Brake System and Booster Troubleshooting (1 Viewer)

[Green Bean]

Beginning in 2025, our state has eliminated annual safety inspections for noncommercial vehicles.

 

[MatthewMcD]

Our annual test centres perform a brake test in the shop and give you a readout of breaking force balance - I guess you have the same?

I asked this before my first "new FJ40" inspection. I had worked for about 2 months to get it road worthy. I asked if they were going to drive it and he said "No, we saw you park it so the brakes must work." This is the last year they are doing "safety inspections" in Texas.

 

[POTATO LAUNCHER]

Something to keep in mind is when the brakes were dragging the pads quite possibly have been glazed form the heat. Rotors may show some hot spots as well.
I'd start with a new set of front pads, adjust the rear drums at 5-7 clicks off / contracted from lockup. Drive and adjust pedal height to where it feels good.

 

[MatthewMcD]

Something to keep in mind is when the brakes were dragging the pads quite possibly have been glazed form the heat. Rotors may show some hot spots as well.
I'd start with a new set of front pads, adjust the rear drums at 5-7 clicks off / contracted from lockup. Drive and adjust pedal height to where it feels good.

I was thinking about changing the pads as well. I'll get the rears adjusted and return here with info.

 

[pb4ugo]

I was thinking the same thing as @POTATO LAUNCHER, you likely glazed the pads and shoe material with the brakes dragging. You might start by sanding the pads and shoe material to remove the glaze. Then adjust the brakes.

 

[MatthewMcD]

adjust the rear drums at 5-7 clicks off / contracted from lockup.

So, tighten to stop the drum then 5-7 clicks off but still have a little drag...right? (I have the FSM, but these are the nuances that I get from your experience.)

 

[hobbes]

For the booster, you can pump the brakes with the engine off. Holding the brakes, start the engine. The pedal should move.

If the booster has a bad enough leak it can actually lean out a cylinder.

 

[MatthewMcD]

For the booster, you can pump the brakes with the engine off. Holding the brakes, start the engine. The pedal should move.

If the booster has a bad enough leak it can actually lean out a cylinder.

I was also going to try and connect a vacuum pump to it and see if it holds steady or leaks down.

Lot's to test and I think I have time this afternoon. Will report back.

 

[hobbes]

So, tighten to stop the drum then 5-7 clicks off but still have a little drag...right? (I have the FSM, but these are the nuances that I get from your experience.)

No. There should be no drag at 5 - 7 clicks.

If the drums drag they will continue to heat up (and perhaps drag worse).

 

[POTATO LAUNCHER]

So, tighten to stop the drum then 5-7 clicks off but still have a little drag...right? (I have the FSM, but these are the nuances that I get from your experience.)

Something that is often overlooked and old hat to those of us that have done this forever is to pump the brakes when you adjust each wheel cylinder. It will center the shoes in the drum.

 

[hobbes]

Potato Launcher’s test will also tell you:

1. If your wheel cylinders are installed correctly,
2. If your drums are still round.

As noted above, your brake pedal height will change as you adjust the wheel cylinders.

 

[45Dougal]

No. Any testing would be done by the individual States. Some States that do testing, seem more concerned about what comes out of the tail pipe. I think there are a few that take a deeper dive into safety.

Wow. So you trust most people to maintain a roadworthy vehicle!?

That explains the surfer dude I met in flagstaff in the early days of January... lost two tyres on the drive up from LA and drove the last 20 miles on the rims apparently. I didn't notice the missing hood until he got it started again and the snow melted out of the engine bay. What a death trap

 

[MatthewMcD]

Potato Launcher’s test will also tell you:

1. If your wheel cylinders are installed correctly,
2. If your drums are still round.

As noted above, your brake pedal height will change as you adjust the wheel cylinders.

While I cannot attest to #1 (I installed them...) #2 is pretty certain, I had them turned when I replaced them last year.

Here's my post checking my work: Sanity Check: Can Brake Shoes Be Installed "backwards"? - https://forum.ih8mud.com/threads/sanity-check-can-brake-shoes-be-installed-backwards.1322064/#post-15149446

 

[aztoyman]

To answer your question about re-installing the residual valve, no don't do it. They are there on drum brakes to keep the shoes from moving too far away from the drum when you release your foot from the pedal. They maintain a few PSI of pressure (there should be a spec) Less travel for the shoes on the first pedal stroke. Disc brake calipers don't have the excessive travel issue like drum brakes do so a residual valve in a disc brake system will cause your calipers and pads to drag as if you have your foot on the pedal slightly.

As far as front or rear brakes locking up first......that can get complicated. But a common test when adjusting a manual proportioning valve for instance is to get on a dirt road, go about 25 MPH and slam on the brakes. You adjust the valve so your rear brakes lock JUST BEFORE the front does. It's to prevent the rear coming around on you in a panic stop. This is a "general" guideline. Maybe read Wilwood valve instructions for clarification.

An "engineered" system will be designed to operate on that vehicle and typically has a proportioning valve designed for the system.

Once you go swapping parts that were not designed for your vehicle, you have some experimenting to do to get it right. The master cylinder size and type has to work with the calipers and/or wheel cylinder sizes. The brake pedal linkage affects things as well. The manual proportioning valves are nice for these situations. However, many swaps have been done enough and available in kit form even and the bugs have been worked out for the most part. In other words, the FJ40 has been around long enough and modded enough that these guys know what works and what doesn't. Understanding how the system is a must for troubleshooting though.

Rubber lines age and deteriorate and even though they aren't leaking, they swell under pressure and it affects system operation. Braided steel lines are an improvement as they don't swell much at all.

I hope this helps. I enjoyed your thread and I like your systematic, logical approach to troubleshooting your problem. Well done.

