cherokee 4:10 rear diff in my truck

[shawn]

i have started driving the '91 again and when i got it ,it seems the PO had rebuilt the rear end with a diferent ratio than the front. - so here's what I'm thinking: i have the chance to pick up an XJ ( 4 cyl, 5 spd) cheap. - i think its about an '88. i understand it's likely to have 4:10s and am thinking it might be an idea to stick both front and rear ends into my '91 MJ shortbox. - i would go spring-over and it of course would already be set up this way. - my question is: would that rear-end already fit in regards to perches or is it a different distance. anything else i should be thinking about ?-------I'm trying to be simple and cheap. - but i don't mind paying for a good lift for the front if the spring-over thing works out.

[shawn]

i have started driving the '91 again and when i got it ,it seems the PO had rebuilt the rear end with a diferent ratio than the front. - so here's what I'm thinking: i have the chance to pick up an XJ ( 4 cyl, 5 spd) cheap. - i think its about an '88. i understand it's likely to have 4:10s and am thinking it might be an idea to stick both front and rear ends into my '91 MJ shortbox. - i would go spring-over and it of course would already be set up this way. - my question is: would that rear-end already fit in regards to perches or is it a different distance. anything else i should be thinking about ?-------I'm trying to be simple and cheap. - but i don't mind paying for a good lift for the front if the spring-over thing works out.

[Geonovast]

The distance between the perches on cherokees and comanches are different, yes. The pinion angle would also be off even if they were the same.

 

How much of a lift are you running? *I believe* an SOA with stock springs and shackles will get you 5.5 inches.

 

I would also consider getting a different rear axle anyway...if you go that high, you'll want big tires, which chances are, a turdy-five won't do too well with.

[Geonovast]

The distance between the perches on cherokees and comanches are different, yes. The pinion angle would also be off even if they were the same.

 

How much of a lift are you running? *I believe* an SOA with stock springs and shackles will get you 5.5 inches.

 

I would also consider getting a different rear axle anyway...if you go that high, you'll want big tires, which chances are, a turdy-five won't do too well with.

[shawn]

so either way i will be changing the perches - unless - i get the same ratios some other way.

[shawn]

so either way i will be changing the perches - unless - i get the same ratios some other way.

[CWLONGSHOT]

I don't think I understand. Your post says 4:10 in the back of my truck.. So do you have that now or just want that?

If you already have the 4:10 in the back the front axle alone is all your going to need.

 

If you don't, you can still use that front axle for the 4:10's and then get your self a FORD 8.8 from an exploder. VERY common to have 4:10's and disc brakes as well!! You will end up with a very stout rear axle for cheap!! Your going to have to do perches and shock mounts anyway, so you might as welll do this ONCE and do it right!! I suggested the 8.8 because its most likely easiest to find and cheapest. But a D44 form a XJ/MJ would also fit the bill as would a 29spline 8.25 from a newer XJ would also work as well.

 

CW

[CWLONGSHOT]

I don't think I understand. Your post says 4:10 in the back of my truck.. So do you have that now or just want that?

If you already have the 4:10 in the back the front axle alone is all your going to need.

 

If you don't, you can still use that front axle for the 4:10's and then get your self a FORD 8.8 from an exploder. VERY common to have 4:10's and disc brakes as well!! You will end up with a very stout rear axle for cheap!! Your going to have to do perches and shock mounts anyway, so you might as welll do this ONCE and do it right!! I suggested the 8.8 because its most likely easiest to find and cheapest. But a D44 form a XJ/MJ would also fit the bill as would a 29spline 8.25 from a newer XJ would also work as well.

 

CW

[shawn]

what i have now for diffs is a couple of unknowns. the only thing about them that i do know is that they are a different ratio in each end. - so when this 4 cyl XJ came available i though " hey, good way to make sure i have the right (same) ratio in each end, -cheaply." - the fact that it is most likely 4:10s just looked like a bonus to me.

[shawn]

what i have now for diffs is a couple of unknowns. the only thing about them that i do know is that they are a different ratio in each end. - so when this 4 cyl XJ came available i though " hey, good way to make sure i have the right (same) ratio in each end, -cheaply." - the fact that it is most likely 4:10s just looked like a bonus to me.

[mvusse]

I would buy a gallon or two of gear oil, a tube of RTV and pull the covers. It can't hurt to drain the old oil and fill with fresh, and while the cover is off, check the ring gear. The ring gear has the number of teeth on it as well as on the matching pinion stamped into it. Divide one by the other to get the ratio. IE 41 10 is 41/10=4.10, 39 11 would be 39/11=3.55.

