4.10s in AOD car?

[whoops]

Curious what everyone's views are for gear ratios. I have an AOD '89 LX 5.0L that I'm putting 4.10's in on Sunday. I'll be converting this to a 5 or 6 speed soon as well.

Good idea for the 4.10's?

Justin

[WADS56]

Yep

[Kamaro Killer]

if you are converting to a 5 or 6 speed soon, you should go with 3.73's. It also depends, what are you planning with this car? Do you travel on freeways a lot? Later, Keith

[Mopar1]

Got 4.10's in the mobile. They were already in there when I bought it. My cruising rpm is 2200. Which equates to aruond 63-65 MPH( shot with a radar gun several times). They work for me, I just dont drive it like a brazened idiot and keep it between 60-65 on the highway.

[whoops]

I don't have any specific plans for the car right now, except to enjoy it more while I work on my jeep. I was told with a manual tranny these gears will be fine, but with the AOD I'll spin off the line more.

Is top end really that messed up with the 4.10 ratio? Would I be happier with the 3.73's? Would I still be getting my butt kicked off the line?

Justin

[jim_howard_pdx]

I've got a great answer for you, but you need to think this through and determine the actual purpose of the car, how the car is driven, and how bad you want to blister the competition.

First AND THIS IS CRITICAL, It makes NO sense to run any gear set without a strong and functional posi system. If you have a drag car, you want a spool or at least a mini until you can afford a good spool.

If you have a street/highway/ or autocross car you need a Detroit Locker, a PowerTrax, or a limited slip posi unit. If you do not have one, wait to install your gears. Cause trying to launch with only one tire supplying traction will kill you, and guys like me will bust their guts laughing at you.

If you have a posi, take it out and have it rebuilt. If it is a spring type unit, have the springs removed and shim the clutch pack to 140-160 ft pounds of pressure. That way the posi will be a torque sensing differential. I will explain this to you later if you do not understand. You can call Currie rearends and they will ship you everything you need to perform this modification. TSD differentials last a lot longer than spring clutch posi units, and they supply traction as a function of torque, so they do not waste the clutches when you really don't need posi at all.

Slicks or Street slicks are important with 3.73 gears and steeper. As the engine turns 4 times per tire turn, the engine reaches maximum torque levels VERY QUICKLY. So on standard tires you will sit there in a cloud of smoke. And I will laugh even harder.

Now, look at your engine. What is your top rpm at this time? Will it improve soon? In my case, the 358 Windsor engine is balanced and blueprinted to run 7k rpm. My cam is good to 6.5K rpm. So if I want to be at 6500 rpm when I hit the trap speed zone of the quarter mile, I would want a 4.30 gear. If you run 7k rpm you could use a 4.40 gear or even a 4.50 gear.

Your top mph will go down slightly as you go lower and lower on the gear ratio. But your ET's will go lower and lower too, so it is a compromise.

If the car is dragged a lot, then I would go 4.30 with a TSD Posi, Locker, or Spool. If it is highway and street car I would go 4.10.

I would not go 3.73 under any circumstance because that is where the majority of your competition will run. The 4.10s will have SIGNIFICANT extra launch capability, and with a small block, it will allow you to rev through the gears easier. It puts LESS load on your bearings and may reduce your engines propensity to detonate or predetonate.

So I hope this helps. I plan on running 4.30's on the track next year. My computer says my package will cut an 11.90 on gasoline and an 11.15 on a 200hp squirt of NOS. These are awesome times for a street/highway car with a autocross suspension.

Plus my 9" ford rearend allows me to swap gear sets in under 2 hours with basic hand tools. So I will keep my 3.25's should I want to run the silver state classic in the 150 mph bracket.

Good luck, I vote for 4.10s or steeper!!!!

[whoops]

jim_howard_pdx:
Thank you for all that information, it definately eases my mind about the 4.10's a little more.

This car sees a ton of highway right now, and ideally I'd like to set it up for auto-x at some point.

The car has a TracLok installed at the moment and it's in good shape. I'll verify that on Sunday.

I don't know what the top RPM of the car is actually. I think it redlines at 6 grand? I've only had the car a few weeks, learning about it as I go. (I know jeeps)

Justin

[Kamaro Killer]

that if you are trying to get the best e.t.'s then 4.10's are good for you. If you would just like a little more power to get off the line quicker, then 3.73's are more than enough. I have a T-5, so that may be a slight difference, but if you are planning a tranny swap soon, then I say go with the 3.73's, especially if you are driving fast on the freeways. It's your choice though, I hope you are satisfied with whatever you choose. Take care, Keith

[whoops]

I hope I'm going to be happy with the 4.10's (especially since they've already been purchased!).

