Brake pedal soft and mushy after new pads installed... (3 Viewers)

[ashooter]

Okay.... I FINALLY got a new Aisin master cylinder installed, properly bench bled, and then bled the sh*t out of the brake lines again... Got nice new fluid coming through all the bleeders, including the LSPV.

NO change in braking. I'm afraid to go out on the road, but going 30 feet backward and forward in my driveway, I get hydraulic pressure throughout the press of the brake pedal, but it's softer than it should be, and the pedal ends up almost at the floor by the time the truck gradually comes to a stop.

Any ideas what I'm dealing with?

FSM "troubleshooting" table says for "low or spongy pedal":

- Replace brake shoes
- Repair leak (no fluid leaking)
- Repair or replace master cylinder
- Bleed brake system
- Repair wheel cylinder (in rear drums)
- Repair brake cylinder
- Repair or replace adjuster (in rear drums)

Seems to be leading me to the rear drums, but that doesn't make sense to me, since braking was fine before I put new pads on the front disks. Would having newer/thicker pads on the front cause something to go wonky in the rear drums???

Only alternative I can think of is to rebuild or replace the front calipers....?

Any ideas?

 

[landtank]

how old are your soft lines?

 

[ashooter]

Replaced brake lines a few months ago after having one blow out.

 

[ashooter]

I went ahead and ordered new (rebuilt) OEM calipers, shoes and "wheel cylinders" for the rear drums. Hopefully replacing all that stuff will make some magic for me.

 

[NorCal97]

I went ahead and ordered new (rebuilt) OEM calipers, shoes and "wheel cylinders" for the rear drums. Hopefully replacing all that stuff will make some magic for me.

You may have compounding issues here, but I don’t recall seeing any mention of a proper “bed-in” of the new pads, which could quite likely be part or all of your problem. There are plenty of bed-in procedures on the web from various pad manufacturers…pick your poison, they’re all similar. BUT, since you are not starting from fresh pads due to the several test runs that have been performed, it would be wise to remove the pads and “de-glaze” them with a coarse sandpaper - lay the paper on a flat surface, then drag the pads across the paper while being careful to apply pressure uniformly and not at one edge or another (don’t grind them into a wedge shape).

Ditto the rotors. Unless they are relatively new or have recently been resurfaced (machined), they could be way out of thickness tolerance and/or parallel, and will not mesh well with new pads. A poor mesh between pad and rotor will cause deflection that will directly translate to a spongy pedal feel. If your rotors are toast, check out the NAPA offering…they’re pretty decent, typically readily available, and are relatively cheap.

 

[SHIfTHEAD]

Curious if this ever got resolved? A new MC should pump up hard, does it still slowly sink to the floor? I'm new to my 80 and immediately noticed the brakes, while they work, are mushy in comparison to my 100. Not sure if this is normal for the 80 or not. I'm guessing not since you started off the thread saying this was a new condition after brake work.

So just sitting here thinking about it, if you sit there holding pressure on the brake pedal, and it sinks to the floor, I would try doing this about a dozen times. Before you start mark the fluid level in the reservoir and sit on a clean section of cement, and then see if the level drops and if you get lucky and see a spot on the cement. Brake lines have been known to spring a leak.

 

[ashooter]

Yeah, it works fine after replacing both front calipers. I think I had a bad piston in one (or both) of them.

Didn't end up doing anything to the rear drums besides cleaning them and taking a hard look at everything to make sure everything was in good shape and functioning properly.