Drum brake job - 1993 Ford E-350

[Vagabound]

Last wrinkle for the moment:

When I picked up my truck from the shop after their brake work last week, they made the comment that the power brake booster was leaking and needs to be replaced. They described an air whooshing sound as you press the brake pedal. I remember hearing such a sound in the past, but I assumed it was normal operation, not having been in a vehicle like that for some years. Apparently that's not a normal sound. They described it as the seal on the brake booster no longer sealing, reducing the effectiveness of the power brake assist / booster.

As I dug into that topic with them, I was told that it is entirely separate from the hydraulic brake system. Meaning that, if true, no problem with the brake booster could cause any air to get into the brake system. For people who understand the system well, that is probably obvious, but not for everybody, like me.

In any case, two-ish questions come to mind about this brake booster situation:

1. Cause and Effect: Based on the information you have now on the symptoms that I've been describing, is there any chance that this brake booster problem could be causing any of my current symptoms? I don't think so, but it doesn't hurt to ask.

2. Break Booster Replacement:  How important is it to get this thing replaced soon, and what's the worst that happens if I don't fix it? And, is it a pretty simple DIY replacement?

Thanks,

Tom

 

[highdesertranger]

the booster is not the problem. do you have a vacuum booster? by what you describe I would say yes. why they put a vacuum booster in such a large vehicle boggles the mind but I have seen it before. the wooshing sound doesn't automatically mean the booster is bad. get them to fix the low pedal first then we will talk booster. highdesertranger

 

[jonsun]

No a booster going out makes the pedal hard to push but doesn't actuate the brakes very much. What everyone has told you about the rear shoe adjustment is right. It's classic and easy to spot.

A booster simply uses engine vacuum to push on a plunger in the master cylinder.

 

[bullfrog]

Okay HDR "no negative waves" never say never. Have you had to add brake fluid to the the system in the past, specifically the rear chamber if it got that low? When a master cylinder rear seal leaks it usually fills up the brake booster some before it starts to leak out where the master cylinder bolts to the booster. The booster's rubber diaphragm can be damaged (rotted) by brake fluid and fail or at least not work as well. Sometimes they keep working because the fluid some what seals the leak if there is enough in there and eventually leaks through the firewall and into the drivers foot well but that is extreme. Sometimes you have to loosen the master cylinder to see if the rear seal is leaking. A simple but not fail proof test of the booster is to with the vehicle not running pump the brake petal several times. It should be hard to pump and you want to push hard. In your case as you have said it should pump up. Hold pressure on it, use both feet if one gets tired and while doing so start the engine. As the engine builds vacuum the petal should sink or go down about half way to the floor. If it does the booster is working and as long as it is working and does not have any brake fluid leaking from it or in it, your booster is probably okay. Rear seals on master cylinders usually only start really leaking when they are completely worn out but when first starting to go bad can allow small amounts of air to be sucked into the system that over time result in a spongy petal like you have described. You are dealing with an almost 20 year old system, as Bardo said you probably need a 50 year old mechanic that has worked on these things at a good shop. You probably now have the knowledge of most good mechanics now you just need the hands on experience.

 

[highdesertranger]

I love it "No negative waves Moriarty". what a great movie. you are correct bullfrog but he didn't have the problem with the low pedal until the brake job. highdesertranger

 

[Ballenxj]

Sounds like bullfrog has a bit of hands on old school experience too?

 

[Vagabound]

... you are correct bullfrog but he didn't have the problem with the low pedal until the brake job.  highdesertranger

Actually, I did have the low pedal problem before, but sequence is important. 

When I first got the truck back in November, the brakes seemed to work normally and feel tight enough; both brake pedal and emergency brake.

Then, sometime in the last month or so, the normal brake pedal became very squishy and would go almost to the floor while barely working. That is what prompted me to start this thread. 

Although I'm not qualified to say what caused that exactly, I can tell you that the brake shoes were nearly worn out. The mystery is that the change in brake pedal pressure happened sort of suddenly. I have a hard time seeing how the wearing down of brake shoes could cause that symptom. Come to think of it though, maybe the one bad wheel cylinder was failing at the same time and letting air into the system. That could be a sudden failure and might be the explanation.

Although my memory on this point is not serving me well, HDR might be partly correct in that I believe the emergency brake looseness didn't happen until after the repair.

Although I would almost rather be dragged behind horses, I'm going to force myself to deal with the owner of the repair shop today or tomorrow. It's a bit ironic to think that they were the ones who were supposed to fix this and make it easy and remove all the stress from the situation. Sure glad I paid all that money to get that result!  ;-)

Tom

 

[bullfrog]

Be sure to document everything, times returned, paper records, money paid, and etc. Some states will accept evidence of repair by a second shop and in small claims court make the shop that did incorrect repair pay for the repairs the second shop did. That is a pretty good reason to take it to a second shop that competes with the first shop, if this is the situation in your state, if you can not get the first shop to fix the problem.

 

[Vagabound]

UPDATE:

I took the truck back to the shop. Things went better than expected. When the wheels were taken off, I inspected it, and everything looked normal, all new pieces in place, etc. They adjusted the brakes, I test-drove it, and both the regular brake and the emergency brake are a lot better. The emergency brake doesn't hold as well as I would like it to (in neutral on a slope), but that's probably because it's a heavy truck.

My one remaining question relates to that brake adjustment. While the brakes all begin to work about halfway down their range, which is good, I noticed after I stopped that I smell hot brakes. It is not very strong, but there is some odor like what you smell when people ride their breaks coming down the mountains. What I'm wondering is whether a little bit of that is normal after a properly adjusted brake job, or whether it's still not adjusted properly, but this time it's too tight?

Tom

 

[jonsun]

it's the new glazing going away, should clear up. You're only smelling it now because they're working for the first time. If it continues then it might be over-adjusted and partially engaged.

 

[Gary68]

monitor it,it should go away quick,a drive or two

a good shop would of fixed the brakes,bleed and adjusted and then do a proper break in procedure

 

[Vagabound]

UPDATE:

The hot brake smell did go away in a short time. The shop owner also asked me to bring it back in somewhere around 500 miles on the new brakes for final adjustment free of charge. I did and they adjusted it again. The brakes now work very well, including the emergency brake. I think part of the initial adjustment problem is that they had a technician work on it in the beginning who should not have been on that job. At the end of the day, I'm happy that the brakes are working again. 

Thanks again to everybody for your help on this topic.

Tom