I am looking at this as a learning experience. If I don't like them now or after the tranny swap, I'll switch and be able to provide other newbies my experiences. I've learned with my jeep that no matter what you do or choose, you'll always change your mind at some point.

Justin

[jim_howard_pdx]

When you pull out the posi unit, you can dissassemble it VERY EASILY once the ring gear is removed. Remember those cutch springs are rated at like 1500 ppsi, so when you remove the phillips head screw that retains the two sides, you want to make sure that if it unloads, that it aims away from you or your friends. Any good rear end shop should have clutch pack shims. Simply leave the springs out, remove the thrust bearing on the clutch side of the trac-loc, and shim it .010 to start. I usually go .010 and add a .015 and bolt that up with the phillips head. Then put two or three bolts and nuts through the ring gear holes and torque them down. Put an axle in on both sides and turn them in opposing directions. If you can turn them with 140 ft pounds of torque or slightly higher you are done!!! If they are tigher, you are ok to about 175 to 180 ft pounds of torque. But that is your range. If they break loose under 140 you need another .050 shim. You will not need more than .020 shims unless the clutches are worn, then replace the clutch pack and start with .015 shim.

DO NOT RUN 3.73's. The goal is to win the race, reduce the stress on your engine and rod bearings and have fun!. 410s or 430s are the only way to fly!!!!!

[ultraflo]

...another vote for the 4.10's

I agree with Jim in regards to addressing the posi unit... never a bad idea.

...a shift kit for your AOD might be a good idea, no? I would stay away from the 6 speed unless your setting up the car for road course or highway cruising. I'd go with the 5 speed for a street/strip setup... just my opinion.

[chico]

Definately! Go with the 4.10's ...I cruse at 75mph and tach 2900 rpms. Of course the Cobra likes the rpms, I shift about 7400 rpms when racing...

[Mach 1]

4.10s are great for AOD car, street or stip. If you will be swapping to a 5 speed, and you drive on the street more than the track, go with 3.73's.

[lx5091]

4.56:1 and a Viper T-56 from D&D

[88coupe]

The only problems I can see with running 4.10's in an AOD car is that you can't shift into OD at full throttle (at least I couldn't). My car was hitting 5000-5100 rpm at the trap in 3rd gear And I only have 3.73's. If I would have gone with a low gear I think I would have gotten worse times with the AOD. Maybe it's just my car... maybe its incredibly fast (haaaaa!) or something.

But now the AOD is gone.. in the backyard in a wheelbarrow. ANYONE WANNA BUY AN AOD!

[whoops]

88coup:
Can I ask what your conversion ended up costing you?

Thanks people. The information is greatly appreciated.

Justin

[88coupe]

I spent about 800 on all the parts but I also but a hurst shifter, which isn't nessecary if you get a stock one but a lot nicer... My car is a lot faster now!

[Mach 1]

Originally posted by 88coupe
The only problems I can see with running 4.10's in an AOD car is that you can't shift into OD at full throttle (at least I couldn't). My car was hitting 5000-5100 rpm at the trap in 3rd gear And I only have 3.73's. If I would have gone with a low gear I think I would have gotten worse times with the AOD. Maybe it's just my car... maybe its incredibly fast (haaaaa!) or something.

I fail to see where the problem is here? You dont want to shift into overdrive under full throttle and you dont have a need or reason too? Can you explain?
I trap at around 5500/5600 (which is perfect) with an AOD and 4.10's, and mine doesnt lock up in third, making the rpm range even higher.

And if for some reason you do want to adjust your trap RPM and keep your gearing the same, this is easily accomplished by changing rear wheel and tire size.

[88coupe]

I guess 4.10's would be alright... figured the rpms would be higher then that. Go for the 4.10's then. Only reason i have 3.73's instead of them is because i put a 5 speed in.

[Kamaro Killer]

the only reason I kept suggesting getting 3.73's is because you are planning the swap to a 5 or 6 speed. You will not even see 6th gear with 4.10's. Oh well, your car, your money. I truly hope you are happy with whatever you choose to do. Take care, Keith