4.56 Ring/Pinion Ratio with a SB350/TH350

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4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Tue Mar 24, 2015 9:57 am

Hi. I've recently torn out the differential on my 74 Chevelle Malibu for inspection and to determine what exactly is in there. I realized that the ring/pinion ratio is 4.56:1 (41 teeth on ring, 9 on pinion) in a limited slip differential. I always assumed it to be a 2.73 or similar. I do not know what engine and trans was in the car before I purchased it. I do know, however, after finding a code on the housing, that the housing is from a Buick and should have a 2.73:1 ratio and open diff (Code: AC B 1191).

I don't know a whole lot about differentials and gear ratios and how one would go about choosing the right ratio for their application. The engine that I have for it is a slightly built 350 with a nothing special TH350 trans. Nothing special, just something to get the car down the road until I can afford to build something with a bit more oomph.

My question: Is a 4.56 ratio too much? Is there such a thing as too much? How do I chose the proper gear ratio for the car? Should I purchase a 2.73 or 3.73 set?

I know that if you increase tire sizes, you want to increase the gear ratio, but I don't know if 4.56:1 is something I should put back in with what I have and I don't know how to determine that. I've been googling my A$$ off trying to figure this out, but I don't think I'm finding the right information.

Thanks!
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Joe73 on Tue Mar 24, 2015 10:23 am

First decide what you want to do with the car. Track racing, just cruising, daily driver???

Then you can pick a ratio. Your t350 is a 1:1 final ratio. Same as my muncie. I run 4.10s in the rear. Is it too much for cruising, I think so. Highway driving is useless with the rpms the motor turning. 4.56 would be worse.

So, for drag racing only, I'd keep them.

For street driving with no highway time, I'd probably keep them until you decide what you like and need. And it would make for real nice "launches".

For all just cruising with highway time, 3.73 max gear.

My car was my daily driver and came with factory 3.42s. It was ok on the highway with mid 2000 rpms at 55-60.

Plenty of rpm charts on the net. Take a look at them and determine what you can live with.

Another option down the road would be an overdrive trans. That would give you a .73 final drive ratio if I remember correctly and a lower first gear than your 2.52 1st gear ratio of your t350. So you would have the best of both worlds. Better launch and highway driveability.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Oldschool454 on Tue Mar 24, 2015 10:23 am

Hello, Just my 2 cents. If you are just wanting something to get around in I think 4.56 is WAAAAY overkill. In fact you would probably want the exact opposite (2.56 or 2.73) for what you are saying you would like to use the vehicle for, for now. If you want a little more performance but still want a decent driver for the streets/interstate driving, 3.73s have always been viewed by most as the best middle ground gear to have. If you want to find out how it will drive at what speed with different rear end gears you can look up a "mph calculator" on google and plug in your tranny gear, tire diameter, and whatever rear end gear you're thinking about putting in, and it will tell you what RPM you will be running at what speed(mph). Hope that helps a little.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Oldschool454 on Tue Mar 24, 2015 10:25 am

....Yeah, what Joe73 said too. lol
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Tue Mar 24, 2015 10:36 am

Thanks guys. For now I just want to be able to get the car on the road and enjoy it before deciding if it's going to be a strip car or not. Having had the car since '07, I've only driven for a max of less than 15 minutes total before it being ripped apart. I will definitely take all of that info into consideration. It gives me a direction to head in. Thanks again!
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Dinomyte on Tue Mar 24, 2015 12:42 pm

Just like Joe said. It's the same advice I got and decided on 3.23s and a Auburn posi. Was a 2.56 open rear before. Works very nice for cruising.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by alowerlevel on Tue Mar 24, 2015 2:31 pm

Like everyone else has said it sounds like those are gonna be way too much for what you want. In my '67 with 3:73s and a 28" tall tire runs about 2700rpm @ 60mph and its the most gear I'd ever run in a car that gets cruised alot. With those 4:56s youd be around 3300rpm @60mph with a 28" tire, and 3500rpm with a 26" tire.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by bracketchev1221 on Tue Mar 24, 2015 5:25 pm

I like to use a 3.42 gear for a street car.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Joe73 on Tue Mar 24, 2015 5:31 pm

