Rear end swap...

[Army_Dude]

How much of a pain in the a$$ will it be to swap my rear out when I go down and look at the 49 Ford.

I also got a 73 Chevy there (Moms) and was just wondering cause I got 2.73 gears in my 85 according to the RPO codes . I;ll have to check but I believe the 73 has to better than that. Is it a days job, less, more? What can I expect out of it. Anything to look out for? If this Ford pans out, I may be selling the 85. Figures, I finished the interioir tonight.. Stock blue, with black headliner, new black carpet. panels around the door handle cup redid in black. bottom of door black with th vent still blue. came out super nice i think.

[79BIG10]

I just did this a couple months ago. I did a complete swap out. When I did it I had a second axle rebuilt from drum to drum including brake pads, drums, shocks, etc. If you're swapping them out look for a couple differences. The one I got from the 85 donor yoke was a different size than my 79 was. I called the guy who did my rear gear swap and told me to take both loose and swap them out. Then I hit both with my impact to bolt back down after starting on the grooves. I did it in about a good weekend with cold weather and painting etc.

Here's a good outline to what to do:
Get 2 pair of jacks and a jack to lift the truck. I jacked up the truck and placed the front end on a pair of jacks. Now drop the drive shaft and move out of the way but make sure to tape the U joint caps so they don't come loose. Then take a jack to either side of the frame in front of the axle as low to the ground as you can. When you do this make sure to take the tire off the side you've got jacked up. Once you've got the frame jacked up the axle should come down to the ground. I disconnected the brake line (I replaced mine) and the breather tube. Next find where the brake cables hook up to the connectors (look like a long "C") and unhook them. Now you can take the springs out at the frame (what I did) by loosing the bolts and nuts 3 on each side or you can take the U bolts off the axle itself (to me this was harder under the truck). Also take the shocks off the axle (I replaced them as well). Now I took the axle out straight back. Swap over the springs to the perch and align the holes with the nub on the axle. Bolt these back down to correct spec (I don't have the book right now). Then the new axle slides back into place and line up the bolts to the frame holes again. Slide the bolts in and start the nuts but keep them loose until you have all them aligned right up. Bolt down to spec and connect the shocks. Reconnect the brake hose, breather hose and brake cables. Reconnect the driveshaft to the yoke and tighten down. Bleed the brakes and fill the axle full till it starts coming out the fill hole. Next take it out for a test drive and see the difference.

[piecesparts]

I changed out a complete rear end on my son's truck, just like 79BIG10 above. The 10 bolt 3.08 went to the shop floor and the 3.73 posi 12 bolt went into the truck. There was adifference in the yokes and I just purchase a new yoke to go with the 12 bolt, before I installed it. The carrier housing on my reaer end was slightly different so the drive line had to be changed to make sure it fit properly. I had two days work total involved and that involved the round trip to the driveline shop and two hours of their work.

I lifted the truck in my shop---I bought a two post lift for my home shop, so life is easier for me at my age. I loosened the axle U-bolts, driveline, shocks, brake lines, and emergency brake cables. Two of us slid the axle out on a pedestal tranny jack by seesawing it one way then the other. The connection of the new axle was the reverse. This can be done with floor jacks and frame stands also, just a little more crawling around. Two people make it easier but not needed.

[Ziptar]

I have started swapping parts between my 79 and 85. I will probably swap trannys last.

The 79:
Turbo 400, Two Piece Driveline, 12 Bolt Rear, Long bed.

The 85:
700R4, Single Piece Driveline, 10 Bolt Rear, Long Bed.

Am I going to run into driveshaft problems bcause of the rear end yoke and carrier size differences?

I'd like to keep the 12 bolt and two piece driveline but, ease of swapping is more important. I thought about getting the front half of a two piece driveline from a 700R4 truck but I don't know if the splines will line up with the rear half on the 79 or if the length will be right.

Should I count on swapping rear ends completely? I'd like to avoid trips to the driveline shop, parts store, wrecking yard, etc. I'd just like to get teh two swapped out as quickly as possible. I can always do a 12 bolt, 2 piece shaft swap later I figure, i do have the parts now though. Can the yokes be swappped between 10 bolt and 12 Bolt??

I'll be swapping leaf springs between the two, just do the whole rear end instead?

Any input appreciated. Thanks

[SSC's76]

It only takes a couple hours if you stay on it. I like to jack just the rear up as high as possible and put jack stands under the frame.Then slide the jack under the pumkin to releive the tension off the leaf springs. Do all your un bolting and drop the jack down until the tires touch the ground and roll it out. Of course there is always the possibility you may have to pull the drums off and disconnect both e-brake cabels internally if your donor has a different setup. I know some newer rear ends have metric fittings on the wheel cyl's so you may or may not have the swap those over.

[Ziptar]

OK, Long but, bear with me..

I have been doing some checking and it looks like swapping an TH350/700R4 front half onto the 79 Rear half might work. This is what I have found so far:

Front Half:

If I search car-part.com for 79 "4x2, 131.5" WB, AT, TH350, two-piece, front section" it brings up drivelines from 77 and up trucks. Some of the descriptions show some are from 700R4, short and long shaft TH350 trucks.

If I search for an 85 "4x2, 131.5" WB, two-piece, front section, AT, TH350" I get pretty much the same results. 77 up Listings for Long and Short Shaft TH350s and 700R4s.

If I Search for an 85 "4x2, 131.5" WB, two-piece, front section, AT, TH700" I get 82 Up results.

If I search on a 79 "4x2, 131.5" WB, AT, TH400, front section" I get 77 Up results all from TH400's.

Rear Half
Searching on an 85 "4x2, 131.5" WB, two-piece, rear section, AT" brings up 82 Up regardless of transmission.

Searching on a 79 "4x2, 131.5" WB, AT, TH350, two-piece, rear section" brings up 74-81. there is no mention of different 10 and 12 bolt rear at least not on the 131.5" WB.

Searching on a 79 "4x2, 131.5" WB, AT, TH400, rear section" Brings up 79-81 results. Again no mention of of 10 and 12 bolt rears on the long wheel base.

In looking at the comments in the descriptions about Weld to Weld Measurements in both the 79 TH350 and TH400 they both appear to be around 34".

So it would appear that all LWB trucks got 12 bolt rears only up to 1981?? At least that's what the interchange would suggest.

Based on that it would seem the rear driveshaft section interchange follows the 12 bolt being unavailable in the 2WD C-10 Starting in 82. The rear sections for the TH400 and TH350 12 Bolt rear could be the same.

It also looks like the Splines between the front and rear sections didn't change between 79 and 85.

So at the very least it looks like I could just use the Front half from a truck with a 82 up 700R4 or a 77 up TH350 with a 9" Tailshaft.

That may not work and what I'll need is a both pieces from a 77 up Long wheel base truck with that has a 9" tail TH350 and 12 Bolt rear.

Or at worst it just won't work at all.

I guess what I'll do is try find a front section that might work or front and rear pieces that might work and have them on hand when I swap tranny's if they work. Great.. if they don't then I'll guess I'll be swapping axles. I'll have to start checking the local U-Pull it's.

Anyone give me some input? The interchange can be wrong I know... Looking for real world experience.

Does anyone have a Pre-82 12 Bolt rear, 2 piece driveline TH350 8FT Bed 2WD 1/2 Ton Truck could get me a Weld to Weld measurement on the rear half to compare to the one in my 79?? That'd be awesome.

Thanks.