Ever Seem Like Your Going Backwards (Differential)

[JRBECK64]

My Son and I have been battleing the rattles and noises that a truck fresh out of Restoration goes through. After about a week of pinpointing all the little raddle, knocks and BANGS we been hearing from the old girl we finally have come to the painfull conclusion that we are going to have to pull the differential out of his 64 Shortwide because the Diff Mount for the Track Bar is directly under the frame (About 1 1/2 inches of travel) and when you hit a bump or a speed bump it hits the frame. This is due to using a 10 Bolt Diff 3.08/1 out of a 1960 that has a 37 inch track bar. We pulled the original (that was in the 64 ShortWide) 12 Bolt 4.10/1 out of my 63 Shortwide parts truck last night and now need to clean and POR15 it before we stick it in the 64. Not to mention put all the New Drum brake shoes, Drums and Emergency brake Cables into the Diff. My Son and I started Laughing Yesterday when I told him we should go to work for a Indy Pit Crew changing out Differentials. So now I am trying to figure out what gear set I want to change the 4.10/1 to. Im thinking about going to a 3.42/1 gear set. I think that will keep the RPM down enough on the freeway and still give it a little bit out of the hole. If anyone is currently running one of these 3.42/1 Gear Sets let me know how you like it.

JRBECK64

[lakeroadster]

We hear ya. It's always something, but at least with our old trucks it's always something we can fix!

What motor, trans and rear tire diameter does your son's truck have?

Check out this link it is very helpfull when picking a rear gear, based on what you want from the set-up: http://www.sierrabronco.com/TireGearRatio.htm

Hope this helps,

[steverino66]

Your noise story reminds me of a funny story that happened with my 65 longbed years ago - a thumping noise from the rear only when turning left; a "mechanic" said bad spider gears so, being a dumbass kid, I swapped out the diff. Turns out it was the stinking muffler swinging over to thump against the driveshaft!
I put 3.42s in my 66 with a 72 posi unit, was recommended as a good all-around ratio. Feels great, no tach hooked up yet for highway rpms, haven't gotten to drive it much since, still a work in progress.

[wild one]

My 1966 panel came with 3.73's, I swapped them out for a 3.40 ring and pinion that came out of my parts donor vehicle ( a 1975 GMC heavy half ton ). The end result - the truck goes down the freeway below 3000 RPM at 65 MPH and the off the line punch is still there. Bottom line - I would deffinitely recommend the 3.42 ratio, it's a great all around gear.

On a side note, you will need a 3 series carrier to use the higher (numarically lower) gear ratio. The carrier that you have is a 4 series and will work for ratios of 3.73 and up (4.10, 4.56, etc...). The only difference is the offset for the ring gear mounting flange on the carrier - this properly spaces the ring gear from the pinion to allow for proper lash and gear pattern.

Pete

[JRBECK64]

Originally Posted by lakeroadster

We hear ya. It's always something, but at least with our old trucks it's always something we can fix!

What motor, trans and rear tire diameter does your son's truck have?

Check out this link it is very helpfull when picking a rear gear, based on what you want from the set-up: http://www.sierrabronco.com/TireGearRatio.htm

Hope this helps,

69 327, TH400 and the rear tires are 27 inches tall. Im begining to think I need to get a 700R for this truck and go with the 3.73/1 ratio. Thanks for the link for the Gear Ratio Calculator. I took the numbers off the differential after we took 40 some odd years of grease and grime off it. Here are the numbers I got off it if you might know what they mean. N3838227, GM8 and WA816.

Thanks,

JRBECK64

[JRBECK64]

After doing some research on the GM8 number on the Differential its telling me that there is a 2.56/1 up to a 2.71/1 gear set in this thing. That cant be right because I used to do burnouts a city block long and if the burnout gods were smiling on me I would even get a little scratch going into second. This is really confusing me. I think I am going to pull the cover off this thing and count the teeth because that will tell the whole story!

JRBECK64

[lakeroadster]

Counting the teeth is the most accurate but another way to check the rear end ratio is to jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

[JRBECK64]

Originally Posted by lakeroadster

Counting the teeth is the most accurate but another way to check the rear end ratio is to jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

My Son just got done POR15ing it. Im not touching any of that stuff. If you dont know what POR15 is its a Rust encapselator (I think I spelled that right) and it doesn't come off your skin very easy. We are going to be installing it tomorrow and I will use your tire rotation calculation. Thanks for the info.

JRBECK64

[Oklahoma]

I had 2.79's in mine and two weeks ago I had the rearend completely redone with 3.73's, with 27 inch tires, with 700r4, and I'm at 2500rpm's crusing at 80. I like the combination.

[Tx Firefighter]

Before I swapped a bunch a ring and pinion parts or the whole differential, I'd just cut the offending track bar off and install a Super track bar from ECE or CPP. Problem solved.

[JRBECK64]

I put the original diff back in it and man is that thing fast. Did a mini butnout in the driveway and I thought my Wife was going to kill Me. It looks like the gear in it is a 3.73/1 and I think for now I am going to leave it like it is until I decide if I want to either pony up for the OD tranny or change out the gear set. This thing sure does get up and go and that power steering makes this thing much more drivable. It was a pain changing out the Diff but it was worth it.

JRBECK64