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Axle is one-ton full floating. Axle is in oil bath, but wheel bearings are sealed and packed. Apparently Toyota is one of the few that did it this way.
And now I'm wondering if the PO might have mentioned "new wheel cylinders". I need to contact him.
I think Mustamrk is correct, that bearing setup would be correct for the Toyota dual-wheel setup. Clearly repackable. I wonder if someone inadvertently putting on the smaller 1/2 ton wheel cylinders may be causing the issue. When braking slowly the piston can handle the pressure, but under hard braking it’s too small. Just a thought.
I thought about the wheel cylinders, too. I sent an email to the PO about it yesterday, but he hasn't replied, yet.
Only thing is, though, even if the wheel cyls are too small, wouldn't the restriction just be momentary? What I mean is, press on the pedal, flow is restricted, but should eventually push the shoes out against the drum. I could see there being a delay, but when I press the pedal fast, I get a hard pedal until I let up for a sec then press it again more slowly. I could live with that for normal driving, but it's unacceptable in a panic stop situation.
It's a long read, but I helped a guy out ages ago upgrading his motor home brakes. Long story short, he used a NON-ABS T100 brake booster, I think it was around +60% extra assistance based on my math over stock. That doesn't fix the problem, just gives better brakes, but if you're replacing it anyway, upgrade. He also went to a manual proportioning valve if I remember right.
On the issue, slow = soft, fast = hard, sounds like the rubber lines might be coming apart inside and acting like a one way valve. Replace the two in the front, and I think there might be one for the rear too. They aren't expensive, and for the age of the vehicle, they should be replaced anyway.
The mastercylinder should just be a metal cylinder in the housing, nothing too special, so fast or slow shouldn't effect it much. How good it seals is it's main thing. Same for wheel cylinders and calipers, but if they start rusting on the cylinder they tend to stick out and give odd pad/shoe wear and such.
I'm no expert on brakes, but that's a little thing I remembered from my dad's experience being a mechanic. My specialty is knowing where to look for different things (info).
Too small of wheel cylinders would just be hard brakes, fast or slow wouldn't matter. Old chevy trucks had small wheel cylinders, fords had bigger ones, fast or slow the pedal didn't really change feeling much. I upgraded the front calipers on my 1990 LS400 with a 93-94 caliper + rotor, larger rotor by about 1in, and the caliper I think was larger too. 100% helped with the poor factory brakes on that car (again hard pedal, it was a challenge to lock the tires up on a dirt road). The 2004 matrix I recently got the brakes work really well in, easy to lock them up. I'd rather have too good of brakes, than too weak.
For brake strength, there's effectively a gear ratio between the master cylinder size and the caliper/brake cylinders. Reversed logic, smaller the master cylinder, the more pressure you get from the same effort, but it moves less fluid and there's a min amount of fluid you need to move to lock the brakes up. It's a big balancing game. Bigger calipers give better brakes, but you might have to increase the master cylinder size too removing some of the benefit. The brake booster just helps you press the pedal in, it does no other function, so upgrading that part is the simplest in the system.
Hopefully my ramblings make sense xD
EDIT:
Oh, also if you can get to some sand (don't get stuck), try to slam the brakes on and see which tires lock up (if any). General rule of thumb is pedal height is rear brake adjustment. You say it's nice and high so it sounds like the rears are adjusted right. A fast press and early harness might suggest an issue with the rear more than the front. Just an idea I had. A gravel road would work, looser the better (easier for a tire to lock up). Note that it will be really hard to lock the rears up, that's why I suggested sand, this is also a solid test for your brake lines, if any pops now, you had it pop in a good situation than when someone cuts you off and NEED the brakes. Really, everyone should do a panic stop once in a while on a dirt road, just to stress test their brakes and be prepared encase a line blows (atleast people in the salt belt).
Wyoming9 funny you should ask - I was going to post here this AM! Unfortunately, I got called away and am just now getting back.
I've been dealing with this issue since April and am pretty sick of it. So I ended up giving in and taking it to my local mechanic. He says everything points to the booster. Sigh. So I packed up my original booster yesterday and sent it off to RockAuto / Cardone for a rebuild with a 20-30 day turnaround. If it turns out to be the booster, all well and good. If not, it's only more money and time (so what the heck) and I'll just have to keep slogging away at it.
