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Username Post: 2 Speed Rear Axle        (Topic#86967)
dnic 
Member
Posts: 10

Loc: Iowa
Reg: 01-10-05
01-10-05 05:11 AM - Post#596426    

I have a 60'Chevy Viking L60 with @16,000 original miles. It was an old fire truck, so it sat indoors most of its life. I'm converting it to a 12'dump/flatbed(Omaha Standard Box). It has a 283/4barrel/dual exhaust/4spd synchro/single speed 7.20to 1 rear axle. It tach's @ 3800 at 55mph. My question is would a 2 spd rear axle gain me any top end speed at a lower engine rpm? Also GM installed a NP 540C/5speed as an option on the L60 series as an option,if a guy could locate one of these, would that also help for higher mph @ lower rpm. Any input is much appreciated. Dave

 
bobschevytrucks.com Ecklers Chevy Trucks LMC Trucks

61APACHE10 
Senior Member
Posts: 183
61APACHE10
Loc: Lancaster,NY
Reg: 03-06-02
Re: 2 Speed Rear Axle
01-10-05 07:22 AM - Post#596427    
    In response to dnic

Welcome Dave, The 5 speed is still only 1:1 in top gear, so it will not change your speed or RPM's. The 2 speed axle will change it only if you can get a higher (numerically lower) gear set such as in the 6's.

Also of note is the standard 2-speed axle is vacuum operated, and are a pain in the ass.-MIKE
WHY BE NORMAL?


 
OL'GRUNT 
Senior Member
Posts: 1098

Loc: Camarillo, California, US...
Reg: 01-29-02
Re: 2 Speed Rear Axle
01-10-05 11:10 AM - Post#596428    
    In response to dnic

So if you spin that 283 up to 7600 rpm, you'll be going 110 mph. Call me silly, but I think that's a little fast for an old truck with a 12 foot dump bed...

Seriously, I'm with Mike on the 2-speed axle. That's the way all the factories reduced the final drive ratio, so you know it will work. But I don't think you have to worry about the vacuum shift. I believe (famous last words) that all the gm stuff was electric shift after about 58 or 59. Jolly will know this for sure.

And, by the way, welcome to CT...
Semper Fi... '87 Corvette '66 Long Fleet


 
dnic 
Member
Posts: 10

Loc: Iowa
Reg: 01-10-05
Re: 2 Speed Rear Axle
01-10-05 12:36 PM - Post#596429    
    In response to 61APACHE10

Hey Guys, Thanks for the replies. Okay, if the 5 spd and the 2spd rear axle don't gain me in my situation, what if I completely did away with the original axle ensemble, and well,what do you suggest? Keeping in mind I'm trying maintain a low rpm (25-2800) with a speed of @ 65-70. Am I out of line for trying to acheive this?

 
OL'GRUNT 
Senior Member
Posts: 1098

Loc: Camarillo, California, US...
Reg: 01-29-02
Re: 2 Speed Rear Axle
01-10-05 12:57 PM - Post#596430    
    In response to dnic

Hang on now, let's review what we are saying: The 5-speed (or any other tranny with a 1:1 top gear) is out, it doesn't change your final drive ratio. The 2-speed IS the way to go. You just need to find out what ratios your getting, do the math, and determine if it's getting you to the rev count you want.
You might look in your manual. It has sections on the C-60 trucks, and I know there is info on the 2-speed rearend.
Semper Fi... '87 Corvette '66 Long Fleet


 
dnic 
Member
Posts: 10

Loc: Iowa
Reg: 01-10-05
Re: 2 Speed Rear Axle
01-10-05 01:21 PM - Post#596431    
    In response to OL'GRUNT

I'm hanging on! Whew! What a ride! I just want to go faster. Any way, I don't have a manual that breaks down gear ratio's and rpm's. But, I do know the original 2 spd. rear axle offered in 60' came with a ratio of 6.40/8.72-1. Maybe you can school me on what the 6.40 will gain me top end speed vs. rpm. Thanks Dave.

 
dvalentine 
Senior Member
Posts: 9355

Loc: Sacramento, CA
Reg: 06-22-00
Re: 2 Speed Rear Axle
01-10-05 01:36 PM - Post#596432    
    In response to dnic

Where is the resident BIG TRUCK Guy ??

