Are short tail 720 5 speeds usable in a 620?

[ahoogakev]

Hello gang, ok an update, first a few months ago I bought a 5 speed from an 85 720 in PYP; I installed it in my 76 King Cab only to find its not very good, it shakes in 5th and the other gears all howl a bit ... so today I went back to PYP and pulled another 1985 720 5 speed,I got it home and I see its a short tail, not long.

I am wondering if the short tail is totally useless for parts or swapping, or not? In other words, how can I change it into a long tail, does that involve swapping out the main tranny shaft ( gasp!) Or will a short tail work in a 620 if you use the ( presumably longer?) 720 drive shaft? Or would the rear tranny cross brace not bolt up? Questions questions!!! If all else fails I can return the thing, I was surprised it was a short tail as its from a 2 wheel drive 720 the same as the first tranny was, it is a FS5W71B for sure since I read it on the firewall data plate.This tranny appears far better just from general appearance,would the 5 speed gears and bearings all interchange? I had to swap the front countershaft bearing onto the bad tranny before it would fit in my 620 front case,that went surprisingly easy considering I never did one before,so maybe I could just swap bearings/ gears and build one good tranny from two? Any thoughts from the experts much appreciated!!! Thanks,Kevin

[ahoogakev]

Just had a new thought this morning, would I be able to bolt the front bell housing case from a 1973 620 with the old style ( I think its called F4W63?) onto this 85 720 short tail 5 speed and run it there, any mods needed,will speedo hook up? ( I have a buddy with a 73 ) I think I read this would work on a 520,but I dont know if that means early 620 also.

Also I see Ratsun has a driveline catagory , I think I am posting in the wrong place ( guess I should be on Ratsun more!) If anyone knows how to move my thread there I would appreciate it a lot, thanks a lot,Kev

[datzenmike]

To convert the short tail to long you would have to remove front and rear cases and remove the mainshaft, disassemble it and swap everything onto the long mainshaft, put it back into the adapter plate and put the long tailshaft back on. Probably easier to replace the growling bearings in the long tail.

 

The FS5W71B parts will not fit the F4W63 from the early 620.

 

You could use the short one with an L series front case and just get a longer front driveshaft. The 720 front driveshaft might be long enough as the frames are very similar. It may be that all you need is that driveshaft.

[ahoogakev]

Thanks a lot Mike, I did a huge google search ( like 5 hours) to find the length of 620/720 driveshafts last night and totally struck out; so thats exactly what I needed to know! I will take your advice and go back to PYP and measure the 720 front driveshaft;if it fits I will be very happy indeed...But I want to clarify when you say quote :

 

The FS5W71B parts will not fit the F4W63 from the early 620.

 

Does that include the front bell housing cover, or were you just talking about internals? It seems to me if the front bell housing cover would swap on , my buddy would have a really nice 5 speed for his 73,I am sure the speedo would be off but at least it would have one, I was checking the OD and I counted 8 1/3 turns so I think its the .83 OD, mated to his 4.38 ( 4.6?) rear end I would think even the 1.6 liter 73 should be able to handle it? Thanks Kev.

[ahoogakev]

Still dont know how to post pics on Ratsun but there might be two pics here:

 

 

http://s946.photobuc...n720tranny1.jpg

 

 

http://s946.photobuc...current=71B.jpg

 

Kev.

Here ya go...

 

.

[datzenmike]

Thanks a lot Mike, I did a huge google search ( like 5 hours) to find the length of 620/720 driveshafts last night and totally struck out; so thats exactly what I needed to know! I will take your advice and go back to PYP and measure the 720 front driveshaft;if it fits I will be very happy indeed...But I want to clarify when you say quote :

 

The FS5W71B parts will not fit the F4W63 from the early 620.

 

Does that include the front bell housing cover, or were you just talking about internals? It seems to me if the front bell housing cover would swap on , my buddy would have a really nice 5 speed for his 73,I am sure the speedo would be off but at least it would have one, I was checking the OD and I counted 8 1/3 turns so I think its the .83 OD, mated to his 4.38 ( 4.6?) rear end I would think even the 1.6 liter 73 should be able to handle it? Thanks Kev.

