Jump to content
Sign in to follow this  
Slartibartfast

Mushy brakes

Recommended Posts

My brakes are driving me mad and I'm running out of ideas, running out of brake fluid, and running out of time to fix this SOB (need it for some volunteer work this weekend). Any ideas appreciated!

This all started recently when my passenger's front caliper started sticking. I replaced both front calipers with remans, figuring if one was giving me trouble, the other probably wasn't far behind. I put them in, bled them, and the brakes were mushy. They would stop the truck, but with the engine running, I could bottom out the pedal. Pumping didn't raise the pedal. Bleeders are on top like they should be and brake fluid comes out clear from all four corners and the ABS valve. I noticed that my master cylinder was leaking out the weep hole and thought, hey, I'll bet these two problems are related.

I bought a Beck-Arnley MC. It came with no instructions or bleed plugs, and after a whole lot of screwing around, all I managed to make it do was lock up the prop valve somehow to where fluid wouldn't come out the rear port even with both fronts plugged and my foot on the pedal. That ain't right.

 

I sent that junk back and ordered a Dorman MC. Came with instructions and plugs, bled properly on the bench, got it down to the 1/8" free travel specified in the instructions. Put it in, hooked it up, did a little bleeding. Pedal felt mushy like before. Bled a bunch at the calipers, the ABS module, and where the fittings meet the master. Zero change. It'll lock up the front brakes on dirt, but with the engine running, I can bottom out the pedal with very little effort. I adjusted the push rod between the pedal and the master, no change there either (not like that's what caused the problem in the first place).

If I remove all three lines from the master and replace the bleed plugs, the pedal is hard as a rock. Clearly the master's not the problem.

I tried plugging one port at a time, thinking I'd find the one line with air in it. Mushy each time. I blocked the rear and passenger's front ports and tried just the driver's front, thinking I'd start with the shortest line, and of course it was mushy. Bled it at the master (propped the pedal and cracked the fitting until air quit coming out), bled at the caliper. Still mushy. I have no idea where air would hide in that line. Maybe the caliper pistons are retracting too far? I'm really running out of ideas here.

Share this post


Link to post
Share on other sites

I think I had this happen before. I ended up gravity bleeding the system and it was better. But the thing is the booster will kind of mind fskc you after getting used to pumping with the truck off. If you're sure there is no air, and all the soft lines are good, then I would just drive it for a bit and see what happens. Do you have drums or disk in the back?

 

 

Share this post


Link to post
Share on other sites

I have the same problem with 1990 I just picked up no abs. Replaced the rear shoes, wheel cylinders front shoes, calipers and did a brake fluid change the brakes are still mushy.

 

Would be interested in what you find out. My 1991 SE brakes with abs are Perfect

Share this post


Link to post
Share on other sites

Four wheel disk, new soft lines.

 

Did a gravity bleed tonight. Drained however much fluid the res holds between max and min marks through each bleeder in the FSM's preferred order (left rear, right rear, left front, right front, ABS block). Took a while but didn't help. Think I might've found the problem, though.

The driver's front caliper is loose--you can grab it with your hand and rock it around. This didn't seem right. My understanding is that the inner seal is built so that the piston will extend out to meet the pad as far as it needs to the first time you apply the brakes after assembly, then retract just a hair when you let off to reduce drag. I propped up my phone with the camera staring at the pistons and inboard pad, hit the brakes, and watched the pistons extend a good mm or so before they even touched the damn pad! When I released the brake, they pulled away just as far.

I jammed some wood in the caliper so the pistons started right up against something, and the pedal felt a little better. This tells me the problem is that the master is wasting its fluid extending pistons through air, just like what you'd get from a drum brake that's not adjusted right.

 

I did a little research and it looks like pistons tend to stick to their seals when the caliper's sat around on some shelf for a long time. I'm going to try and break them free. Figure I'll swap the inboard pad for something thinner, extend the pistons, retract with a C clamp, extend again, retract, then button it back up and see if that did the trick.

Share this post


Link to post
Share on other sites

You have the worst luck!

 

Crappy aftermarket parts strike again...

Share this post


Link to post
Share on other sites

The question is whether I'm getting bad parts, or whether I'm an idiot and I'm destroying everything I touch.

