Weak Brakes, potential causes.

I'm getting back to the truck after getting the frame patched and capped over the last several months. When I got it, the feed line to the rear was rusty and leaking at the LSPV. I've fixed that line, replaced the LSPV with a manual one at same place, and replaced the lines and hose on the rear end. Drums and pads in back look OK, no leaks on cylinders and everything moves. Didn't touch the front. Bled all four corners in proper order with a Motive pressure bleeder. First test drive the brakes work, but not well at all. Pedal has resistance, but it's not stopping well for the amount of pressure being applied. Braking is delayed and weak. Just starting to look into it and looking for guidance on where to look first.

May have air in master cylinder? The thing drained pretty much all the fluid out through that rear line leak while it was sitting. I think previous owner was having some sort of issue with the brakes but not sure if it was that leaking line or something else.
My thoughts were to pull the front apart and inspect/clean everything first off. Does it make sense to bench bleed the master? I should be able to just disconnect the two output lines and form a couple that wrap back into the reservoir?
Could it be a bad vac booster? I guess that isn't unheard of, but is more work to get it out. Can I test it? I have a manual vacuum pump.
What else am I missing? I've changed a lot of brakes but haven't delved into the master or booster before. I want to go about it intelligently if I can and not just throw parts at it.

 

It sounds like you haven't gone through the front brakes yet. I would do that just to rule anyting out.

Then I would bleed, bleed, bleed some more. I have had some pesky air that took forever to get out. Also try different methods of bleeding, and tap on calipers, wheel cylinders, etc to free trapped air bubbles.

As you stated, you can bench bleed the master in the truck, I would do that first and then bleed at each wheel.

 

First clue. ^

While the master *may* be bad I don't think you're quite to that decision yet. The master can fail internally and bypass fluid, meaning low pressure, weak brakes yet no fluid loss. But I'd be redoubling the bleeding process again.

After you service the front brakes. If pads/rotors/calipers appear good, just a cleaning/lubing will be good PM, even if it doesn't cure the ill.

 

I don't like asking a question like that before I've exhausted my alternatives, but it's frigging cold out there so I want to be as efficient as I can. Appreciate the input. I'll knock out the front inspection ASAP and then bleed the master and then all four corners again. I wanted to look at them closely before I put it back on the road anyway.
I know I bled at least four ounces from each corner and was getting clean fluid so I think the lines are good so if there's a bubble big enough to make them this bad, it will be in the master. Will update as I progress.

 

Is the Pedal Hard...or spongey?

 

Battery was dead and couldn't test until this morning after charging all night. I could only test statically in park with the engine running. I'd say it starts out normally but when you'd expect it to bottom out and get hard, it is squishy. Definitely not firming up to a solid bottom.

I was in a hurry this morning but I think the brake light came on while I was pumping it. The parking brake was off so I guess maybe there is a pressure sensor up front? I haven't gotten that deep into it yet. I don't have a code reader but can get hold of one.

 

If it slowly goes to the floor and never firms up, that might indicate a leak or bad master cylinder. Spongy/bouncy would be air in the lines somewhere, bleed and bleed again. Once you get it to be firm, you can run through a simple test to see if the booster is working: https://piratejack.net/brake-booster-test/

 

It could easily be a bad M/C, sometimes they don't come back after running dry. And it's 20 years old..

But check the rear shoe adjustment and make it's not way loose. That can make the pedal feel low and crappy

 

Did the master cylinder run empty when you were bleeding? Doubt it would have air in it if it was working before. They can go out, but sounds more like a booster problem

 

If it wasn't empty, it damn near was. It sat with the broken rear line making a huge mess for a couple days before I noticed it.

I did the static test, think I did it right. Engine off pumped brake to get a hard pedal, then keeping pressure on started engine. Once engine started, the pedal moved to floor, more than just a little bit. Not sure if I was pushing too hard or not.
Fronts need to be cleaned up and maybe rebuilt for sure, they are rubbing a little. Understandable for how long its been sitting.

 

Probably shouldn't have gone to the floor no matter how hard you were pressing, but sounds like the booster might be OK. I'd take the master cylinder off and make sure it hasn't leaked into the booster. If it has, order a reman booster and new master cylinder, otherwise replace just the master cylinder. Run plenty of fresh fluid through all the lines. If the lines sat empty for any time, there might be some internal corrosion that needs to be flushed out. If that improves things, run it for a bit and flush again in a few weeks to give the fluid some time to break down the corrosion. Anyway, that's what I would do.

 

Do you have ABS? I accidentally drianed my master once and brakes initial bite was okay but overall soft. If you don't have Techstream to properly get air out of ABS unit, then do what I did. Drive around and get ABS to engage by slamming on pedal. Bleed brakes and repeat. It took my like 5 cycles of doing this but feel great now.

Also make sure your rear shoes are adjusted correctly. You'd be surprised how much this effects pedal feel.