Calling Dr Jolly .....


 
glenfred 
Senior Member
Posts: 140

Loc: minnesota
Reg: 01-19-03
Re: 2 Speed Rear Axle
01-10-05 02:51 PM - Post#596433    
    In response to dvalentine

If my calculations are right, with a 6.4 ratio you would be running around 3700 rpm at 60 mph. I used the calculator at http://www.richmondgear.com/101032.html and your previous post to figure that you had about a 35 inch tire. From there on it was pretty straight forward to just punch in some numbers. What part of Iowa are you from?
Glen You only live once but if you work it right once is enough


 
62BillT 
"13th Year" Silver Supporting Member
Posts: 5004
62BillT
Loc: Moneta, VA
Reg: 09-24-01
Re: 2 Speed Rear Axle
01-10-05 04:38 PM - Post#596434    
    In response to dnic

A 2-Speed rear end is designed to split the trans gears to give you 8 speeds with a 4-Speed trans or 10 speeds with a 5-Speed trans. It won't work as an overdrive. But like stated above, if the 2nd speed of the rear you would be putting in, happens to be higher (lower in number) than the single speed rear you have now, you would then be able to go faster at the same RPM than before. And also as stated above the 5-Speed trans swap will only give you an extra gear on the lower end, not the top end like an overdrive would. The best combo would be a 2-Speed with a higher rear along with the 5-Speed as you will be losing some take off, low end power with the 4-Speed, but still may not be necessary.
Member:
-National Impala Association
-Vintage Chevrolet Club of America


 
62BillT 
"13th Year" Silver Supporting Member
Posts: 5004
62BillT
Loc: Moneta, VA
Reg: 09-24-01
Re: 2 Speed Rear Axle
01-10-05 04:43 PM - Post#596435    
    In response to 62BillT

Just to add a little extra, I'm not sure about 1960 original equipment, but my '62 GMC had an electric 2-Speed.
Member:
-National Impala Association
-Vintage Chevrolet Club of America


 
raycow 
Honored Member
Posts: 18974

Age: 71
Loc: San Francisco, CA
Reg: 11-26-02
Re: 2 Speed Rear Axle
01-10-05 08:33 PM - Post#596436    
    In response to dnic

On at least some versions of the NP540 5th gear is an overdrive. If you can find one of those and combine it with a taller rear axle you should have the gearing you are looking for.

Ray
Bacon is the gateway drug for vegetarians - Bridget Lancaster


 
Jolly 
Senior Member
Posts: 721
Jolly
Age: 54
Loc: 6066 GMC Trucks
Reg: 12-11-02
Re: 2 Speed Rear Axle
01-10-05 11:54 PM - Post#596437    
    In response to dnic

I'm Here, I'm Here.....

My 1960 Chevy L60 has the two speed rear axle, the SM-420 four speed & a 400 CID Small block. I drove it to the town center one year for the Great Basin Antique Machinery Association's Thrashing Demo, My mother-in-law followed me up, I showed 50 on the speed-o, she said I was doing 65. You mite be going faster than you think. Do a speed-o check.

with that said, the stock axle for the 1960 L60 is a single speed with a gearing of 7.20:1 & should have the 8-22.5 tires. as an option you could get a two speed axle ratio of 6.40:1/8.72:1.

The two speed is vacuum controled, & they are not that hard to install, the trick to doing it is to find a parts truck with one still inplace with all the parts and remove it all for your truck, including the entire rear axle.... I did this once on a Chevy school bus, I used parts from a short wheelbase GMC truck, so the lines were a bit short, but that's not a problem, just add some vacuum hose.

There is a five speed that was used in the sixtys that was an over drive, it was used mostly on diesel trucks. I have a list of transmissions used in GMC truck here, GMC Transmission Data many of these also seen use in the Chevy trucks as well.

These are old truck & were not really built for todays drive conditions. there was not many interstat highways back then either. you don't want to be going to fast in an old truck unless you know for sure you can get it stopped in a hurry too.
The 6066 GMC Guy

1965 GMC 3505 Rescue Squad
2008 GMC HHR Panel


 
Jolly 
Senior Member
Posts: 721
Jolly
Age: 54
Loc: 6066 GMC Trucks
Reg: 12-11-02
Re: 2 Speed Rear Axle
01-11-05 12:13 AM - Post#596438    
    In response to dnic

School is about to begine, every one take your seats now.....

