Rear End

[Matt Peetz]

Okay guys, give me the low down on swapping rear ends.

Right now i have an 8" with 2.79 gears. I am thinking of swapping the whole assembly with my other project mach that has the 9" 3.25 traction lock.

Is it just as easy as just swapping the whole rear end out or is there other things i need to look out for? I am thinking the drive shaft will be an issue. I do have a spare drive shaft if needed.

These are drum brakes also.

 

[will e]

Not an area where I have a lot of expertice in. I doubt the drive shaft is an issue, the U joints might be different. Brake line shouldn't be too much of an issue, mounting plates are probably the same. I would think this is a pretty straight forward swap.

 

[Chris Womack]

Hi Matt,

I had the same problem, a 8" rear end using 2.75 gear with Conventional style differential, i.e., only one wheel would spin at a time.

I got a 9" rear end at a salvage yard and had the third member rebuilt with 3.50 gears and new differential, Traction-Lok is a good choice.

I didn't have any problem with the driveshaft length, I rebuilt the drum brakes and replaced the leaf springs. This was a great upgrade!

(One thing I have been thinking of recently is swapping C4 for AOD transmission and using 4.11 or 4.86 gear instead of 3.50 -- maybe next car after more research.)

Chris

 

[Matt Peetz]

Chris

If i do the swap i was planning on doing my leaf springs along with it (hence my other thread). I think the 3.25 will be a good fit for me.

 

[luxstang]

Won't you have to recalibrate the speedo?

 

[Qcode351mach]

Okay guys, give me the low down on swapping rear ends.

Right now i have an 8" with 2.79 gears. I am thinking of swapping the whole assembly with my other project mach that has the 9" 3.25 traction lock.

Is it just as easy as just swapping the whole rear end out or is there other things i need to look out for? I am thinking the drive shaft will be an issue. I do have a spare drive shaft if needed.

These are drum brakes also.

Matt..I just finished a complete rear end swap in my camaro..Check my fb page..I went from 3.73's to 3.08's big improvement & I think your planned swap to 3.25's should be fine ..The only issue you may run into is the u joint at the rear may be different..I had that issue in my swap..Check the yoke on the pinions to see...If they are different no fear..they make whats called a combination u-joint..http://www.dennysdriveshaft.com/c130_universal_joints.html A few things very worth while to do besides all new brake hardware is new rear axle bearings & seals..Also check the axles themselves..new brake lines.http://www.inlinetube.com/..I had my drive shaft balanced WORTH EVERY PENNY !!!! & you want to check your pinion angle http://www.hurst-drivelines.com/files/Universal_Joint_Alignment_Proc_111606.pdf Doing all the above will make a HUGE improvement in the way the car drives & feels..

 

[Chris Womack]

I too replaced the leaf springs with rear end upgrade, and replaced the gear attached to speedometer cable inserted in the transmission to recalibrate speedometer. If you are going from Conventional to Traction-Lok differential it is well worth the swap. The 3.25 gears will be fine, moreso if you plan on driving on highway.

I don't recall any issue with u-joints.

 

[Don C]

Won't you have to recalibrate the speedo?

Yes, whenever axle ratios are changed the speedometer driven gear must also be changed. A good way to calculate the new speedometer gear size (number of teeth) is divide the new axle ratio by the old ratio and multiply that by the old number of speedometer gear teeth. If you also change tire sizes at the same time more calculations are required.

 

[droptop73]

Trans swaps, rear gear changes, tire size changes all affect the speedometer. I'll be doing all 3 so i'll wait until the changes are done to recalibrate. Short term I'll get some speed differences between the speedo and a GPS.

 

[Wolverine]

I got a 9" rear end at a salvage yard and had the third member rebuilt with 3.50 gears and new differential, Traction-Lok is a good choice.

What are good donors for this?

 

[Chris Womack]

I believe I have seen something on this website about 9" rearends, here is a link I found that lists donor cars. Years ago... it was so easy to find parts in salvage yards.

http://www.mustangsandmore.com/ubb/FordRearDimensions.html

 

[ramair]

I believe I have seen something on this website about 9" rearends, here is a link I found that lists donor cars. Years ago... it was so easy to find parts in salvage yards.

http://www.mustangsandmore.com/ubb/FordRearDimensions.html

The best place to find a 9" 28 spline carrier with 3:50 gears or lower is to look at pre 71 Ford F100 pickups. Ford put out alot of 3:50 ratio gears in the F100 pickups. I had a 67 F100, 240 6 that had a 9", 3:50 locker in it. My poor truck got wrecked and sent to the junkyard, some person run a stop sign and I t-boned him totaling the truck. If you want to find 3:55 in a 8" look at the 75-78 Mustang II's with the 302 engines. I think they only had three ratios in them, 2:80's', 3:25's and 3:55's and some of them were even lockers.

 

[Totalled]

pre 73 truck. Bump sides were 28, dent sides were 31 spline.

 

[ramair]

72's you have to be careful, some of them have 31 spline carriers, 71's and earlier are a safe bet for finding a 28 spline carrier.