I agree with bracketchev. 3.42 would be best all around for a street car. If there is a possibility of putting in an overdrive in the future, I'd go 3.73.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Tue Mar 24, 2015 6:20 pm

Ok. I think I'll check out the 3.42 then. Thanks everyone!
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by 77mali on Tue Mar 24, 2015 7:00 pm

A 3.08 rear end gear is also a good choice.  Good hi-way RPM's as well as very streetable "daily driving".  What engine are you running?
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Tue Mar 24, 2015 7:36 pm

It's a mild 350. Nothing special. It's been completely rebuilt, but unfortunately I managed to lose all of the specs for it.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by dynchel on Tue Mar 24, 2015 7:44 pm

I have 373's with no overdrive & i wouldn't recommend it on a "road trip car"  It is fun around town though...
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by 77mali on Tue Mar 24, 2015 8:11 pm

Either way from 3.08-3.43 you're more than good w/ a mildly built engine & TH350 combo. The 3.43 gears will increase your RPM's on the highway driving a bit but would def. add to the fun-factor and put your Posi to good use. Very Happy
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by pila on Wed Mar 25, 2015 9:08 pm

The rule of thumb in the old days was not to run over 3000 RPM on the highway, with high ratios in the rear, but I suppose it's up to the owner to determine how much RPM he wants to buzz it up to on the highway...

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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by jerry46765 on Wed Mar 25, 2015 9:50 pm

We used to drive 28 miles one way to the drag strip with 4.10s, 28" tires, big block and turbo 400. It was not bad, just hard to pass a gas station.

The Malibu in the shop has 3.42s with 28" tires but it feels so tame to drive compared to 4.10s. 4.10s feel like you are racing all the time.

It just depends what you want to do.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Thu Mar 26, 2015 9:20 am

Well that's the problem, guys. I know that I'd eventually like to take the car to the strip, if nothing more than just to see what it can do, but I don't want a trailer queen, either. I would like to take it on the highway for trips and what not. I haven't driven the car in almost 5 years. In total I only have less than 15 minutes behind the wheel since I've owned it (since '07). Also, when I did drive it, it had that 4.56:1 gear ratio, 4 different sized tires, shot suspension, and the body was falling apart. I never really got a chance to see what it actually feels like under normal conditions. I know that the vehicle was horribly bouncing the one time I tried to burn out (the rear control arm bushings are shot as well). From what everyone here has pretty much agreed on, I think the 3.42 will be my best option at this time, until such a point that I can build the drive train up and put in a 4:10 or put the 4:56 back in (which I don't currently know when it would be appropriate to use a 4:56). All I do know is that you all are awesome and I will definitely be posting more questions here as I continue the build!
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Thu Mar 26, 2015 11:01 am

Does anyone have a preferred brand for ring and pinion gears? I've read richmond gear can be noisy, but otherwise has good quality. I want to stay away from value brands, but not sure I need the top notch quality brands either. Somewhere in the middle would be nice, but I don't want to sacrifice quality. I'm currently looking at USStandardGear, but not sure if this is good quality or not. Thanks!
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by bracketchev1221 on Thu Mar 26, 2015 11:35 am

If you go with the Richmond, use their street gear. They have a cheap excel series or something that hasn't worked to well. But I think Motive, Yukon, Richmond, they are all good.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Joe73 on Thu Mar 26, 2015 11:59 am

I've installed two sets of Motives and they worked out good. I removed and replaced my 4.10s, which are Richmonds from the 80's) and they're holding up well.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by dynchel on Thu Mar 26, 2015 12:04 pm

I have Richmond street gears & they are quiet.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Sat May 30, 2015 1:33 pm

Gentlemen, I've just now gotten around to put the new ring and pinion in. I have the specs right where they should be, but I am unsure about the contact pattern. What do you all think? &
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by 77mali on Sat May 30, 2015 1:56 pm

Did you use a dial indicator while re-shimming?
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Sat May 30, 2015 2:22 pm

For backlash, yes. I checked a few spots around the ring. 7 thousands backlash. spec calls for 6-10.
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

Post by Silentknight85 on Sat May 30, 2015 2:31 pm

additionally, i used test bearings, and set the bearing preload to 8 inch lbs, (spec: 6-8 ).
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Re: 4.56 Ring/Pinion Ratio with a SB350/TH350

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