what rear end ratio for 327/Powerglide

[likaroc13]

i'm just brainstorming for the near future...my '66 has a 327/Powerglide combo...i'm leaning toward continuing to run the Powerglide for a while, then switch to the 700R4 later down the road...i plan to switch to 5-lug front & rear...my question is, what gear ratio would be best for this motor/trans combo? i would like to add that i plan on static dropping the truck significantly & running a skinny/fat tire combo...wheels will be either 15x7 or 15x8 front, & 15x8 or 15x10 rear...currently i just drive around town, but i'd like to be able to do some highway cruising in the future...so, let me know what you think/suggest....thanks

[robby5323]

Hmmm.... Powerglide, 327, a short/fat tire & some highway use... I would say something between 3:73s to 3:23s... Nothing to steep in the gears if you still want to be able to cruise highway at reasonable speeds for any length of time... 3:73s would still be a good choice with the overdrive.

[Shaky]

I go with a minimum of 3.42.

Have you considered putting a TH350 in? It's a real easy swap - you don't even need to change the driveshaft.

[rain_man]

Originally Posted by Shaky

I go with a minimum of 3.42.

Have you considered putting a TH350 in? It's a real easy swap - you don't even need to change the driveshaft.

i have a a 327 with TH350 love it.
3:73 gears

[Russ65C10]

If your really planning on dropping a 700R4 in (you love it if you do), I'd stick with 3.73's. I have a 65 that came with 283/powerglide and 3.73 limited slip rearend. Dropped a 700R4 in I cruze down the freeway at 65 mph cranking 2200 rpms 85 mph = about 3000 rpm.

BTW - I am not knocking 3 autos but I ran a TH350 for a while before I dropped the 700R4 in, didn't really see a big advantage, I go over hill on my daily drive and I found the powerglide actually provided more engine braking than TH350 and I didn't see any noticeable improvement in accelleration or hillclimbing ability. Of course it could've been that I pulled it out of junked 80's malibu ;-0

[jchav62]

For 327/PG combo, around town, 3:73's will be alot more fun. It will a perfect ratio for the 700r4. In the future, if you are not able to get the overdrive transmission and you still want to be able to go out on the highway, 3:08's or 3:42's. 3:73's are okay with a non-overdrive 1:1 transmission, but they are still a little on the low side. You'll be well above 3,000 rpms at freeway speeds.

[TwoFiftyShifter]

This all depends. 3.73 is great if you A] were only hot rodding around town or B] had the 700r4 in. The 3.73 powerglide will put you at 2600 or so at 60mph, which is slow these days. 3.42 would be ok for the glide too, alittle more sluggish in town. IMO, gear for the 700r4, and rev out a little on the highway for the time being.

3.73

[likaroc13]

Originally Posted by Shaky

I go with a minimum of 3.42.

Have you considered putting a TH350 in? It's a real easy swap - you don't even need to change the driveshaft.

thanks guys...if/when i do any swapping, it'll be for the 700R4...i had first thought of doing an exchange or even selling the Powerglide...however, i have the original 283 for the truck, so i'd like to hang on to the Powerglide too(that way i have the original equipment)...& if i have a good working Powerglide, i hate to just let it sit around in favor of another tranny...at least i can use the Powerglide for now & put the extra money towards other repairs/modifications...then later i can go the 700R4 route...i'll try to find a rear with 3.73's....i think those would work best since i plan to go with the 700R...at least i wouldn't have to switch gears again, which i assume i'd have to do if i go with 3.08's...would it be very hard to find 3.73's in a '71/72 rear?

[Russ65C10]

I am pretty sure the 3.73's were one of the more common gear sets so it should be easy to find one in 71/72 or any other year for that matter. They're about as good a all round as you could've ordered in these old truck. I both my 66 & 65 came standard with them and they're still pretty common in today's trucks. If your looking for 5 lug rear end I think you need to go newer than 72 but I could be wrong.

Do you know what you currently have in the truck?