 

Or, if the tag is still there (a little metal strip bolted to the diff cover, clean it up and read the ratio off it.

 

Another option is to jack up 1 (one) tire, leaving the other one on the ground. Put your transmission in neutral and count how many times to spin it for one revolution of the drive shaft, then divide by 2. (this will not work if you have a locker). Almost 8 and a quarter turns is 4.10, just over 7 is 3.55 a bit more than 6 is 3.07 etc. If you have a disconnect in your front axle, put the truck in 4wd with the engine running until the light comes on, then shut if off and shift back to 2H.

 

But I would pull the covers.

[mvusse]

I would buy a gallon or two of gear oil, a tube of RTV and pull the covers. It can't hurt to drain the old oil and fill with fresh, and while the cover is off, check the ring gear. The ring gear has the number of teeth on it as well as on the matching pinion stamped into it. Divide one by the other to get the ratio. IE 41 10 is 41/10=4.10, 39 11 would be 39/11=3.55.

 

Or, if the tag is still there (a little metal strip bolted to the diff cover, clean it up and read the ratio off it.

 

Another option is to jack up 1 (one) tire, leaving the other one on the ground. Put your transmission in neutral and count how many times to spin it for one revolution of the drive shaft, then divide by 2. (this will not work if you have a locker). Almost 8 and a quarter turns is 4.10, just over 7 is 3.55 a bit more than 6 is 3.07 etc. If you have a disconnect in your front axle, put the truck in 4wd with the engine running until the light comes on, then shut if off and shift back to 2H.

 

But I would pull the covers.

[shawn]

I would buy a gallon or two of gear oil, a tube of RTV and pull the covers. It can't hurt to drain the old oil and fill with fresh, and while the cover is off, check the ring gear. The ring gear has the number of teeth on it as well as on the matching pinion stamped into it. Divide one by the other to get the ratio. IE 41 10 is 41/10=4.10, 39 11 would be 39/11=3.55.

 

Or, if the tag is still there (a little metal strip bolted to the diff cover, clean it up and read the ratio off it.

 

Another option is to jack up 1 (one) tire, leaving the other one on the ground. Put your transmission in neutral and count how many times to spin it for one revolution of the drive shaft, then divide by 2. (this will not work if you have a locker). Almost 8 and a quarter turns is 4.10, just over 7 is 3.55 a bit more than 6 is 3.07 etc. If you have a disconnect in your front axle, put the truck in 4wd with the engine running until the light comes on, then shut if off and shift back to 2H.

 

But I would pull the covers.

 

thank you - this is very valuable info to me.- i knew there was something about counting the revolutions but you have laid it out very clearly. - can't wait to see what I'm dealing with.

[shawn]

I would buy a gallon or two of gear oil, a tube of RTV and pull the covers. It can't hurt to drain the old oil and fill with fresh, and while the cover is off, check the ring gear. The ring gear has the number of teeth on it as well as on the matching pinion stamped into it. Divide one by the other to get the ratio. IE 41 10 is 41/10=4.10, 39 11 would be 39/11=3.55.

 

Or, if the tag is still there (a little metal strip bolted to the diff cover, clean it up and read the ratio off it.

 

Another option is to jack up 1 (one) tire, leaving the other one on the ground. Put your transmission in neutral and count how many times to spin it for one revolution of the drive shaft, then divide by 2. (this will not work if you have a locker). Almost 8 and a quarter turns is 4.10, just over 7 is 3.55 a bit more than 6 is 3.07 etc. If you have a disconnect in your front axle, put the truck in 4wd with the engine running until the light comes on, then shut if off and shift back to 2H.

 

But I would pull the covers.

 

thank you - this is very valuable info to me.- i knew there was something about counting the revolutions but you have laid it out very clearly. - can't wait to see what I'm dealing with.

[mvusse]

Yeah, except I was backwards. Rotate one wheel two revolutions while the other one is on the ground not moving, and count how many revolutions the drive shaft makes. A little over 4 is 4.10, 3 and a half is 3.55 etc.

 

Don't know what the heck I was thinking when I wrote the other message. Probably wasn't thinking at all.

 

But I would still pull the covers to change the oil and read it off the ring gear while it was open.

[mvusse]

Yeah, except I was backwards. Rotate one wheel two revolutions while the other one is on the ground not moving, and count how many revolutions the drive shaft makes. A little over 4 is 4.10, 3 and a half is 3.55 etc.

 

Don't know what the heck I was thinking when I wrote the other message. Probably wasn't thinking at all.

 

But I would still pull the covers to change the oil and read it off the ring gear while it was open.