brakes

General discussion about our beloved Tercel 4WD cars
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Erikwi
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Posts: 63
Joined: Fri Mar 13, 2020 3:31 pm
My tercel:: 1988 stock auto
Location: lacrosse WI

brakes

Post by Erikwi » Fri Jun 19, 2020 12:40 pm

what are the stock brakes like? mine are acting funny
symptom? no assist. like manual.

it did not start that way, it became more intermittent as time went on. one day i have power brakes, then like an off switch its manual. couple days later power again.

what i have done is
bled them, needed it because the old fluid was kinda wore out, it did fade. better now
lubed the rear shoe adjuster screws. they were pretty seized up before.
checked the check valve, it works perfectly.
checked the booster, it holds vacuum.

bad pushrod adjustment? what else can i check?

Erikwi
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Posts: 63
Joined: Fri Mar 13, 2020 3:31 pm
My tercel:: 1988 stock auto
Location: lacrosse WI

Re: brakes

Post by Erikwi » Sat Jun 20, 2020 9:43 am

so
today the first couple stops i had power brakes
then manual the rest of the day.

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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: brakes

Post by Mark » Sat Jun 20, 2020 11:22 am

First thing I'd do is check the vacuum hose to the brake booster. Make sure it's fully attached and the hose looks good with no cracks.

Erikwi
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My tercel:: 1988 stock auto
Location: lacrosse WI

Re: brakes

Post by Erikwi » Sat Jun 20, 2020 3:14 pm

i investigated. if i pull the hose off and let it go to atmosphere, then reconnect, it will work for the first two stops.
if i leave it on, it does hold vacuum and there is a big hiss when i pull it.

can anyone understand this? why does letting it go to atmosphere work?

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: brakes

Post by Petros » Sun Jun 21, 2020 2:04 am

sounds like the vac check valve is sticky. I have had that before, especially noticeable when it is cold, first few stops are like no power booster, after it warms up it starts to work again.

I was going to just replace the valve, but I was having trouble getting it out, so I sprayed carb cleaner down the vac line to where the valve was located and let it sit. than I blew it out and did it again. worked perfectly after that, have not had to clean it again.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

Erikwi
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Posts: 63
Joined: Fri Mar 13, 2020 3:31 pm
My tercel:: 1988 stock auto
Location: lacrosse WI

Re: brakes

Post by Erikwi » Sun Jun 21, 2020 8:54 am

thats whats confusing me, because if it was sticking, why would it hold vacuum? im not saying you are wrong, im just confused

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: brakes

Post by Petros » Sun Jun 21, 2020 8:14 pm

the brakes are fairly wimpy as it is, without the power assist, it will not be easy to stop safely.

the behavior you describe is not exactly clear, when you have power boost, and when you don't. is the car running, not? at idle, on the road, what? an intermittant power brakes, on and off, will not be affected by any adjustment or by bad fluid or worn brakes shoes. it is either the vacuum supply, the hoses, the check valve, or the booster/diaphragm itself.

the booster only holds vacuum for one or two application without a source of vacuum (you have a source when the engine is running, not when it is not running), after that it will not act like power assist. if you are not getting power assist with the engine running, I would check you have the vac hose connected and not cracked or leaking, and also see if perhaps the check valve is sticking closed, not allowing the booster to get reactivated.

this kind of intermittent power brakes will not come from bad brakes, but bad vac supply or booster.

OTOH, I have had a situation where a leaky master cylinder allowed hydraulic pressure to lock up the brakes, so it did not work at all, pedal was rock hard, would not compress. I have also had brake flex hoses decompose internally and act like a check valve, where it would not allow the caliper to depressurize, so after brake application it would keep one caliper engages (I pulled over and loosens the brake line to relieve the pressure to release the caliper, than drove it home using only the parking brake)
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

Erikwi
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Posts: 63
Joined: Fri Mar 13, 2020 3:31 pm
My tercel:: 1988 stock auto
Location: lacrosse WI

Re: brakes

Post by Erikwi » Sun Jun 21, 2020 10:12 pm

ok
it works with the engine running
either at idle or driving, gives up after two stops. i tried pumping the brakes and it did not have affect.
it seems to work ok if i do not let the brake pedal reset all the way, meaning if i pump the brake from 1/2 to full stroke i have power...
until it resets.

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: brakes

Post by Petros » Tue Jun 23, 2020 12:34 am

the vacuum is bleeding off when it is not supposed to be. I do not know why it would do that. holds vac, than will not hold vac.

funky check valve. partly torn diaphame that acts like a flapper valve, held close it works, gets displaced it will not make a seal?
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

The Professor
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My tercel:: 1987 Tercel SR5 4WD wagon
Location: Western Washington
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Re: brakes

Post by The Professor » Tue Jun 23, 2020 9:53 am

Disclaimer:

Unpowered brakes are not "unsafe," they just require a whole lot more pressure to achieve the same stopping force than is required with vacuum assisted brakes. This goes for any car, not just the Tercel. Most racecars have manual brakes and they seem to stop just fine... :lol:
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon & Turbo-Traction hardtop
1987 Subaru RX 3-door, x2
1987 Subaru RX Type-RA 3-door
1987 Toyota Tercel SR5 wagon
1999 Subaru Forester S
2002 Subaru WRX sedan
2019 Subaru Outback 2.5i Limited

Erikwi
Advanced Member
Posts: 63
Joined: Fri Mar 13, 2020 3:31 pm
My tercel:: 1988 stock auto
Location: lacrosse WI

Re: brakes

Post by Erikwi » Thu Jul 02, 2020 1:34 pm

update

i dont know, the car sat for two weeks, and the whole time it held 20" vacuum in the diaphram so i really do not think its a bad check valve?

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