85 300zx clutch

I’ve been having shifting issues in the 85 z31 i bought recently. on cold startups its impossible to get it into first and sometimes second. i took out the master cylinder and bench bled it then bled from the slave so i could know it was neither of those and it was good for a bit until this morning. first and second were gone (second was grinding) so i had to start it in first and go straight off that. nearly everytime all problems resolve after driving for around 20 minutes but it did not this time. changing gears with the engine off feels completely fine. it was EXTRA cold this morning if that means anything. any suggestions?

The clutch master cylinder may be leaking internally and not producing enough hydraulic pressure to operate the clutch.

Tester

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Yeah, old rubber cups can lose flexibility in the cold. Any rebuild kits available (if there’s no corrosion in the bore)? Or just replace it.

I just checked Rockauto, the master cylinder is cheap, lest than $20, same for slave. I’d replace them both.

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theyre both only a couple months old?

Is there a flex line that might be deteriorating on the inside? Sometimes old rubber brake line develop blockages.

You can get bad parts.

Look at it logically.

The master cylinder is what produces the hydraulic pressure.

From your description, there isn’t any.

Tester

Are you asking us? How are we to know?

Are you telling us? Then don’t end the sentence with a question mark!

I once had a new or factory rebuilt brake master cylinder that did not work. Exchanged it after much messing around. The new one was fine from the get-go. Good luck to you.

could definitely be the line. thanks for the tips i didnt know about the rubber reacting to cold

Blockquote very true i understand. ill replace em later today. does the shifting while the engines off eliminate any potential for gearbox issues? my buddy mentioned a synchromesh problem and spooked me. also would old transmission fluid mean anything?

With engine off, the transmission gears aren’t rotating.

So it’s easy to shift thru the gears.

With the engine running, and the clutch doesn’t disengage when the clutch pedal is depressed is like trying to sift thru the gears without stepping on the clutch pedal.

Tester

If you don’t know how old the transmission fluid it, replace it with the factory-recommended fluid. Do that before making other repairs, just on the (slight) chance it helps.

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Try quickly pumping the clutch pedal 2-3 times before making the otherwise difficult shift. Does that have any positive (or negative) effect? If so (positive), pretty good chance CMC needs replacing. I’ve had to replace my Corolla’s CMC about every 10 years, symptom is hard to shift into first or second gear from N w/engine idling. I’ve learned to replace the CMC very soon after first noticing this symptom, b/c it won’t be long before car is un-driveable.