Can't seem to bleed clutch

[enbay1]

Hello all,

I've been having an issue where my transmission grinds into reverse after doing clutch work. (replaced slave and rebuilt master.) I've bled it about three times, and every time I get bubbles. After the bubbles stop I think I've fixed it, but it still grinds into R. I'm looking for any help. Ive got lots of brake fluid and a helper on call!

[datzenmike]

I you repeatedly get bubbles out of the system after you are sure you got it all out, then the master or the slave is letting air in. Check the fittings are snug on the hard and flex line.

 

You have that clutch damper bolted to the firewall. Does it have a bleeder fitting?? You can always remove the damper and join the hard lines to get rid of it.

[enbay1]

I'll check the fittings. I did replace the hard line from MC to damper. The damper does have a bleeder, I've used it. I also went and bought the part to eliminate the damper.

EDIT: Fittings checked, all tight. I also did a 3 pump bleed into my single-person bleeder and the fluid was all clear and bubble-free. However the truck still grinds into reverse. I'm 99% sure there's still air in there somewhere.

[datzenmike]

What year 720? Did you swap transmissions?

 

 

 

What exactly did you keep and what did you replace when you did the 'clutch work'????

[LenRobertson]

Unlikely it is part of your problem but easy to check - you need to have a slight amount of free play at the pedal before you feel the hydraulics engage. Nothing like the amount of a mechanical clutch; more like 1/16" or so. I put in a new clutch master cylinder and this ended up being my problem, not hydraulics. Since you didn't change your MC you will probably still have the original free play but check anyway.

I'm not familiar with the different rod lengths (some of which are adjustable) at the slave cylinder but that is another possibility. You need to have about 3/4" movement at the slave when the pedal is depressed. Hopefully someone will post a more accurate number if 3/4" is too far from correct.

And there is the depressing possibility that the new slave you installed is defective. Never know anymore about new parts.

 

Len

[datzenmike]

3/4" will probably be enough movement but the Nissan slave spec is 1.18" of travel. (not that you need it all)

[racerx]

U bench bleed mc before install?

[enbay1]

I've got an '85 720 4x4 with 5 speed manual. I put a clutch, pressure plate, pilot bearing, and throwout bearing in. I bought a new exedy slave cylinder and rebuilt the OEM master cylinder.

Len - I probably don't have any play in the pedal. I took off the lock nut and the connector when I rebuilt the master ( to remove rust). Why's the free play important?

Tomorrow I'll:

Check for pedal free play

check the slave cylinder's throw.

I'd be ok with the slave cylinder being bust as it's right there. If it's the pressure plate I'm going to be a little miffed.

 

Racer, I did not bench bleed the mc before installing.

[Crashtd420]

 

Racer, I did not bench bleed the mc before installing.

 

Start here ^ ....

I used vacume bleeders and everything.... no bubbles good fluid flow still no clutch.....

 

Bench bleed the master....

Make a small line right at the master going to a catch container not back in the master....

When I did mine I pressed the pedal down, before I released it i covered the end of the brake line, released the pedal and it drew in fluid.... did that a few time and you could feel the difference...

reconnect and bleed the slave,

adjust you pedal free play...

And even the slave cylinder push rod if you can... not sure if the 720s were adjustable....

[LenRobertson]

I honestly can't say why you need a slight amount of free play at the clutch pedal. It's too early in the morning and coffee hasn't kicked in yet. Later in the day I might be able to fabricate an explanation which may or may not be correct. :D

 

I rebuilt my 510 slave and put in a new NAPA clutch master cylinder. Bled it and still it wouldn't go into gear without grinding. Probably datzenmike told me about checking for free play. It turned out the threaded length of the rod on the new master was so long it was pushing against the pedal arm and not allowing proper adjustment to give free play. I had to hacksaw a slight amount off the threaded end of the brand new rod. I love made in China parts; always a guessing game if they will work or not! You won't have this same problem since you are using your original master but if you changed the position of the clevis on the threaded rod it is possible you lost the needed free play. Easy to check and relatively easy to re-adjust.

