Front differential questions.

[Tercel_jon]

Hey guys, my car is an 83 so I think its safe to assume it has 3:73s right?

However I swapped the trans to a newer one from an 87 or 88. I believe the front diff that came with it has 4:11s. I can use the car the way it is, but I must have larger tires on the rear in order for the 4wd to work properly.

My question is, is it possible to swap the front differential back to the stock one with 3:73s without removing the engine or trans? Also, if I do so, will It fix my gearing problem?


Or would it just be easier to swap in a 4:11 gearset from a 87-88 into my 83's rear end?

[toughtercel]

if you replace front diff that came from with it has 4:11s into to the stock one with 3:73s , you gonna have to do same thing to rear end. changing tires aren't gonna help.

[Tercel_jon]

I knew my explanation was gonna be confusing. :/ Lets try this again.

I have 3:73s in the rear right now.

In the front I have 4:11s.

To compensate for this I WAS running different sized tires. It works.

I dont want to run different sized tires anymore.

I want to put the front back to 3:73. Is this possible without removing the engine or trans?

[toughtercel]

OHHHH ha ha , I see your point , short cut is more differcult , let see what they say .

[takza]

Think this has come up before and the easiest solution was to change out the rear axle or diff.

[Tercel_jon]

Why was it easier? was it because in order to change the front diff you have to remove at least one of the drive axles? I have to replace the passenger one anyway so I was just gonna pull it off and then pull the diff off. Put the old one on, than put the new axle in.

If anything, could someone post a link to the last discussion about it? I searched, but I guess I didnt search very well.

[Highlander]

In checking through the FSM, it looks like you need to pull the whole of the differential case off of the tranny in order to get to the pinion to change it-Ring and Pinion are usually a matched set, I wouldn't even think of trying to mate a 4.11 ring to a 3.73 pinion- the gear teeth MUST mesh correctly. Changing the rear diff out as a unit (axle housing and all) is probably easier, especially if you can find one in a JY. A yard diff would save you the trouble of setting the face contact between the ring and pinion, which is critical and can be a bugger if you've never done it.
Bear in mind, I haven't done this, so it's just my $.02

[Tercel_jon]

In checking through the FSM, it looks like you need to pull the whole of the differential case off of the tranny

But can this be done without dropping the trans? I crawled up under there and it seams there IS enough room to get a wrench in there. And I remember reading either my chiltons of the FSM and said when removing the transmission (not my main objective here) one of the first steps was to remove the front diff assembly (my goal).

I really want my 3:73s back in there cause Ill get better mileage when I go to florida this winter. ~800 miles

I would change the rear end out with a corolla all-trak one...but that is gonna cost me around $100...not bad I know...but I already have the other front diff assembly.

[xirdneh]

edited 9-29-10 for future users

You will have to change the pinion gear to get a change in gearing. The rings on the 3.73 and 4.1 both have 41 teeth. The pinions make the difference with 11 teeth on the 3.73 and 10 teeth on the 4.1. I doubt the rings are interchangeable with the different pinions.

If you replace the ring gear portion of the differential all you would have to do is pull the front cover and pull the front axels. But you would be taking a risk by not changing the pinion gear also. The ring and pinions are kind of a matched set. I suppose if you did take the risk and managed to set the lash and whatever else is done to tune the (non-matched set) ring and pinion together, you may get away with it.
As noted above the gear ratio would not be changed.

Removing the pinion requires removing the transmission from the differential/bell housing assy. There is a large nut that has to be removed. Even so you would still have to tune the ring and pinion to each other. Seems like a lot of work to me. Changing the rear differential is much easier and no tuning is required. Disconnect driveline pull rear axels.

Mismatching the 3.73 and 4.1 differentials will cause a difference of one revolution per ten between front and rear tires (3.73 has 11 teeth on pinion vs 10 on 4.1, ring gear on both is 41 teeth)
If your tires are normally around 24 dia the difference in diameter (between front and rear sets)would have to be plus 2.4” (26.4 dia) or minus 2.4” (21.6 dia) depending on which way you go. That’s according to my math skills which I admit are rather poor.

additional info
The 3.7 ratio is from 8/82 - 8/84. So, if you are in a junkyard check
the metal tag inside the drivers side door (on the body, not the door).
It will have the month and year of production. After 8/84 they are 4.1.
Also check numbers stamped on firewall in engine compartment
Z52F is 3.73
Z54F is 4.1

[Highlander]

Yes, you can probably do this without dropping the tranny, but you have to separate the diff housing from it and drop that out of the car. Then you can get to the pinion nut to change the pinion out as xirdneh said...

