1.Just did the breaks on my 1996 Dodge Ram van 2500 3.9L 186, 294 miles; new rotors, calipers, rear shoes, and cylinder, flushed and bleeded. Does is normal for this van to has that hissing sound, when the pedal is depressed? only if I get very closed to the pedal to hear it.
2. Since I have this van never change the differential oil, should I do it or let it be as ?
3. tranny is service every year, oil and filter.
4. I do have the 1996 service manual for ram vam/wagon, and I did not find any reference about break pedal hissing, did the test for vacuum at the break booster and is ok. Master cylinder not visible leaks. I am think to replace the booster and the master cylinder as maintenance due to high milages. I am a home mechanic, did learn with this van since 2000 when I bought it.
Thank you and be safe
GOD BLESS

 

1. If your brakes work good, then leave it be.
2. Yes.

 

No it is not normal, it means the diaphragm inside the brake booster has a leak and will fail to give you power assist at some point. Replacing the brake booster is the correct solution.

 

Well, yes and no. Just a hiss and you have to get close to the pedal to hear it, means the vacuum is helping you push the pedal down. Give you step on the brakes and the engine speeds up or dies, then the booster is bad. A very faint hiss is just it doing its job.