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1981 Toyota brake grab

1K views 11 replies 3 participants last post by  Provience 
#1 · (Edited)
As the weather has gotten colder, the passenger side rear brake has started locking up on me. It started on my way home fom work one evening, i stopped a couple stoplights and all was normal, then all of a sudden i went to slow down to another from about 40mph and the rear pass side tire locked up pretty hard and skidded up to a stop.

When i release the pedal, everything releases fine and nothing makes any noises out of the ordinary. It feels like the other 3 wheels grab like they used to, if i push harder on the pedal while the pass rear tire is skidding i can feel the truck wanting to stop faster, so im guessing that might mean the problem lies only in the pass rear.

I researched brake grabbing issues, and from what ive rear, its usually leaky rear axle seals or a bad wheel cylinder. I have some experience with rear seals, ii put a set in my 84 some years ago, these dont appear to be leaking, but i have never experienced brake grab issues before so im not totally sure how to tell if the pads are saturated or not. Mine looked in decentshape, i cleaned them and they didnt look oiley or anything and were in pretty good shape, lots of shoe material.
I do not have any experience in replacing or diagnosing wheel cylinders, the ebrake seems to function and actuate correctly on both sides in the rear.

I have limited space for working at my place, but later this weekend i want to tear in to it further at a garage i have access to. I have only been in so far as the problem wheel and brake drum removed and looked over by me. The shoes were tight and holding thed drum to the wheel so i readjusted the shoe clearance roughly hoping that might help. It made it easier to work on but did not change the issue.

Im still researching, if anyone has any links or things to look for that will tell me what needs to be done, id love to hear it all. Im hoping to start taking it apart tonight after some turkey.
 
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#2 ·
Sorry for the grammar and text issues, im anal about that stuff and i cant figure out how scroll within the edit post text field on my mom's Ipad. This easy to use interface can suck my nuts. Il take a ball mouse and clicky keyboard anytime over this crap.
 
#3 ·
Steve Jobs hated the iPad so much that it literally killed him :flipoff2:

Is your braking system stock? Wheel cylinders are really basic, and generally if they aren't leaking then they are good. These trucks are all so old that you could be having an issue with the brake lines being degraded and casuing something to block the return flow and holding the pressure in the line. Tough to say for sure without seeing it/being there when it happens.

On the plus side, the brakes are very very simple systems. If you crack open the bleeder on the cylinder, how does the fluid look? How does it flow when the brakes are applied and released?

Is it possible that you were simply applying the brakes and that tire hit an area of low traction that caused it to lock, and then stay locked once it got back onto the pavement? Been there, done that as well.

Take some time and go to the Toyota FAQ in the Toyota section, find and follow the links for a Factory Service Manual Online, there are several, and read up on the brake section for a minute before you go out there and start tearing into it, just to get yourself familiar with the setup first.
 
#4 ·
I have not looked the the fluid at the cylinder, though its fresh in the resivoir. The problem is easily repeatable in its current condition, so that would rule out the slippy patch. I thought about that as the first time it happened was right when leaves started collecting on the roads.

The brakes are all stock, and work very well. When it was not locking up the rear tier, it would stop much better than my 84 even.

Il keep readin the bible, thats been my starting place so far. Im also going to take apart both sides tonight, so i can compare them to eachother too, as the drivers side seems to be functioning as intendded.

I should mention, i forgot, there is no proportioning valve, removed by the PO.

Thanks for the input so far. Hope the tear down goes well and i see something that sticks out to me as the problem.

What do you look for in the shoes totell if they havebeenkilled by oil?
 
#5 ·
what are the specs on the truck? unless you are running bigger tires and heavy load, such as a gnarly exo or some such, you are going to need a rear proportioning valve to keep from locking up damn near all the time. open rear diff? that would explain why it is only locking one tire tire up, as power gets routed to the other side.

you can tell if the brake pads are contaminated by visual inspection, if they are not so bad that you cant tell by looking, then they are likely not bad enough to cause such a major issue. if you dont have an axle leak or a wheel cylinder leak, then look at the drum. if the drum looks good, then you probably dont have any contamination on your pads. if the fluid bleeds clean then you are probably good on that front as well.

inspect the springs and make sure that they are still in good condition and not overheated. also, add in a prop valve, if you need to really jam on the brakes from high speed, you Will lock up the rear when you really dont want to...drums do not need as much pressure to go into a lockup as disks do, hence the reason for the valve.
 
