Master Brake Cylinder, Booster Nightmare

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mrdance123
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Joined: Sat Feb 21, 2015 9:03 pm
My tercel:: 84 and 85 4wd wagons

Master Brake Cylinder, Booster Nightmare

Post by mrdance123 »

I made the mistake of using a re-manufactured master cylinder. Too late did I realize it was bad. Struggled a long time trying to get a good bleed at all 4 wheels, the front bled out fine, but only a slow flow weak pressure ever made it to rear wheels. Did a lot of pumping bleeding with 2 persons trying to get that going. Finally noticed fluid leaking down the booster underneath the master C, which had a bad seal where the push-rod goes to push it's piston, the fluid leaked out here and was forced straight into the booster during bleeding, a bit leaking out through the mounting flange. I'm sure the booster is now ruined, can hear liquid squishing around inside it while pushing brake with the master C removed. Test driving, the petal is soft with excessive travel, and it brakes at extremely non-linear rate. Braking lightly is ok, then the slightest further increase in petal pressure rapidly brakes harder, making difficult to avoid locking and skidding. It's like the booster suddenly exerts excessive force past the point of light braking, it is nearly uncontrollable. The pads did not get contaminated by fluid, I rode the brakes extensively to burn off any possible contaminants, no improvement.
Any thoughts on how to get the fluid out of the booster.... can it be salvaged?
85 T4 Speedy Blue, SR5, 270-312k, operational R12 A/C, in use.
84 T4 Curmudgeon Copper, 188-294k, my first T4 in 1990, now Dad's daily driver.
RIP - 84 T4 Foxy Blue, 256-288k, engine died 2021, sold to PNP
Sold: 86 T2 Silver, VIN ending 5847, 194k, cherry condition, now in a good home.
RIP - 83 T4 Smokin' Gold, 270k, rusted out body, parted & scrapped
RIP - 84 T4 Quicksilver SR5, 125k, blown engine no oil, had sat 10+ years, parted & scrapped.
RIP - 80 Corolla (purchased new), 0-473k, 358k original engine, rear-ended totaled in 2003.
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Master Brake Cylinder, Booster Nightmare

Post by Petros »

too bad, I always avoid buying re manufactured parts, too many are junk right out of the box. Not worth any savings, but sometimes you have no choice. Get that master changed out. I had the same issue once, need one fast and local parts store cold only get remans, I spend hours trying to bleed the system (with a family member pumping the brake pedal) but kept getting bubbles out all bleeders. finally I took out the new master and bench blend it again, still getting bubbles so I took it back. they were able to get a replace by next morning, but it delayed my departure to return home a whole day.

If the fluid got in the booster seems you should be able to get it out, but you will have to remove it from the firewall (so you can dump it out, put a shop vac on it, etc). Removing is not hard, but you have to get up under the dash, there are (4) 12mm nuts holding it on, and the pin on the brake push rod. you will need a deep socket and an extension with a u-joint helps (can be done with an open end 12mm wrench I think, but it would be very slow).

if the diaphragm is shot (put a vacuum on the vac line nipple to see if it holds), than it is a gonner. I may have an extra stock one you can have for $20 plus shipping if you need one. Frankly I would recommend you get a first gen MR2 booster and master cylinder rather than the stock one, these bolt right in and will improve your braking performance (you need to replace both as a set, booster and master). I wrote a thread on doing brake up grade over in the repair guide section. Factory brakes are too small for this car.

Get it sorted out, do not take risks with bad brakes.

Good luck.
'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)
mrdance123
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Posts: 152
Joined: Sat Feb 21, 2015 9:03 pm
My tercel:: 84 and 85 4wd wagons

Re: Master Brake Cylinder, Booster Nightmare

Post by mrdance123 »

Thanks Petros for sharing your experiences. I wonder why there is not a weep hole in the flange bottom where the master C bolts onto the booster, so any fluid leaking past the piston would just drip down rather than being forced into the booster. There was no gasket there either, just metal on metal. This is my sister's 83 Corolla wagon, not one of my T4's, and very similar. Rock auto has only rebuilt boosters, would you use one from them,or avoid those too?
85 T4 Speedy Blue, SR5, 270-312k, operational R12 A/C, in use.
84 T4 Curmudgeon Copper, 188-294k, my first T4 in 1990, now Dad's daily driver.
RIP - 84 T4 Foxy Blue, 256-288k, engine died 2021, sold to PNP
Sold: 86 T2 Silver, VIN ending 5847, 194k, cherry condition, now in a good home.
RIP - 83 T4 Smokin' Gold, 270k, rusted out body, parted & scrapped
RIP - 84 T4 Quicksilver SR5, 125k, blown engine no oil, had sat 10+ years, parted & scrapped.
RIP - 80 Corolla (purchased new), 0-473k, 358k original engine, rear-ended totaled in 2003.
xirdneh
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My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: Master Brake Cylinder, Booster Nightmare

Post by xirdneh »

When bench bleeding its important not to push too far in.
Love those Tercell 4x4 wagons but they sure suffer from road noise.
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Petros
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Posts: 11930
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Master Brake Cylinder, Booster Nightmare

Post by Petros »

these boosters are pretty reliable, any one from a wrecking yard would likely be a safer bet than a remanufactured one. those should be fairly common, I do not know if they are the same one in the Tercel as the Corolla, not likely they are the same, but it would not be difficult to find out (cross reference part numbers from parts suppliers).
'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)
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