rotorsownyou7

How tough is it just to swap the rear. I just bought a 4.10 rear with an auto companion flange. Will this just bolt up in place of my 3.90 or is it a lot of trouble?

RX7Wishing

Should just bolt in place.

RX7Wishing

the 4.10 from an FD BTW?

RotaryResurrection

iTrader: (8)

It bolts right up. however your speedo will be off unless you run the 4.1 speed sensor from the manual trans (put it into your auto). It does fit, though it isn't the exact same looking part.

I've done this and the car didn't seem much more responsive...I suppose if you get a good deal and are bored, then go for it, but don't expect it to make the auto much more fun than it is already. Perhaps a 4.33 would make more difference.

FWIW, I didnt even change the input flange...just slotted out the holes so the auto DS would bolt up. The DS/input flange has an alignment bevel in the center so you don't run any risk of getting it off center.

rotorsownyou7

Oh well, speedo will just have to be off. I got a good deal, and I am going to be doing the manual swap sometime anyway, and I don't have much to do I know it won't make much difference, but it should be a little better from what I hear.

So by the manual you just pull the driveshaft, the axles, then just pull differential? Then reverse to put them back? Will I need to get the car aligned?

rotorsownyou7

Yeah.

RotaryResurrection

iTrader: (8)

You dont even have to pull the axles. You do need to take loose the rear wheel spindles/housings from the control arms enough to allow you to get the axles out of the diff. They're each mounted at 3 points, and removing the bolts at 2 of these points gives you enough room to get the axles out. However, it's not much more work to remove the last one and the abs/brake stuff and pull the whole spindle/hub/axle assembly off the car and out of the way. But yes, once you get the DS and the axles out, then the diff unbolts from the upper subframe using 2 long bolt/nut combos. ON the way down, be sure to unbolt the 12mm bolt holding the brake cables on top of it.

Reinstall in the same order. Use a large rubber mallet (or a block of wood and a sledge) to seat the axles firmly back inside the diff...just take aim on the outer end of the axle/nut, the force is transferred throughout. Note the small clearance between the axle housing and diff before removal, and be sure you have no more than this after it's all reinstalled. Failure to do so can damage axles and cause a fluid leak. Its not a bad idea to change the oil seals on the new diff before installation, btw.

No, you shouldn't. Your alignment settings are not on the spindle or axle/diff.

unixpilot

Also, if you haven't changed your fuel filter recently...Its the perfect time while the diff is out.

2 minute job.

jeff p

I am going with the 4.3 gears . its in the shop right now. I'll get it back on sunday since I was paying the money I didn't want the 4.10 gears not enough HP for the money involved. my auto has the 3.9 gears so the 4.3 should make a big improvement
Jeff

rotorsownyou7

Already changed the fuel filter. Anyway, I have me differential, it looks damn good. A question is though, what should I replace in it? Any seals? I took the back casing off and it says in my workshop manual it needs to be sealed. What do I seal it with?

RotaryResurrection

iTrader: (8)

rtv.

turbojeff

iTrader: (30)

Buy new axle seals also. It takes maybe 5 min to install them while the diff is out.

a3dcadman

iTrader: (1)

i did the change from 3.9 to 4.1 and even at 5% ratio difference, i felt it made a noticeable difference in acceleration and responce especially with the auto tranny gearing ratios being what they are.

use a good quality rtv silicone on the rear cover. i always clean all residue off of all gasketed surfaces and swab it down with lacquer thinner to remove any greasy film. it also promotes better adhesion.
clean the magnetic drain plug.

check the wear pattern on the teeth of the gears. replace axle seals. if you decide to replace the input shaft seal, you will need to get a new crush sleeve too. removing the companion flange necessitates an adjustment of the preload and flange bolt torque. the gear contact patterns will have to be checked and calibrated. use a premium quality synthetic gear oil.

its not too tough of a job to do. have fun.

chuck

a3dcadman

iTrader: (1)

1. does the speed sensor from the manual use the same connector as the auto speed sensor.
2. are they mounted the same way.
3. what is the sensor "sensing" to create the signal that goes to the speedometer.
4. i believe that the speed sensor provides data to the auto tranny "ecu" / controller. so are there any adverse affects evident from using a manual sensor in the auto.
thanks,
chuck