Get out your calulators.....

Now here is were your'll find some info to help you figure out the mhp from you gearing and engine speed. I worked up some gearing charts for my 1965 GMC 2500 Project, but just about all the info is here you'll need to work out your own numbers.

Gear Charts For My 1965 GMC 2500.

You'll need to figure out tire revolutions pre mile, To get "tire revolutions pre mile" paint a spot on the tire & ground, then roll the truck forward tell the paint spot on the tire meets the ground again, then paint the ground there. Move truck out of the way & measure the distance between paint spots in inches, then divide that number into how many inches in a mile (63360"). That will give you "tire revolutions pre mile".

Also you mite want to check out the info I have here, but once again, this is GMC info, it may not be the same for Chevy, Rear Drive Axle Information.
The 6066 GMC Guy

1965 GMC 3505 Rescue Squad
2008 GMC HHR Panel


 
61APACHE10 
Senior Member
Posts: 183
61APACHE10
Loc: Lancaster,NY
Reg: 03-06-02
Re: 2 Speed Rear Axle
01-11-05 01:00 AM - Post#596439    
    In response to Jolly

By the way Dave, we definitelly have to see some pictures of this beast.-MIKE
WHY BE NORMAL?


 
dvalentine 
Senior Member
Posts: 9355

Loc: Sacramento, CA
Reg: 06-22-00
Re: 2 Speed Rear Axle
01-11-05 07:25 AM - Post#596440    
    In response to Jolly

Quote:

School is about to begin, every one take your seats now.....




When it comes to the Big Trucks, you can find me seated in the corner with the pointy hat....

Thanks Jolly !

 
dnic 
Member
Posts: 10

Loc: Iowa
Reg: 01-10-05
Re: 2 Speed Rear Axle
01-11-05 10:40 AM - Post#596441    
    In response to glenfred

Glenfred, thanks for the input. I'm from Jesup, Iowa. It's bout 15 minutes from Waterloo and 30 minutes from Cedar Rapids.

 
dnic 
Member
Posts: 10

Loc: Iowa
Reg: 01-10-05
Re: 2 Speed Rear Axle
01-11-05 11:08 AM - Post#596442    
    In response to Jolly

Everyone...,thanks for all the useful knowledge. I think I have a game plan. I already know where there are (2) 2spd vacuum axles, price to be determined, but is definately the way to go. And after reading Jolly's page on 5spd Trannies, I've now found yet another item to add to my "gotta have" list, the NP 540 GO 14. The GO I've learned designates "Gots to have Overdrive", which in 5 th gear is 0.82-1 final drive. So here's the set up I'm shooting for; 5 spd w/OD,2spd axle w/6.40-1(high side)gears, and currently the truck has 8.25-20 tires @ 37.5" diameter. Fella's what do you think my RPM will be @65-70MPH? Also Ol'Grunt, Semper Fi right back at ya, Devil Dog! I served in th Marines from 87-91 at Tustin,CA- ElToro Air Base. Yep an "Air Winger" HMM-163 helicopter squadron. 61 Apache/Mike I'm working on those pictures. Have'nt played with this site enough to figure how to post them, any input? Any how, thanks again people.

 
raycow 
Honored Member
Posts: 18974

Age: 71
Loc: San Francisco, CA
Reg: 11-26-02
Re: 2 Speed Rear Axle
01-11-05 11:25 AM - Post#596443    
    In response to dnic

Quote:

Fella's what do you think my RPM will be @65-70MPH?



About 3060 rpm at 65 mph and 3295 at 70. You can probably pull taller gearing than that. Can you find a rear that's better than 6.40?

Ray
Bacon is the gateway drug for vegetarians - Bridget Lancaster


 
62BillT 
"13th Year" Silver Supporting Member
Posts: 5004
62BillT
Loc: Moneta, VA
Reg: 09-24-01
Re: 2 Speed Rear Axle
01-12-05 01:55 AM - Post#596444    
    In response to dnic

Just to add a little extra, if you wanted a quick way to go a little faster, you could move up to 900-20 tires. But be careful on the old original rims. Some of them were 2-piece and 3-piece and were not of the best design, especially when they got a liitle old and rusty. You may want to check on a newer style one piece for replacement. You would also have to make sure on your clearances to the truck and to wheel to wheel on the rears.

