I have a 71 GS 350/350 with 3.08 posi rear, 60k miles on it. If i would change to 3.73 gears, should i only take something like this https://www.ebay.com/itm/NEW-Rear-D...17628306?epid=24016995883&hash=item5455da6292 or do i need this https://www.ebay.com/itm/Dura-Grip-...ear-Set-Super-Master-Bearing-Kit/282946205665 is this new posi unit better than an old original ?
Depends on what kind of OEM posi unit it is.. I'd look to talk to the people who knows these axles inside and out, your got 3 to choose from here on the board - Ken at Everyday Performance (Techg8), Jim from JD Race (Monzas), and Brian Trick (dont know his screen name). If you've got an OEM Eaton style clutch posi in the car now (and it works), I'd leave it - those are good. It'll take any 3 series gear. If you have the Auburn style, I'd replace it with an aftermarket Eaton style. Any of the folks I mentioned can supply you with the right parts and all the advice you need to walk through the job, or you can ship the posi or whole axle to them to work on for you. Shipping via Fastenall pallet is cheap compared the alternative. For ID purposes, the Auburn style posi is on the right, the Eaton Style is on the left.
I believe if your car is a keeper you should invest in better parts...lol. Jim Do you have a freight forwarder?
Plus as what was stated buy from someone who will help you with your set-up.... There are TONS of places that sell parts and sell them cheap. What if you get the wrong part? What if something is not going the way you expect? Do not think that they are going to be able to or even want to help. These parts have a long expensive travel and you want to be sure the parts are all correct and if the car is a keeper ones that will last a good long time. It is your choice and can buy what and where you want . Just shooting from 25 years of Business diff set-up experience. and 30 years for actual differential set-up. We are all here to help you on the site. Jim J D Race
The linked parts are only for example to describe my question can i change the gears only or is changing all with bearings etc a must, its difficult with my bad english, sorry when the season is over i will look which posi i have and if the parts around are in good shape assuming i have the OEM Eaton style clutch posi and everithing else is ok, what gears would you recommend ?
Had no idea you were in Germany! Cause we all think Germans are driving 150 MPH (240 kph?)on the Autobahn, I would suggest no more gear than 3.42. If you only change your ring and pinion, you dont HAVE to change anything more than the pinion bearing, but it just makes sense to change all bearings and seals. Find a way to do business with Jim - He'll get you the right parts, and on an 8.5 thats very important. The wrong axle seal (and most are) can really cause problems.
Just to correct some info. The square clutch tab unit is a Trac lock style not Eaton style (eaton looks totally different than the s spring unit) Plus Eaton has nothing to do with this 's' spring unit. The other is a Auburn / Borg warner cone unit. I do not prefer (get as good a deal) the Auburn units BUT I also have not had trouble with the unit that we have install either.
If you have a posi already with 3.08 gears you can use all the parts you have and just change the ratio. I would suggest you swap out new bearings and seal on the pinion too. as you will need to remove most of those parts. and that it appear to be all original from 1971 it is about DUE for a rebuild. So a ring and pinion set and a master rebuild kit will be all you will need as long as you limited slip posi is in good shape. Jim J D Race
If you can remove your cover to identify which posi unit you have,that will help with the suggestions. If it is the cone style that came in some of those Buick rears,I would get a new unit. If it has the clutch style unit,with the square tabs,and S-spring,I would keep that,and just get new gears,bearings,and an installation kit. A few of us can help you with the install,or any issues,since this is what we do. We don’t just sell parts.
I ditto the 3.08 keep and just check out the posi to be sure the clutch pack is tight and just re-bearing the rear and be done. If you bump up the stall convertor to 200-2500 you will get your harder hit off the line for burn outs. Still keeping your drive-ability for the freeway.
Ok, i have forgot something in the first post, if i change the gears i plan also a swap to a th200-4r, so i have better acceleration and still drive-ability for the freeway. Or is that a bad plan ? The 3.73 rear gears was a suggestion from Jim Weise, when i asked him about a converter for my car. He said: "In that combo, the thing that is killing you is the 3.08 gear. We get away with that gear in a Big block car because of the torque, but the small block really needs at the very least a 3.42 gear. 3.73 would be better.. Maybe not the greatest thing for the autobahn, but if you were worried about that, you would not be asking me about a converter.. I assume your trying to improve your acceleration."
It really is your call. If the 350 has a 280 or steeper duration (230 at .050) then you might want the 3.73 gear The 3.42 will be fine with a more stock 250 260 270 duration cam lots of low end torque cam. AND AGAIN you the customer have to know what you are going to do more ...burn outs and low end torque fun or more driving longer distances. THAT will tell you what ratio to use also. Hope that helps.
If your getting a new tranny do not forget to pick a good stall for the driving your doing again...steeper stall more light to light action and less stall for more freeway driving and mileage. DEPENDS on if your going to install the lock up converter also... Lots of home work to do. Jim
I have 3.73 gears in my car with a turbo 200-4R. It is a great combo, takes off like 4.10s and cruises like 2.73s.
