Another Auto Transmission Thread

[Jeff10]

Hey Everyone,

I've searched through the forum and read various posts about automatic transmission swaps.

We have a T18 behind a slightly built 302.

In general, I love the T18 with this setup. The only drawback with the 4.56 gearing is the top end on the highway (although it isn't terrible) and the convenience of an automatic on moderate rocks we crawl on.

I have a rebuilt C4 with a low stall speed converter that I purchased a couple of years ago. I'm wondering if other folks think that it helps enough with the top end.

If I look at anything other than the C4, it's probably important to mention that I'd like to stay away from anything that's computer controlled. Also looking for a strong transmission with a good track record.

Thanks,

Jeff

 

[triracer67]

I have 351w, c4, and 4.56 gears with 33’s. I’m turning 3100 rpms at 60 mph. I’ve been looking at AOD, and 4r70w auto trans with adapters to get an O/D. Neither are electronic, they are basically newer C4 with overdrive.

 

[needsmoarturbo]

T18 and c4 both have a 1:1 final as far as I know, so your not going to gain lower highway rpms there... Need an overdrive if that's your goal. The early aods we're not computer controlled, but will need other input as to how stout they are, I've got no experience there..

 

[rpmgarage22]

As needs said, you are still at 1:1 in top gear...no benefit to top end.

Early AOD is non-electronic, but requires a little tuning savvy with the "TV" cable adjustment. You can use 2wd or 4wd version...you just have to know which you have when ordering your adapter so you get the right shaft. Either way, you are in for a rebuild, as the shaft is the last part out/first part in on an AOD. But, if set up right, you would be very happy with the AOD.

In my opinion, the 4R70W is not worth all the extra expense for the controller. The "strength" gain is arguable, and there is no true "benefit" to having the converter "lock-up" in all gears, IMO.

BUT, since you already have a third pedal, why not consider the AX15 swap? Decent low gear and moderate overdrive, with an excellent spread between gears. Fuel economy will be better, only moderately larger than the T18, can handle far more torque than you are gonna generate with the 302, etc., etc. For crawling, you can hook up a manual throttle control so you are staying off the clutch.

Just a thought...

 

[Jeff10]

Hi Guys,

Thanks for all of the input.

The main reason for the swap would be the top end... although in the overall scheme of things I really am not looking for too much on the top end.

If I did a swap, I would probably lean towards an automatic. I really am okay with the manual. I drove someone else's rig on a trail in Moab and was pretty spoiled with how easy the automatic was to drive. (One less thing to make a mistake with. lol)

If I get more serious with this, I'll need to get into the details you guys describe with the 4R70W to see what really goes into the install.

Thanks again. I really do appreciate the input.

Jeff

 

[garberz]

If you went up in tire size to 37”, that will gain you about another 150 less rpm at 60 mph. If you’re gonna go through the expense of an overdrive auto trans over the C4, stay away from the AOD’s. The OD gear in those is a bit tall compared to the more useable OD gear in the 4r70w. But the best upside to the 4r70 is the lower 1 and 2 gear ratios. The AOD has the same 1-3 as the C4. There’s several that have put the 4r70w gearset in the AOD case, but not using the electronically controlled valve body is a wasted opportunity. 37’s and a C4 may keep you happy for several years. That’s where I am right now.

Mark

 

[Nothing Special]

A C4 will hurt your top end slightly. Same 1:1 ratio, plus torque converter slip. Won't be much of a change, but maybe 100 - 300 rpm in the wrong direction.

 

[Broncobowsher]

It might just be the fan roaring away making too much noise and thus the want for less RPM. An Explorer accessory drive with a clutched fan might do the trick. Still the same RPM, just a lot less noise while doing it. And still enough airflow to keep things cool.