UCA mount swap?

[athoose]

So I've been considering swapping my 73 frame out for a 720 but got to wondering, if the frames are so similar can you just cut off the 720 upper control arm mounts and weld them onto the earlier frame? From what I've read these mounts are the main difference between the frames. I am hoping that adding these UCA mounts would allow the use of the ball joint control arms and discs.

 

Found this thread ... Doesn't look promising

 

Edited October 31, 2021 by athoose
More info

[Stoffregen Motorsports]

I don't think the 720 control arms can be made to fit on the 620 without much modification. I could be wrong, but I did a similar swap a few years ago and chose to cut the frame and install the entire front clip because some of the measurements I took showed the two suspensions to be vastly different.

 

You can see the swap I did here on Ratsun -

 

[athoose]

10 hours ago, Stoffregen Motorsports said:

I don't think the 720 control arms can be made to fit on the 620 without much modification. I could be wrong, but I did a similar swap a few years ago and chose to cut the frame and install the entire front clip because some of the measurements I took showed the two suspensions to be vastly different.

 

You can see the swap I did here on Ratsun -

 

Awesome job! I'm thinking it'll be easiest to swap frames at this point, for me. 

[620slodat]

The other big difference between the frames is the idler arm mount locations. The 620 idler arms mount on the inside, and the 720 idler arms mount on the outside of the frame. The mounting bolts are in different locations. It seems like they are off by only half a bolt hole. Its been a while since I checked that, so my memory is a bit fuzzy.

 

Don

[Stoffregen Motorsports]

11 hours ago, 620slodat said:

The other big difference between the frames is the idler arm mount locations. The 620 idler arms mount on the inside, and the 720 idler arms mount on the outside of the frame. The mounting bolts are in different locations. It seems like they are off by only half a bolt hole. Its been a while since I checked that, so my memory is a bit fuzzy.

 

Don

And having the idler and steering box mount to the outside of the frame give much needed room inside the engine bay around the engine. If you plan to add PS or AC, this is important.

[620slodat]

27 minutes ago, Stoffregen Motorsports said:

And having the idler and steering box mount to the outside of the frame give much needed room inside the engine bay around the engine. If you plan to add PS or AC, this is important.

 

This is very true!! This is exactly why I chose to use a 720 frame. The extra room the frame has on the inside next to the motor when the idler arm and the steering box are outside the frame. The frame for the 720 is almost the same as the frame for the 620. The six bolts that hold the cab of the 720 to the frame will interchange exactly with the 620 cab bolts. It looks like the bolts that hold the bed to the frame for the 720 will also interchange for the bolts that hold the bed of the 620.

 

The only thing about using the 720 frame under the 620 body is the state you live in. Will the state accept the frame swap because of its regulations? Oregon will. 

 

Don

Edited November 1, 2021 by 620slodat
correction

[Stoffregen Motorsports]

Here in CA swapping an entire frame is tricky. Technically, once you swap in another frame, it needs to go through an inspection process, which nobody ever does, and then there's the issue of how to register the vehicle after. Some insurance companies will not insure a vehicle if the frame is swapped. These are written rules that are very rarely followed up on or enforced.

 

I know other states have similar rules which are actually enforced, but here in CA, if you're not in the business of selling vehicles, and you're building it for yourself, nobody will ever know, unless it gets transferred out of state or if you let the reg lapse so long that it needs to be VIN verified. In both cases, an inspector would find the mismatched VINs and it may or may not be a problem.

Note - some frames don't actually have a VIN, but a part number that strongly resembles a VIN. I'm not sure which is the case for Datsun frames. I think they have an actual VIN stamped into them.

[thisismatt]

521 and 720 have the vin stamped on the top of the frame behind the passenger suspension/motor mount, so I assume 620 is the same.

[athoose]

1 hour ago, 620slodat said:

 

This is very true!! This is exactly why I chose to use a 720 frame. The extra room the frame has on the inside next to the motor when the idler arm and the steering box are outside the frame. The frame for the 720 is almost the same as the frame for the 620. The six bolts that hold the cab of the 720 to the frame will interchange exactly with the 620 cab bolts. It looks like the bolts that hold the bed to the frame for the 720 will also interchange for the bolts that hold the bed of the 620.

 

The only thing about using the 720 frame under the 620 body is the state you live in. Will the state accept the frame swap because of its regulations? Oregon will. 

 

Don

 

Are particular years of 720 more desirable for this swap? I'm thinking the 83-86 have different suspension components. Whether or not the frames themselves are different, idk. I'm considering adding Bell tech drop spindles to the mix.

[datzenmike]

1 hour ago, thisismatt said:

521 and 720 have the vin stamped on the top of the frame behind the passenger suspension/motor mount, so I assume 620 is the same.

 

620 us behind the right engine mount. The 720 is in front or the right engine mount behind the alternator.

[thisismatt]

Potatoes tomatoes

[620slodat]

9 hours ago, athoose said:

 

Are particular years of 720 more desirable for this swap? I'm thinking the 83-86 have different suspension components. Whether or not the frames themselves are different, idk. I'm considering adding Bell tech drop spindles to the mix.

The only 720 frame I'm familiar with is the 1982 long wheel base frame, which is the one I took my measurements off of. I currently have a 620 cab setting on the 720 frame, and the bolt holes for the cab to frame line up. From measurements the bed will line up. There are 8 bolt holes for the 620 bed and there are 6 holes for the 720 frame. I don't remember the exact measurements, but the 620 bed should fit on the 720 frame. I will have to make the front 2 mounts for the 720 frame since the 620 bed has 8 bolt holes.

 

Don 

[Farmer]

If your sticking with a l20b or simular engine, get the 1980 720 frame.

[Stoffregen Motorsports]

The early 720 used solid brake rotors while the later ones had vented brake rotors. Was the change made in 1982?

[datzenmike]

11 '82 or the start of the '83 model year. A LOT of changes then.

[thisismatt]

I would definitely get the newest...heck, do a hardbody swap 😅

[athoose]

2 hours ago, thisismatt said:

I would definitely get the newest...heck, do a hardbody swap 😅

 

Here's a 521 on d21, 

 

 

Looks fairly involved. Has anyone done a 620 on here? 

 

I kinda like fiddling with the L motors, keeping it old school but yeah, KA, fi, etc.. is pretty tempting. 

[620slodat]

10 hours ago, Stoffregen Motorsports said:

The early 720 used solid brake rotors while the later ones had vented brake rotors. Was the change made in 1982?

 

1 hour ago, athoose said:

 

 

Looks fairly involved. Has anyone done a 620 on here? 

 

Stoffregen, the frame I'm dealing with is from a 1982 diesel, and it has solid rotors. I don't know when the vented rotors for a gasser started, late 1982 or in 1.983.  

 

A 620 body on a 720 frame has been done before, but I don't know if a 620 has been put on a D21 frame though.

 

Don

Edited November 3, 2021 by 620slodat