Hyrda-Matic tranny in a CJ-6

I currently have a GM hydra-matic tranny of some form between my Dauntless and Dana-18. Would you recommend I stay with it, or go back to a standard? If so, which standard would you suggest?

I will use this truck occasionally on the freeway, 80% city and 20% off road.

thanks.

 

It's likely a Turbo-Hydramatic 400 (TH400), an excellent transmission. The TH400 was used in Jeepsters, Wagoneers and J-trucks for many years, and is therefore the most likely transmission for a transplant. The TH350 is also available, but was never used in Jeeps, so it would have to have been swapped in with an aftermarket adapter. Thus, the 350 is less likely than the 400.

The only reason you might change it is becasue you don't like automatics, or to upgrade to a more modern overdrive automatic with a locking torque convertor, like a TH 700R4 or 4L60E. The more modern transmissions are more efficient, but you'd incur a big expense changing over that you'd need many, many miles to make back.

The TH400 is excellent - likely the strongest and most reliable automatic passenger car and light truck transmission ever made. The 350 is also good, although a lighter-duty transmission, still strong and reliable. The 350 is somewhat more efficient than a 400, and the 700 is more efficient than either.

 

darn... I was hoping you guys would tell me it's crap so I could tell the wife I *need* to replace it.

Well, I'll keep it them, thanks for the knowledge guys!

Now I gotta get them brakes working better so it can stop that automatic! (I currently press as hard as I can and can *just* get it to slow down)

 

not good. any fluid dripping or wet areas around the brakes or lines?

 

It's a Jeep.... there's fluid ALL OVER THE PLACE!



but seriously, I haven't had the wheels off, and I haven't cleaned the thing underneath yet. I have seen lots of ATF drips so I know the TH400 is working R) The gunk is an inch thick in places, I've got lots of work ahead of me. But I've got lots of beer,... so alls good

 

If the brakes are in good condition, I'd wonder if the PO rebuilt the trans with a high-stall convertor? I'm not an expert re build-ups of automatics, but I think that would make the car hard to hold back at idle. I also recall that the high-stall is a popular change for radical rock crawlers... sometimes people mimic these "trick" ideas in street cars, with varied results. IMO you don't need anything more than a stock TH400 for anything but competition use.

 

A high stall converter should not make it hard to hold back at idle since the transmission will be unable to move the vehicle until the torque converter builds up rpm to its stall speed. The stock converter will let the vehicle move at about 500rpm, most aftermarket converters are at least 2000rpm converters, which means the engine will need to be running around 1500 rpm before the transmissions pump will have a enough speed to move the vehicle. I would also crawl under the Jeep and actually see what transmission you have, turbo 350's are a dime a dozen and easy to find, make sure of what you have before going farther, I wouldn't just assume its a turbo 400.

 

I second Mcruff, sounds like you have a stock converter. Check your idle speed and timing - an advanced timing could cause a rapid idle that will make that hard to hold at stop lights. If the problem is just coming to a stop from any speed, then you've got brake work ahead of you. Even if it is a TH350, and they are a dime a dozen, it doesn't mean its a flawed trans. With the curb weight of the Jeep being what it is, that thing could probably take a lot of abuse before it gave out.

 

well just to close out this thread,... it is a TH400, based on the pan and compared to Novak's site.

This Jeep hasn't run on the street for years,... the only moving I've done with it is to move it around a little so other vehicles can pass it in the driveway.

I lifted the rear to check what gears I have via the spin the drive shaft and count the revs vs one rev of a tire. But then I noticed the front driveshaft was also spinning. The D18's shift lever is broken, but with a gentle tap from a BFH I got it into 2wd (hi or lo, don't know). When I spin I get 1.9 DS revs to 1 tire rev. To me this makes no sense, later this week I'll pull the pumpkin cover (which had to be done anyways) and count teeth.

Thanks for the help, maybe when I get a little further into it I'll have more intelligent questions.

 

There's no tag?

If you have an open differential, and you turn one wheel and let the other wheel not turn, your driveshaft will turn by 1/2 the gear ratio, so 3.83 is likely.

Think of both wheels as having to turn the same number of turns as the driveshaft divided by the ratio - the average of 1 turn and 0 turns at the wheels is 1/2 turn times the ratio at the driveshaft. If you turn both wheels one turn, the driveshaft will turn once times the ratio.