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Username Post: Rear End Gear Ratio        (Topic#73851)
Edispets 
Member
Posts: 27
Edispets
Loc: Pinehurst, NC
Reg: 07-28-04
08-24-04 03:50 PM - Post#501727    

If a gear ratio is indicated as "4:11", does that mean for every 4 revolutions of the wheel the drive shaft turns 11 times? I saw this on an earlier post but can't find it anymore. What is a good ratio for a '66 short step with a 6 cylinder 250 if you want to ease around at 55 mph and not pull any loads?
David

http://community.webshots.com/user/clipwing

 
LGriffin 
Contributor
Posts: 436

Age: 68
Loc: Gateway to Yosemite
Reg: 04-16-04
Re: Rear End Gear Ratio
08-24-04 04:15 PM - Post#501728    
    In response to Edispets

No 4:11 means for every 4.11 turns of the engine your wheels will turn one time in what ever your highiest gear is. With 4:11 you shouldn't have any problem at 55 mph. It could be a problem depending on what your rear wheel tire diameter is.
Larry
68 C20 327/465 daily driver
63 C20 292/420 Camper truck
65 C10 ? /powerglide Custom Cab AC,PB,PS,$flashe
70 C10 250/3spd org/Gauge dash,Wood bed,HDSpr, 4Sale$1300
I don't own a vehicle that isn't old enough to drink.


 
Jolly 
Senior Member
Posts: 721
Jolly
Age: 54
Loc: 6066 GMC Trucks
Reg: 12-11-02
Re: Rear End Gear Ratio
08-24-04 11:56 PM - Post#501729    
    In response to Edispets

I did a "Gear Charts For My 1965 GMC 2500" webpage, it also has some other info about figuring gears and hph with a link to a site you can just plug inyour numbers and get your speed.
The 6066 GMC Guy

1965 GMC 3505 Rescue Squad
2008 GMC HHR Panel


 
sixty5short 
Frequent Contributor
Posts: 1565
sixty5short
Loc: NC
Reg: 05-20-02
Re: Rear End Gear Ratio
08-25-04 05:20 AM - Post#501730    
    In response to Edispets

Another way to write 4:11 is 4.11:1, "4 point eleven to 1", 4.11 revolutions of the drive shaft for every revolution of the rear wheels. Most folks don't consider 4.11 to be highway-friendly gears, (although everything is relative). 55mph probably won't be unbearable unless your tires are on the small side.
-Doug
my outdated website


 
Piranha-z 
Frequent Contributor
Posts: 1213

Loc: Just South of North
Reg: 05-21-03
Re: Rear End Gear Ratio
08-25-04 08:05 AM - Post#501731    
    In response to sixty5short

I have 3:73 gears in my truck and have 15" wheels. I am pushing 3000 RPM's at 55 . Not great for cruisin the freeway up to the cities when the speed limit is 70 MPH
Go fast or stay home


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
08-29-04 06:04 AM - Post#501732    
    In response to sixty5short

Is it fair to assume then that reducing the ratio will allow higher top-end speeds from the truck? As a novice, I am interested in possibly lowering this ratio to accomplish this. Is this a practical approach or is installing an overdrive more practical?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
sixty5short 
Frequent Contributor
Posts: 1565
sixty5short
Loc: NC
Reg: 05-20-02
Re: Rear End Gear Ratio
08-29-04 06:25 AM - Post#501733    
    In response to rincon101

Reducing the ratio will allow for higher "top-end" speeds with less rpm. I changed from a 4:10 to a 3:08- the difference on the highway is significant. Another significant change is the loss of power off the line. Be prepared to lose some umphh going to 3:08. That's where the overdrive trans comes into play. You get the best of both worlds- takeoff power AND highway speed comfort. To me, a trans switch would be preferable, but usually a little more expensive.
-Doug
my outdated website


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
09-21-04 06:13 PM - Post#501734    
    In response to sixty5short

Thanks for the reply. I have a four speed with a granny gear. If I reduce the differential's ratio as you did by about 25%, I should still have plenty of power off of the line. Agree?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
09-21-04 08:10 PM - Post#501735    
    In response to rincon101

Yep, with a granny 4 speed you can run any axle ratio you want and still have no problems getting started from a standstill.

