How do I find out what transmission I have?

[JTD]

Good evening. I'm new to the forum as i just purchased a 79 Wagoneer w/ the automatic trans. From what I understand, it could be 1 of 3 different transmissions for 79. I've tried a VIN decode, but doesn't tell me which transmission I have. How do I find out? Thanks in advance.

[Mikel]

Likely a TH400.

[JTD]

My VIN breaks down as being a "Custom Wagoneer". I know the transmission options are either the THM400, A727 or the A999. How does one find out for sure?

[joe]

Only AT avail in 79 was a Jeep bolt patterned TH400.

[JTD]

The reason I ask is cause Wikipedia shows 3 different AT's and I also had stopped by a local mechanic shop and he stated the same thing. With regards to my transfer case, since I have the low range gear lever down on the floor, does that mean I have the BW1339 transfer case?

[Crankyolman]

Crawl underneath and look at the pan shape. Take a picture if you need to to show people but mine has GMC (or something like that) right on the pan which would instantly tell you it's a TH400 this is a TH400 pan






this is a 727 pan

[Mikel]

If the front differential is on the passenger side, it is a TH400/Quadratrac. If it's on the driver's side, it is a TF727.

[UnkleMunky]

All good points above. Should help you narrow things down.

Properly, you should have a TH400 as that's all that should have been available in '79, but there are some (rare) exceptions to things, especially if it was say end of '79 model run and beginning of '80 production. Who knows if there were a few oddballs at the transition point.

As you probably know...places like Wikipedia and that are to be taken with a grain of salt. Same with lots of other sources on the internet. But also same with lots of *mechanics*. Those of us who have had these old Jeeps for a long time have heard about everything over the years. My first Jeep was a '77 Cherokee with a 360/t-15/D20, and was back in the late 80s'/early 90s when I had it. I cannot tell you how many *mechanics* were so uninformed even at the time (when there were still more AMCs on the road). I had been told *yeh, that's a Ford 360 in there* and *they put Dodge 360s in those* and so on and so forth. Jeep DID use parts from the major brands of the time (Th400 is a GM tranny, TF727 is a Chrysler, and so on), and is one reason people have said the AMC initials stood for *All Makes Combined*. And you do have to be aware of what they did use, but in those years, the engines were ALL AMC. So, when mechanics tell you things....I learned you sometimes have to be more informed than they are.

So, you're doing the right thing by asking here. Afterall....even if you know what is *supposed* to be under the hood or in the driveline.... if you're not the original owner of a 30+ year old vehicle, it could well have other than original parts at this point.

Take all the points above together and you should be able to narrow it down. Check front differential first....as mentioned above....passenger drop would indicate the pre-80 format used with the TH400. Driver drop would indicate 80+ use of the Chrysler trannies. Then check the pan style. Maybe even ask to see a gasket at a parts store to verify shape with the pan cover. Look for any labeling on the tranny/pan itself as well. Then you should be pretty certain by that point what you have. Maybe look at the transfer case as well. The QT(BW1339) is definitely different than the 80+ usage of the New Process cases. NP cases will have a nice little round tag on them with model number. I forget what designation there is on the QT cases. But add all those things together and you should be good!

[tgreese]

A lot of words ...

If the VIN starts with "J9", it's a 1979 model.

Production for the 1979 model began in late 1978, and similarly for 1980 in late 1979, so build date can help but not necessarily.

The ultimate authority is the 1979 TSM (technical service manual) from Jeep, online to read or download here: http://oljeep.com/gw/79_tsm/79_Jeep_TSM.pdf

The TSM will confirm that the only automatic transmission used in 1979 was a GM Turbohydramatic 400 (TH400) with an AMC-patterned case. None other.

[rang-a-stang]

If the front differential is on the passenger side, it is a TH400/Quadratrac. If it's on the driver's side, it is a TF727.

Easiest way to check right there. You don't even need to crawl underneath.

The only other thing to think about, our rigs are old. People messed with them. we can all say with a fair amount of certainty that your rig left Toledo with a TH400 in it. BUT that was 40 years, probably a few owners, and countless miles ago. If it puked a trans in 1992 with 180k miles on it, whoever owned it may have wanted a 4 speed auto and swapped one in. Or maybe he had a 727 laying around and put that in, but didn't connect the front drive line. I would put on an old t-shirt (becuase I am sure your rig leaks like all ours), crawl underneath and look at the oil pan shape. Compare it to the pics Crankyolman posted. The factory TH400 pan will have "Hydramatic" and "Div of GMC" stamped on it with no drain plug. If you see anything else, take a picture and post it here.

[JTD]

Thanks everyone for the information. I have a lot to learn about these Jeep and the Quadra-Trac system. My diff is on the passenger side, so I'm confident I have the TH400 w/ the BW1339 TC. I will be getting up in the air tomorrow and I will verify and take a look at the tranny pan.

I have also ordered some TCL-1 fluid for the TC so I can drain it and check the chain slop. My Wagoneer has 111,350 miles on it. Definitely not bad mileage considering it's 40 years old.


What does everyone use for front/rear differential lube?

[rang-a-stang]

Go to this link and you can download the factory service manual for free and a lot of other good info. Use the factory recommended stuff and you will almost never be let down.

http://oljeep.com/edge_parts_man.html

Gear oil: again, lots could have happened between when ur truck was sold and now. If you have stock open diffs, just gear oil is fine. If you have a locker or limited slip, you have to do some research.

[wiley-moeracing]

80/90 weight for open standard diffs, you can use 75/140 for heavy duty use(towing) and if you have limited slips you need gl5 raiting- limited slip additive to gear oil. Some syn. gl5 has the additive in it already.

[JTD]

Crawl underneath and look at the pan shape. Take a picture if you need to to show people but mine has GMC (or something like that) right on the pan which would instantly tell you it's a TH400 this is a TH400 pan






this is a 727 pan

My transmission pan says "Hydra-matic", "Div of GMC"

[rang-a-stang]

My transmission pan says "Hydra-matic", "Div of GMC"

Definitive proof of the TH400.