3.42 blues

bulachip · 05-08-2008, 07:29 AM

1989 4x4 extended cab longbed 5.7tbi

The code on my Dash says that I have 3.42s in my truck. However I know that the guy I bought it from said he just had the rear diff replaced with all new or rebuilt gears. Is there any chance that his shop put something different in there? I know that one can check by counting the teeth but am not sure exactly what the procedure is.

Also if you change the ratio for the back do you have to change the front?

Sorry for the dumb questions I am just getting into trucks and starting to do my own work.

87c10slammer · 05-08-2008, 08:20 AM

well if the guy did the rear then he would have stayed the same if he ever used the 4x4. if you change the rear you have to change the front or youll blow your transfer case real quick. i dont know the prosidere exactly but i think you count the teeth on the big gear and divide it by the teeth on the little gear. could be wrong but that is the most obvious conclusion to me.

03chevy · 05-08-2008, 08:52 AM

or you can jack up the rear end and mark the drive shaft and mark the tire and count how many times it takes the drive shaft to make on complete tire rotation and that will be the gear ratio.

Chevy_Finatic79 · 05-08-2008, 09:55 AM

I have heard people say that you can jack up the rear mark the drive shaft and the tire and turn until the drive shaft makes one full rotation. now how can that be accurate? how could you possibly tell weather or not you had 3.42's or 3.40's that way?or how do you determine weather or not it is a 3.73? how do you accurately acount for the decimal point with that method of finding the gear ratio? everyone makes it sound so easy but I still havent figured out how to do it that way.

I've always had to pull the pumpkin cover and divide the ring gear by the pinion for example: if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10)

I'm not saying that the tire and drive shaft way doesnt work, I personally have never figured it out and feel that there is too much room for error that way when some gear ratios are so close together.

If someone can make it make sense to me please feel free

87c10slammer · 05-08-2008, 10:01 AM

you read my mind chev.

bulachip · 05-08-2008, 03:59 PM

I know that they did not touch the front. So i am guessing that it is still 3.42's... So sad but perhaps better gas mpg.... I do not tow much or often so I am not going to get too bummed out. At least I can really fly on the highway. I guess if i need to tow something super heavy I will have to start out in 4low... lol

chevyguy · 05-10-2008, 09:14 AM

You wont want to to anything heave with a 10 bolt rear end.

fbhart@wk.net · 05-10-2008, 09:42 AM

try the jackup method first
as long as you and buddy have not been into the brew you can do this.

If front was not worked on then do it first, if back turns the same number turns you are good to go.

Be thankful if you have a 3.42 with gas going to $4+

drive it like grandmother would, and be happy,

I have 350 with 3.73 gears and lucky to get 15 on road and 12/13 around town. 10 mpg towing.

Good luck and be sure to use jack stands, they are your friends.

Zoomy · 05-10-2008, 05:36 PM

Quote:

Originally Posted by Chevy_Finatic79

I have heard people say that you can jack up the rear mark the drive shaft and the tire and turn until the drive shaft makes one full rotation. now how can that be accurate? how could you possibly tell weather or not you had 3.42's or 3.40's that way?or how do you determine weather or not it is a 3.73? how do you accurately acount for the decimal point with that method of finding the gear ratio? everyone makes it sound so easy but I still havent figured out how to do it that way.

I've always had to pull the pumpkin cover and divide the ring gear by the pinion for example: if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10)

I'm not saying that the tire and drive shaft way doesnt work, I personally have never figured it out and feel that there is too much room for error that way when some gear ratios are so close together.

If someone can make it make sense to me please feel free

It works because a 1/2 ton Chevy will be 2.76:1, 3.08:1, 3.42:1, 3.73:1, 4.11:1 (i think), Etc. there ain't no 3.40:1, or 3.75:1, so all you need to get is close. If you have about 3& 1/2 wheel turns you got a 3.42, about 3&3/4 you got a 3.73.
[Yeah they did make a 2.76, my '78 had 'em,with a locker, when i got it back in '79, the guy i bought it from ordered it that way!!??]
Runin 3.42s now. Luv 'em.