 

[MatthewMcD]

To answer your question about re-installing the residual valve, no don't do it. They are there on drum brakes to keep the shoes from moving too far away from the drum when you release your foot from the pedal. They maintain a few PSI of pressure (there should be a spec) Less travel for the shoes and the first pedal stroke. Disc brake calipers don't have the excessive travel issue like drum brakes do so a residual valve in a disc brake system will cause your calipers and pads to drag as if you have your foot on the pedal slightly.

As far as front or rear brakes locking up first......that can get complicated. But a common test when adjusting a manual proportioning valve for instance is to get on a dirt road, go about 25 MPH and slam on the brakes. You adjust the valve so your rear brakes lock JUST BEFORE the front does. It's to prevent the rear coming around on you in a panic stop. This is a "general" guideline. Maybe read Wilwood valve instructions for clarification.

An "engineered" system will be designed to operate on that vehicle and typically has a proportioning valve designed for the system.

Once you go swapping parts that were not designed for your vehicle, you have some experimenting to do to get it right. The master cylinder size and type has to work with the calipers and/or wheel cylinder sizes. The brake pedal linkage affects things as well. The manual proportioning valves are nice for these situations. However, many swaps have been done enough and available in kit form even and the bugs have been worked out for the most part. In other words, the FJ40 has been around long enough and modded enough that these guys know what works and what doesn't. Understanding how the system is a must for troubleshooting though.

Rubber lines age and deteriorate and even though they aren't leaking, they swell under pressure and it affects system operation. Braided steel lines are an improvement as they don't swell much at all.

I hope this helps. I enjoyed your thread and I like your systematic, logical approach to troubleshooting your problem. Well done.

Thanks, I appreciate your reply.

Do you know a source for the braded steel lines? (I'll run through and check the usual suspects after I get them all measured.)

 

[aztoyman]

Another thing with drum brakes that should be done is arcing in the shoes. IDK of anyone that even does it anymore. Take a look at your shoes when you pull a drum. Many times there are only patches of contact evident. Especially after turning drums and replacing the shoes after the first few miles. They tend to wear fast and need a lot of adjustment until they kind of arc themselves in over time.

Lots of places sell braided brake hoses. Local shops often make them. I've made my own. The safe thing to do is buy DOT approved brake hoses. Crown Automotive makes some really nice lines but they are on the expensive side of your many options.

 

[MatthewMcD]

For the booster, you can pump the brakes with the engine off. Holding the brakes, start the engine. The pedal should move.

If the booster has a bad enough leak it can actually lean out a cylinder.

This afternoon I adjusted my rear brakes. I also pulled the front pads and flat sanded the gloss off of them. I bled the lines and only saw clear fluid, no bubbles.

While the truck was up on jack stands I started the engine and the brake pedal did not change. In the past, before "adjusting" the booster rod, the pedal did used to move.

I ran the truck in 1st gear to spin the rear wheels and stepped on the brake pedal, they kept spinning. I shut off the engine and reached down while holding the brake pedal, and I could turn the rear wheel with my hand. Previously, again, before I changed the booster rod length. I could step on the brakes and stop the wheels.

I disconnected the vacuum hose to the booster and the valve works correctly. I attached a vacuum pump, drew about 10 inHg and it held that number for 30 seconds before I disconnected it.

I haven't done any pedal adjustments, yet.

So, previously, I did not have the fancy depth gauge, I used a caliper to measure the depth on the master cylinder, subtract the depth of the fitting on the master cylinder and then adjust the booster rod to that final measurement.

For anyone who has the SST or has used a brake booster adjustment tool...does this look correct to you? I would think that the rod should be exactly the same length as the legs of the tool. That amount of overhang is almost exactly the same depth that I showed in Post 480. Is this right?

 

[aztoyman]

IDK what to say about your SST use. Just guessing that it seems like it would be even like you mentioned.

As far as the rear wheels still being able to turn.......do they seem like they are at least slightly applied? the rear adjustment can be a little tricky if the shoes aren't arced in like I mentioned.

If you have turned the drums and then put on new shoes they can adjust out and sound or feel like you have them adjusted properly. But.....if the shoes are just barely touching or only touching on the ends ( Like I mentioned about arcing in) they do not have enough surface area grabbing the drums. You can power right through. Even though you can hear and feel it rubbing.

I hope that makes sense. It might not be your problem, it's just something to be aware of. Obviously you have to get full pressure application from the master cylinder. If your system is completely bled and you still get too much pedal travel it's definitely something to look at though. Assuming your master cylinder is the correct type. (disc/drum) and the rod is correctly set.

Some master cylinders are front port to front brakes and some are the opposite so be aware of that as well.

Good luck, I hope you get your brakes sorted out. You will definitely KNOW your system once you're done.

 

[MatthewMcD]

Progress today. I removed the master cylinder and used an idea from @Pin_Head and put a blob of putty on the booster shaft. Then I carefully put the master back on. Here is the before and after shot.

I know, it's only one shot, because it came out exactly the same. The push rod is WAY too short. So, I drew a line on the rod where the ruler is in the previous post, and I adjusted the length out to just under that line. I did the putty test again and it left a paper-thin layer of putty on the tip of the rod. I tightened everything up and set off on adjusting the brake pedal height, which was about 9.5" off the floor.

As I was adjusting the pedal I noticed that the stop light switch was not activating correctly, so I removed the brake pedal entirely. I cleaned everything, lubed the pivot, replaced the dried out crusty stop light switch stopper. Cleaned the switch and reinstalled everything and now my brake pedal doesn't squeeeeeeeeek when I press it.

I'll bleed the system tomorrow.

 

[aztoyman]

You sir are being VERY methodical and thorough. Soon you will be THE brake guru.