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The TH400 that came in my 442 is not the original transmission, and does not have the original tag on it. Here are some pics of the various markings. Can anyone tell me what this transmission actually come out of?
Your last pic shows a casting # of 8623801, that seems to indicate an early TH400 case. And there is a date code on the extension housing, right under the big "C" which could be 68. Or it could be 89 but I think not because that would be a truck trans. (Chevy bell)
It looks to have 8 pump bolts rather than 6, also indicating early 400 production.
Your best indicator may be your first pic of what I believe to be a partial vin#, that more than anything, may be a clue as to the origin.
But my guess is you have a 1968 trans, from something with a short output shaft. 442, GTO, GS400 etc.
P.S. the 40 -43 tooth speedo gear housing backs that up as well.
Last edited by 65vistacruiser; July 4th, 2016 at 09:56 PM.
read the VIN stamp
I thought it started with a 2
but it's hard to read
2 is Pontiac I believe.
Yup. Looks like 27A256024
2 = Pontiac
7 = 1967 or 1977 (I suspect it's 1977, since a 1967 TH400 would have used the early style filter with the "horseshoe" dimple in the pan)
A = Atlanta, GA assembly plant (actually, Lakewood Heights, GA, not to be confused with the Doraville, GA plant)
Ok, thanks at least this is a start. I was on to the Lakewood assembly plant, but I have not found much on which poncho's were built there. I think I know that the LeMans/GTO all were 1xxxxx as the last six digits, but what would a 2xxxxx series be?
What is a horseshoe dimple in the pan look like?
If it is a 77 what would it have come out of?
I am making a couple of assumptions for the 70 442 it is going in.
1) I assume the output shaft is the same regardless of the model as long as BOP.
2) I assume, and this may not be the case, that I will only need to change the speedometer gear for my 3:23 rear, and not both the speedometer gear and the drive gear.
I just had the transmission rebuilt, but looking to determine what I need now or should be aware of.
Ok, thanks at least this is a start. I was on to the Lakewood assembly plant, but I have not found much on which poncho's were built there. I think I know that the LeMans/GTO all were 1xxxxx as the last six digits, but what would a 2xxxxx series be?
It depends on the year and the division. I can't speak to Ponchos, but for Olds this changed over the years and even by plant. For example, in the 1960s, all non-Toro cars built in Lansing were lumped into the 100001 through 500000 range, and Toros started at 500001 and went up. In the early 70s, Olds changed that so that A-bodies were 100001 through 400000, B/C bodies were 400001 through 700000, and Toros were 700001 and up.
What is a horseshoe dimple in the pan look like?
If it is a 77 what would it have come out of?
Assuming it's a short-tail, I'd guess an A-body Poncho (LeMans, Grand Am, etc). I don't know what models were built at Lakewood.
1) I assume the output shaft is the same regardless of the model as long as BOP.
If you mean for yoke purposes, yes. Obviously there's the short tail vs. long tail issue. And I ASSUME this is not a TH375, which is the light duty TH400 that uses a TH350-sized output shaft. I don't think those were used that much once the TH350 was released.
2) I assume, and this may not be the case, that I will only need to change the speedometer gear for my 3:23 rear, and not both the speedometer gear and the drive gear.
It depends... Most likely you only need to change the driven gear, but it depends on how the trans was set up and your current gears and tire diameter.
It depends on the year and the division. I can't speak to Ponchos, but for Olds this changed over the years and even by plant. For example, in the 1960s, all non-Toro cars built in Lansing were lumped into the 100001 through 500000 range, and Toros started at 500001 and went up. In the early 70s, Olds changed that so that A-bodies were 100001 through 400000, B/C bodies were 400001 through 700000, and Toros were 700001 and up.
That was kind of my thoughts, but after I posted, I thought 150-160,xxx would be a small production run.
Interestingly enough, I have been reading up on the 77 Grand Prix they had 288,430 produced in 77, the th400 was standard on all GP with V8s since March 71. Depending on the plant and destination you could get a SBO 350 or 403. Poncho 350 couldn't pass emissions, but since the Cutlass was selling so well there was limited supply of these engines so some GPs got a Chebby 350.
Still doesn't answer what I got, but it was interesting reading.🙃
Well that can be overlooked, although I must say I never saw one😀
Assuming it's a short-tail, I'd guess an A-body Poncho (LeMans, Grand Am, etc). I don't know what models were built at Lakewood.
Still haven't found that yet, but still looking.
If you mean for yoke purposes, yes. Obviously there's the short tail vs. long tail issue. And I ASSUME this is not a TH375, which is the light duty TH400 that uses a TH350-sized output shaft. I don't think those were used that much once the TH350 was released.
Yes, definitely short tail 400, and yes the yoke was what I was referring too.
It depends... Most likely you only need to change the driven gear, but it depends on how the trans was set up and your current gears and tire diameter.
I was hoping this would be the case, going to stay close to stock size wheels and tires. So is that28" or 28 1/2" height? Also how may teeth, or what color gear should I have?
Last edited by Troys Toy 70; July 26th, 2016 at 04:40 PM.
You can always look up the tire specs to get a diameter so you can get close.
Yup, but the problem is, that will be the diameter of an unloaded tire. Once you put weight on the tire, the sidewalls deflect, which reduces the rolling radius. The meaningful data point is loaded revs per mile. Unfortunately, most car tire vendors don't provide this piece of data. Since the loaded tire will have a smaller effective diameter, picking the gear based on the theoretical diameter will result in a speedo that reads slow.
reads slow?
wouldn't a reduced rolling radius result in the car going slower than the meter indicates? Therefore the readout is fast[er than actual]. Is this #3?
reads slow?
wouldn't a reduced rolling radius result in the car going slower than the meter indicates? Therefore the readout is fast[er than actual]. Is this #3?
Yeah, you're right. I'm crunching on a major proposal for work and obviously wasn't thinking.
The dimpled pan suggests its a 68 or older trans, 69 and newer use the flat pan and flat filter.
If your willing to take the trans apart for a autopsy, 72 and newer trans will have a roller cam style direct drum, 1970 and older with have the thicker center support, it wont have the .040 spacer. The spacer was added to prevent the center support from chewing up the case. Around 1975, stamped steel pistons replaced aluminum, late 70s had plastic thrust washers and accumulator pistons started showing up. Of course, after almost 50 years, any of those 0arts could have been changed.
The dimpled pan suggests its a 68 or older trans, 69 and newer use the flat pan and flat filter.
I posted the photo of the dimpled pan as an example. We don't know what the OP's pan looks like. I believe 1968 model year was the first to use the flat filter, not 69.
May 21st, 2016, 07:21 PM