Atcfixer, thanks for your detailed post. I had another friend mention the flexible brake hoses, too. I asked the mechanic about it and he said he seriously doubted that was the problem. Regardless, I think I'll go ahead and change them out, anyway, and see if it makes a difference. Already had to change the passenger front one to pass inspection - cracked rubber - so I expect the other two aren't far behind.
Now I just need to find a flat gravel road to some lockup skid testing - probably easy enough find up here in the mountains of Virginia....
When I get this fixed, I will definitely post back here. I really appreciate all you fine folks who have chimed in on this. Thanks again.
I have a new symptom that seems to be pointing to a problem with the rear brakes (I can hear you all saying "told ya so...").
Truck is parked in my driveway on a very slight uphill grade, hand brake set, transmission in park while I troubleshoot an idle issue. For the heck of it, I put it in drive and give it a bit of gas to see if it'll stall. It doesn't, but the truck moves forward about 4 inches and stops. Huh? So I put it in neutral, it drops back the same amount, and stops again due to the hand brake. I try it again, forward, back, a few inches of play each time followed by a good hard emergency brake stop. The downhill (reversing) stop is accompanied by an audible click.
Doesn't seem right to me. Even if it has nothing to do with the hard / soft pedal thing, I guess it's time to pull the axles and see what's going on in there.
Wow, what an odd design, have to pull the axle to check the drums, the shoes are probably original since no one wants to do that xD. That axle is for sure a unique setup, I have a 1 ton pickup, but it had the v6 style rear diff (singles), but only had a G56 trans behind the 22r. The "upgraded" brakes on it are something like 67mm vs 60mm front calipers, just over 10% more braking power. The 4x4 calipers were a massive upgrade, but it's also a big design difference, dual piston if I recall right too. Newer yet the 4x4's got 4 piston calipers which potentially doubles the clamping force.
My dad just got a 2002 Lexus RX300 (basically a Toyota Highlander), front caliper looks real similar to the old 2wd 86 era pickup front caliper, single piston etc. Never know what machines have parts that interchange, makes buying parts in the future a pain, but mismatching parts can do some amazing things for the brake system too xD.
In the ATV world, calipers are pretty universal, it's the mounting bracket where the differences are generally speaking.
Anyway, good luck with the rear brakes, make sure the wheel cylinders move back and forth freely while it's apart (push the shoes forward and backward). Check the drum for rust on the wear surface, if there is, the brakes haven't done anything at all for a while. If they look really old (and/or rusty), replacing the shoes aren't a bad idea since the brake material can separate with age, or get weak depending on what materials it's made of and how it's constructed and how much oil/brake fluid it's been exposed to.
Don't forget a handy can or two of brake clean and some clean rags.
Atcfixer - the internet is remarkable. I found a link in the thread you mentioned to a page from "daysofexploration", here: http://daysofexploration.blogspot.co...third.html?m=1
That's my RV - literally - I bought it from him a few years after he posted that. At any rate, one photo has him holding the old wheel cylinder next to the new one. The body of the old one appears to be longer than the new one. Maybe I have the 1/2 ton wheel cylinders in there...
As the saying goes, small world xD. The yota motor homes aren't exactly super crazy common, so I think there's reasonable odds for that to happen. Either case, that writeup was in 2013, 8 years ago, it might be time for some brake parts back there, it's not a crazy long time, but getting up there. Nice to see what things used to look like at one point in time lol.
I learned a LOT by helping the guy on that thread, the whole brake system is about surface area basically, and displacement of fluid. Mechanical brakes for example had a major design difference from the "power" brakes. The lever the brake pedal is on is a bit longer to get you more leverage and I think the master cylinder is a smaller bore to give you the "gear ratio" in your favor. I seem to recall something like 25 or 30% longer, but it's been so long I might just be pulling that out of my butt lol.
At least you know what was replaced, how it was done, and such. That should help narrow down if there's issues back there.
On the rubber lines, there's a mesh in the middle of them that helps with the pressures, the outer layer can come apart and they still work fine, but the inside coming apart can act like a flap. My dad had experience with them both doing similar to what you're seeing but normally in the front, so it would lock one tire up but the other side would do nothing, even with new caliper etc. He also has had it the opposite way, you slam on the brakes, both tires lock up like normal, but when you let off, one tire still is locked up just from the line. I remember him telling me about that kind of stuff growing up, the oddity stuff is what I remembered the most from his stories working as a mechanic lol. Best part is, I had no clue how that stuff worked back then, i've pieced the puzzle together pretty well by now though.
