64 Skylark Rear End Ratio?

[Guest]

I'm preparing to upgrade my open rear end with 3.55 gears and a Powertrax unit but I've come across something I can't figure out. If anyone can explain this I would appreciate it. The question is this--- I wanted to know what gears I currently have so I used the "count the tire and drive shaft" approach rather than pulling the cover and counting teeth. What I found is that 1 full tire revolution translated to just under 1.5 revolutions of the drive line. If I understand the math, this tells me my rearend ratio is 1.5:1. CAN THIS BE TRUE? I've never heard of this tall of gears in this car. My Chasis Manual says 2.78 was the tallest gear available stock. Am I doing something wrong in the way I'm calculating this?<P>Thanks for any info...<P>jc<BR>

[The Old Guy]

If you only jacked up one wheel , you will get a wrong number ,as the differential gears come into play. I would wager if you jack up the whole rear end ,and turn both rear wheels one revolution ,you will find that you do have a high 2 ratio.

[Guest]

I did make sure to jack the whole rear of the car so both sides were off the ground. I tried rotating tire seperately and came up with the same figures. I guess my next step will be to pull the cover and count the teeth.<P>jc<BR>

[66400]

JC, Just multiply by two and you'll have it! Henry.

[Guest]

Henry,<P>Are you serious? That does make some sense as it puts the ratio about 2.78. HOWEVER, I still don't uderstand why it needs to be multiplied by two. Can you explain? OR, are you just kidding me.<P>jc

[Guest]

It has to do with the spider gears in the non posi axle. If memory is correct, the side gears that the axle shafts go into have twice as many teeth as the gears that go on the shaft in the housing. So, for one turn of the axle, the gears rotate around the non spinning axle only 1/2 turn. This means the ring gear only spins 1/2 turn as well. <BR>Therefore, you have to double the turns of the pinion gear(drive shaft) in order to get the axle ratio.<BR>The stock ratio for a 64 Skylark automatic should be a 2.78 to one. So, a little less than 1.5 turns would be correct.<BR>Mark

[The Old Guy]

I guess I didn't make my last post clear. You must turn both rear wheels at the same time or you will still bring the spider gears into play. I usually mark the driveshaft and then roll the car one revolution of the wheel while watching the mark. You can get close enough with this method to figure your gear.

[Guest]

Thanks Everyone,<P>I've got it now. Looks like my 2.78 is actually a 2.78!<P>Now for my upgrade. 3.55, Powertrax, and a BIG 455! <P>Hope it all works.<P>jc

[Guest]

JC,<BR>If I can add my 2 cents here. I went through the same thing with a 64 Skylark years ago.<BR>Rather than work up the 64 rear, look for a Canadian Buick rear (aka Chevy 12 bolt)out of a 68-70 Skylark. The parts availability is much better and you have a wider variety of ratio's. One differene I found was that the springs pads don't bolt down like the 64-66, which is not a big deal. The other is that the upper arms may rub against the axle on the drivers side as the 12 bolt is a 8.78 ring gear instead of the 8.25 Buick. All you will have to do is get a drivers side arm from a 67 Chevelle which is modified and should not be too hard to find.<BR>Finding a posi unit for a 3.55 gearset for a 64 will not be an easy task. However, you should be able to find 12 bolt parts available new through a few suppliers.<BR>Good Luck,<BR>Mark

[Guest]

Thanks Mark for the Info. I'll give that some consideration for sure.<P>I've also thought about a Ford 9" modified for a GM A-body. But the cost is a little steep and I would hate to disapoint my fellow Buick enthusiasts by puttting a FORD part in a BUICK!<P>Thanks again,<P>jc

[Guest John Chapman]

jc...<P>Following info is from the 1964 Special/Skylark assembly manual.<P>Data in following format.<BR>Diff Type/Ratio/Stamped Code Letter/Color Code/Standard Application-Notes<P>Std/2.78/C/Black/V8 auto<BR>Std/3.08/A/White/V8 Auto Air<BR>Std/3.23/B/Green/V6 Auto/V8 Wag Auto<BR>Std/3.36/E/Yellow/V6 Auto Air<BR>Std/3.55/D/Pink/V6 Wag Auto<BR>Std/3.90/F/Brown/SCO<BR>Posi/2.78/CircledXC/Black and Orange/all posi as above<BR>Posi/3.08/CircledXA/White and Orange<BR>Posi/3.23/CircledXB/Green and Orange<BR>Posi/3.36/CircledXE/Yellow and Orange<BR>Posi/3.55/CircledXD/Pink and Orange<BR>Posi/3.90/CircledXF/Brown and Orange<P>Marking Location:<BR>Paint color daubs on carrier... location not specified.<P>Field Identification Stamp (Letter code and assembly date):<P>Stamped into the bottom side of right axle tube appx 1.5" toward the wheel from tube joint within a 0.5" circle in following format example:<P>Std 3.08 Ratio assembled on July 22 "A-203"<BR>Posi would be "CircledXA-203". The date would be the 203rd day of the year.<P>Assembly Plant ID:<BR>Stamped in Yellow ink on bottom of carrier at the center. Manual didn't have codes listed for assembly locations, but they may coincide with assembly plant coding.<P>Posi axles are also identified by the POSI tag attached to the rear cover by one of the bolts... but this is not certain.<P>To find a low ratio, I'd look for the V6 wagon or AC sedans.<P>Happy hunting.<P>John

[Guest]

Thanks a lot John.<P>That's great info... Looks like I'll have to clean the GRIME off the darn thing and do some looking around.<P>Jeromy