Removing the pinion requires removing the transmission from the differential/bell housing assy. There is a large nut that has to be removed.

Then you've got the whole ball of wax that is measuring and adjusting backlash and checking and rechecking the contact patch to get it centered. If it were me, I'd go get a 4.11 rear end and end the suffering. Don't mean to dump on your parade, but I work hard enough keeping my cars on the road (all 9 of them) and I don't need another long, drawn out process when there is a more efficient (though a bit more costly) answer.
....And don't forget, that you'll have to buy gaskets and god knows what else once you start tearing things apart.

[Tercel_jon]

Damn... Everything is always more complicated than It seams. Guess Ill just drive down there with the 4:11s than. :/

Thanks for the in depth reasons why I cant just "swap it". If I didnt have you guys Id probly tear up something bad.

Good thing Im buying that all-trak rear end at the junkyard.

I started another thread on the front springs out of the all-trak basicly asking if I could substitute the all-trak front springs and hat in place of the camry springs and hat for the Bartos Lift.

[Petros]

Get the 4.1:1 third member for the rear axle. The 4.1: 1 ratio is MUCH BETTER for this car, it is an easier change out and you are better off with this ratio anyway. You will not regret it, I have drive both, the 4.1:1 is a much better ratio for this car because of the underpowered engine. All should have come that way.

And it is much easier to change and you will not have to disturb the lash since the whole diff center assembly can be swapped out as a unit without too much trouble (I did it in about 2 hours). You pull the two rear axles out about 6" (hang them if you are not removing them so protect the axle seals, and be careful of the rear axle seals when you do this), remove the rear drive shaft flange and than unbolt the 12 or so 12mm nuts from the diff flange, and it drops out. clean out the housing and install the new third member, seal it up good with form-a-gasket.

There is more effort, and too many things that can get messed up big time trying to swap out a front diff. I would not do it.

Good luck.

[Tercel_jon]

Hey petros, thanks for the how-to.

I agree with the gearing being better with the cars so underpowered, but I was looking for mileage on my trip to florida this winter. But its all ok.

My plan now is to just swap the rear axle with the corolla all-trak in the junkyard that I frequent. How can I know for sure it has the 4:11s?

[Petros]

My plan now is to just swap the rear axle with the corolla all-trak in the junkyard that I frequent. How can I know for sure it has the 4:11s?

There should be a tag on one of the mount bolts of the center member, but I have found it is not always there. If you remove it you can see it stamped on the side of the ring gear, or you can count the teeth. If you do not want to remove it you can count the number of turns the input shaft makes to make one turn of the axles (make sure they turn together). There is also a diff code on the data plate on the fire wall or door frame, but I have also found the diff code is not always present either.

BTW, I have found that there is no noticeable difference in fuel economy between the two different diff ratios. Despite the engine turning at different speeds, I guess the performance cure of the engine is so flat it uses the same amount of fuel at the same power output at the different RPMs.

[xirdneh]

I got a 4.1 rear differential out of a Corolla that fit the Tercel
not sure what year Corolla it was.

I've checked mileage on every tank with the various Tercels I've had over the last 7 years. All of them have the stock carburator. Some have 3.73 and some have 4.1 diff's.
The mileage varies from 26 mpg at the lowest to 33 mpg at the highest for "All Around Driving" only (whick is what i do 90% of the time).
My experience has shown that a clean well working carb with size 101 primary jet gets the best mileage overall .
The worst mileage was with a 106 primary jet. (other jet sizes i've seen are 102 and 103)
The differentials did not make much difference , maybe 1 mpg less on the average for the 4.1's.
Peak mileage has been in the warmer months with a drop of 2-3 mpg during cold months.