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New 620 owner here!


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That's was what I was trying to weigh, whether it makes more sense to wait or not so I was checking for pricing. Mike I appreciate all the info. I'm thinking I'm going to need to pull this trans then and see what's going on with the reverse issue. 

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Mike, I came across a guy locally selling a 5speed supposedly out of a 78 280z. So I saw from an old post of yours how to tell if it’ll work with the L series engine and it looks like it will. Top bolt on left of center line rib. I measured it from end of tail shaft to the end of the bell housing and it was 32”. 

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he’s willing to practically give it to me.

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If you take a straight edge and but at the back of the case and come up level with the front, about 9 " and measure horizontally front to back it's 31.5.


That is an L series FS5W71B consistent with being from a '78 280z. It does not have any switches so not from a truck that needs emissions switches, the 280z is EFI. The slave is also from a car, the truck has the flex line come in from the front.


If you shift it into first gear, lightly clamp vice grips on the input spline set at 12 o'clock, mark the output spline in a similar fashion you can prove this is a mid ratio transmission. Turn the input spline 20 times while counting the output spline turns....


5.5 turns............ wide ratio with a 3.592 first

6.0 turns............ mid ratio with a 3.321 first

6.5 turns............ close ratio with a 3.062 first (only the '80 and up 280zx non turbo had this and this ain't it)


The mid ratio is a great all round gear set for any vehicle

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It's as 'drop in' as there is for any '74-'79 620 truck. A good idea to change the rear seal. The old one may leak it may not it may start leaking later. Easier to do now that taking the drive shaft out later and doing under the truck.


GL-4 oil 80w90 is fine. Do not use GL5 no matter what they might say. I find synthetics tend to seep past old seals and gaskets. Next oil change in 5 years 30k miles. The drain bung on the bottom has a magnet, be sure to clean so you can look at it in 5 years. 

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On 7/16/2021 at 6:07 PM, 280Dan said:

Would you also recommend removing those rubber bump stops

IMO keep bump stops, you can swap them out to a lower profile one but the point of them is to keep the axle from making direct contact with the frame.

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So I got the 4 speed out after removing the passenger side torsion bar. Having a lot of difficulty getting the donor trans in however. I realize swapping a trans on your back in your 30s isn’t the same as swapping one when you were in your teens lol. Does anyone have any tips for getting the trans back in solo? Ie positioning, rotating, etc. I’m trying to avoid bothering a friend as it’s not most enjoyable thing to do in 80+ degrees. 

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41 minutes ago, datzenmike said:



Pull out of the hole in the floor and push it back between the floor underside and the torsion bar anchors.

That’s what I was thinking but when I do that the bell housing doesn’t seem to clear the bottom of the clutch. I’ll try again thanks for the response Mike 

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So after some help from a friend, we were able to tilt the motor enough to get it in. While trying to break the fill plug free, my arm ended up being the casualty of a hot wrench that slipped…



Drove the tuck yesterday and felt great, trans shifted smooth. However, I sprung an oil leak which seems to be coming from the rear main. Soooo trans will be coming back out. Shame on me for not replacing it while the trans was already out. 

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I'm a old time datsun lover but new 620 owner as well here in Australia.  Had a 510 20 yrs ago.  Down under the sr20 is a very common swap for 510s here.  A sr20 turbo with an exhaust wi go close to your 250hp at the wheels and if maintained will last a long time.  Have seen my brother in laws s15 sr20 go from stock to over 1000hp...at those numbers she ain't reliable...but fun lol.



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Okay so small update. I replaced the rear main seal and clutch today (figured just replace it since the trans was coming out again). It’s amazing how much quicker things go when you use a lift and air tools lol.

I started to notice a higher pitched whistling noise that comes when I let off the gas and the throttle is “closed”. It goes away if I accelerate.


Separately the engine has been violent when shutting off. I turn off the ignition and the motor kind of bogs down, shakes heavily and then sometimes backfires.

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You likely have a small vacuum line off to cause the whistling. Does it idle alright? If it didn't and you turned the idle speed up this is the cause of the dieseling or 'run on' after shut down.


Check the block vent hose to the PCV valve, left rear under the carburetor on the intake manifold. There is also a vacuum line from the intake to the air filter housing also near the PVC valve.



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Thanks Mike, I did a little research after posting and learned about “dieseling”…I’m familiar with fuel injection but this is my first carbureted vehicle. I read that it could be a few things, one site said to check the idle adjustment screw and adjust if needed. Mine was tightened all the way in so I backed in off about 1/8 of a turn and it increased the idle a bit but didn’t seem to have the run on after turning off. Shortly after I noticed a vacuum leak and the eve block off plate the previous owner installed so I need to make a new gasket for that and then recheck.





I've also been wanting to clean up the engine bay and remove any unnecessary components since it doesn’t need to pass emissions. So I’ll probably be going through that and some of the wiring that needs to be fixed for the gauges.

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I can't see the by-pass hose from the intake to the thermostat housing. There's a fitting on the intake between the two pair of runners at the base of the carb. You really should have that connected and running.*


I don't see the vacuum advance hose either. This improves throttle response and betters part throttle mileage. Should keep that functional.


The purge line on the canister is also missing and should connect to the vacuum advance line. The disconnected hose should go to the vacuum in the intake. Easier to keep this operational than letting gas fumes into the cab. It is absolutely benign in operation.


I've always thought block off plates look hokey. And here is a perfect example of removing 'emissions crap' and causing problems. (not you but the PO) All you need do is pull the hose off the EGR and it stops working and it never leaks.


I see that the air injection pump and plumbing is gone and good riddance. Though it doesn't draw a lot of power it does draw some unlike most of the other emissions equipment. That round blue thing bottom right is the air filter for it... it can go too.


Is that an EI matchbox distributor? I can't see the matchbox.**


* and ** this could be explained away if this is a '75-'77 L20B swapped in. Is that a points distributor? Is the head a U67?

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