Differential swap advice

[Spitfire1975]

Kinda new at this...Was thinking of swapping out 3.73's (LS) for 3.45's in my 86 B2. Obviously need to do both front and rear. What all is involved in swapping the front third members? Could it possibly be as easy as exchanging the pumpkins or am I going to be disconnecting the entire front end? Any insight would be appreciated.

 

[Ozwynn]

I don't quit understand what you are asking. on a 7.5 and on an 8.8 rear axle you will need to do a gear set up.

If I were you I would stick with the 3.73. 3.45 will not get you better mileage on a 2.9L and it will seem more like a turd than it already does. In fact I would look for a 4.10 LS explorer and grab its axles and swap them in...... way easier than a gear set up.

 

[Spitfire1975]

what I am trying to accomplish is an end result ratio of about 3.73. With the larger than stock tires that are on the truck now (235/75/15), going to the 3.45 should (if I have done my math correctly) leave me with a 3.76 ratio. Right now the ratio is closer to the 4.10. What exactly is involved in a gear set up?

 

[Ozwynn]

what I am trying to accomplish is an end result ratio of about 3.73. With the larger than stock tires that are on the truck now (235/75/15), going to the 3.45 should (if I have done my math correctly) leave me with a 3.76 ratio. Right now the ratio is closer to the 4.10. What exactly is involved in a gear set up?

????????????

I think your math is in error.

when you go up in tire size you want to go up (numerically) in gear ratio.

if your relative to stock gearing is 4.10 then leave it alone iunless you plan on a tire size change.

as far as gear set ups ...... I have never done one. I have assisted and (much like working on drum brakes) have decided it is much easier to swap in an axle with the gears I want. plus with getting the explorer axle then you get the D35 and 8.8. both upgrades to what you got now (f your rig is stock).

go look in the tech library. there are several articles on gear set ups.

 

[Spitfire1975]

Thanks for the info. Think I may just let it be. Just thought I would use the MUCH better condition 3.45's sitting on my shop floor. Think I will just sell them instead.

 

[Ozwynn]

your math was right, I miss read your post but still 3.45 would not be an improvement over anything. what gears do you currently have?

 

[Spitfire1975]

Currently in the truck are 3.73. They have AT LEAST 200,000 miles on them. The 3.45's have 100,000 and came out of a frame damaged truck I completely dismantled.

 

[Spitfire1975]

I was hoping I could take the backside of the front differential off and swap with the backside of the 3.45 sitting on the floor.

 

[Ozwynn]

http://www.therangerstation.com/tech_library/Gear_Tire_RatioChange.html

here is a gear calculator. your tires are 29" dia.

unless your axles are sloppy I would leave well enough alone

 

[Ozwynn]

I was hoping I could take the backside of the front differential off and swap with the backside of the 3.45 sitting on the floor.

yeah you can do that with the front, but not with the back, AFAIK the 7.5 does not have a drop in 3rd member.

 

[Spitfire1975]

lol! Ya. Back axle is grinding and is just gonna get replaced completely along with spring shackles, sway bar and bushings, etc... Only thing on this truck that is going to be original is the shell....
So, just to be clear, I can simply take the front third member off of one and put on the other, correct?

 

[Ozwynn]

well its a little more involved than that. telling ya though ...... I would swap that D28 out for a D35 from a 91 - 94 explorer along with the explorer's 8.8 and 4.0L. as long as you are replacing you might as well upgrade.

 

[rednine4]

Yeah you can change the front over like you're saying but +1 on the the dana 35 and 8.8 while you're there do it right.... however if you have no plans to wheel this rig or run huge tires I suppose you can go with the existing d28.... It just depends on what you use it for... If it was mine I would upgrade knowing that the D28 spans like a twig when you load it, but do some research and search around you can truely find alot of good information as this is a common issue debated haha.

 

[heptofite]

i think you're doing your gearing math backwards.

if you're running bigger tires, you'll get less functional gear reduction, so you're want a diff with a higher reduction ratio to get the stock ratio you're shooting for.

 

[Spitfire1975]

i think you're doing your gearing math backwards. if you're running bigger tires, yo

I think your right. Got my info originally from a gearing calculator I found online and it was either wrong or (more likely) I misread it. So, If I want a 3.73 ratio in the end, I should be looking for a set 4.10 diffs., right? I don't wheel this truck. It is my daily driver and I would like the best mileage possible without completely bogging down. I do take it it in the woods (logging roads, etc..)