Ford 8.8 conversion

I'll beg to differ on the bold part of your statement Frank from the experience I had last year doing the exact swap you're talking about. I posted it in Frankenrambler and I'll repost it here again so someone else doesn't make the same mistake I did in my 73.

I know from experience earlier this year that having an offset pinion angle can add vibration if not properly done. I put an 8.8 Explorer rear in my Javelin and since I needed the full width, I ended up with the pinion 2" offset. With the standard 2.5° down angle on the engine/trans and the pinion going up 2.5°, I had over a 3° U joint angle and it vibrated so bad it wasn't drive able above 60 mph. I managed to raise the trans a little so I was at 2.1° and matched the pinion to it and it only lowered the operating angle to 2.9°. It still vibrates but it's not bad until I get to 75 -80 mph is where it's the worse. That rear is coming out and getting a 9" with a centered pinion because I can't straighten out the engine/trans angle enough to lower the operating angle. Since you're building it now, you can avoid a situation like this by reading that book and watching your angles and offset. The best tool I found to measure the angle is called "Bubble level" a free app I got for my phone. It reads angle with one decimal point which is enough. This whole deal was a big, time consuming, learning experience for me as I thought I knew what I was doing having messed with U joint angles when I worked at dealerships.

I highly suggest doing some reading in this book from Spicer before you start welding to much.
http://media.spicerparts.com/cfs/files/media/4ohobHpp8jBQnRpq4/j3311-1-dssp.pdf?token=eyJhdXRoVG9rZW4iOiIifQ%3D%3D&store=original
They also have U joint angle calculator and a Torsional Analysis calculator on their website that will show you what the operating angles will be. The latter is really good when working with compound angles but be sure to read how they relate to the angles when entering your numbers in.  http://spicerparts.com/calculators/torsional-analysis-calculator

Basically the offset adds to your total joint angle. For example, if you use the torsional calculator with the following numbers which is close to what I have, on the first page I entered 3700 rpm for shaft speed.
Second page, 0 angle and 38" long.
Third page, 2° down for driving and 2° up for driven - that's the parallel angels to cancel U joint vibration.
Fourth page, this is where you enter the offset. I have 2".
Now go to the results page and now it's showing 3.62° for each joint and 4.91° torsional. You'll note what the maximum angles are shown in the red down at the bottom.
If you go back to the offset page and change the number to 0" and then go back to the results page, you'll now see the U joint angles are 2° and the torsional is 0 because the parallel angels on the U joins are the same. I also have read somewhere, maybe in that manual, that above 3° U joint angle, it will cause vibration which I have come to find out is true.

One other thing to note is the shaft speed does play heavy on this. With the 3.73 gear and 26" tall tires on my car, 3700 on my car is about 80 mph but if you have a lower gear ratio, your torsional numbers are going to be lower. Try going back to the first page and lower the shaft speed to 2600 rpm and see what you get. By changing the numbers around and see the effect they have, you can get a good idea of how it all works together and what you need to change before welding it all up. Its a great tool to avoid driveline vibration while you build your car.
Here's a link to all their calculators. http://spicerparts.com/calculators
If it helps just one person with their build/problem, it's worth posting then.

The post is here with tomj and I discussing it. http://theamcforum.com/forum/1964-rambler-classic-street-strip-conversion_topic90597_post804254.html?KW=#804254

 

Also of note, the 71-74 Javelin has a Tread Width = 60".  The WMS to WMS width = 61" (+/- depending on drum thickness).  The wheel disc is offset from the rim centreline, so the tread width is narrower than axle mounting surface width.   The pinion is also not centred.  I measured my '74 and it was offset 9/16" to the passenger's side.

 

Maybe a later Mustang rear would be a closer fit for the Javelin?

 

My conclusions from this thread:

 

(1) If you have an AMC 20 in good condition and your car is a cruiser, keep it.   There is a pretty good selection of ring & pinion ratios, carriers, disc brake kits (if you really have to have discs), differential covers, etc. ... and it keeps one more factory part in your AMC (... if you like to keep your car mostly factory).

 

(2) If it's a mild street-strip build with sticky tires, get one piece axle shafts, reinforce the perches and see (1).  Dr.Diff's for an economical option, if you have the ability to cut them to suit.   Moser, Dutchman, etc. if not.  Weld on Ford 9" ends or retube completely for more serious use, and to get better bearing and brake kit options ... but if not an AMC purest, option (5) may be a better plan.

 

(3) If you are a scrounger and trust your local fab shop to rework it, or your own skills, go to the boneyard and find a good Ford 8.8" or two and go from there ... but it may also need some upgrades, depending on application ... but a bit lower cost than similar upgrades to the AMC 20.  Some mating parts need to change.

 

(4) If you "know a guy" who has an early Ford 9" or Mopar 8 3/4" for sale that's the right fit, it may be the closest to a "bolt-in-no-weld" option ... without spending a bunch of cash to choose option (5).  Expect some bolt-on parts may also need changing, e.g. driveshaft, u-bolts, shock mounts, etc.

 

(5) If your AMC 20 is junk, you've had no luck finding one in the "Wanted" section, your build will push the old AMC 20 beyond its limits, or you simply want something with unlimited options, custom order a 9" to your specifications (as mentioned earlier in the thread) ... or if fewer options are ok and you hate Fords, a Dana 60 ... or a Mopar 8 3/4 ... or a custom 12 bolt if you like Chevies ... or a custom 8.8 if you really want an 8.8.   Depending on options, typically range from $2500 up.  Lots of places building various custom rear axle combinations ...  Ford 9" is still most popular with best selection of gear ratios, carriers, etc. ... but can get expensive quick depending which options you select.

 

Hope this helps, RD.