720 rear in a 521, wheel related question

[javier302]

Hopefully somebody can give me some info on my new project, you guys been awesome since before I got my truck, as a matter of fact, you guys are the reason I got a 521 and not a 620, since the 620 I was looking at was overpriced for what it was, so I ended up getting a 70 521 from the west coast, needs tlc, but its a cool project.

has a 2litter motor and 5 speed, not sure of the year or miles but runs pretty good.

found out after doing my brakes that I have a newer rear also, I was under the impression that was a 75/76 as previous owner stated, but brakes would of been the same, instead I had to get another set that was for an 80/81 720.

so, getting to the subject, I reindex the front (thanks for the info on the stickies and that search botton), wanted to maybe come down some in the back, but my rear wheels stick out due to the wider rear I imagine. I can probably figure out the offset and backspacing of the current wheels, but my questions...

by what I found searching here, the 72 rear is 2" wider than the stock one on my 521 ?

if I figure the offset, would I be able to figure what I need to clear the fenders ?

or on a 15x8 what do u guys run as far as offset and bs on a stock rear 521 to tuck em.

then I could add either an each of backspacing, or +26mm ? offset, or a combination of both when looking for wheels ? 

 

Am I overthinking it too much ?

 

I don't know how much sense this makes right now, I kinda have it in my head, but its harder than I thought to explain it.

 

javier

[mrbigtanker]

15x8 is hard enough without the 2" wider rear end.WHy did they swap it in the first place,only thing i can think of is higher gearing.I do know depending on offset 15x8 wheels and depending what tires you will rub the leaf spring plates or were the U bolts go in to.I would look at getting another 521 rear end. 

[wayno]

It's kinda tough where he is located, they have lots of classic European stuff on that coast, while we have lots of classic Japanese stuff on this coast, I would trade him straight across for what he needs as I have it right now, but he is 3000+ miles away.

See if you can find a 520/521/early 620 being parted out on your coast guy, or leave it the height it is for now till you do find something, and the other avenue you can take is go to a tire shop and have them figure out what rims you need to make it work with what you have.

[mrbigtanker]

Good call wayno I forgot about east coast,but hes right also see if you can source a ugly ass 620,good gearing and it is the same demensions and that would fix almost all your problems right there.

[ggzilla]

521 wheels are 4" wide so with wider than stock rear axle it will be tough to fit 8" wide wheels.

[javier302]

oh wow, I wasn't aware that they were that narrow, maybe I'll look into 7" wide or less, I was trying to find some cragars...

I wish I knew why the rear was changed.

[ggzilla]

Because bigger brakes? Oh wait - 521 and 720 have the same size rear brakes.

 

One reason would be if it is LSD as the center won't swap with a 521. The normal diff center will swap.

[javier302]

rear shoes for most rears part #511 at auto parts store

and 81 720 comes up with 511's and 571's the 511 is shorter than the ones on the truck

[ggzilla]

Both are 10 x 1-3/4, right? Even though the Type 511 may have less shoe material. The 720 also has auto-adjusters and metric fittings and bolts.

[wayno]

Someone likely thought it was easier to switch over the whole rearend than to just switch out the gears for better gearing since the mount perches are the same, or maybe they thought it looked better with the tires out that far, it's hard to say, now you have to work with what you have for the time being.

 

oh wow, I wasn't aware that they were that narrow, maybe I'll look into 7" wide or less, I was trying to find some cragars...

I wish I knew why the rear was changed.

 

I would look around for the trucks I mentioned before being parted out, that way you can likely run the same rim on all 4 corners.

[javier302]

will do wayno, a friend of mine is looking for parts in PA

 

thanks for the info guys

[javier302]

I wanna do a clutch but I don't know what disc to order cause I don't know which year flywheel I have....

[ggzilla]

Most likely you have a 1970 521 flywheel. Since the clutch is available at local auto parts stores, just wait until you get it out. For example Autozone $76 with 3-day order.

[javier302]

cool. thanks again ggzilla. is straight forwards like any other car ?

Ive done the clutch in my foxbody mustang in a couple of hours, exhaust, driveshaft, shifter, starter. and 6 bolts, crossmember and tranny down,

6 pressure plate bolts, and back up.

[ggzilla]

Yes

[datzenmike]

Most likely you have a 1970 521 flywheel. Since the clutch is available at local auto parts stores, just wait until you get it out. For example Autozone $76 with 3-day order.

 

Negative. He said he had an L20B, and the flywheel for them are 6 bolt. All L16 and L18s are 5 bolt.

 

If it was a car L20B the flywheel takes a 200mm clutch, if from a truck it will be a 225mm clutch.

 

If looking, look for a 521 rear end complete, and get it back to stock so your rims all make sense. If you have a 720 rear end it's even wider than the '75-'76 620 and it's wider than the 521.

[Charlie69]

The 1980 720 rear end is the same width as the 78-79 620 rear ends I have one in my 66 520 and I still have wheel /tire clearance with the bed/wheel well with stock rims..

 

I know my 86 720 rear end is wider than the 2 1980 720 rear ends and my 78 620 rear end.

[EastBay521]

Because bigger brakes? Oh wait - 521 and 720 have the same size rear brakes.

 

One reason would be if it is LSD as the center won't swap with a 521. The normal diff center will swap.

why wouldnt the lsd center fit?