Replacing a Clutch in a Datsun 620 pickup
Scott’s little Datsun pickup has had a long and happy life. The speedometer quit working a long time ago so all we know is that it has well over 300,000 miles. Recently the clutch started slipping so he brought it home for a clutch change. There was also a noise when he depressed the clutch so we thought it might have a bad input bearing on the transmission as well. We were prepared to reinstall the old four speed that was pulled years ago to make room for a five speed.
We began by securing a clutch kit. The kit came with a new disk, pressure plate, throw out bearing, pilot bushing and an alignment tool. We were somewhat surprised that the local parts store had the kit in stock for this old truck.
We put the truck on the lift and removed the drive shaft. The drive shaft is in two parts so I separated it in the muddle and left the rear part attached to the rear differential and just removed the front section.
Next, we supported the transmission on a stand and removed the cross member and mounting pad.. Then we had access to pull the speedometer cable. There were two sensors on the side of the transmission so we disconnected the wires and labeled them. Then we disconnected the shift lever from the transmission. We should have done this from the top before lifting the truck, as you will see later. We also removed the clutch slave cylinder.
Next we pulled the starter. Again this would have been easier before lifting the truck. Scott used a ladder while I assisted from below. We measured the position of the torsion bars and then loosened them to get the ends of the bolts out of the way. They block moving the transmission backwards.
Next we removed the bolts that secured the transmission flywheel cover. Ten we used long extensions and a flex joint to remove the four bolts that hold the transmission to the engine. With these out, we were able to slide the transmission back from the engine. We were not however able to remove the transmission from the truck. There is simply not enough room to get the transmission over the center part of the frame and past the flywheel with the pressure plate in place.
At this point we checked the input shaft to see if we were really going to have to change the transmission. It seemed fine; in fact it felt tighter than our spare, so we elected to leave it. Since we could not get the transmission out of the truck it seems a good choice. We still could not remember how we had swapped the transmissions years ago.
We then removed the pressure plate and inspected the flywheel and disk. The disk showed very little wear and the flywheel still had the machine marks from the last time it was resurfaced. We were not sure why it was slipping or where the noise was coming from.
After careful inspection we saw where the pressure plate was contacting the clutch disk when released. That was likely the source of the noise he occasionally heard. Also, the throw out bearing felt a little rough. We elected to change all the parts in the clutch kit since we had them just to be safe.
Pulling the pilot bushing became the next challenge. One tool I have never added to my collection is a pilot bearing puller. Scott went to town to get one from the Advance Auto loan a tool program.
While he was gone, I looked at how to get the transmission out. It was in the way of extracting the pilot bushing. I finally realized that it was hitting the floor of the cab and that there was a panel around the shifter that could be removed to get more clearance. I lowered the truck and removed the center console and the plate around the shifter. It would have been much easier to remove the shifter from this side. With the panel removed, the transmission could be tipped up and there was just enough room to remove it from the truck.
With the transmission out of the way we focused on pulling the old pilot bushing. We set the tool in place and followed the instructions carefully several times. Each time the tool would pull out and the bushing stayed in place. We finally compared the puller to the new bushing and quickly saw that there was no way it could catch the end of the bearing. The fingers looked bent or simply miss shaped. I put the fingers in the vice and reshaped them to fit. I also ground off a little of the face to get a better grip on the bushing.
The next time we tried it, the bushing pulled out easily. We tapped the new bushing into the crank and moved on to he next step.
We set the clutch disk in place makes sure to turn it the correct way round. There is a story that floats around all our family reunions on how my Uncle and Cousin installed a clutch disk backwards so we made sure that we did it right.
With the disk sitting on the alignment tool, we set the pressure plate in place and carefully brought down the bolts evenly and torqued them to specs. Next we pressed the old throw out bearing off the sleeve and pressed on the new bearing. We installed it on the fork and snapped the fork in place in the transmission.
Then we lifted the transmission into place. At least we tried to. There was simply no room to get the transmission past the center part of the frame with the pressure plate installed. We looked at every option and finally decided to remove the pressure plate and se the transmission up before installing it.
There is plenty of room to work inside the bell housing of the transmission. But the pressure plate needs to be slipped over ht input shaft before the disk is set on the alignment tool to have enough room to get it in. We retorqued the pressure plate bolts and then prepared to slip the transmission in place. We used the supplied lube on the input shaft before installing it.
The transmission easily slid into the clutch disk and we reinstalled the mounting bolts. Every thing went back together easily with the exception of the slave cylinder. I had to loosen the bleeder screw to get the piston to retract. Once I did it fit easily.
As we were putting up the drive shaft, we noticed that one of the U joints was rough. I pulled it out and replaced the joint while Scott finished up the center console replacement.
We reset the torsion bars to the measurement that we made before and put the transmission mount and cross member back in place. Reconnecting the speedometer cable was simply a matter of aligning the key and slipping it in.
With it all back together, the slippage and the noise was completely gone. In the process of removing and reinstalling the transmission we also swapped the old fluid for synthetic. Scott says the shifting is greatly improved in the old transmission.
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