Dually Axle and Wheel Offsets

[djmac]

Offset? Backset? I am not sure of the correct term but my issue is I am installing a '78 ford d60 front and dually d70 rear axle on my truck. (thanks for the help everybody for getting me this far!) And I can see that those massive dually rear drums are going to come into play when finding wheels for my truck. I am going to sell my old wheels and tires so I can start with a clean slate but I am looking for a TSL tire about 38x15.5x16.5 and I would like the outside edge of the front tires to be projecting out about the same as the rear tire. I am uncertain of how to calculate the offset/backset so I can accomplish that. Any experience out there?

[Elliott]

The info you will need to start with to get help on this is to post the WMS (wheel mount surface distance) for both axles. For example, I have a dually Ford Van D70-U sitting here and the WMS is 72.5"s.

[djmac]

The info you will need to start with to get help on this is to post the WMS (wheel mount surface distance) for both axles. For example, I have a dually Ford Van D70-U sitting here and the WMS is 72.5"s.

Ok, so I will get the WMS for both front and rear and post it up this evening. Thanks Elliott. I can't believe how massive these axles are!! They make my stock axles look like toothpicks. I have the front axle on with the perches welded up and now I have to start on the hi steer and inboarding the rear springs.

[Elliott]

Just a heads up on this, I have two D70s, a U and an HD... in either case if I wanted to use a spring plate at the top of the springs rather than under the axle it would require inboarding the spring mounts under the frame if I was going to retain the brake drums. That will also create more lift. If you are going to use rear discs that may not be a problem.

[djmac]

Just a heads up on this, I have two D70s, a U and an HD... in either case if I wanted to use a spring plate at the top of the springs rather than under the axle it would require inboarding the spring mounts under the frame if I was going to retain the brake drums. That will also create more lift. If you are going to use rear discs that may not be a problem.
Inboarding on my d70 was no brainer. I only have 48" between the dust covers. I have the adapters from Tad so I am all set to inboard. Started cutting off the old brackets this evening. Do you know exactly how much lift the inboard creates? I don't have a problem with the drum brakes. Between the huge 2 piston calipers up front and the massive drum brakes in the back along with hydro boost I am going to be 500% better off than the stock arrangement. I took the WMS dimension this afternoon:
Front = 69"-3\4
Rear = 65"-0

I read somewhere that having one axle or another wider helped tracking somehow but I cannot remember if the front or rear that was beneficial. Thanks for the help!

[Elliott]

That rear axle must be a cab and chassis axle. You can add some longer studs and 2" wheel spacers to bring it out to match the front closer.
Not sure exactly how much lift that resulted in because I never took a pre measurement on my '65 truck. The frame I'm working over now was 12" from the centerline of the D44 axle to the underside of the frame rail with stock/worn springs. If my buzz box keeps crapping out on me it'll be awhile before I get to the back hangers to tell how much lift it gives... some of that will also depend on if you swap springs out or not. Thought I was going to get all my front hangers under the frame today (post mount swap out for the DRW D60 frt) but the Lincoln took a breather... might be on it's last legs. :banghead:

[djmac]

That rear axle must be a cab and chassis axle. You can add some longer studs and 2" wheel spacers to bring it out to match the front closer.
Not sure exactly how much lift that resulted in because I never took a pre measurement on my '65 truck. The frame I'm working over now was 12" from the centerline of the D44 axle to the underside of the frame rail with stock/worn springs. If my buzz box keeps crapping out on me it'll be awhile before I get to the back hangers to tell how much lift it gives... some of that will also depend on if you swap springs out or not. Thought I was going to get all my front hangers under the frame today (post mount swap out for the DRW D60 frt) but the Lincoln took a breather... might be on it's last legs. :banghead:

Sorry to here about the welder, I have been fighting with a dirty cutting torch tip today but we got thru it. I think Tad said inboarding the springs brings you close to the same amount of lift that the SOA brings up front +/- an inch. Regarding the wheel spacers: Is it possible to get the front and rear axle within an inch or so without the spacers? BYW what is a cab and chassis axle.

[Elliott]

As far as I know you need spacers. Some rigs you can swap hubs to get the wider WMS, without requiring longer axle shafts... but I think the C&C is the exception to that. Cab and Chassis (C&C) is factory cab n'chassis where you put you own bed on it, the axles are always narrower when dually. Then you have the dually van axle and the wider yet dually pickup axle.

[djmac]

As far as I know you need spacers. Some rigs you can swap hubs to get the wider WMS, without requiring longer axle shafts... but I think the C&C is the exception to that. Cab and Chassis (C&C) is factory cab n'chassis where you put you own bed on it, the axles are always narrower when dually. Then you have the dually van axle and the wider yet dually pickup axle.

Thanks, looks like I need to go shopping for lugs and spacers.

[Elliott]

Maybe check with Rob (Dmntxn77), he did this and wrote it up for his Dodge C&C axle: http://www.ifsja.org/forums/vb/showthread.php?t=79027
Somewhere he posted what studs he used.
Here you go, page 4: http://www.ifsja.org/forums/vb/showthread.php?t=75429&page=4&highlight=wheel+studs
and check page page 8 for the installation: http://www.ifsja.org/forums/vb/showthread.php?t=75429&page=8&highlight=wheel+studs

http://i4.photobucket.com/albums/y130/dmntxn77/79%20Chief/1%20Ton%20Swap/WheelSpacer2.jpg

[Mahamotorworks]

You can change the front axle to SRW Brake parts and not need the spacers on the back. In most cases this will be about $500 per side. It is a lot easier to go with spacers. My boss ran into the same problem on his CJ project.

MAHA

[djmac]

[quote=Elliott]Maybe check with Rob (Dmntxn77), he did this and wrote it up for his Dodge C&C axle:



Oooooooooh the plot thickens......... thanks for the tip. I will read up on the post. I only need 2 inch spacers but even that will expose even more of the brake drum but so be it. I have my out looking for rims and tires now. I believe 16.5 rims should be big enough?

[Elliott]

The stock dually rims were 16.5, H1's are 16.5 and they fit.

[djmac]

The stock dually rims were 16.5, H1's are 16.5 and they fit.

Elliott,

Am I going to owe you a rather large "consultation fee" when this is over with??:D

Thanks again

[Elliott]

Awe, I'm just sorting a lot of this myself lately and passing it on.:thumbsup: I'm building a dually stake bed so that if'n I want I can just swap the bed out for a 126 wb bed and change the dually rims for H1 that I have. I'm using a GM dually D60 up front and GM dually pickup D70HD out back, both have the 74" wms so (as it is now) on H1 rims it needs no spacers. I cropped all the post mounts off the frame, just put front hangers on and will set the rear under the frame also and use Ford 3" rear springs from a dually van.

[DAHoyle]

I'm building roughly the same setup as Elliot, as far as axles and wheels, but I'm linking it all the way around. Just about have to link the front, because I'm running a late model HP 60, and the spring perches are too far apart to run leaves, so the front gets linked by default. If the front gets linked, may as well do the same on the rear.

Doug