 

The pistons extended just fine, but working them back and forth didn't fix the pedal. I swapped in the old caliper, which wasn't wiggly at all but didn't improve the pedal either. It actually seemed to be dragging on the rotor too much, so I swapped it back for the new one. Both front brakes will lock the wheels on dirt or gravel, even with the pedal bottoming out, so I'm inclined to rule them out as the problem at this point.

 

I found an old ETCG video where he said his fix for Hondas with mushy brakes after bleeding is to lock up the and cycle the ABS. "Works every time," he says. Trouble is, I've never gotten the ABS to kick in, even when the brakes were good. But the ABS computer just has the one speed sensor on the rear axle, so all I need to do is spin that up, then stop it suddenly, and then the ABS should cycle, right? I jacked up the back end, put it on stands, put it in drive, spun up the rears to 25 or so, and then stabbed the brakes.

 

And nothing happened.

 

I don't just mean the ABS didn't kick in. I mean the wheels kept spinning.

 

The engine tone changed slightly, so I guess the brakes were trying, but they barely had the power to stop the wheels in neutral (took them a good few seconds with the pedal to the floor). My best guess at this point is that the dump valve in the ABS block is jammed open, giving the fluid that should be going to the rear brakes a nice accumulator-looking thing (labeled "Reservoir" in the manual) to fill instead. I'm not sure how replacing the front calipers made the ABS block unhappy, but I can think of a few things I did between then and now that probably didn't help matters.

I'm clearly out of my depth here and pouring more time and money into it ain't gonna change that. It's got an appointment on Monday. Hopefully a real mechanic with brake tools that aren't a Snapple bottle and a piece of vinyl hose can explain a few things to the ABS valve. Otherwise, I suspect an ABS delete is in this truck's future.

Either way, I'll be much happier when this cluster is over with. :tired:

Share this post


Link to post
Share on other sites
Posted (edited)

Forgive me if this has been covered already, if so then I missed it in my quick skimming... what condition are the soft lines in? K9 had an issue a couple of years ago that he traced to a line bulging when the brakes were applied. Now in his case, iirc, was due to replacing the line and getting the wrong type of hose. Change that, problem solved.

I'll see if I can find it...


:clickdalink:

Edited by RedPath88
Added Link

Share this post


Link to post
Share on other sites

You could just manually cycle the abs by applying power to the pump thing on the frame. Now I remember this issue, it wasn't my truck but another member in Toronto. I remember something about the pump and air trapped inside.

Share this post


Link to post
Share on other sites

ABS pump has a bleeder screw as well. a lot of people miss that after opening up the system and trying to get all the air out.

 

But I am having this issue with a 1990 without ABS

Share this post


Link to post
Share on other sites
Posted (edited)

I remember that one! No fuel hose here, though. Soft lines are new.

 

The ABS block looks like a simple enough circuit, just two solenoids with a shared ground. My only reservation with digging into it is that I'm not sure the solenoids take 12v. I mean, I assume they do, but I don't want to bleed smoke from the lines instead of air. BR-46 suggests I should see 0.3-3.5v at the connector when the module's doing its self-test, but I assume that's the logic checking for the correct resistance rather than actually cycling the solenoids.

 

Anyway, it's got an appointment with a professional this morning. Sounds like they've dealt with this kind of crap before. If they figure it out, I'll ask what the hell they did. If they don't, I'll throw 12v from a drill battery at it and see how it likes that.

Edited by Slartibartfast

Share this post


Link to post
Share on other sites

The mechanic couldn't figure it out either, so this turd's back in my punch bowl.

 

I'll throw some power at the solenoids tonight.

Share this post


Link to post
Share on other sites

Any updates?

Share this post


Link to post
Share on other sites

Didn't get to it last night. Planning on screwing with it tonight and figuring out the size of fittings I'll need to delete the ABS if it comes to that.

Share this post


Link to post
Share on other sites

I removed the seat, unplugged the ABS brain, and found the two solenoid wires side by side at one end of the plug. The isolation solenoid has a light green wire with a red stripe and the dump solenoid has a grey wire with a red stripe. Both ground to the chassis somewhere. Both ohm out close to what the FSM says they should be. Both click when given 12v.