[likaroc13]

Originally Posted by Russ65C10

I am pretty sure the 3.73's were one of the more common gear sets so it should be easy to find one in 71/72 or any other year for that matter. They're about as good a all round as you could've ordered in these old truck. I both my 66 & 65 came standard with them and they're still pretty common in today's trucks. If your looking for 5 lug rear end I think you need to go newer than 72 but I could be wrong.

Do you know what you currently have in the truck?

that's what i thought...not sure what mine has for sure...it's low though, so i'm figuring 4.11's...with the '71/72 rear, you can just swap it in...it's a tad wider but still utilizes the trailing arms without modification if i'm not mistaken...'73-87 is same width as 71/72, but you would have to cut off & mount perches for the trailing arms

[Captainfab]

I would suggest pulling the rear cover and seeing just what you do have before you get excited about finding another rear end.

[fleetsidelarry]

For years, I drove my '66 (with a th375) with what I would have sworn was a 4:11 because of how wound up it was at 55, when I checked it, it turned out to be a 3:73. So, as Captainfab suggested, you might want to find out what you have as a starting point. You can also check the ratio without removing the cover.

I now have a 3:08 (or is that 3:07) with my 700r and couldn't be happier. Around town I can keep it in 3rd (which is 1:1 remember) for anything up to 45 (about 2000 rpm), on the highway 4th (OD) is perfect and, when I want to keep up with the Interstate bunch, I reach down and throw the manual lockup switch. The 700r's low first gear gets you launched just fine, I can still light up a tire if I want BUT, of course, it doesn't accelerate like a 3:73.

BTW, the 71-72 rears ARE 5 bolt

[jchav62]

I run a th350 with a GearVendors overdrive unit. I had 3:08's for a while, and it did great on the flats, but with the mountains around here, 3.08's made it feel a little 'doggy' on the highway. Switched to 3:73's and I'm much happier. Not only that, it's alot better 'off-the-line' gear.

[fleetsidelarry]

Originally Posted by jchav62

I run a th350 with a GearVendors overdrive unit. I had 3:08's for a while, and it did great on the flats, but with the mountains around here, 3.08's made it feel a little 'doggy' on the highway. Switched to 3:73's and I'm much happier. Not only that, it's alot better 'off-the-line' gear.

good point about the terrain, it's pretty flat here in coastal Georgia, north of Atlanta might be a different story, gear-wise

[Shaky]

Originally Posted by likaroc13

thanks guys...if/when i do any swapping, it'll be for the 700R4...i had first thought of doing an exchange or even selling the Powerglide...however, i have the original 283 for the truck, so i'd like to hang on to the Powerglide too(that way i have the original equipment)...& if i have a good working Powerglide, i hate to just let it sit around in favor of another tranny...at least i can use the Powerglide for now & put the extra money towards other repairs/modifications...then later i can go the 700R4 route...i'll try to find a rear with 3.73's....i think those would work best since i plan to go with the 700R...at least i wouldn't have to switch gears again, which i assume i'd have to do if i go with 3.08's...would it be very hard to find 3.73's in a '71/72 rear?

I thought you might be tight on money - that's why I suggested the TH350. If you can afford the 4-speed then it's all good.

[likaroc13]

i see 3856525 on the pumpkin...will that tell me anything?

[likaroc13]

Originally Posted by Shaky

I thought you might be tight on money - that's why I suggested the TH350. If you can afford the 4-speed then it's all good.

no, it's cool & i really appreciate your input...and currently i am tight on money...for that reason, i plan on keeping the Powerglide for a while...but when i can switch, it'll be for the 700R4...after all, this is just a toy for me...i don't have to depend on it everyday

[likaroc13]

Originally Posted by Captainfab

I would suggest pulling the rear cover and seeing just what you do have before you get excited about finding another rear end.

"To check rear end ratio jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading."

i followed this trick today, & it seems that it very well might be 3.73's...i'll know for sure when i get the rear serviced...even so, wouldn't it still be cheaper to find a donor '71/72 rear? i looked at CPP & Early Classic, & those 5-lug axle conversions aren't cheap...not to mention, wouldn't the rear track width be shorter than the front if i keep the '66 rear & switch to 73-87 front crossmember?