 

Len

[datzenmike]

Push rod must return to it's rest position so it goes through the full stroke to move fluid.

[enbay1]

Just went out and adjusted my pedal. I've now got the 1.0-1.5mm free play at the top, and a full stoke of about 7" (out of spec from the 7.04-7.44 I'm supposed to have, but there's no adjustment left!). Going to try bleeding some more and see where that gets me.

[enbay1]

I bled my clutch some more today hoping to find why it won't throw the slave cylinder far enough. I measured the travel of the slave piston at .5", so something's wrong. Is my next step here to remove the master and bench bleed it? Should I bypass the damper?

[datzenmike]

The slave can only move as far as the master tells it to. If it's only moving 0.5" then this is all the master is sending it. If you have all the air out then the master is not working properly. If you rebuilt it, maybe a seal is in backwards or torn (easily done) Did you clean the master's bore? Was it scratched?

 

New ones are $80 @ Nissan so probably half that at NAPA. Don't expect much from a $9 made in China POS.

[enbay1]

I honestly expect air somewhere. The bore of the master looked perfect, and the rebuild kit was a piston with seals I dunked in fluid and put in there. Backwards would be difficult, ripped is a possibility.

[wayno]

I honestly expect air somewhere. The bore of the master looked perfect, and the rebuild kit was a piston with seals I dunked in fluid and put in there. Backwards would be difficult, ripped is a possibility.

 

It's not hard to put plungers and seals in backwards, I bought a brake master (rebuilt in China?) that had the rear circuit plunger in backwards, didn't work worth a shit, took it back.

Either the clutch master is bad, the slave is bad, the pedal isn't adjusted correctly, or you have the wrong throw out bearing collar installed and the clutch arm is hitting the case and cannot move any farther back, but would need photos at the proper angle to diagnose that.

It's hard to figure stuff out using a screen and keyboard without photos, did the throw out bearing come on it's own collar in the kit, or did you press the bearing on the collar yourself?

[enbay1]

I'm currently waiting on a fitting to bypass the clutch damper as I expect that's where my air is and I was mostly looking for an excuse to get rid of it.

 

If you can tell me what to take pictures of I'd be more than happy to supply you with them. I pressed the bearing into the carrier myself.

 

Spring goes on plunger, plunger goes into bore. I'd be surprised if I could mess that up.

 

There's a chance my pedal is still not right, but based on my fooling around down there with the manual I could not get it into spec (see previous post.)

[datzenmike]

From front to back..... spring, piston assy. (in your picture the bottom end to the front) then the push rod against the piston, stopper spring to hold it in place and the dust boot covering it.

 

In operation the long spring should return the piston and the push rod back against the stopper spring. This is it's rest position allowing any residual hydraulic fluid back into the reservoir. You will need some slight pedal free play for this to work.

[LenRobertson]

Just went out and adjusted my pedal. I've now got the 1.0-1.5mm free play at the top, and a full stoke of about 7" (out of spec from the 7.04-7.44 I'm supposed to have, but there's no adjustment left!). Going to try bleeding some more and see where that gets me.

 

I measured the free play on my 510 clutch pedal. Rather embarrassingly it is about 5/8"! That is bordering on what a mechanical linkage clutch free play should be. I suspect that isn't what I originally adjusted it to. Maybe something has worn in in the pedal linkage since my original adjustment. I'm going to try taking some of that free play out if I can get to it before it gets too hot one of these mornings.

 

However, my clutch does work. Your 1.0 to 1.5mm doesn't seem like very much free play. 1.5mm is about 1/16" which maybe is enough. If you have found a factory spec that says this is enough, ignore my thoughts on the subject.

 

When you say there is no adjustment left, why not? Maybe use a mirror to check and be sure the end of the threaded clutch rod isn't pressing up against the clutch pedal arm.

 

Len