Ford Rear Ends

Dave · Post by **Dave** » Fri Feb 06, 2009 5:31 pm

I've seen this before on other sites but never found a really good reason why the rear center section (pumpkin) is not centered. The newer Mustangs have theirs centered. I've heard reasons like "Well, thats to clear the gas tank" and others that just don't make sense. The old Fords had a non centered axel but the gas tank was centered under the trunk. Was thinking that the trans is not really centered in the car/truck to allow a centered shifter location but shifted to the passenger side by 2". Against that I think the early F-1's had their shifters come up in the center of the transmissions. Any good ideas?
Dave

v8ranger · Post by **v8ranger** » Fri Feb 06, 2009 5:57 pm

I cant say I have ever seen one thats not centered.

usmcrp1044 · Post by **usmcrp1044** » Fri Feb 06, 2009 6:09 pm

I dont actually know, but I was watching some show on the speed channel one time and they said that Mopar's did it so the U joints in the driveshaft didnt go bad.

Basically if the transmission and rear end are straight on with each other both vertically and horizontally, the U-joints dont move much and go bad. So some manufacturers would have a height difference, while others would offset the motor and transmission. Possibly Ford decided to move the pumpkin?

No idea if any of that is right or not, it's just an idea.

Warpig Racing · Post by **Warpig Racing** » Fri Feb 06, 2009 6:25 pm

i believe that if they are perfectly in line that there will be a vibration that will occure. a slight offset of a few degress will prevent this harmonic vibration. If it is centered, it still may not be in line (transmission higher than rearend) until the vehicle is loaded down. then it could be in perfect alignment. Since it is offset a couple of inches it will never be in perfect alaignment. Seems like you idealy want less than 6 degrees in the u joints but more than zero.

rojam18801 · Post by **rojam18801** » Sat Feb 07, 2009 3:16 pm

warpig is your narrowed 9 inch centered, i think mine is but never measured it. have to do that when i get home again. it looks center...the old trucker

broncobowsher · Post by **broncobowsher** » Sat Feb 07, 2009 11:23 pm

A lot is balance. engine is slightly offset to the passenger side to balance the vehicle side to side with just a driver (typical loading).
The ring and pinion have an offset to them, the pinion does not line up with the center of the 2 shafts.
Sometimes left and right axle lengths are the same, other times they are not.

Fun one. When setting up my V8 I had just visited the dentist. Had a whole package of that worthless dental floss. So I put some to use. There was more then enough in that little sample to reach from the rear axle to the front bumper. I had 3 fixed points and was after the 4th. Diff, carrier bearing and trans mount were all stock to the ranger. Engine mount had some adjustability to it as I built my own mounts. Lets just say that nothing lines up. U-joints don't care what angle they are at. Can't even guess how to properly phase a driveshaft that has compound vectored angles in it. Just put it all in and let it work. Little driveline shudder in a hard launch in 1st, but the rest is OK.

Bazowak · Post by **Bazowak** » Mon Feb 09, 2009 12:14 am

You will see that most Ranger RE's have axles that are different lengths. This is done so that the U-Joints do infact move. MOPAR offset the whole engine and trans, Chevrolet did it by having the back of the trans higher than the pinion angle and Ford did it by having offset RE's

If the U-joint is allowed to operate completely aligned they do wear out faster and actually will start to "flat spot" the needle bearings inside the joint. If allowed to move slightly the bearings can roll to help move the grease around in the joint which also helps to dissipate heat in joint. Hope this helps some.

Also, if you go on to pretty much any Mustang board you will see where guys have used the long side axle of the 7.5 RE to put into their cars so that they can have a cheap and easy 5 lug conversion for the back.

Dave · Post by **Dave** » Mon Feb 09, 2009 10:04 am

Well the best I can come up with is that the engine and trans are not exactyl centered but off to passenger side 2". Think that goes back to allowing room for the petals. Don't know that I have ever seen a drive shaft paralle to the ground required the axle off-set. Checked my shop manual and the driveshaft angle can vary from 2 degs up to 11 degs. The later Mustangs can use the centered pumpking cause they wide enough not to have any problem with clearance (plus a top-loading trans type).
He's some info I grabed off the web:

Driveshaft Alignment
A recent posting to the HAMB (a rodder's discussion forum on the Internet) by world renown freelance author Skip Readio bears repeating here. It is an important aspect of rod building that is often overlooked. Reproduced here with Skip's consent:

A handy tip for the amateur builder...

Differential pinion and transmission tailshaft universal joint (driveshaft) vertical angles get a lot of attention when folks build cars but one of the angle combinations that often get overlooked is the lateral angle. Often times the universal joint angles, as viewed from above the vehicle, between the transmission mainshaft and the pinion shaft are not equal.

One of the more prevalent occurrences of the oversight occurs when the builder grafts a late model subframe under an older vehicle and utilizes the stock transmission-mounting hole. Narrowing a subframe also results in odd engine placement angles when exhaust manifolds and power steering pumps won't clear the upper control arms and the engine gets shifted to the right.

Once the front engine mount placement has been determined, it is imperative that the rear engine mount on the transmission tailshaft be located in such a manner as to put the transmission tailshaft centerline parallel to the pinion centerline. Quite often this will require that the tailshaft be moved towards the right side of the vehicle.

Assuming you have cross-checked your axle alignments and your differential housing is square with your chassis, one of the simplest ways to check that the angles are the same is to clamp a couple of long straight edges to the U-joint cups. An aluminum carpenter's level works quite well for this.

Take a large nut that will just fit into the cavity of the yoke on the transmission and act as a spacer so that you can clamp the carpenter's level to the U-joint cup, not the rough yoke forging. If your U-joint cup sticks out of the yoke, you won't need to find a spacer. Lay the nut on a flat surface and use a carpenter's square to make sure it's flat.

Put the spacer (nut) on the U-joint cup and clamp the level to the cup so that the level extends alongside the driveshaft. The straight edge should be beside the driveshaft, not over or under it (i.e. the U-joint cup you have the straightedge clamped to should be orientated to the 3:00 or 9:00 o'clock position.)

You should be clamping your straightedge to the U-joint cup that is in the pinion yoke and/or the tailshaft yoke, not the driveshaft yoke(s).

Clamp the other level to a U-joint on the other end and check to see that the two straight edges are parallel. If they're not parallel, slide the transmission mount to compensate for the error.

Warpig Racing · Post by **Warpig Racing** » Mon Feb 09, 2009 2:31 pm

rojam18801 wrote:warpig is your narrowed 9 inch centered, i think mine is but never measured it. have to do that when i get home again. it looks center...the old trucker

Mine is offset 1/4 inch. Not by design, just how it all got welded up. I bought the narrowed housing on ebay (like $200 shipped) which was 40 inch flange to flange. was slightly offset but close enough for me.