Rear end swap

[1969 Flatbed]

I have a 69 GMC 3/4 ton flatbed that is mostly a work truck but I need to be able to go free way speeds. It currently has a 4.56 rear end in it with a 3 speed with a granny standard trans. I want to try to keep the trans because it comes in handy with and many jobs we have for it. Looking for suggestions as far as if there is a easy swap to a different 3/4 axle. I've also looked at a different ring in pinion but I can only go down to a 4.11 without changing the whole carrier.

[LONGHAIR]

3/4 ton trucks just had lower gears back then, you are not overly likely to find anything a whole lot higher.....of course it will depend upon which axle you actually have and whether is is coil or leaf.

[treveiger]

If you want to keep the 3/4 ton axle i cant see it being easy or cheap to switch it out. What size tires do you have? That may be your best bet.

[Longhorn Man]

dana or eaton
leaf or coil?

[Jacfourteen]

Originally Posted by Longhorn Man

dana or eaton
leaf or coil?

Same questions I was gonna ask.

[into69z]

I changed out the rearend on my 69 to a 14bolt semi floater with 3.23 gears by using CCP brackets and panhard bar. The rearend came out of a 1986 3/4 ton truck with leave spriings and I converted it to coil with the brackets. Works great for me, I can actully keep up (80+) on the freeways!

[Jacfourteen]

Originally Posted by into69z

I changed out the rearend on my 69 to a 14bolt semi floater with 3.23 gears by using CCP brackets and panhard bar. The rearend came out of a 1986 3/4 ton truck with leave spriings and I converted it to coil with the brackets. Works great for me, I can actully keep up (80+) on the freeways!

aren't the semi floaters 6 lug?

[Critter]

Originally Posted by Jacfourteen

aren't the semi floaters 6 lug?

The 14b semi-floater came in 6 lug and 8 lug versions (along with a few different width options). Also, there is an ultra rare 5 lug version that came in the mid 90s model 454ss trucks.

[Longhorn Man]

Why would one want a semi floater?

[Jacfourteen]

Originally Posted by Longhorn Man

Why would one want a semi floater?

I considered one so that I wouldn't have an ugly hub sticking out of the wheel, but other than that there is no good reason that I can see.

[Jacfourteen]

Originally Posted by Critter

The 14b semi-floater came in 6 lug and 8 lug versions (along with a few different width options). Also, there is an ultra rare 5 lug version that came in the mid 90s model 454ss trucks.

I only knew about the 6 lug and the 5 lug in the SS's.

[LONGHAIR]

The 8 lug semi-floaters were used in the light duty 3/4 ton trucks of the 88-98 generation. There was a recent thread about this...

[1969 Flatbed]

Its leaf spring with the original dana axle

[treveiger]

My truck cruised around 80mph with the stock drivetreain all the way home the day i got it(350mile trip back)with i think a 4.56 rear gear... the rpms were a little high but it handled great
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[into69z]

Originally Posted by Longhorn Man

Why would one want a semi floater?

I choose it mainly for the gear ratio-I wanted to get the best gear for the highway I could find. If I had it to do over again, I would have gone with the 14 full floater and been satisfied with a 3:54 or 3:73 rear gear. Now I have too much money in the rearend I choose to get rid of it It works fine for what I need. Unless you are really hauling heavy loads, this should hold up and I could probably get higher gear ratio if needed.

[cerjio]

when I was in High School a Teacher had an old 66 chevy that had an 5 speed tranny in it out of an old school bus , when I talked to his son about it seemed to work good an keep the hiways Rpms low !

[Critter]

Originally Posted by LONGHAIR

The 8 lug semi-floaters were used in the light duty 3/4 ton trucks of the 88-98 generation. There was a recent thread about this...

I know its getting off the subject...but the 8 luggers were also available in the 99-07 body style. The 1500HDs and the 2500 non-HDs had them.

Bottom line is a 14b full floater is probably best for the OP's needs if he decides to swap axles.

[1969 Flatbed]

Originally Posted by treveiger

My truck cruised around 80mph with the stock drivetreain all the way home the day i got it(350mile trip back)with i think a 4.56 rear gear... the rpms were a little high but it handled great
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How much is a little high? Mine looks like it will be running about 5000. I have a friend that had the same trans and rear end ratio and he drove it 75......... but also spun his main bearings.

[1969 Flatbed]

Originally Posted by into69z

I choose it mainly for the gear ratio-I wanted to get the best gear for the highway I could find. If I had it to do over again, I would have gone with the 14 full floater and been satisfied with a 3:54 or 3:73 rear gear. Now I have too much money in the rearend I choose to get rid of it It works fine for what I need. Unless you are really hauling heavy loads, this should hold up and I could probably get higher gear ratio if needed.

What trucks should I look for to get a 3.54 ratio full floater? I think this would work fine, the truck is still going to do some heavy work so I don't think I want to go semi.

[Critter]

Here is a great tool for figuring out what you want to do. I like the fact that you can compare two setups side by side. The trick in my opinion with any of these calculators is to be accurate with the tire sizing. Don't go by what is stamped on the the sidewall. Get a tape measure and measure from the ground to the center of the wheel hub, then multiply times two to get the effective tire diameter.

http://www.grimmjeeper.com/gears.html

[1969 Flatbed]

Originally Posted by into69z

I choose it mainly for the gear ratio-I wanted to get the best gear for the highway I could find. If I had it to do over again, I would have gone with the 14 full floater and been satisfied with a 3:54 or 3:73 rear gear. Now I have too much money in the rearend I choose to get rid of it It works fine for what I need. Unless you are really hauling heavy loads, this should hold up and I could probably get higher gear ratio if needed.

Bump
What trucks should I look for to get a 3.54 ratio full floater? I think this would work fine, the truck is still going to do some heavy work so I don't think I want to go semi.

[treveiger]

Originally Posted by 1969 Flatbed

How much is a little high? Mine looks like it will be running about 5000. I have a friend that had the same trans and rear end ratio and he drove it 75......... but also spun his main bearings.

I figure around 3600 to 3800 rpms on the way back(i hand calculated it). When i pressed the gas is accelerated like nobodys business and was running normal temp and staying there in 90 degree temp with a nasty cross wind at times, i wanted to see what she could do(as in how fast) but figured i better play it safe as i have no seatbelts and the only car we took out there is the prius.
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[Longhorn Man]

3.54 was in the 3/4 ton dana rear. If you plan on working your trucks hard with a lot of weight, I don't recomend it. The axle shafs tend to shatter.

[Green 1959]

To go freeway speeds the rear end almost has to be changed. I switch my 4.11 rear end for 3.38. But it is a 1/2 ton sorry.

[kwmech]

Originally Posted by Green 1959

To go freeway speeds the rear end almost has to be changed. I switch my 4.11 rear end for 3.38. But it is a 1/2 ton sorry.

You do realize this thread ended 2 years ago, right?