are you certain that all four brake wheel cylinders/calipers are actuating and not frozen, when heavy pedal pressure is applied, will the brake system stop the vehicle?

Then, verify that there is manifold vacuum available with the engine idling at the vacuum port where the booster hose connects. A nice "target" manifold vacuum level for a sii/345 is 20"hg at say an altitude of 1,000ft. Some can be as low as 16"hg depending upon engine modifications and/or internal engine condition. Below 13>15"hg ya start running into potential loss of "booster power"...and that gets worse as the altitude the rig is running at becomes greater.

Next verify that the "check valve" that is stuck in that grommet on the front of the booster is functional, you can see that item in the pic here on the old booster. Those are dirt cheep to replace and available along with a replacement grommet at any parts house, it is not a part specific to IH only.

Try those simple checks and if ya don't find sumthin' get back to us.
 

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  • SII Disc Booster.jpg
    SII Disc Booster.jpg
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Yes all that you have mentioned has already been tried and applied where applicable. The parts vehicle I got this from is an exact copy of mine in a local salvage yard even sold from the same dealership in another state lol. It does stop with a very very firm push all brakes are working. I tested this in the recent snow we had by pushing the brakes in on a slick spot and all 4 wheels locked up, nothing seems to be hanging and the brakes make no noise or seem to have any other issues.
 
The first question that comes to mind is why was the original booster r&r'ed?

If the original booster was determined to be t.u, then replacement would have been the answer. But if the booster wasn't the problem initially, replacing it with another one won't change the original problem.

In my experience, boosters seldom go bad.

What does go bad are check valves and hoses.

You are also working on the assumption the replacement booster from a wrecking yard is in working condition.

If the donor was in a wreck, perhaps a contributing factor to the wreck May have been a faulty booster.

I have always found that going cheap on brakes, batteries, and tires is never cost saving in the long run.
 
Well the booster has not worked since ive had the vehicle which is just a couple of weeks. The one in the salvage yard is in great shape other than usual rust no wreaks and I replaced the hose with a new one the vaccuum is fine. I usually dont do things the cheap way but im not going to spend 100.00 for a booster if there might be another solution I opted to try another used one figuring the odds of two bad ones were in my favor. Looks like ill just buy a new one anyway and if that doesnt fix it ill go from there.
 
I hopes not to junk up your question hillbilly, but on my 75 Scout I had a booster that would not work in below zero weather. After the engine compartment was warmed up it worked fine. A local IH guy had never heard of this problem before. I replaced it with a reconditioned booster and never happen since.
I assumed it to be a moisture problem, plus the fact the booster was 25 years old.

Ron
 
Well hopefully a new one will cure it all. Funny thing is my local parts store sells just the booster for 110.00 but the booster and master cylinder together for 109.00 so I guess ill be getting the complete package. Ill post after I get it installed. And thanks for all the help you guys gave me. That booster link was quite interesting reading. Believe it or not in my years of buying old vehicles ive had alot of bad boosters. Was just hoping for a 109.00 miracle I guess with this one.
 
After changing mine to hydra-boost, I would never go back to vac. Boost.

My 78 terra now has as good if not better brakes than my 07 f150 fx4 super crew!

I have about $200.00 in my set up.
 
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