Gearing Question

[MrChips]

Ok, so I need to get into the pumpkin, have way too much pinion slack. So while I am there I am going to get rid of the open 2.73's that are there. But I am not sure what to go back with.

car is a 37 Chevy, 10 bolt 8.5" rear, 425 HP 406, 400TH tranny w/TCI Saturday Night Special torque converter. I know I am going back with a posi, but don't know if I want 3.42 or 3.73. Wish to keep it trip drivable without big RPMs at highway speed but want something more than 2.73's.

Any thoughts??

Brett

[jerry clayton]

non od you might want to be closer to 3.00---

a lot of pinion doesn't necessarorly mean too much back lash---backlash is measured from the ring gear

[HOSS429]

if you`re not racing the car .. time to step up to overdrive ..

[MrChips]

Not racing it. May just stick witht he 2.73 then. As far as backlash, yea I know it is measured at the ring. I am trying to track down a clanking noise I have when it shifts from 1<2 and 2<1. The only thing I can find is about 1/2" rotational play in the pinion when i unhook the driveline. That is about 1/2' in both directions before it turns the ring gear. So i knew I was going in the rearend for a fix. So thought while I was there would change to a posi and possibly a little lower gear. But was not sure where to go on the gears and still be able to keep a decent RPM at highway speeds. Not really looking at chaning trannys at this point.

[pat mccarthy]

crush sleeve may be getting beat out on tall tire cars i use 3.50 s so low 3.08 gear if you still want some zip but i do not know what size tire your runing

[MrChips]

Rear tires are 255/60/15.

[pat mccarthy]

Rear tires are 255/60/15.

about 2133 RPM AT 60 MPH

[jerry clayton]

So I take it that you didn't drop the pan on the trans????

1/2 inch turn on a drive shaft is not out of reason before the wheels turn--you also have to take up the slack in the spider gears/axle splines

you either have a trans problem or possibly a bad engine mount, converter /flex plate loose,

[MrChips]

I did drop the trans pan. Found nothing out of the ordinary. Just tranny fluid. both engine mounts look good, trans mount looks good. Have not been able to take it out and drive in locked first and second to see what that does, do to weather. If I wasn't already bald I would be pulling my hair out. Really has me stumped as to what the noise is. I will find it at some point. I figured that much slack was too much. I had the pumpkin open a coulpe weeks ago and everything looked good inside.

[pat mccarthy]

bad U joints ? how much back lash on the ring gear ? pinion climbing

[Itoldyouso]

IMO 3:50 gears or thereabouts are just about perfect for out of the hole performance and good cruising rpms. I think you would notice a big difference in seat of the pants feel if you go from 2:73's to 3:42's.

Don

[cajunace]

IMO 3:50 gears or thereabouts are just about perfect for out of the hole performance and good cruising rpms. I think you would notice a big difference in seat of the pants feel if you go from 2:73's to 3:42's.

Don

I agree here is the breakdown,these are +/- 1%

2:73 @ 2350 rpm @ 70mph
3:23 @ 2800 rpm @ 70 mph
3:42 @ 3000 rpm @70 mph
3:73 @ 3250 rpm @ 70 mph

[pat mccarthy]

i have had 4.56.4.33. 4.11.3.10 .3.23.3.50. 3.89 .3.70 for the street 3.23 work good on the hi way right now both cars are running 3.89 i do not do alot of hi way driving use to drive the car to the race track 40 miles one way or so. i like the hi gears track time did not drop much with a DOT tire 3.50 is a good fit on a street rod tub out with 32 tall tires

[MrChips]

We primarily just drive to car shows and that type of driving. Not alot of highway stuff really. I think if i end up having to replace stuff in the rear i will look at either 3.23 or 3.42. If I can find that the problem is not in the rear then I will just leave as is. Unfortunately the snowstorm this weekend left my garage to cold to work in and the roads to bad to be on for awhile. So she sits.....
Thanks to all for the info, once I figure out what my noise issue is I will be sure and share.