#7 · (Edited)
About the proportioning valve, that was my understanding too. I had a 1994 doved and exod truck without one, and it would drag the rear tires all the time. I know how that feels.

This truck when i got it, the PO mentioned he took it out for some reason, and for the time ive been driving it, its been awesome. Not even a hint of locking the rear first, i had to jam the breaks hard once from 55 to 0, the front locked a couple times while i was pumpin a bit, but i never felt the rear.

Then all of a sudden the rear pass is dragging. Is it possible ive been driving everywhere with front brakes only and then all of a sudden the rear kicked in?

Another thing i feel might be pertinent, when i get on the brakes currently, i feel the rear locks
up before i get into the "normal stopping pressure". As if everything stayed the same, but someone just turned up the sensitivity to the pass side rear.



I had the problem sided apart for a quick look a couple days ago, it all seemed ok spring wise. Ebrake returns correctly, and the shoes suck back in when pressure is released. I only ever pushed the pedal a tiny bit though to check that, i hear its bad to fill the wheel cylinders without thebrake drums on.

Tear down starts in an hour or two, as soon a my warm stomache of turkey and ham settles down.

Happy turkey and other assorted meats day!
 
#9 ·
the front locked before the rear with the proportioning valve removed completely :confused: sounds like you have been driving around with no/very little rear brakes, how long have you been driving it with it working "fine"? it is possible if you have only been driving it for a few months that the rear was not adjusted properly and it has simply taken this long for them to self adjust to the point of getting good stopping power. if you were having some real issue removing the drums, then it might be worth measureing them for wear, they do have a wear limit, similiar to disc rotors.
 
#10 ·
what size tire? when i had 5.29 gears with a spool and 31" tires i locked up my rear a couple times, havent had any issues with a steel rim and a 37" tire. the lockright should be essentially unlocked when you are brakeing, provided you are off the gas as well, lol
 
#11 · (Edited)
Tires are 35in Bfg MTs.

I have had this truck for a few months, i guess it is possible that i drove with fronts only. I hesitate to say this is the case as i had a properly setup (all factory original) 84 4x4, and on stock tires it stopped well. I feel this truck stops as well as the 84 did, and when i did my hard stop on the freeway, it "felt" like it had more stopping power. Also once in the rain before it was acting up, i got on the brakes and im pretty sure i felt the front and then with a little more pressure the rear lock up and into a 4wheel skid. I cannot for sure say this was the case though, it was slippy and its possible the rear just walked sideways on me.

I am not familiar with how the Toy brakes self adjust, im pretty new when it comes to brakes in general. I would assume it has something to do with the thumb wheel and the little pawl that only lets it go looser. One thing i noticed as well, that im not sure supports the front brakes only possibility or not, when i took it apart the first time and found the drum held on the by the shoes, i tightened the thumb screw a bit to set the gap between the shoes and drum to approx. the same as the other side, and it felt like i lost a little pedal, just a little bit. To me, that says the rears were getting fluid and putting pressure on the drums, though maybe it just was not nearly enough to stop properly.

When i mentioned above that the problem side drum was held on by the shoes, i mean the brakes were slightly applied so that they were holding the drum. When i got it off, there was hardly any lip on the outer edge and the drums showed no signs of being worn out or needing a new surface. The drums slid off fine, there was no edge hooked around the inside of the shoe, like it would be if the drum was really worn. If that makes sense.

I got the truck on stands, and the wheels and drums off. Both backing plates look in similar condition with no signs of GL5 seeping in. The springs are all rusty, and the shoes seem to move freely swinging side to side on the bottom, and pivot freely on the top. Ebrake feels like it actuates fine, both shoes move out the same ammount.

Im going to finish reading a couple sections in the bible and go compare what i read to what i see. I have a feeling the brake lines are in good shape, but thats the next thing i want to go over.
Thanks again.
 
#12 ·
hmm...well it sounds like everything is there and functioning properly, aside from some rust on the springs, but that shouldnt be too big a deal.

yes the self adjuster has to do with the pawl and wheel setup, it is a slow process, hence why it could take a couple months for them to set their own proper gap. there should be some light constant drag between the drum and the shoes, typically about enough so that the tire will spin about once around.

if they are going out and retracting just fine, then it doesnt sound like a mechanical problem and is probably pressure related, hence why a prop valve would probably be a good idea. a cheapo junkyard one would work just fine even

if you want to verify if you have been running just front brakes, you can always just unscrew the rear brake line and plug it, go drive around the block and see how it feels. ghetto testing? Yes, but it is a fairly safe way to get a feel for how it reacts.
 
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