Ray

 
tommegow 
Senior Member
Posts: 109
tommegow
Loc: Valdosta, Ga
Reg: 11-10-03
Re: Rear End Gear Ratio
09-22-04 01:20 AM - Post#501736    
    In response to Edispets

I have a 250 and a 4spd Granny manual. I switched from a 3:78 to a 3:08 and LOVE IT. It cruises so much better now.
I still haul big loads up to 1800 lbs. Gas mileage has improved 20% or so.I have not noticed any negatives thus far
I still use it like a 3 speed and rarely use 1st (occ. pulling some one out of a ditch, etc.)
Tom
So.Ga.
1966 LWB Step C-10


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
09-26-04 06:13 PM - Post#501737    
    In response to tommegow

With the input I've received on this question, I'm ready to buy a new ring/pinion set up that will reduce the ratio by 30%.

Now I've got another question and thanks in advance for any insights. My son and I are by no means expert mechanics, but we are tenacious and persistent; and we do own a repair manual for this application. How difficult is it to open up the differential and replace the ring and pinion gears? I would assume that while its open, we would want to rebuild it, e.g., bearings, races, seals,etc? Do you agree that this is wise to do? Do you know of such a kit and who may sell one?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
dvalentine 
Senior Member
Posts: 9355

Loc: Sacramento, CA
Reg: 06-22-00
Re: Rear End Gear Ratio
09-26-04 08:08 PM - Post#501738    
    In response to rincon101

Milt,

Try posting that last question in the Performance Forum. I think you will get more input in that forum.

Dennis


 
Anonymous 

Re: Rear End Gear Ratio
09-26-04 10:30 PM - Post#501739    
    In response to rincon101

Quote:

How difficult is it to open up the differential and replace the ring and pinion gears?



The mechanical installation is fairly straightforward and not terribly difficult. However, adjusting the gear mesh properly can be a tedious and finicky procedure. If this is not done correctly you can end up with problems ranging from gear noise to premature failure.

Having said this, and assuming you still have your stock 60 rear, replacing the gears is probably not a good idea. There is no gearset available for this rear which will offer enough of a ratio improvement to justify the expense and effort of replacement. If you don't want to do a complete rear end swap your best bet would be to install some type of overdrive transmission.

On my 60 C-10 with a 3.90 rear, which is probably the same as you have, I replaced the 4 speed transmission with a T-5 from an S-10 truck and it made a very enjoyable difference at highway speeds.

Installing the transmission was not difficult at all. It bolted up to the stock bellhousing after I enlarged the screw holes with a 1/2" drill. The other modifications needed were a new clutch disc, a new driveshaft, and a bit of cutting on the floor hole where the shifter comes through. I found the driveshaft at a salvage yard just by measuring, so I can't tell you what it came out of originally. If you have any other questions about the tranny swap I will be happy to answer them if I can.

Ray

 
dvalentine 
Senior Member
Posts: 9355

Loc: Sacramento, CA
Reg: 06-22-00
Re: Rear End Gear Ratio
09-27-04 06:43 AM - Post#501740    
    In response to

Quote:

If you don't want to do a complete rear end swap your best bet would be to install some type of overdrive transmission.




I'll second that !! The overdrive will retain the nice 1st-2nd launch you have now while the upper gears will give you the cruise capability. Further down the road if you still want to get even better MPG, then I'd consider the a differential swap to a later year that will give you the ring & pinion ratio you are looking for.

That will be 2 cents please.....


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-01-04 07:18 PM - Post#501741    
    In response to

This is great information and very much appreciated. You indicated in your prior post that there is not a gear set available to offer the kind of improvement I'm looking for. The solution (I thought) I found was from Chrismans (chrismans.com) I'm considering is a change in the ring:pinion ratio to the 2.73:1 ring gear that Chrisman's sells for the 7.5 GM rear end. Since the current ratio is 3.9:1, and if I'm calculating this correctly, a change to a 2.73 ring gear will increase the top-end speed/performance of the drivetrain by 30%.

Assuming my math is correct, would you agree that this is a reasonable solution?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-01-04 07:20 PM - Post#501742    
    In response to dvalentine

Thank you for the reply. I look forward to any input that you may have along with "raycow's" on my follow up post.
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
10-01-04 10:51 PM - Post#501743    
    In response to rincon101

Quote:

I'm considering is a change in the ring:pinion ratio to the 2.73:1 ring gear that Chrisman's sells for the 7.5 GM rear end........

Assuming my math is correct, would you agree that this is a reasonable solution?




This would be a very reasonable solution if you had a 7.5" rear, but I was under the impression that your truck still had the stock 60 rear. If that is correct, then the 7.5" gears won't work in it.

