Spongy brakes and frustrations. Ideas? (1 Viewer)

[andersonoverland]

So I changed out my brakelines, MC & booster and I’m still getting a spongy pedal. I’ve bled the system several times, adjusted my booster rod several times, and it just seems to not be right. I didn’t buy an AISIN master cylinder and I’m kinda wishing I would have. Thinking that might be my problem. When I first installed the MC I didn’t know you had to adjust the throw on the booster rod and I took it for a drive and smoked my pads and rotors. I’m wondering if I damaged the MC too by having too much rod pushing into the MC. You guys have any suggestions? I am running 35’s but my other FJ80 has way better braking and basically the same setup.

 

[baldilocks]

Spongy brakes are an old 80 series syndrome that could keep you reading for days. Use Mud search or google search which is very useful to find threads on subjects discussed here on mud.

The bottom line is that if the brake pedal feels spongy there is air in the system. If the pedal feels normal-ish but continues to sink slowly after it comes to the end of its travel, the problem could be a failing master cylinder.

 

[greentruck]

I think you mayb be starting at the wrong end of the system by focusing on the MC. You said nothing about the LSPV. Start bleeding at the back and work your way forward and that may solve the sponginess. The FSM has a step by step procedure and IIRC it advises starting in the rear and working your way forward.

 

[Malleus]

@baldilocks is correct; spongy brakes are an indication of air in the system.

My recommendations is:
1) bench bleed the master cylinder; use the blue fittings from the aftermarket kits (you'll need two kits) and bleed according to the instructions in the service manual;
2) bleed the wheels and LSBPV, according to the instructions in the service manual; I use a Motive pressure bleeder, but you can make one yourself from a garden sprayer.
3) bleed the ABS pump; the instructions are in this thread, post #35

 

[jonheld]

So I changed out my brakelines, MC & booster and I’m still getting a spongy pedal. I’ve bled the system several times, adjusted my booster rod several times, and it just seems to not be right. I didn’t buy an AISIN master cylinder and I’m kinda wishing I would have. Thinking that might be my problem. When I first installed the MC I didn’t know you had to adjust the throw on the booster rod and I took it for a drive and smoked my pads and rotors. I’m wondering if I damaged the MC too by having too much rod pushing into the MC. You guys have any suggestions? I am running 35’s but my other FJ80 has way better braking and basically the same setup.

When asking questions, please state the vehicle details or add them to your signature so we know what you're talking about.
Brake systems vary between years.

 

[Outsane]

Is the abs system still in? People have said it can trap air too

 

[OffRoadScott]

Is the abs system still in? People have said it can trap air too

This is why I deleted my ABS to avoid this headache. I deleted mine along with the LSPV and have frame to axle stainless steal lines and new booster and a master cylinder waiting to go in that has a Wilwood proportioning valve plumbed inline. I am looking forward to seeing how the new setup goes.

 

[andersonoverland]

Sorry guys. Here’s my setup.

1991 FJ80 with no ABS / 3FE Engine

I bled the brakes from the right rear, left rear, LSPV, right front, and front left. Did this several times and had a shop do it yesterday again with the same results. I have a new LSPV I can install, but it seems to bleed ok from the PV.

It feels like you don’t get any braking until the last 1/4 of pedal throw and I just got it off the trail a few ago and had pretty sketchy brakes on the way down a steep trail. Like they start braking, but slip and there just isn’t enough stopping pressure. No air in the lines. Bench bled the MC twice.

 

[jonheld]

Some things to consider are below, but you never mentioned rebuilding/replacing the calipers/rotors or the rear drums/shoes. That would be the very next step before moving forward with anything else.

1. Front wheel bearings.
Loose wheel bearings will force the pistons back into the calipers as the rotor assembly wobbles. This will cause excessive pedal travel until the brakes grab.

2. Rear drum brake setup/adjustment.
While most of the brake force comes from the front brakes, if the setup of the rear drums is too loose, this will cause longer pedal travel. Proper use of the handbrake will keep the shoes in proper alignment assuming the rest of the rear brake assembly is working correctly. Proper adjustment of the rear brakes on a semi-float axle is crucial for a firmer pedal.

3. EGR valve/vacuum modulator/vacuum system. The 2 flying saucer like devices mounted the to top left of the intake manifold both have rubber diaphragms that can disintegrate over time and clog vacuum lines. Be sure that all the hard and soft vacuum lines (there are a lot of them on a 3FE) are clear and free flowing from end to end. The vacuum system has a large effect on brake feel as the booster is vacuum driven.

 

[andersonoverland]

Figured out what the issue was. I forgot to put a second gasket on my spacer between the MC and booster. I also ordered new pads, drums, rotors, and hardware. Hoping this fixes it.

 

[jonheld]

Figured out what the issue was. I forgot to put a second gasket on my spacer between the MC and booster. I also ordered new pads, drums, rotors, and hardware. Hoping this fixes it.

Why was a spacer needed between the booster and master?

 

[Rusty Marlin]

Figured out what the issue was. I forgot to put a second gasket on my spacer between the MC and booster.

This doesn't pass the "sniff test". further explanation required, please.

 

[andersonoverland]

Lol. The aftermarket booster rod was too long by about 1/8” into the MC, so I just made a simple spacer to give me more adjustability since it was screwed all the way in and still activating the MC just barely enough to actuate the brakes. After I put a 1/4 spacer in between them, it gave me WAY more precise adjustments. Just thinking outside the box without having to replace the booster with another one since my return period is over. I just modified the setup to give me the right tolerance. After I sealed up both sides of the spacer with new gaskets, it worked.