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Discussion Starter · #1 ·
Hi!

I have a 1991 rev 1 mr2 na (no abs),

Ive recently had to replace a caliper as the piston got stuck (front right), and in doing so I decided to flush my brake fluid. However I cant quite get all of the air out. I have tried multiple techniques and I am at the point where there is no air in the lines and I still have a spongey pedal feel. I have however realised that when I changed the caliper I re-used the old copper washers on the banjo bolt... So I will change those tomorrow and see what happens.

However more concerning... When pumping the brake on idle, my revs will increase from maybe 1200 rpm to 1800rpm! When holding this will not happen.

I'm not sure if this is normal because I understand the brake servo creates vacuum and is powered by the vacuum into the engine block. However I have done some tests, and my brake servo is air tight and functioning fine. There are some tests in the manual.

After I stop pumping the brakes the engine returns to idle as before.

Is this normal? Or is this because maybe I have a vacuum leak somewhere? However I would have assumed that a vacuum leak would be causing the revs to drop if I pump the brakes? Or do we think the valve in the hose is faulty?

I'm not really sure :/

Thanks guys.
 

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Discussion Starter · #3 ·
Vacuum leaks on an NA will increase engine speed due to sucking in more air.

Is the caliper bleeder facing up or down?
Caliper bleed nipple facing up, ok so will follow the hose going into the brake servo from the manifold to look for any splits or to see if it has perished at all? Thanks
 

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Caliper bleed nipple facing up, ok so will follow the hose going into the brake servo from the manifold to look for any splits or to see if it has perished at all? Thanks
All good. It is possible to mount the calipers backwards so the left is on the right and right on the left making it impossible to bleed.
It's an interesting description on the RPM increase. Maybe remove and plug the hose on the booster to rule out the hose/pipe to the engine. Then you can see if it is the booster leaking.
 

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Discussion Starter · #5 ·
All good. It is possible to mount the calipers backwards so the left is on the right and right on the left making it impossible to bleed.
It's an interesting description on the RPM increase. Maybe remove and plug the hose on the booster to rule out the hose/pipe to the engine. Then you can see if it is the booster leaking.
Okay, ah yeah.

Okay, so essentially there has to be a problem with that hose for the revs to increase?
 

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Discussion Starter · #7 ·
No. Not necessarily. Based on your description the hose/pipe is fine otherwise it would be at 1800rpm all the time.
Okay thank you, I think removing and plugging the hose is a good idea :) I guess there could be a small leak in the servo. Thanks
 

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Okay thank you, I think removing and plugging the hose is a good idea :) I guess there could be a small leak in the servo. Thanks
Could be. Interesting that it showed up after changing the caliper. They aren't really connected as such.

Did you let the master cylinder empty of fluid? If you did then the master might have air in it an need to be bench bled. No amount of bleeding at the calipers will get that air out.
Also have you bled the other 3 calipers too? Left rear first, right rear next, left front then right front. And before anyone explodes with "that's the wrong sequence" the car is RHD.
 

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Discussion Starter · #9 ·
Now you say it, I do remember seeing the fluid a bit below the minimum mark once but there was always always fluid in the reservoir. And yeah I did furthest first,

So handbrake down, jack car up, hose on. driver pumps pedal 3 times so its hard, i crack nipple, i tighten when his foot hits the floor. Do this till no bubbles,

Did this on all corners. Multiple times, the only way air could be introduced into the system is through the banjo bolt on the new caliper I would say, I know I ran the reservoir below minimum but there was still around an inch of fluid in the reservoir. If i see nothing from the washers, then yeah... Will probably have to either bleed the master cylinder or replace it.
 

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Now you say it, I do remember seeing the fluid a bit below the minimum mark once but there was always always fluid in the reservoir. And yeah I did furthest first,

So handbrake down, jack car up, hose on. driver pumps pedal 3 times so its hard, i crack nipple, i tighten when his foot hits the floor. Do this till no bubbles,

Did this on all corners. Multiple times, the only way air could be introduced into the system is through the banjo bolt on the new caliper I would say, I know I ran the reservoir below minimum but there was still around an inch of fluid in the reservoir. If i see nothing from the washers, then yeah... Will probably have to either bleed the master cylinder or replace it.
Sounds like you know what you are doing. The level sounds like it didn't get air in the master. Sometimes over extending the master can make the old seals fail.
Some people like to use a vacuum bleeder too. I'm all out of ideas for now.
 

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Discussion Starter · #11 ·
Sounds like you know what you are doing. The level sounds like it didn't get air in the master. Sometimes over extending the master can make the old seals fail.
Some people like to use a vacuum bleeder too. I'm all out of ideas for now.
Thanks :)
You've given me some ideas, if all fails then the master cylinder seals could well have gone just from age you're right. That's worst case scenario :)
 

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If all else fails, pick up a pressure bleeder. I have had nothing but perfect results with mine, including bleeding a dry master cylinder. I have even use it to push air into the system before doing major brake work, and then when pushing fluid back through it was immediately perfectly bleed. No issues with air getting trapped in the master cylinder.

 

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And before anyone explodes with "that's the wrong sequence" the car is RHD.
I have often heard this "bleed the closest one first" (or is is bleed the farthest one first, I don't remember). I don't see how it makes any difference. No matter what order you do it in, you are going to bleed one line all the way to the caliper, and potentially have other lines that T off of that line that will then get bled later. Which one you do first doesn't matter.
 

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I have often heard this "bleed the closest one first" (or is is bleed the farthest one first, I don't remember). I don't see how it makes any difference. No matter what order you do it in, you are going to bleed one line all the way to the caliper, and potentially have other lines that T off of that line that will then get bled later. Which one you do first doesn't matter.
Yeah thinking about how the brake lines are setup wit the T junctions and the front and rear being separate it doesn't really matter but for people who have less of an understanding of the brake line system in the car it's a helpful way to do it systematically.
 

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I've had good luck with bleeding by setting up a hose that runs up from the bleeder, then down to a can or something. Set it up, crack the bleeder and get some liquid in the hose, then very slowly pump the brake pedal. The extra pressure will make any air pockets smaller and more likely to find their way out of the bleeder. The column of liquid in the hose will prevent air from getting back into the caliper. Do that a few times and you should be good to go. This also works really well for bleeding the clutch.
 
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