I had posted this several months ago, but I guess messages expire after so long? I have a 1985 Buick LeSabre RWD, with 307 V8. It has a 2.73 (7.5 inch) open end rear axle, according to the RPO sticker in the trunk. The car is 1 step away from showroom new condition, and I am just looking to get a little more snap out of the old dog, without having to dump too much money into it. The car is a gutless wonder, even for a 307. Before I bought it I didn't know that the 1985 use different heads than the 1980-1984 models. I am looking to just replace the inside gears/guts without having to drop the diff or replace , or replace axles or carrier. So what's the highest ratio I can go with an open end or posi without having to replace anything but the gears? I believe I was told 3.23, but I can't remember now. And also where to buy this stuff new? Posi would be nice but if it is too spendy I would just stick with an open rear. Also, is there anywhere to buy the replacement gears for the speedo cable (If I swap the rear gears)? I know after 25 years they might be a little scarce even from a GM dealer.
Would be nice if you added your city and state to your header info....members will ask where you live. Many of the S10 Blazers and GMC Jimmys had 7.5" rears and 3.42 gears. Contact Jim at www.jdrace.com or on this board as Monzaz to help you out with details.
IF you have 2.73 gears in your 7.5 rear. You can ONLY go up to 3.08 with the carrier you have in the housing. Finding a open 3 series will be VERY easy and you can use 3.23 3.42 3.73 4.10 4.56 etc. Posi units can be still NOT be terribly hard to find... you will need 26 spline posi or open. I have plenty open 3 series diffs (cheap) if you want to try 3.23 3.42 etc. Most any Transmission rebuild shops will have the correct speedo gears and might now the correct combo of tail shaft gear and speedo gear. Dealer ship will have the parts BUT may not know what the right combos go together and sometimes are not very helpful with time for customers restoring cars... At least around here they don't. Jim
Couple of Questions: Will I be able to use my current axles in the 3 series diff? Or does your diff come with axles, and if so will they match my wheel pattern? My car is the non-trailer-towing version if that helps. Will the series 3 diff fit in without any mods such as cutting drive shaft, different u-joints, etc. Saving $$$, time and headaches is of the essence for me. Also, I believe you mentioned buying thick aftermarket gears above 3.08 that WILL fit in my current carrier. If i go that route do you think its necessary to buy the install kits that are sold with them? I don't know much about diffs, and what all is involved with replacing the guts. But the websites selling them are not very descriptive.
I was not offering the whole rear end / Diff Just the diff carrier which YES would use your original 7.5 axle shafts. I do have thick gears 3.42 3.73 4.10 If you want to go that route. Watch how much gear you install as you will loose top end driving like freeway etc. Your RPMs will be much higer than with thew 2.73 gears. Jim Give a call and will discuss as it sounds like you have plenty of questions. Jim 330 659 7117
My dad had a '90 Estate Wagon with the factory towing package 3.23 limited slip and 307 Olds engine, that car was still a dog with 3.23's. The Olds 307 is a good running little engine, it just doesnt have much horsepower or torque in stock form.
Yeah no argument there. The 1980-1984 307's were slightly better, fairly comparable to the Chevrolet 305 in power if you compare same year to same year. What most people don't realize (And I didn't know till I bought one) was most of the 1985's and all the standard 1986 and newer (Non high output versions) had even smaller intake and exhaust ports than the 1980-1984 models. The new heads are stamped 7A on the upper front corner, instead of 5A for the older models. The new heads gave the motor better torque at lower RPM, and were smoother with roller valve lifters, but high RPM power is virtually non-existent. There were also a few early models sold in the US (1980-1981) that didn't have Computer Controlled Emissions, and quite a few Canadian engines were sold without it for some time. I think I am just going to leave the rear gears alone on this car for now. If the poor motor can't breathe like it was meant to I guess I'm going to heed everyone's advice and leave well enough alone. Perhaps things will change someday if I can get my hands on a good used 350 or big block.
Any pics of your car? I know it sounds like a copout, but did you ever consider dropping in an Olds 350 or 403?
Yeah I would definitely consider a 350 or 403. The 307 is a boat anchor, especially the 1985 and newer ones.