The normal pickup rear wheel cylinders I think do look a lot like those pics, it's been a while since I've seen one but I kind of remember them being stubby short like that and fairly big around. I don't think there was a difference in the rear brakes though, even 4cyl vs v6 besides the bolt pattern. Looking up one on a parts site, checking the interchange, it shows 22re, 5vze (4runner) etc. If you look at the pic carefully, look at the 4 bolts that hold the axle on and "measure" the wheel cylinder based on that, it looks the same size to me. It just looks different at a quick glance since one is so bare (and clean).
Based on those pics, it might be possible to swap the dually system to a standard axle assuming the 3rd member spine count is the same. Pretty interesting, never loooked into it but I suspect the whole outer bearing holder system pulls right off with those 4 bolts, which means the load from the outer tire is on those bolts too. On a typical setup, the axle bearing is on the inside edge of where those 4 bolts go, just 1 bearing, and it's axle housing to the backing plate and pressed on the axle/backing plate holder. Seems like the standard setup and full floater would be similar strength, just one has a better bearing setup, and more tire surface area on the road. Guess that goes to show just how well built the toyota axles are if they can be adapted to be a "1 ton".
Btw, the 1 ton badge actually means pay load capacity is 2000lbs (or so), the old school of what a 1 ton meant. Anymore it's just a "class" of truck, not it's actual ability. The normal trucks I think were rated pretty close to the same as the 1 tons, atleast for GVWR, just some upgraded brakes and that axle thing (some didn't have the axle change though), besides that I think everything else was the same besides the booster (v6 style if I remember right). Anyway, what I'm getting at, the toyota Motorhomes are pushing it's capacity to the limit for the bigger ones, atleast as far as specs go, but they take it no problem it seems like. Have to love Toyota quality even if they do some things kind of weird at times.
Oh, I looked at the pic side by side, they are a tiny bit different for size, could be as simple as the brand is different though. The housing length only effects how far the "throw" is, the bore inside is what matters for how much it pushes out, clearly can't have the wheel cylinders pop apart when the shoes are worn out.
It is kind of difficult to picture exactly what you are describing, but if I understand correctly then it sounds like your drums might be warped so it is only grabbing on a certain part of the drum. It is still a good idea to check it out to make sure everything is still in good shape. Something might have rusted or snapped causing the problem you described. Also check the leaf springs and bushings. If there is enough free play the axle can roll with the parking brake on enough to feel like the brake is not working for a few inches. I am thinking this is a separate issue from the hard/soft pedal.
I looked on Rockauto, and for 1987 it appears all the wheel cylinders are the same diameter for 1-tons, 1/2-tons, and 4x4s (I wonder if this is correct?), but they are slightly different shapes. Brand differences look a lot different, also. It looks like the best way to tell is where the brake line attaches. 1-tons have the line at an angle, and 1/2-tons are straight in.
As I understand the issue, if the brake pedal is pressed slowly but with solid pressure brakes work great, slam on the brakes fast, and the pedal is hard and brakes perform poorly. Kind of like cornstarch and water, move slow and it's easy, move fast and it turns solid, but for the brake pedal. If you've never seen what that's like, check this video out.
In other words, if the pedal is pressed down slowly, the pedal is soft and brakes have more stopping power, pressed fast and they get stiff really fast and brakes perform poorly. An emergency stop would be the worst thing for this situation.
The_ supernerd - I tested it a bit more after posting yesterday. I actually only move just over an inch between stops, not 4 inches. Guess I was so surprised by it I overestimated the distance. I'll have my wife go forward and back today and see if I can tell where the play is.
And atcfixer, exactly. Sort of like cornstarch but with brakes.
Got it. On a wing and a prayer I sent my original booster in via Rock Auto for rebuild (luckily I had decided to keep it rather than return as a core since this particular one is nearly impossible to find). It came back yesterday, I installed it this morning, and my brakes are working great. It was that craptastic reman booster all along. What a monumental waste of time and money.
Thanks again to all who posted here. Your suggestions and moral support really helped. This is a great forum.
Thanks for posting what the issue actually was. It's great to close a thread with all the info needed for someone else having the same issue.
I could be wrong, but I think the V6 brake boosters are the same as the 1 ton versions, if not it might be a small upgrade over stock (like the T100 one being a pretty big leap in brake assistance).
Anyway, glad you got it figured out, and return that junk part and be sure to complain that a new part shouldn't be bad right out of the box xD. What brand was it so other's know what brand to steer clear of because they have bad quality control?
08-07-2021, 07:24 AM