 

If I press the pedal, engine off, and then energize the dump solenoid (which opens a path to the accumulator to relieve brake pressure), the pedal falls. This means the dump is working properly and isn't jammed open like I thought it was. If I energize the isolation solenoid (which cuts off the rear brakes from the master), press the pedal, and then release the iso, the pedal falls a little as fluid enters the rear brakes. The pedal is not hard with the iso on, and doesn't fall far when it opens, so clearly the problem is upstream of the iso.

 

If there's air between the inlet and the iso, I might be able to bleed that by cracking the fitting going into the ABS block, or test it by removing the fitting and capping it to see if the pedal improves. Seems like a long shot. I'm also not sure how air would've gotten that far back just from installing and bleeding the fronts.

Perhaps there is something wrong with the front calipers. Installing them started this mess. Perhaps the prop valve in the master is waiting for a certain pressure in the front brake circuit before it provides jack crap to the rears, and I'm running out of pedal stroke before the fronts pressurize, which is why the rear system's getting dick-all. The driver's side caliper (wiggly though it is) is probably not the problem, or at least not the whole problem, given that swapping the stock one back in changed nothing. I don't have the hooped passenger's side one to re-test with (sent back as a core), but I do have bleed plugs, so I could block off that side and see if the pedal changes.

 

Come to think of it, some weird crap came out of that caliper when I first bled it. Looked like dirty lumpy (but not rusty) bubbles, but they weren't air bubbles. I assumed it was some kind of assembly lube. There wasn't much and it quit coming out pretty quick, but it makes me wonder what might be in there now.

Share this post


Link to post
Share on other sites
Posted (edited)

You could have gotten air back there when you changed the master? Try clamping the flex lines one at a time with some vice grips with hose on it and see which corner is the issue? I remember this happening to me a long time ago and I had the calipers on backwards lol. There is an L and R on them.

 

Also have you tried bleeding in the order the FSM says to? It's actually LR RR ABS RF LF. Most cars the bleed order is RR as it's the furthest from the master, but on our trucks the lines are on the passenger frame rail which makes the drivers rear the furthest if you think about it.

Edited by adamzan

Share this post


Link to post
Share on other sites

Where does the manual show that bleed order? BR-3 of the '95 manual says to bleed the LSV (if equipped, which mine isn't), LR, RR, LF, RF, ABS. The '89 manual shows the same except no ABS block. This doesn't make a whole lot of sense to me but that's the sequence I gravity-bled it in. And yes, the calipers are on the correct sides, with the bleeders on top. The issue started when I replaced the calipers, which is why I doubt air in the rear system was the original problem (although who knows at this point).

 

I tried blocking things off tonight and got nowhere. Clamped off driver's front, passenger's front, no change in pedal squish. I undid the line going into the ABS block, threaded it into an old soft line, bled the line, and crimped that off. Still spongy. So I know the problem here isn't the calipers, the hoses, the ABS block, or anything from the ABS block back.

 

All it can be at this point is a buggered master or air in the hard lines. Looking at the hard lines, two of the three come out of the master and then go up higher than the res and across the firewall before going down again. If air got into those lines when I did the calipers (or during my monkey vs football experience with the first MC), I doubt my gravity-bleeding flowed nearly enough volume to move that much air all the way down to the bleeders. I've watched the fluid in the clear hose while bleeding, and it can and does flow around larger air bubbles if it's not flowing fast enough to carry them away.

This has me looking into reverse-bleeding. It seems logical to push the bubbles out the hole they're already close to rather than fighting them all the way down. It seems less logical to dump $200 on a commercial kit. I have a pasta sauce jar, shop air, a regulator, some vinyl hose, and the handyman's secret weapon, duct tape.

 

This can only go well.

Share this post


Link to post
Share on other sites

Well, it didn't go badly, but it didn't go well, either. No bubbles. I can still get a three-inch stroke out of the pedal with the engine off.

My dad asked if it was the correct master, so I checked the Amazon again. It says "this part fits your vehicle!" but (like most listings on Amazon, or eBay, or even some of the parts on Rockauto) they don't say if it's for rear disk or rear drum. I looked up the Dorman PN (Dorman M39976) on Fleabay and found a listing with interchange PNs, including Nissan PN 4601092G01, which factorynissanparts lists as the drum master. The disc master is 4601006P02. So, yes, it's very much the wrong damn master. :headwall:

Master cylinder number three (Cardone 11-2585, listed for 4-wheel disk on Rockauto) should be here Friday.

