I changed my brake fluid out on my 2002 Ram 1500 day before yesterday and noticed a firmer pedal, but accompanying that firmer pedal was a hiss I havent noticed before when I pushed the brake pedal. I searched on this and found...........well nothing. Some say its normal, some say air in the lines....whatever. In my opinion it cant be normal if I didnt hear it before and am hearing it now. It doesnt hiss all the time, just during pedal travel. Once the pedal has traveled to where it there is no hiss. It sounds almost like a rush of air.

Anyway, yesterday I decided to rebleed the system to rule out the air idea. The hiss is still there, but now the pedal is really hard. Not the typical brake booster is bad hard but way firmer then it used to be. Also it has no problems stopping the truck at all and will lock up the front brakes (rear ABS). I havent checked the vacuum lines to the booster yet but will when the sun comes out.

Basically I think my booster is on its way out though, heres why. When I shut the engine off, I have the normal 3 pumps or so of vacuum left before the pedal gets hard. If I shut the truck off and dont pump the pedal, and go back 10 minutes later the pedal is hard already. I think Im losing vacuum (reserve vacuum) somewhere. Also, when I push the pedal in and then start the truck, it does travel normally with little effort.

Any ideas on where the problem may lie? If it is the booster, how would bleeding the brakes suddenly cause this problem to manifest?

Heres what I did to bleed the brakes and change out the fluid to eliminate any guessing there:

With one of those "one man bleeder" kits, store bought not homemade, I started at the right rear tire, then left rear, right front, left front. I drained them all until I saw fresh fluid come out into the container. The bleeder bottle was always kept above the bleeder valve on the calipers, and also had enough brake fluid in the bottom to reach the hose on the inside of the bottle. I pumped the pedal by hand and made sure it didnt travel all the way down. The range was between half to 80% of motion. The reservoir never went below half full as well. Thanks in advance for any help, ideas, criticism or speculation offered.

 

I have a video of my foot working the brake pedal, its dark but you can see that theres definite travel, I just dont know if its normal or not. This is the first vehicle I have ever actually changed the brake fluid in, so that may just be how its supposed to be and Im not used to it.


I did look at the vacuum lines and I do have vacuum on big line going to the booster, and the pedal definitely does change when I press the brakes with it unplugged, it gets waaaaaaaaaayyyyy harder then it currently is. Most 3rd gen Rams I have seen, where the vacuum line plugs into the booster, there is normally only that 1 nipple for the vacuum line, others have 2 nipples but the smaller one on top is capped off. My booster has this going on:


And sandwiched between those lines appear to be a check valve or one way valve of sorts:


I pulled the valve out and ran the line straight........no change. I unplugged the thing completely and the only change was a bit higher idle. The only real change I can get is when unplugging the vacuum line, then the pedal is almost impossible to move.

 

Update. A possible solution, or at least some conclusions I can live with.

1) I went home last night and pumped the pedal with almost every pair of shoes I own as I noticed in the past that the type of shoe will change the way the pedal feels. There is the same variation in each pair of shoes I tried on the pedal. So regarding the hard pedal I mentioned in my original post, Im going to chalk that up to the fluid change. That is the purpose of changing out the 10 year old (at least) fluid right? lol. It stops the truck the same as it did before, no extra effort required, just a firmer pedal.

2) I changed the spark plugs a couple weeks ago, and noticed a vacuum hiss I hadnt before the first time I started the truck after the plug change. I was at work and had to actually get back to work so I didnt have time to chase it down. When I got home the hiss was gone. While playing with the booster vacuum lines yesterday I was able to make the hiss come back........from the check valve on the booster itself. Apparently I bumped, twisted, pulled this thing just right when changing the plugs and the grommet started leaking. Last night on the way home I stopped at Oreillys and they sell a new check valve and grommets. Dodge says this part cannot be replaced and the whole booster must be replaced, KMA, its the same barbed pull out design it has been for as long as I can remember. My only issue with the new one is that it only has one nipple for the big vacuum line, it doesnt have the top one as seen in the picture I posted yesterday, so I capped off the other line. THe rubber grommet was hard and had a small crack in it allowing my reserve vacuum to leak as I now have a 3 pump reserve 3 hours after the engine is shut off (I forgot to check it this morning before I left the house so 3 hours is all I know for sure), where yesterday I only had it for 5 minutes or so. I will look in a junk yard when I get off Wednesday to try and find one like the original so I can reconnect the top vacuum line. It doesnt seem to be hurting anything capped off right now though.

3) Im not going to worry about the "pfft" of air while the brake pedal is traveling down. I looked again at my wifes truck last night to be sure....same thing, my little brothers F150........same thing, my neighbors Chevrolet.........same thing, a friends Liberty....same thing. So Im not going to worry with it, if it is my booster going out Ill get as much as I can out of it until it does. Then Im going to prepare myself to change a whole heck of a lot of boosters in the neighborhood.

Even though I didnt get any replies, Im posting this in case any one else may run into a similar situation and tries to search.

 

Ive got a working master cylinder and booster out in the shop I pulled off mine when I did my conversion. I would re-bleed them and check for air bubbles. If not any and all fluid is clear then I would swap it out.

 

UPDATE- I did end up having to change the booster. 2 Days after changing the valve worked, I ended up with the same issue....no reserve vacuum. So apparently my booster was bleeding off the vacuum within 2 minutes of shutting the truck down. I initially installed a remanufacutred unit from Cardone (bought at AAP), finding a new unit is almost impossible. The reman unit also bled off reserve pressure. Rather then wait for AAP to order a new one and wait for it to get here, I went to my local junk yard and picked one up for $25. This one held reserve pressure over night and throughout today, so I guess I am set for now. Both the reman and the jy booster makes the same "psshhtt" vacuum release noise I heard on the other one, as well as everyone elses car that has vacuum brakes, and pedal feel was the same between all 3. So I guess bleeding the system firmed up the pedal a bit.

What would go wrong in a booster to make it behave the way it should but bleed off the reserve pressure? What would cause the diaphragm rupture beside brake fluid leaking?