Also Jolly gave good advise about these old trucks traveling at high speeds. It is true that they weren't designed to stop quick at some of todays highway speeds. My old '62 GMC 6500 would top out at 62 MPH and for an old big truck, it felt like 80. Keep us posted.

 
Jolly 
Senior Member
Posts: 721
Jolly
Age: 54
Loc: 6066 GMC Trucks
Reg: 12-11-02
Re: 2 Speed Rear Axle
01-12-05 10:02 AM - Post#596445    
    In response to dnic

OK School is still in eh,

8.50-20 tires will have a RPM of 542
9.00-20 are 520
10.00-20 are 504

So useing the numbers from the page I posted above,

RPM x 60 divided by Final Ratio x tire revolutions pre mile = Miles pre hour

2500 x 60 (150000) / 6.40 x 542 (3468.8) = 43.24
3000 x 60 (180000) / 6.40 x 542 (3468.8) = 51.89
3500 x 60 (210000) / 6.40 x 542 (3468.8) = 60.53
4000 x 60 (240000) / 6.40 x 542 (3468.8) = 69.18

I have a Spicer 5831-B Auxiliary Transmission that will be going into my 65 GMC it has an over drive of 0.85:1, that will help out my top end some but the 4.57:1 rear axle has to go. I'm looking for a 14 bolt with either a 4.10:1 or 3.73:1 ratio.

My BIG TRUCK has 9-22.5 tire on the back, which for some reason have the same revolutions pre mile as the 8.50-20 do, the differance being that the 9-22.5 are tubeless. I do have the two speed rear axle.
The 6066 GMC Guy

1965 GMC 3505 Rescue Squad
2008 GMC HHR Panel


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15703

Loc: Colorado Springs, CO
Reg: 08-08-04
Re: 2 Speed Rear Axle
01-12-05 11:23 AM - Post#596446    
    In response to Jolly

You might be able to use an overdrive version of the Clarke transmission that was used in medium duty trucks into the 80's. Look for truck wreckers in the big metropolitan area. I have heard that a reasonably good source is in Denver. They came with an .80 overdrive.

If you are going to switch axles, look for dump truck axles, light/medium duty delivery trucks (possibly a numerically lower ratio) or Army deuce-and-a-half 6x6 axles (Boyce Equipment in SLC, Utah rebuilds them). The 6x6 axles are generally used in monster trucks, so there are a number of places around the country that carry them. I think they have a 6.39 ratio, and they have square axle tubes which makes it easier to mount. If you have a local Army base, call the DMRO office. They are in charge of getting rid of old equipment, you could get a wrecked 6x6 for reasonable cash. It's a bid process, by the way.
The cheapest you are likely to get would be the dump truck axles, but you might have to rebuild them.

 
Floyd B. 
Senior Member
Posts: 605

Loc: Colorado
Reg: 07-14-04
Re: 2 Speed Rear Axle
01-12-05 12:11 PM - Post#596447    
    In response to Vaughn

Would a "Ranger" work for this?
Ranger Overdrive
1991 Silverado, 350 TBI, 4L60 1973 GMC PU, 350, SM465 1984 GMC S-15 PU, 2.8L, 4 SPEED 1970 Toyota Landcruiser with 1985 SBC 350, SM420, Q-Jet.


 
Jolly 
Senior Member
Posts: 721
Jolly
Age: 54
Loc: 6066 GMC Trucks
Reg: 12-11-02
Re: 2 Speed Rear Axle
01-12-05 12:16 PM - Post#596448    
    In response to Vaughn

Quote:

Boyce Equipment in SLC, Utah rebuilds them ...




Boyce Equipment is in Ogden Utah, just down the road from were I work. Those axle use in army truck hill be lower geared then what you want in this truck. Best bet would be to get a two speed and go that route.

If you get one from a 60-62 truck it will be a bolt in with out much fab work.
The 6066 GMC Guy

1965 GMC 3505 Rescue Squad
2008 GMC HHR Panel


 
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