MNMike Posted February 13, 2012 Share Posted February 13, 2012 Anyone have any advice on what products I should look at for converting my rear end to posi and going from 2.73 to 3.42 rear gears? I've got a rebuilt TH350 and a very strong 400 small block in a '70 Monte. I don't drive the car that often, but I live out in the boonies, so when I do it's usually a 100 mile round trip or more. Any advice would be appreciated, and I'm sure there are members on here that have done this before. What worked well for you? Quote Link to comment Share on other sites More sharing options...
Leghome Posted February 13, 2012 Share Posted February 13, 2012 My 72 has Richmond gears and they work well. I have a 700R4 tranny with 3:73 gears so 3:42's should be a good setup for a TH350. Quote Link to comment Share on other sites More sharing options...
bigtankjones Posted February 13, 2012 Share Posted February 13, 2012 I am running a Auburn Posi unit with a 3:73 gear in my 10 bolt. My '70 has a 454 bolted to a TH350. Not very good on the highway but allot of fun on the street. I have had this set up for 3 years with no problems. Quote Link to comment Share on other sites More sharing options...
MNMike Posted February 13, 2012 Author Share Posted February 13, 2012 Thanks for the replies - any suggestions where to buy from? Should I stay with the stock axles? Quote Link to comment Share on other sites More sharing options...
dbreese Posted February 13, 2012 Share Posted February 13, 2012 Hey Mike, Several options. Eaton Posi are reliable and can be rebuilt. I had an Eaton P track with 3.73 motive gears and moser axles in an 8.2 rear and a h/d rear cover with a th350 and a 385 s/b. I beat the snot out of that combo at the track for 5 years and never had a problem. 8.2 10 bolt is by far the weakest of rears but it held up. New engine combo is pretty stout for a s/b. I stepped up to a moser 12 bolt housing w/ detroit tru-trac center, 3.73 motive gears, 33 bolt-in style axles and a h/d rear cover. Same th350 with a 10" coan converter(4100 stall). 3.73 gears seem to be a good all around gear for street/strip use with non od transmissons. You could go deeper but then as you know ya start sacrificing street manors. David Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted February 13, 2012 Share Posted February 13, 2012 I agree with Dave on the Eaton posi but would go with 3.55s unless some track time is in your future. Quote Link to comment Share on other sites More sharing options...
dbreese Posted February 13, 2012 Share Posted February 13, 2012 Thanks for the replies - any suggestions where to buy from? Should I stay with the stock axles? Moser and Randy's Ring and Pinion are just a few places. Axle upgrade is a good thing and not much more money since your upgrading the rest. David Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted February 13, 2012 Share Posted February 13, 2012 Just a note, I noticed you mention that when you drive the car, it is for long distances (i.e. 100+ miles), presumably at relatively high speeds. If so, you will find better fuel economy if you stay with 2.73. I debated the idea of changing gears on my car but am not willing to take a drop in mileage across the board making me less likely to want to drive it. However, if you change the tranny to a 700R4 you can apparently have the best of both worlds. Just some food for thought. Good luck, no matter what you decide. Quote Link to comment Share on other sites More sharing options...
Blue502 Posted February 13, 2012 Share Posted February 13, 2012 Good advice.Too bad you already had the TH350 done.A hi stall convertor and gear will make a huge difference.You will still need a posi.After a posi,gear and axles installed you may find a nice 12 bolt or 8.5 for the same money.I would stay away from Richmond gears.Their quality has gone way down in the last couple of years. Good luck Just a note, I noticed you mention that when you drive the car, it is for long distances (i.e. 100+ miles), presumably at relatively high speeds. If so, you will find better fuel economy if you stay with 2.73. I debated the idea of changing gears on my car but am not willing to take a drop in mileage across the board making me less likely to want to drive it. However, if you change the tranny to a 700R4 you can apparently have the best of both worlds. Just some food for thought. Good luck, no matter what you decide. Quote Link to comment Share on other sites More sharing options...
Chevyss Posted February 13, 2012 Share Posted February 13, 2012 We installed Richmond gears (3:73) and an Auburn posi in my 12bolt about four years ago and no problems yet. I have Moser axles w/c-clip eliminators. Very satisfied with a job well done. Quote Link to comment Share on other sites More sharing options...
AL M Posted February 13, 2012 Share Posted February 13, 2012 I'm w/ Mike....3:55s are tuff to beat...best of both worlds. I have an Eaton. My 355s were richmond and my new 411s are Liberty. Both have given me nothing but great performance. Quote Link to comment Share on other sites More sharing options...
Dans '70 Z20 Posted February 14, 2012 Share Posted February 14, 2012 My tranny guy swears by the 3:55 also. If your looking for some gear but want decent cruising rpms I'd go with a set of 3:42 or 3:55's. If you had a big block you could get away with 3:31's due to the extra torque down low but with a small block 3;42's or 3:55's will suit you fine. Just don't expect to be cruisin at 70+mph for that long. Here is a website with calculators to calculate you rpms at highway speeds with varying gear sizes. It will help you decide. Wallace Racing Calculators Dan Quote Link to comment Share on other sites More sharing options...
Ian Posted February 14, 2012 Share Posted February 14, 2012 I went with an Eaton and 3.42's behind my pretty much stock 402 and love them! A little wound up at 70+ on the highway but not bad around town and on the long back roads. Someday I am going to get a overdrive (not sure which one yet...) Quote Link to comment Share on other sites More sharing options...
Leghome Posted February 14, 2012 Share Posted February 14, 2012 My 3:73's witht he 700R4 is only running about 2750RPM's at 72MPH Quote Link to comment Share on other sites More sharing options...
RARE MC Posted February 16, 2012 Share Posted February 16, 2012 I'm with MG. Stay with the 2.73's. I had 2.56's and went to 3.31 and can't stand them. I am spoiled by my OD cars. Installing a GV overdrive now. Not sure what new gears I'm going to need to go to, if any. Quote Link to comment Share on other sites More sharing options...
dbreese Posted February 17, 2012 Share Posted February 17, 2012 3.73 gears a non od transmission, 3" exhaust and an angry s/b @ 70 mph= low gas mileage, 3500 rpm, lot's of noise and big smiles. David Quote Link to comment Share on other sites More sharing options...
gjmike72 Posted February 18, 2012 Share Posted February 18, 2012 I'm running a 350HP/350CID with TH350 trans and 3.42 gear w/detroit locker and Moser axles in a 12 bolt. The gear is a great compromise on the street and turns around 3100RPM @ 70 on the highway. The locker can get a little tricky in parking lots and tight turns...posi would have been a smoother choice! The set-up has held strong for 5 years with the occasional 175 shot of N2O at the track. I only get around 12MPG on good days...that's the downside. Quote Link to comment Share on other sites More sharing options...
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