Sneakysportsman · 05-10-2008, 10:22 PM

If you jack up the rear and mark the drive, Accuracy is not that difficult. 3.42 is closer to 3 and 1/2 than 3.73 or 3 3/4 turn.

05-08-2008, 07:29 AM	#1
bulachip Full Member Join Date: Aug 2007 Posts: 33	3.42 blues 1989 4x4 extended cab longbed 5.7tbi The code on my Dash says that I have 3.42s in my truck. However I know that the guy I bought it from said he just had the rear diff replaced with all new or rebuilt gears. Is there any chance that his shop put something different in there? I know that one can check by counting the teeth but am not sure exactly what the procedure is. Also if you change the ratio for the back do you have to change the front? Sorry for the dumb questions I am just getting into trucks and starting to do my own work.

05-08-2008, 08:52 AM	#3
03chevy Senior Member Join Date: Dec 2006 Location: jax,fl Posts: 1,053	or you can jack up the rear end and mark the drive shaft and mark the tire and count how many times it takes the drive shaft to make on complete tire rotation and that will be the gear ratio. __________________ A dirty mind is a terrible thing to waste!

05-08-2008, 09:55 AM	#4
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 442	I have heard people say that you can jack up the rear mark the drive shaft and the tire and turn until the drive shaft makes one full rotation. now how can that be accurate? how could you possibly tell weather or not you had 3.42's or 3.40's that way?or how do you determine weather or not it is a 3.73? how do you accurately acount for the decimal point with that method of finding the gear ratio? everyone makes it sound so easy but I still havent figured out how to do it that way. I've always had to pull the pumpkin cover and divide the ring gear by the pinion for example: if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10) I'm not saying that the tire and drive shaft way doesnt work, I personally have never figured it out and feel that there is too much room for error that way when some gear ratios are so close together. If someone can make it make sense to me please feel free __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 5.7 Liter/THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

05-10-2008, 09:14 AM	#7
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,160	You wont want to to anything heave with a 10 bolt rear end. __________________ When i die, i dont want to walk gracefully thu the pearly gates and turn in a unused body. i want to go sliding thru sideways and turn in a body that has been completely used up.

05-10-2008, 09:42 AM	#8
fbhart@wk.net Senior Member Join Date: Mar 2007 Posts: 90	gear ratio try the jackup method first as long as you and buddy have not been into the brew you can do this. If front was not worked on then do it first, if back turns the same number turns you are good to go. Be thankful if you have a 3.42 with gas going to $4+ drive it like grandmother would, and be happy, I have 350 with 3.73 gears and lucky to get 15 on road and 12/13 around town. 10 mpg towing. Good luck and be sure to use jack stands, they are your friends.

05-08-2008, 08:20 AM	#2
87c10slammer Banned Join Date: Mar 2008 Location: levittown pa Posts: 2,197	well if the guy did the rear then he would have stayed the same if he ever used the 4x4. if you change the rear you have to change the front or youll blow your transfer case real quick. i dont know the prosidere exactly but i think you count the teeth on the big gear and divide it by the teeth on the little gear. could be wrong but that is the most obvious conclusion to me.

05-08-2008, 10:01 AM	#5
87c10slammer Banned Join Date: Mar 2008 Location: levittown pa Posts: 2,197	you read my mind chev.

05-08-2008, 03:59 PM	#6
bulachip Full Member Join Date: Aug 2007 Posts: 33	I know that they did not touch the front. So i am guessing that it is still 3.42's... So sad but perhaps better gas mpg.... I do not tow much or often so I am not going to get too bummed out. At least I can really fly on the highway. I guess if i need to tow something super heavy I will have to start out in 4low... lol

05-10-2008, 10:22 PM	#10
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 233	If you jack up the rear and mark the drive, Accuracy is not that difficult. 3.42 is closer to 3 and 1/2 than 3.73 or 3 3/4 turn.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
spring time blues	mudseeker	Off-Topic	3	04-07-2008 04:10 AM