How can I tell if I have a dually rear end

[G. Mann]

Just bought another truck. An OBS 86, long bed, stretch cab Lariat. No engine or trans, and no wheels.
Been setting for 9 years, it had a 460 gas engine / auto transmission, that was pulled and sold.

I have a truck that was wrecked [with me driving it] that bent the frame in 7 places, cab, front clip, and bed bent also... [pulling a loaded trailer full of 20 ft 2x12 lumber when some guy brake checked me in heavy traffic.... when I swerved, trailer started whipping, I steered into a concrete barrier wall rather than kill a bunch of people.]

Anyway, the diesel engine and 5 speed trans, and other good parts will go in the "new truck".
While putting wheels on the truck to load on trailer, I noted the rear end wheel studs are very long, and it had been used to tow a 5th wheel [Trailer brake setup, gear vendors controls still in truck.] I think it may have been a dually since the bed is missing also. [I had a spare regular bed that I set on the frame].

How can I identify if the rear end is actually a dually? What will tell me clearly what I have.
I'm hoping it is, I have a dually bed available, and would like to build it as a dually.

Anybody know how to tell?

 

[chillman88]

I'm not 100% certain, but I believe only Dually axles had the wider brake shoes, 3-1/2" wide maybe?

I'm sure you could check spacing between the backing plates to verify SRW VS DRW, but I don't have those dimensions.

 

[riphip]

All '86 truck SRW Sterlings have the long studs even the 4wd w/1-1/16" lug nut. Have to use 3/4 impact on mine.

 

[G. Mann]

Thanks for that info on stud length for SRW sterlings.
Still I don't know how to tell a dually rear end when I find one in the salvage yard, just by looking at it... Anyone know what to look for?

 

[The_Josh_Bear]

Thanks for that info on stud length for SRW sterlings.
Still I don't know how to tell a dually rear end when I find one in the salvage yard, just by looking at it... Anyone know what to look for?

Well shoot if you're in the salvage yard look for the big wide fenders on the bed.

Wish I knew so I could help but I do know that my 89 F250 has the wide shoes so that's out...

 

[G. Mann]

Hahaha... duhhh... now I have a clue..
Actually... every dually bed I've found already had the fenders GONE... it seems they are in really high demand... or get broken and trashed easily.

Diffs are gone before the beds are parted also... so I can't find one to measure, look, or find the details of how they are different.
I am hoping someone on the board knows the magic way to identify one as "Dually rear"...

 

[lotzagoodstuff]

FYI: Sounds like the dually axle is definitely wider. If you trust that a 1995 dually rear axle is the same as the era you are searching for, I'll be happy to measure mine and report back what I get for measurements, but I don't have a SRW to compare to it.


https://www.powerstroke.org/threads/dually-rear-width-vs-srw.119657/

https://www.powerstrokenation.com/threads/can-you-use-a-dually-axle-on-a-srw-obs.84665/

 

[riphip]

DRW is supposedly 6" wider than the SRW but may have bolt on 3" spacers on each hub. Just don't remember on the '86 but will search my manuals tomorrow.

 

[chillman88]

I have both, but not enough time to crawl under and measure. If nobody comes up with anything I may get time this weekend.

 

[G. Mann]

No rush, I am happy to wait for good solid information. This is going to be a long bare frame rebuild, so it's not like I will be installing the dualy rear end [which I don't even have yet] this weekend..

To all of you who go out and measure your rear ends.. err.. make that your trucks rear ends... thanks..

There has to be an easy way to ID a dualy rear, just by looking at it... I just don't know what that is... But, knowing how Ford does things, I'm betting they changed as little as possible to make a truck dually.
Ohh.. I have a set of dualy front hubs in my parts pile... now to find wheels... and a rear end.

 

[u2slow]

SRW pickup diff is ~65" across the wheel mounting surfaces. The DRW is ~72". The dually drums are wider; mostly for the wheel offset. Its a wider housing with longer shafts. Not some hub trick.

Raybestos #'s for reference; rockauto has pics of each
- 1661R (DRW)
- 1657R (DRW)
- 2751R (DRW)
- 1665R (SRW)
- 2320R (SRW)

The other diff to confuse things is the cab & chassis DRW. Its also narrow like the SRW, but uses the DRW drums. Other nuances:
- skinny spring perches for 2-1/4" wide leafs on a 40" spacing (~45ish on pickup)
- both shocks angle forward (if I recall correctly)

EDIT: A DRW diff should also have a roll-pin in the hub to locate the wheels. Of course, these can be snapped off, or removed for use with other wheels.

 

[G. Mann]

So, the key points to identify a dualy rear end are:

75 inches between hub outside to outside.

Roll pin location to index and clock the dual wheels. [first quick check, I think]

45 inch spacing outside to outside on spring perches..

3.5 inch brake shoes.. wider drums than SRW.

That is golden... Now I'm armed with something solid.

 

[u2slow]

So, the key points to identify a dualy rear end are:

75 inches between hub outside to outside.

Roll pin location to index and clock the dual wheels. [first quick check, I think]

45 inch spacing outside to outside on spring perches..

3.5 inch brake shoes.. wider drums than SRW.

I'm not sure the hub 'stickout'... could put it near 80" overall. 72-73" across the wms anyway.

The roll pin is iffy, but if its there, definitely a DRW.

Spring spacing is center-to-center on perches. ~40" (C&C) or ~45" (pickup)

3" or 3.5" shoes depending on the year. DRW drums are wider than SRW either way. They have a pronounced 'step' in them when you dig up the pics of the part numbers I posted earlier.

 

[chillman88]

72-73" across the wms anyway.

To clarify, WMS is "wheel mounting surface" so not tip to tip of the hubs, but the flat on the rotor that the wheel actually sits against.

As far as the roll pin goes, I've seen three of these trucks and maybe one or two roll pins between them all. Seems they either fall out or get removed so if they're there it's a good indicator but if they're missing it's irrelevant.

 

[riphip]

I can't remember where my '86 manuals are located at present. Been a while since I've had them out.