1980 720 4x4

[Grahem]

im slowly assembling my 73/80 4x4 and need to know a couple things 

 

are the divorced 720 tcases a 1 to 1 ratio when in high range?

 

and what is the most likely ratio for the rear diff?

 

it is a L20b truck and had a 4 speed when i tore it apart and i dont have the factory engine bay tag (had fake vins from an 82) i dont have a speedo cable long enough to reach the tcase and the trans im using has a speedo out put so im hoping to use it and have a decently accurate speedo in hight range. thanks

[datzenmike]

1:1 in high and almost 2:1 in low.

 

'80 4x4 would be 4.375

 

The transmission will work for the speedometer in high range, but be out in low. Has to have the correct pinion gear for the differential and tire size.

[wayno]

My 1980 Datsun 720 4X4 had 4.625 gears all around, a 510 racing guy back east bought the front one because of that.

[datzenmike]

You're right. The long bed 4 speed 4x4 was 4.625. It's the only model and year with this.

[Grahem]

ok do the tcase speedo drives interchange with the standard transmission speedo drives? then i could just swap the one from the original tcase into the new transmission and hope for the best. its a short box btw

[datzenmike]

Maybe.... you can try it. They have different diameters, seen this before. Can't even get it started. If it goes in but jams try it turning it 180. If this works,remove and nick a new keyway slot with an angle grinder to hold it.

[Grahem]

ok does anyone know anything about ebrake cable interchangeability? the cab and back half is a 73 620 the front of the frame and rear axel are 80 720 4x4 both shortbox. i have rear ebrake cables from an 81 2wd im hoping to use and somehow i dont seem to have any front cables at all. i havent asked at the local parts store yet but im willing to bet 73 parts are nla, but im hoping maybe 720 or d21 cables will work and be available.

 

thanks

[wayno]

Totally different systems, I suspect that the 73 has a center pull system like the 521, that would mean that there was two bellcranks on the carrier cross member, if they are gone, then you are going to have to build a system from scratch.

If the bellcranks are still there you need to come up with the rear 521/620 cables, then all you will need to do is figure how to connect a 720 front cable to the first bellcrank, you may also need to put a late 620/720 e-brake pull lever into you 620 cab.

I have made my own system before with the later rear cables, but it just doesn't work well, it's hard to do what you are trying to do with 720 cables using the 620 rear frame, you basically have to start from scratch, as the later e-brake systems are a complicated lever system that has to be perfect to work.

ok does anyone know anything about ebrake cable interchangeability? the cab and back half is a 73 620 the front of the frame and rear axel are 80 720 4x4 both shortbox. i have rear ebrake cables from an 81 2wd im hoping to use and somehow i dont seem to have any front cables at all. i havent asked at the local parts store yet but im willing to bet 73 parts are nla, but im hoping maybe 720 or d21 cables will work and be available.

 

thanks

[Grahem]

ok i had a feeling this was going to be a challenge all the original 620 hardware was rusted solid and is long gone except the pull lever in the cab and the 720 didnt come with any ebrake hardware the po had rigged up a manual hydraulic shut off made out of a plumbing valve lol.

[datzenmike]

The frame you got is an '72 long bed and has the e brake and it worked.

[Grahem]

i thought about robbing parts from your old truck but the brackets are welded to a cross member and wouldn't they be too long? 

[datzenmike]

Yeah long by about 9"

[wayno]

If the 73 had a center pull type e-brake like the 521 had, then the bracket with the pin that the e-brake cable goes thru to pull the cables from the center can be put on an extended shaft coming from the last bellcrank in the e-brake system, I extended my work truck frame over 24 inches, so I had to extend that part 24 inches also.

But I had all my stock e-brake cables from the rear drums to the center connection mounted properly, to make anything work the rear cables have to be mounted properly.

