MC and Brake Booster Test

[jhumphrey]

Hey all,

So I've noticed that my brake pedal is pretty soft. This was more apparent when I was pulling a trailer over the weekend. When I have the car off, I can pump the pedal and it gets hard. I then press on the pedal and it slowly goes down to about halfway over the course of 45-60secs. I read that this is the MC test (using this method, the MC is bad). I looked at the MC and it looks pretty much brand new. I have no idea how old it is, but like I said, it looks brand new (no fluid leaks, etc., it looks like it was just taken out of the box).

Is there a test for the brake booster and what are some symptoms of a bad booster? I did a search and found the test procedure for different gens, just wasn't sure if they were the procedure was all the same. I was getting ready to do some brake work (tundra upgrade) and replace the rear shoes since I have no idea when that was done last. No squeaks or anything from the brakes and the front pads still have some meat on them.

Thanks all

 

[LittleCaesar]

I'd pull off the drums first and see how the rear pads are. OEM shoes are your best best. Check to make sure both cylinders are nice and dry. Then do a full bleed of the system and see how the pressure is then. If the MC is new, all the air may not have been forced out of it the first time.

The booster seems OK provided the info given.

 

[jhumphrey]

I'd pull off the drums first and see how the rear pads are. OEM shoes are your best best. Check to make sure both cylinders are nice and dry. Then do a full bleed of the system and see how the pressure is then. If the MC is new, all the air may not have been forced out of it the first time.

The booster seems OK provided the info given.

So I finally got around to testing the system. Everything looked dry, so I bled. I did have some air in the lines, but when I got to the driver side, the bleed valve wouldn't let any fluid out. I had to almost completely unscrew it just to let it weep. I immediately closed it up (before my helper got the brake pedal all the way down). I hope this minimized my risk of air.

Question is, what causes this? Is the caliper bad? Everything looked dry on the lines and around all brake line parts.

Oh, if it helps, I bled the passenger rear, driver rear, passenger front, then driver front (well, attempted). The 3 other wheels let fluid through the line with barely turning the valve. Like I asked, is it a bad caliper? I did drive the runner down the street a little ways just to see how the brakes felt. They seemed much more responsive at first, but then turned even softer than before. If I slam on the brakes (trying to engage ABS), the vehicle comes to a stop (slowly) with no ABS/lock up.

 

[Millerad1651]

When looking at that brake, do the pads engage when you press on the pedal?
I would keep trying to bleed the driver side caliper. It sounds like there is air in the line heading to that one.

 

[jhumphrey]

Good question, I didn't notice the pad moving while the helper pumped the brakes. I will have to double check again later today when my helper returns.

If the pad doesn't engage, does that mean the caliper is bad? What if it does move, but no fluid comes out?

 

[Millerad1651]

If nothing moves, it could mean the caliper is frozen, or there is something blocking the fluid from reaching the caliper. While you are under there, also check the lines heading up into the engine bay.
If it does move, release the bleeder screw and keep pumping to see if fluid eventually starts to come out.

 

[LittleCaesar]

Remove the brake line from the caliper and see if there is fluid flowing out.