Clutch jammed!! 1987 D21 SD25

Dealing with all subsystems specific to the diesel powered Datsun-Nissan 720 pickup trucks.

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niseamer
Posts: 19
Joined: 6 years ago
Location: Ucluelet, B.C. Canada

Clutch jammed!! 1987 D21 SD25

#1

Post by niseamer » 6 years ago

Hi Folks

Looking for some suggestions...

I just put in a transmission from a newer truck (FS5W71C). While I was at it I replaced the engine with another SD25 with less time/miles on it....the other one had 500K km and still ran well but getting a little tired.

I had to swap the bell housing of course since the tranny came out of a gas truck.
So...I put the transmission on the engine and then lowered the lot into the truck and after much (and more muches) fiddling got it going and ready to test.
When I first put it in the truck and hooked up the clutch it seemed to work fine although one time the clutch pedal was slow to release from depressed position...though when it did release it came up as normal. That had happened a few times over the two and a half years I have had the truck so wasn't too worried about it ~ perhaps I should have been..?..

Tonight when I went to take it for its first test drive, I discovered that I couldn't push in the clutch. It is stuck all the way back (released) and can only be moved about a 1/4" or so. It is like a hydraulic lock as though it is pushing against oil...not spongy like air. I climbed underneath and the slave cylinder is out (clutch is disengaged). This seems very odd to me as it is the opposite combination to what it should be. I tried to bleed some fluid out of the system to see if it would release but it didn't release - there is a little "distributor gizmo in the line where there is also a bleed screw (or may to accommodate one). I tried to push the slave cylinder back in but couldn't...I didn't get a bar to try to pry it - yet!

I am wondering if there is some way for the slave cylinder to be extended but not return and then for fluid to beed in behind the master cylinder so it is full while the slave cylinder is extended...resulting in a total locking of the system?
Or has something happened inside the clutch mechanism (in the bell housing)...which strikes terror into the heart of someone who has just installed it out in the yard and would have to remove it out in the yard.

Naturally the 'take-apart' option is a last resort scenario since I really have no way of lifting (or more to the point 'moving') the transmission while the truck is on gravel (usually wet!).
I can't figure out what would have happened in there ...or what I would have missed or installed incorrectly to cause this issue.

Any help would be greatly appreciated.

Thanks all

Niseamer

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asavage
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Re: Clutch jammed!! 1987 D21 SD25

#2

Post by asavage » 6 years ago

niseamer wrote:I am wondering if there is some way for the slave cylinder to be extended but not return and then for fluid to beed in behind the master cylinder so it is full while the slave cylinder is extended...resulting in a total locking of the system?
Yup, that can happen, as it did to you.

I'm sure enough time has passed that you've already figured this out for yourself and repaired, but . . .

Generally, I've only seen this happen with a bad clutch pressure plate. You take it apart and all the diaphragm springs are bent up and won't push the throwout bearing and fork back, and that can get the hydraulic actuating system in a state like you found it.

I'm posting this for the other poor folks who find their way here via a search engine in the future.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

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