Can anyone tell me if I need a new master cylinder? My brakes seem to work fine except I have a leak where the brake fluid piston assembly bolts onto the master cylinder. It is a two bolt flange assembly that looks like there should be a gasket between the assembly and the master cylinder. The brake lines hook into this assembly that bolts onto the master cylinder.

Thanks

 

I think you have your terminology confused. The large round thing with the vacuum line going to it is the brake booster. The master cylinder is the thing with the flange on it that the brake lines go into. The plastic thing on top of the master cylinder is called the resevoir.

If you're leaking between the master cylinder and the booster, you need a new master cylinder. You also may need a new brake booster if enough brake fluid has leaked into it.

 

Thanks ANDYM for reply I should know the proper names just got things goofed up. Could it be just a bad gasket between the Master Cylinder and the Brake Booster? What do you suggest try the Master Cylinder first? Like I said my brakes seem to work fine just have the leak at the master cylinder and the brake booster. I have noticed every once in awhile when I go to apply the brakes the brake pedal seems to be a little soft and spongy. Then the next time they seem to be firm.

Thanks for you help

 

There's no gasket between the booster and master cylinder that keeps fluid from leaking. The fluid does not flow from master to booster. You want it to leak so you know your master cylinder needs replacing. Brake fluid is only in the master cylinder and brake lines and should not be leaking from the either. If it is leaking from between the master cylinder and booster then you have a leaking seal within the master cylinder and need a new master cylinder. You can rebuild yours if you want but I've never had luck with doing that. Your brakes will work fine as long as there is fluid in the system and the worn seal doesn't rupture. And it probably won't rupture. It has just worn enough that it is no longer sealing like it is supposed to. Its still sealing pretty well because you do have brakes and fluid hasn't blown out all over the place, but it is not sealing properly. Replace the master. Its the right thing to do. Plus any fluid getting sucked into the booster is getting sucked into the engine and burnt and you don't want to be burning brake fluid.

 

Thank Gman for all the help I will give the autoparts store a call and see if they have a master cylinder. So far I dont think any brake fluid got sucked into the booster. I pulled vacuum line at the booster and did not see any signs of brake fluid. Any advice on changing Master cylinder I never have change one before?

 

It's pretty easy to change. Unbolt the two lines, disconnect the fluid sensor, unbolt it from the booster, and bolt the new one in place. Then, of course you will have to bleed all your brakes THOROUGHLY. You will have some air in the lines, and you will have to keep pumping until no more air comes out.

If you can borrow a good set of line wrenches, you'd be better off. If you snap a brake line, or round off the nut, you're in trouble.

Also, just because you don't see any signs of fluid in the vacuum line doesn't mean your booster isn't full of fluid. Take the master off and look inside with a flashlight. Chances are you'll see some inside.

The worst I've ever seen was one where I took the master off, and fluid POURED out the booster. How do you keep adding fluid to a brake system and not realize anything's wrong?

 

ham4ever, sorry but I've been away from the computer all weekend. Its not a hard job. andym is right on. The hard part is bleeding the lines and that isn't hard, it's just takes time. I was just reading another thread the other day. Some mechanic suggested that instead of pumping the brake to bleed the lines, just open them up and let them flow. I would place a piece of that clear tubing on each bleeder valve and have it empty into a jar or something. I think the thread was refereeing to replacing fluid instead of getting rid of air. Air is what will be in your lines when you undo them from the master. Not much but just a little bubble is enough that you will need to bleed them. That little air bubble is what you have in there now. Remember in an earlier post you mentioned that the brakes were a little soft and spongy and then got strong after a pump or two. That's because the air bubble compresses. On that first pump the air is compressing so instead of hydraulic fluid pushing your brake pistons, the air is just collapsing. Once it is compressed then you get a strong brake. You need to get that air out of the line. Go out and buy yourself a Haynes manual. They're about $15 bucks and have step by step instructions on how to do all of this. Although for a master cylinder just follow andym's instructions. A master cylinder is cheap and replacing it is easy. If you're not comfortable with bleeding the brakes you can buy yourself a vacuum gun. It will allow you to bleed the brakes all by yourself. I even think Walmart sells one.

 

whats up all. i think i need a new master cylinder too. whats a good place to get one and about waht should it cost?

 

Autozone has a reman one for $28 and a new one for $48. Either way is probably fine. I've never had a problem with reman parts. You'll have to swap your core. By the way ham4ever, how did it work out for you?

 

Thanks to everyone for the help on the Mater Cylinder, I think I got it fixed. Has anyone ever changed out the Fuel Pressure Regulator On a 1988 f-150 4x4 4.9l engine without tearing everthing off to get to it?

Thanks, Ham4ever

 

your best bet is to start a new thread.