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Rock hard brake pedal issue help


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 I bought my KP61 after it had sat unused for over 8 years. I replaced the fuel system. Engine and transmission and bled the brakes. But the pedal was rock hard and had little stopping power. "No problem" I thought. And I replaced the brake booster, master, all flexible lines, the calipers, rotors, drums and rear wheel cylinders as well as shoes and pads.

Yep. Same crap!!

Hard pedal and almost no brakes. Just like before I did ANYTHING. The brake booster holds vacuum for days and the vacuum is very strong. The vacuum line is an actual vacuum line and the check valves are new.

My first thought was that the new booster is also no good. But I noticed when I bled the system that the rear brakes bled easily and quickly. But the front brakes required more work. With less flow. I didn't think much about it at the time. But do you think I could have a blocked steel line? I've never heard of that before. And would a blockage or partial blockage to either front wheel after the "splitter" make for a hard pedal? Or would it be more likely in the line from the master before the splitter?

Is this something anyone has encountered before?

This is a U.S. spec 1981 Toyota KP61 Starlet RWD. With stock brakes. Double master. Separate front and rear reservoirs. I'm not yet familiar with all of the lines or where exactly they go. Or if a blocked or partially blocked line would cause a hard pedal.

I cant really drive because I can barely stop.

 

 

20181002_163151.jpg

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You probably need to adjust the master cylinder pushrod. I'll bet there's no free play in it.

images?q=tbn:ANd9GcQQg7j4GdaERmcl5oUNnfh

 

 

 

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When there's no free play the piston can't fully return and let the fluid flow back into the Res.

Resulting in a very hard pedal and sometimes locked brakes

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If there was not much flow when bleeding the front. I would start at the master cylinder, remove the brake line, for the front system, from the master cylinder and pump the pedal, you should get a lot of fluid. If you do, reattach the line the line to the master cylinder, and disconnect the other end of it from the "splitter", pump the pedal. If you get lots of fluid, move to the next join and so on.

 

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Thanks

I have the master and booster both out of the car.

Tomorrow I'll get the front end up and pull the wheels off to blow compressed air into each line.

There's not much room under the hood with the master and booster installed since it now has a later model 16 valve 4 cam motor in there.

I'll report back what I find

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22 hours ago, yetchh said:

I had an issue like that when I bled the crown brakes a while back, no idea what it was but blew air through the system backwards and it fixed the problem.. 

That's what I'll try first. If just because it sounds like the easiest thing to do with the master and booster off.

I'll get some clean rags ready and see what kind of crap comes out of there.

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22 hours ago, Adoom said:

If there was not much flow when bleeding the front. I would start at the master cylinder, remove the brake line, for the front system, from the master cylinder and pump the pedal, you should get a lot of fluid. If you do, reattach the line the line to the master cylinder, and disconnect the other end of it from the "splitter", pump the pedal. If you get lots of fluid, move to the next join and so on.

 

I must say that that makes a great deal of sense.

Thanks.

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1 minute ago, ZEROPILOT said:

 

There's not much room under the hood with the master and booster installed since it now has a later model 16 valve 4 cam motor in there.

It's okay, you can say "4AGE" in here, it's a safe place. 4 cams! Where did you fit those? 

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22 hours ago, tortron said:

You probably need to adjust the master cylinder pushrod. I'll bet there's no free play in it.

images?q=tbn:ANd9GcQQg7j4GdaERmcl5oUNnfh

 

 

 

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When there's no free play the piston can't fully return and let the fluid flow back into the Res.

Resulting in a very hard pedal and sometimes locked brakes

This was one of my initial thoughts. I adjust the pedal. Adjusted the booster pushrod and at one point even made a shim to slip between the master and booster.

None of it made a bit of difference except pedal height.

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15 minutes ago, Adoom said:

It's okay, you can say "4AGE" in here, it's a safe place. 4 cams! Where did you fit those? 

I did say 4 cam. Didn't I? Sorry.

It's a drivetrain yanked out of an '88 SR-5 COROLLA. AE86.

Rebuilt and mostly stock.

Rear end from a Celica (U.S. Starlets had no limited slip diff)

So it had about 60 hp in 1981 and now its pushing maybe 115-120.

It's pretty fun! At least it would be if the brakes actually worked.

This is one of a few vehicles. So it wont get much use anyway. But at this rate. I'm afraid to use it at all.

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I got a spare booster, master, lines and junction blocks for parts today. These parts are very hard to find. But at least I have a few spare parts if I find a clogged line or something rusted closed.

Its night time here in the east coast of the USA.

I'll get on it in the morning and report back.

Thanks

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3 hours ago, mjrstar said:

I had a seized proportioning valve on my kp years ago. I would crack one bleed nipple with the pedal hard down and see if it makes the pedal sink. 

Thank you for that.

I've got the whole thing taken apart and I'm blowing compresses air through.

I just found a blockage in the left rear from the proportioning valve. But now there is flow. A chunk of what I think is solids from some 35 year old brake fluid came out. And now air can flow both ways.

The 4AGE makes access to the proportioning valve very difficult because the intake manifold sits right up next to it. So removal might be needed to remove the valve for cleaning.

The new booster and another master have now been installed. So, soon I can check the action.

And YES I know that that is a "wonky" vacuum hose.

I'll use a correct but ugly one for testing that is less prone to collapsing.

20181119_142714.jpg

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Certainly worth whipping the whole thing apart and cleaning it out. I had brake balance issues on mid 90 toyotas and found both times TINY bits of dirt in the proportioning valves. Different cars. Pulled apart and all cleaned up for perfect balance come WOF time. 

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On 23/11/2018 at 20:05, Muncie said:

Does your brake vacuum line have a check valve in it? Might be in backwards or just jammed shut.

It's mentioned in the first post the check valve is in place and new. Still worth testing it's working properly or swapping out. 

OP, have you tested the booster with a vacuum pump to check it can hold a solid vacuum (not just a "by ear" or "feel" test)?

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On 19/11/2018 at 15:29, tortron said:

How old are your rubber lines? They can swell up on the inside when old

Got that tee shirt. Car sat for a couple of years and back brakes were jammed when tried to move it. The rear rubber brake hose had collapsed inside. Cut the hose off and bing back brakes freed up

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