When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Cashman was over today with his F100 which has the 4.5" bolt circle wheels, a 302, and a C4. With a little research we found that his GVWR is 4700 lbs and his rear axle is a 9" with 2.75 gears and a 2800# rating. Since 2.75 and a 302 aren't a good combo for towing, or even spirited driving, we talked about the options.
My suggestion was to convert the gears to 3.50's, which lead to a conversation of how best to do that. Probably the best approach is to find a complete 9" rear axle from an F150 or Bronco since that would come with the correct brakes and the 5 1/2" bolt circle axle shafts. But, we also wondered if it is possible to upgrade his existing 9" housing with the 5 1/2" axles, backing plates, and brakes. So I set out to figure that out, and would like your input as to whether I have or not.
In the following table we can see that the non-locking 9" was used for both F100's and F150's, and came in both 2800# and 3750# capacity. Further, we see that the parts for those axles are enumerated in Parts List #88.
Here's Parts List #88 and we see that there is but one axle housing. And, as shown by the highlighting, there were two axle shafts used in that housing.
Here are the axle shafts used in that housing, and we can see that both have 31 splines. But one has a center-to-stud distance of 2 1/4", meaning the bolt circle is 4 1/2", and the other has a 2 3/4" distance for a 5 1/2" bolt circle. So, other than the slightly different lengths, the two could be swapped.
But, what about the wheel bearings. Here they are and, as it turns out, both applications use the same bearing, although the 3750# axle had a different one to begin with. And, that was subsequently replaced by D8AZ-1225-C, as Number Dummy explains here.
So, does it make sense that the only difference between the 2800# axle and the 3750# axle is the size of the wheels that fit it? (Yes, the brakes are different as well.) I plan to put this on my web site, but want to ensure I have it correct before I do.
Gary, I am on my phone so bare with me.
Look at the 2 cirt stickers I sent you. Both same weight 4700 iirc, sane motors 4.9 six, both 9" rears and brakes iirc.
Both have stick trany but 1 is a T18 the other srod, srod also has PB where the T18 did not.
The T18 truck has the big bolt pattern wheels the other small.
Only thing I could find to make this bolt size change was power & non-power brakes.
Same for king pin size & spindles are different between the two.
I would say if you want to keep the bolt size and change gearing is buy a center unit as swap it in.
Dave - - - -
And, you think your brakes are the same, even though you have two different wheel bolt patterns. That seems to be reasonable since the GVWR's are the same.
So, can you do me a favor and check your brake sizes? And, could you post pics of the tag on the axles?
As for Cashman, we were thinking he needed to go to the truck 5 1/2" bolt pattern wheel and larger brakes in order to get the GVWR up since he's going to be quite close if not over the limit with his boat. But, since his trailer has brakes perhaps just changing the gear ratio would be enough. Hmmmm.
Dave - can you do me a favor and check your brake sizes? And, could you post pics of the tag on the axles?
Maybe a bit before I can get out to the garage to check brakes & tag.
Brakes are EZ but where is this tag located? Is it a metal tag on 1 of the center housing bolts? I cant remember seeing one on either rear but also was not looking for it.
Dave ----
It is a metal tag under a bolt at about the 10:00 position. Here's what Cashman's looks like. You can see the 2.75 gear ratio, but the WDM - CL tells which parts list to use.
For 9" you can swap everything, shafts/third/brakes as long as the bearing type (big/small/torino) and axle width is the same. Which for two axles of the same vintage should be easy.
I would definitely go for upgraded brakes whenever possible.
Ok got up off my tired azz and out to a 104* garage to check brakes & tags.
Let me wipe the egg off my face. Brakes are not the same size – my bad. Big wheel brakes are 2-1/4 x 11 with tag
Small wheel brakes2-1/2 x 10 with tag Hope that helps Dave ----
edit: I want to say the drum brakes when I looked them up on line parts stores did not list by size but power & non-power brakes. Been a few months when I went thru all this to rebuild the big wheel drum brakes.
Thanks, Dave. The WDM-CJ does show to be the large bolt-circle axle, and I expected it to have larger brakes. The WDM-DB shows as the smaller wheel, and that fits as well. So, maybe I have got it figured out.
For 9" you can swap everything, shafts/third/brakes as long as the bearing type (big/small/torino) and axle width is the same. Which for two axles of the same vintage should be easy.
I would definitely go for upgraded brakes whenever possible.
Like Gary mentioned in one of the earlier posts, the axle count has to be the same. Most 9 inch axles in the 70's and earlier were 28 spline. The hole in the carrier is too small to accept a 31 spline axle, though a machine shop can open it up to make it fit. And of course you then use 31 spline spider gears.
And, fortunately, even the 4 1/2" bolt-circle axles have 31 splines. So, you can swap axle shafts, backing plates, brakes and drums 'tween a light-duty early 80's F100 axle and the heavier duty F100/F150 axle. (I haven't checked to see how far back that goes, meaning if the 70's F100's used 31-spline axles. Could do, but haven't, so won't say.)
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
