LUVTruck.com

My 1978 stock engine truck has the 4.56 rearend gear ratio with the automatic transmission. I found a 1984 Isuzu P'UP in a nearby Pick-A-Part with what should be a 3.90 geared rearend. Does anyone know from experience what the top-end speed would be with a 3.90? I have read where the 4.56 has a top-out of around 60 MPH. I just want to know if it's worth it to buy for a swap out. I was quoted approximately $165 for the drum to drum rearend and have no problem doing the upgrade as long as it is worth it. The truck did have the electronic ignition distributor and coil so I did purchase that complete set-up for a very reasonable price. Also got a set of factory plug wire looms that I was missing.
Ironically, I wasn't there for LUV related reasons - I was looking for a driver side seatbelt for my son's Ford truck. Got one for $5.00.

Any help would be very much appreciated!

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1978 LUV Mikado - all stock with automatic/AC

I thought all automatic luvs had 4.10 gears. If so, then it wouldn't be much different. Look in the information section of the main page here and there's a gear ratio calculator.

Here is a link to a gear ratio calculator. You need your tire size to figure it out.

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

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Three Amigos

You're right drummer. I got the 4.56 ratio from info from another topic on gear ratios. I looked in my Series 8 manual and the ratio for 1978 is 4.10. You just saved me a bunch of needlessly spent money!

Thank you!

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1978 LUV Mikado - all stock with automatic/AC

Glad I could help.

I've owned luvs with 4.56 and 4.10 rears. The 4.56 will hold around 70 just fine, but it sure doesn't sound like it's healthy. The 4.10 is much better on the highway. There are options if you want higher gears though.

And one more thing...

No P'ups had the 3.90 rear end. It could be 4.10, 3.73, or 3.42.

Jack

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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.com
IsuzuPup.com

According to to my '78 LUV factory service manual a '78 LUV with auto trans came with 3.73 gears, manuals came with 4.10's. I have evidence to support this since I used the 17-tooth speedo gear from an auto LUV in place of the 19-tooth in mine to help correct the speedo when I went with bigger tires.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

The news just keeps getting better! 3.73 should be just fine.

I was reading on other Isuzu sites, etc. when I got the misinformation on the ratios.

Thanks again for all the help.

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1978 LUV Mikado - all stock with automatic/AC

so what year and model isuzu pup can i get the 3.73 or 3.42 can somebody help me i have the same problem with my luv 77 manual just 60 mph on freeway thanks

All 4x4's gas or diesel had either 4.10 or 4.56 gears, so look at 2wd only.
I have both a '78 & '80 factory service manual, they both say an auto trans has 3.73 gears, manual trans has 4.10s, it's logical a '79 would be the same. I don't know if the same trend continued after 1980.
I once found a 3.42 rear in an '84 P'up with the 1.9 engine & 4sp tranny. This was often refered to as the MPG model.
Some 4sp diesel P'ups also had 3.42 gears, 5sps usually had 3.73 gears.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.