I did put my stock 521 cables in the 86 dually axle drums, what I would do is find used e-brake parts for the year of the back half of your frame and put it together, now if your cross member where the carrier is is the 73, then all that e-brake hardware(bellcranks, ect.) should be there, all you would need to do is have a threaded rod coming off the last bellcrank to the e-brake cables and cut it to the proper length, install the center pull hardware and put that part together loose, now use your 1980 e-brake lever/cable, connect the cable end to the first bellcrank and weld a mount on the frame that the 1980 cable end will fit in, just tack it in place till you get everything adjusted and all the cables are adjusted right hand tight, you have to make sure the bellcranks are both at the start of the movement for it to work, once everything is right, weld the mount onto the frame.

Now if you have the 1980 cross member, your going to have to fabricate a bellcrank, and then set up the front cable as I described, it takes trial and error to figure out the bellcrank arm lengths, I do know that I tried pointing the front cable straight towards the rear directly at the center of the rear cables and I made a connection, but I could not pull on the e-brake handle hard enough to hold the vehicle on any hill, nor would it hold the truck when I let out the clutch even at an idle.

[Grahem]

well i may have been wrong about the local parts store the had a listing for the 73 front cable and nothing for the 80 so hopefully on monday they call to say the can get me the 73 620 cable. im going to have to go crawl around and see what crossmembers have been used, i didnt do the frame work my self i traded wiring work with a buddy.

[wayno]

Before you start buying stuff, you need to figure out exactly what you have.

The front cable is not as important as the back cables, I would go as far as to say that you will need the proper rear cables for a 73.

The front cable depends on what cross member you have where the driiveline carrier bearing is, if you have a hole dead center that has a rod possibly sticking thru it connected to a bell crank, that is likely a 73 cross member, if the cross member has an angled setup set to the side or on top of the cross member, then it is likely a 720 cross member, you will then have to fabricate a new e-brake system, as the 720/late 620 and the early 620 e-brake systems are not compatible.

Photos would help a lot.

[Grahem]

i have absolutely no ebrake hardware from the original 1980 4x4 (it came that way) and all of the 73 hardware was seized so it was stripped from the 73's frame, there is nothing left bolted to the crossmember. all thats left is the stock 73 dash pull lever and some random used rear cables from an 81. I may have misunderstood but i thought you indicated the 73 was a simpler set up than the later ebrake system.

[wayno]

OK, here is my 1971 Datsun 521 rear e-brake cable connection, the individual side cables are in their frame connections on each side and meet in the center, you can see the driver side/passenger side cable connection to each other in the upper right part of the photo, it casts a shadow onto the driveline, the driver side cable is shorter than the passenger side cable..

You can also see the center pull hardware for the center pull part of the system, it is connected to a long threaded rod, that is the extended part of my system, I lengthened my frame just over 2 feet, so I had to extend that rod just over 2 feet also.

In the photo below you can see the hole in the cross member that the rod comes out of, and the connection point to the rod I made to extend the rod.

In the next photo you can see the two bell cranks and all the hardware used to make the 521/early 620 e-brake system work, also the front cable connection I have to adjust the front cable to the bell crank.

In the next photo you can see a 720 type e-brake system, you can see how the back of the cross member is wide open and how the driverside cable enters it, you can also see how the passenger side cable enters in a different place on the other side, in this photo I had to lengthen the driver side cable about 4 inches, the other cable length was fine.

Here is the 720 e-brake system in front of the cross member, it's way more complicated than the early systems, and has to be set up perfectly to work.

 

 

The 720 system is really complicated, it would be better to try and buy 73 620 rear cables and put together a one bell crank system and make a center pull system.

[Grahem]

Ok hopefully the new 620 front cable comes in and maybe I can still order rear cables. Which section is longer between the short and long box 620s? I have a longbox Datsun trailer that still has intact rear cables they might be usable

[Grahem]

Double checked and I only have the 2 rear most 620 crossmember the rest are 80 720 4x4 and there is nothing left of the 720 hardware. I then looked again at Mikes old truck and found the 620 hardware welded to a custom crossmember, so hopefully I can source new cables for the 620 then fab a new crossmember to mount them to.