Ray

 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-03-04 05:20 AM - Post#501744    
    In response to

Now I'm confused. I thought the 7.5 was the stock rear end. How can I I.D. the type of rear end I have?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
10-03-04 03:11 PM - Post#501745    
    In response to rincon101

The stock 60 1/2 ton rear has a perfectly round cover plate and also a carrier or "pumpkin" that can be unbolted from the front of the axle housing. Apart from the 54 and earlier passenger cars, this design is unique to the truck rears and was last used on the 1/2 ton in 62. 3/4 and 1 ton trucks had a similar design (but a larger size) till 72.

If your rear does not look like this, then you will need to determine what you have before attempting to buy any parts for it.

Ray


 
Gary 
enthusiast
Posts: 281
Gary
Age: 56
Loc: Teague, TX
Reg: 01-06-03
Re: Rear End Gear Ratio
10-03-04 03:46 PM - Post#501746    
    In response to rincon101

Ray is correct about the 60's rear end.

You can Call or EMAIL drivetrain.com, I have dealt with these people before and where great help. I have purchased Ring & Pinion goears from them also. For the 64-82 GM 12 bolt Rear Ends they have gear ratio ranged from 3.08 up to 4.56. Here is a LINK to there 12 bolt 8.75 Page.

If they can't help you with Ring/Pinion Gears for the 60 I would consider getting a 64-66 12 bolt to put in there.
Gary gary@garysgarage.net http://www.garysgarage.net


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-03-04 06:32 PM - Post#501747    
    In response to

What you describe is exactly what I have. I used Chrisman's ID chart and their photo looked like a 7.5. Shall assume that the 1960 1/2 ton is a 7.25?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
10-03-04 08:31 PM - Post#501748    
    In response to rincon101

I went to the Chrisman site and didn't find anything listed for the 60 1/2 ton rear. It's definitely not a 7.25. The 1/2 ton ring gear is way bigger than that. From when I had mine apart I would guess it was maybe about 9".

As I was saying before, I don't believe anyone is selling taller gears for this axle, with the possible exception of Patricks, who I believe had a 3.55 a while back. One likely reason might be the lack of a suitable differential case, the part the ring gear bolts to. As the ratio goes down, the pinion gets bigger in diameter. This means the ring gear would get too thin if you had to use the original case.

Ray

 
1962Chevy 
Member
Posts: 24

Loc: Tulsa, OK
Reg: 10-17-02
Re: Rear End Gear Ratio
10-04-04 03:11 PM - Post#501749    
    In response to rincon101

I have the same rear end, I think. Chevy Duty offered a 3.35 gear for it a year or so ago. Wasn't cheap, but it helps on the highway somewhat.
Heath 1962 LWB Fleetside 283 4sp.


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-06-04 03:15 AM - Post#501750    
    In response to

I very much appreciate your help and the time taken to offer thorough answers.
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-06-04 07:09 PM - Post#501751    
    In response to

Okay, if changing the ring gear in the differential is a lost cause, how about changing the gear ratios in the transmission?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
10-06-04 07:55 PM - Post#501752    
    In response to rincon101

Quote:

how about changing the gear ratios in the transmission?




That's probably the most practical solution. You don't actually replace the gears in the transmission though. What you do is replace the entire transmission.

If your truck has a 4 speed now, the cheapest and easiest replacement is a T-5 5 speed overdrive transmission from an S-10 truck. It will bolt to your stock bellhousing and will let you keep your stock hydraulic clutch linkage. You will need to replace the clutch disc and driveshaft. This is really a very easy swap, and extremely rewarding for the time and money invested.

Ray

 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-09-04 06:27 AM - Post#501753    
    In response to

Okay, fair enough. Any particular year(s) for the s 10?
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
Anonymous 

Re: Rear End Gear Ratio
10-09-04 09:25 AM - Post#501754    
    In response to rincon101

Any of them should work, but the earlier ones would be a better choice, before they went to electronic speedometer drives. I think the change was in the early 90s. You would be able to tell just by looking at the transmission though.

Ray

 
rincon101 
Member
Posts: 16

Loc: Orange County California
Reg: 03-04-04
Re: Rear End Gear Ratio
10-10-04 05:37 AM - Post#501755    
    In response to

You've been a great help. Thanks.
1960 Chevy 1/2 ton, stepside long bed First project, Father/Son--learning as we go restoration to a stock truck.


 
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