 

Made some progress this weekend, despite the snow.
I found a leak at the plug I made for the return line from the old LSPV. It needed another 1/4 turn to fully seat. I put that on the crappy cupro-nickel tube I used to make the plug, it doesn't form an even flare with the Eastwood die tool. Steel line is no problem.
I pulled the front brakes apart and found that the discs were horribly loaded with pad material. Never seen anything like it. I decided to put some elbow grease into them to see if I could clean them up. They measured as new thickness so I had nothing to lose but some time. The first one I used a slightly dull 1.5" 50 grit disk on the right angle die grinder to knock the pad material off and get down to the cast iron. It was easy to control and the dull disk didn't want to cut into the base metal. Once that was done I put a 100 grit disk on the DA sander to clean and smooth it up. On the second disk I decided to use the carbide scraper that I use to hand scrape milling machine ways. It worked well and I could get the final glaze off without over working it. The random orbit finished it again and the surfaces were now 85% clean. I dressed the pads with the scraper and DA and then hit everything with brake cleaner and blew them out. Cleaned and lubed the calipers but left them alone for the most part because the pistons seem to move OK. They will get a rebuild kit in the future. Had my son help me bleed all four corners again using the peddle method.
Took it out on the street after the plows got most of the snow off and breaking action is MUCH better. I played with the PV in the back to try and get it to the point where it would just start to lock up the rear on a panic stop. Still a little ways to go but for now I think the system is sound and it is more the different feel of the small truck. Braking is smooth with no chatter or shuddering. I can't say that the peddle is as firm as on my 2020 Ram but that really isn't a fair comparison.

Here are a few pics of the de-glazing process.
The ugly



You can see the area where the buildup has been knocked off without damaging the cast iron


Surface after a little attention with 100grit DA. Could be made better but I'm already miles ahead. If I had used the scraper on this one, those black rings wouldn't be there. They are not grooves, but hard glazing.


Scraper in action. Really allows me to get the glaze off and open the pores of the CI. There is a technique required.

 

Dude, those things are toast. Just get new rotors and pads, and follow the bed-in procedure.

 

Thems Rotten...

 

I'm glad you said this, it was what I was thinking while scrolling, lol. Rotors are cheap, like $20.

 

I mean, I do see some on rock auto for that cheap, but most of the local auto parts stores don't carry those super cheap ones. They tend to have higher priced items. Rotors are wear items and should be replaced, so I wouldn't spring for the expensive stuff, but I personally wouldn't put $20 junkers on my rig either. In OPs case though, $20 junkers would be drastically better than what he's got.

I'm currently running

$62 Akebono ACT436 Proact Ultra Premium Ceramic Disc Brake Pad kit, GREY

Akebono ACT436 pads and like them. But again, for the OP any new pad would better.

 

Its OK to spend 100+ on a good set of rotors. The truck just got some frame repair, it's worth it to spend a few bucks on brake parts

No disrespect to OP, but the amount of penny pinching on this site is insane. I charge customers 400-600$ on brake jobs all day long and they're happy to keep me in business

 

The pads are junk, no doubt. The rotors were junk. Now that the rotors are clean, I could/would still use them. They are just under new width and have light scoring, less than what my wife's Honda or my son's car have. Should I change theirs out immediately too? You might have a different take on it if you lived in a climate where the roads are covered in salt and brine 4-5 months of the year.

This wasn't an effort to penny pinch, I'm trying to find the source of the problem, why the brakes weren't working to expectations and I did that. Throwing shitty rotors and pads at it are going to end up just like the garbage that was on there. I now know that I don't have an issue with the booster, and most likely the master cylinder is OK. It cost me nothing more than a couple hours in the garage on a cold crappy day. I also learned a bit about the Tacoma braking system. Just trying to share some knowledge and experience for others that may want to learn. For me, that is part of the enjoyment of owning old rusty crap like this Tacoma.

The plan has always been to replace the brakes with known good parts once I was sure the system was sound. I'm not crawling around the junk yard looking for used pads and rotors....I plan on getting a set of EBC Green Stuff pads for the front, I've had very good luck with those on several cars and trucks. I may or may not get new rotors, depends on what I can find. If factory rotors aren't too expensive I'll look at them. The rears were still good, plenty of meat on them but the drums suffered some rusting on the flange that may affect balance so I'll do them in the spring. I'll rebuild the calipers up front and adjusters and maybe the wheel cylinders in the back but that was all functioning normally back there. I don't see the point with replacing correctly working old parts with crappy new parts. Most of the average parts store stuff you are getting these days is garbage unless you are buying the top of the line name brands and at that point you may as well go with Toyota parts.

 

At a minimum, you should have those rotors turned if you plan on reusing them at all. The current surface even after all your effort is hosed, and needs to taken down to good metal.

You need to fix the rotors and pads (and probably calipers) before you address the performance of the brakes. Those rotors and pads were not properly worn in, resulting in the pad transferring to the rotor like that. I doubt the brakes ever felt great like that.