Share this post


Link to post
Share on other sites
Posted (edited)

Aftermarket bull@!*% strikes again! These trucks are tanks, I'd take used oem over aftermarket.

Edited by adamzan

Share this post


Link to post
Share on other sites
Posted (edited)

 

I don't know if you have ever watched The Red Green show, but it is classic. This is an ad he did. Look up red green handyman's corner on YouTube. Like he says, if women don't find you handsome, they should at least find you handy.

Edited by Citron

Share this post


Link to post
Share on other sites

Yep, that was a Red Green reference. :) Used to watch his show when I was a kid.

Share this post


Link to post
Share on other sites

New master came today. Cardone 11-2585, which the Rockauto catalog says is correct for four-wheel disk. The picture on Amazon showed a reworked factory casting, but of course that's not what I got. The new one came in a Cardone box with the right PN on it, but is clearly a new aftermarket part. It looks almost exactly like the last one, right down to having "AB-36" cast into the side (though it is in a different place).

I bled it (the hoses they include for this are useless, so I went back to plugs), installed it, did some bleeding, and the pedal feels exactly the same as before.

 

Either I've bought another defective or incorrect master cylinder, or the master cylinder was never the problem.

 

I stumbled on this a while ago and thought, nah, can't be that. I'm running out of ideas and I'm sick and tired of brake fluid, so tomorrow, the booster's coming off, and I'm going to shake it and see if pieces fall out.

Share this post


Link to post
Share on other sites

Booster came out (easier with the alarm siren removed). Nothing obviously broken, not that I've had a good one on the bench to test against. The master-side pushrod adjuster is frozen up, but seems fairly close to where it should be (and I can't come up with how that adjustment would've gotten screwed up by a caliper replacement), so I put it back together. I adjusted the rod from the booster to the pedal, re-bled the master, and installed it with plugs so I could test it on its own. Press the pedal and it's the same three inches of squish with all three ports blocked off, so that's got me back to thinking the master ain't right. Third one in a row tells me it's probably me screwing something up rather than bad parts.

 

I've watched a bunch of videos on bleeding masters and all these guys with old American cast-iron stuff make it look easy. I don't know if I'm an idiot who can't bleed brakes or if whoever designed these master cylinders was dumped by a mechanic once and swore vengeance, but holy crap this is not going well. I couldn't make it do jack with the hoses this new one came with at first, so I used the plugs, bled it as far as that would go, swapped on the hoses, got a bunch more air out, let it sit, pumped a little more clear fluid through it, then installed the thing, bled it, bled all four corners and the ABS, hit the pedal and it feels exactly the same. Also, the master's making squelching noises now, so either the bleed didn't work somehow or air bubbled back into the master when I reconnected the lines.

 

:headwall:

I'm half tempted to try the half-ton Chevy MC swap. (Anyone still around who's tried this?) I'd rather not make this into a science project, but if the stock master's really this hard to get air out of, I'm inclined to rip it out and get rid of the bloody thing before it takes what's left of my sanity.

Share this post


Link to post
Share on other sites

Took it to a different shop. Got a call this morning that they'd managed to get some air out of the system and thought they were done. Pedal still bottoms out and the rear brakes still do nothing, so, no, they're not. :tired: They had another look and determined that the rear disks are doing less than the e-brake, which is saying something given how clapped my e-brake is. They're going to keep digging.

  • Like 1

Share this post


Link to post
Share on other sites

I'm a bit late to this thread but wow! I had a similar problem as to what you are describing, but after swapping my MC all my issues seem to be resolved...

 

Considering I just went down to my local O' Reily's and had them order a new one, I'm glad the one I got was the correct one and not for the drums as you said. My rear brakes definitely don't work near as well as my fronts, I'm assuming the ABS system is at fault for that... now if only I could find that damn computer lol.

Share this post


Link to post
Share on other sites

I don't see how someone could have relocated yours without tearing out the carpets and cutting the taped loom open. Perhaps on the 1992 model it was never under the seat.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

Welcome to NPORA Forums

 

Please REGISTER to gain full access to the forum.

Make sure you read the Forum Guidelines and don't forget to post a new intro in the New People Start Here! section, to say hi too everyone.

 

-NPORA

×