Clutch pedal immediately loses pressure

[VeryWell]

After much searching around I haven’t been able to find a thread about this and it’s been driving me nuts.

A couple months ago I replaced the engine in my 95 Runner with a rebuilt, and ever since I cannot for the life of me get the clutch pedal to build and keep pressure. I was able to shift it into first and drive it around for a bit but here’s my issue:

I can pump the pedal like an ape for a minute or so and it builds up pressure and snaps back like it should. But if I let it sit for a second the pressure goes away. And I can hear an audible hiss like fluid is getting back through a seal? I’ve bled about 2 tall cans of dot 3 through this thing until no bubbles appear but that didn’t fix it.

I’m just getting into working on cars and the engine was my first big project so I’m struggling to figure out what this could be. Thanks in advance.

 

[4Reak Show]

For the amount of money they are, toss in a clutch master and slave cyclinder with AISIN products. That's the OEM brand. I think I got a set for like $95 or something on eBay. It sounds like there is an internal leak inside the master cylinder. Not worth the hassle. The clutch hydraulic circuit is simple. Replacing those 2 pieces with quality new parts rules out all the moving parts of the hydraulic circuit..

That being said, since you did an engine, what was the physical clutch's condition?

 

[VeryWell]

Thanks for the reply 4Reak Show. I’ll probably take your advice with the OEM cylinders just for peace of mind. Just a bummer since I’ve already gone through 2 masters thinking they were the culprit.

The clutch worked perfectly before I messed with it. On a buddy’s advice I replaced the master and slave since I had everything apart anyways.

 

[4Reak Show]

What brand of hydraulics did you use on the first go round? I had a box store brand initially when I did my trans swap and the first master was bad out of the box. Ten years later I decided to change both to AISIN and the master (which was from the same box store) had a decent outer seal leak. The slave cyclinder (yup, also a no-name) had a slow leak for a long time that didn't show itself until I changed it and took it apart. All gunked up and crummy looking inside the piston bore.

I can't promise it'll fix your issue, but there is a reason Toyota has the reputation it does. So it's wise to at least upgrade it all to the stuff that's stamped AISIN in the casting, same as the day it rolled off the floor. I wasn't a believer until I dove in myself. There is a difference from my experience.

Edit: I wanted to ask: did you do a good bench bleed of the master? I've seen it where air gets trapped in the end of the stroke, and the pedal itself may not achieve the master's full stroke, hence leaving a tiny bit of air stuck in it. Bench bleeding is simple (a bit messy) but is damn near fool proof on results.

 

[VeryWell]

I used off brand for both from Rockauto. I replaced the master again with a Duralast from autozone but that didn’t fix the issue. I’ll order some Aisins and update you when I get them installed. And yes I did bench bleed the master but I’ll make sure to look up a video about it again and make sure I do it correctly. Thanks again!

 

[fourwd1]

A.few years ago I replaced both with Asin parts from RA, no problems.
(The slave was bad )

 

[VeryWell]

Update

Quick update: replaced both cylinders with Aisin, bled the clutch and... no luck. Thinking it might be a crack in the line somewhere. I’m considering getting one of those stainless steel braided lines from Summit Racing if you guys think that would fix the issue.

 

[VeryWell]

A.few years ago I replaced both with Asin parts from RA, no problems.
(The slave was bad )[/QUOTE/]

Well I gave up trying to figure it out. Called a mobile mechanic to look at it and he found that when I installed the rebuilt engine I forgot to re-mount the clutch cable bracket and the exhaust crossover pipe had snagged the rubber hose and linked it. Easy fix

 

[4Reak Show]

That's awesome. Shouldn't be too bummed over that! Solid, simple resolution.