 

I don't know the length off hand. At worst it will be too long and you can just get it shortened and away you go. Not sure but I think the 720 uses a different rubber isolator on the carrier bearing.

 

"The FS5W71B parts will not fit the F4W63 from the early 620." Nothing at all will swap. The front case comes off the FS5W71B but all the gears are mounted inside the F4W63 case, even reverse. Everything about them is different.

 

I have found that the clutch arm is very close and may work if swapped and the output splines and the input spline for the clutch disc are the same but that's about it.

 

Two different length F4W63 4 speeds. (610 above 510) All gears are contained within the 'waffle' part of the main case.

 

 

FS5W71B with front case/bell removed. All gears and shift rods are 'bolted' to the one inch adapter plate just forward of the tailstock, which is also removable and covers the reverse and 5th gears.

 

 

F4W63 abd FS5W71B clutch arms. Close but not identical.

 

 

The '83-'86 2wd 720 did have a 0.833 od ratio.

.

[ahoogakev]

Thanks for the info Mike,I will check the driveshaft length tomorrow at PYP and then make a decision as to what to do, Gee maybe I'll see another one down there , maybe I can buy it too, what are the chances of me buying the wrong one THREE times in a row???!!! ( please Don't answer that...a fool and his money???!!!) Thanks ,Kev PS, thanks to you or whoever posted my pic for me,here is the truck I am trying to add the 5 speed into:

 

http://s946.photobucket.com/albums/ad306/ahoogakev/Kev76Datsun/?action=view&current=KevOldBlue.jpg

 

http://s946.photobucket.com/albums/ad306/ahoogakev/Kev76Datsun/?action=view&current=2SeatCovers2.jpg

[crackerjack69]

Keep in mind, it's not terribly expensive to have the driveline length changed.

[ahoogakev]

Well I thought I would post an update in case anyone was wondering how my tranny saga turned out, so I went back to PYP as Mike suggested and bought the 720 front driveshaft that matched the 85 720 short tailed 5 speed that I wanted to install in my 76 KC; I found out the driveshaft was about 1 inch too long, but after shortening it all was fine, it installed no problems ( in fact real easy since I had all the bolts broken free a couple months ago installing the bad 5 speed I bought in PYP in January.)

I thought the bad 5 speed had a bad OD bearing since it shook in 5th but wasn't too bad in any other gears, well once I opened it up I saw the center bearing was falling right out WOW its funny it drove at all! I am very glad its out, it wouldn't have driven far.( see pic)

Anyways I had better luck this time, this unit is very smooth and all gears work well, I only took it for one short test drive today but the gear ratio's seem nice and should be fine for general driving.I am sure the speedo is off 10 MPH or so, since the donor truck had a 4.3 rear end and mine is a 3.9.I did not have to swap the front countershaft bearing this time, nor modify the shifter rod hole, so I think this tranny was a few months older than the first one.

I welded up the gear shift ( very badly, you will do better) but it works and now fits the console hole,so all is well I can move on to other things...Thanks a lot to Ratsun and especially Datsun Mike for all the great info, I really appreciate it! Kev.

 

http://s946.photobucket.com/albums/ad306/ahoogakev/Kev76Datsun/?action=view&current=71BadBearingWithBallsFallingOut.jpg

 

 

http://s946.photobucket.com/albums/ad306/ahoogakev/Kev76Datsun/?action=view&current=9My720TrannyGetsTheFancyBottomGearshift.jpg

[datzenmike]

Well I'm so glad that worked out for you. 5 speeds are nice.

 

Re the mainshaft bearing. That bearing race has come apart. 4 th gear transmits power directly through the mainshaft so minimal noise and wobble. 5th gear is the one shown in the picture and transmits power onto the mainshaft from the side and that bearing really isn't up to supporting anything.