White_Knuckles

I asked this before but now I'm back due to a trans shop owner having a completely different opinion.

Okay, I have a 70's Olds 350 engine with the original 2-speed JetAway trans in my '67. I have a free TH350 that can be rebuilt as an "upgrade". My prior question was, can this GM baby bolt up directly to the 350? The response was yes, no modifications were needed, everything moves over.

So I drag the trans to the shop and explain the plan. The owner explains no, it will not bolt to the Olds bell housing without an adapter kit where he recommends rebuilding an Olds 350 trans core which he prices around $700. It's not about the savings using my core, it's about getting the facts on this. He went on to say he can rebuild the Jetaway and claims they are a great trans. Really? I thought there may be a benefit to having a real 1st gear for launching off the line and a snappy shift kit. He recommends to go to a TH400 with some vac/electric modulator kit and a manual lock-up gizmo. This would exceed $1000 real quick before installation.

Can you subject matter experts chime in with facts and advice? The thing is, the stupid 2-speed works fine and I have the pitch-shift kick down operational from the throttle linkage. The bugger just leaks no matter what! I've had it serviced and no one can figure out the leak source. Time for it to go away or keep topping it up? A $1500 investment seems like it needs to be a killer upgrade.

MDchanic

Maybe you bought a Chebby-pattern TH350.

- Eric

lemoldsnut

I agree the trans you got must be a Chevy version. Post a picture of it to be sure. You should be able to find a BOP (Buick Olds Pontiac) core TH-350 for $50 or so. The th-350 would be fine and shift nice if built correctly and is a very easy bolt in swap. A th-400 takes more to swap it in but is do-able. A th-350 built well is a great trans. The ST-300 in your car should also be a very good trans. But, yes I have had leak issues with them. Not all trans guys know them due to the age of them.

Hope this helps.
Larry

Rickman48

Get a dual pattern 200r4, as it's almost a bolt in, and cores are available cheap.
With the right mods, holds up to 9 second G.N.'s!
Plus overdrive and a lock-up converter - fuel ain't gonna get cheaper!!

White_Knuckles

It's clear my TH350 is a Chev flavor. It was given to me as a working unit but I thought a rebuild was in order to make sure it would hold up. I agree a 200-400r4 would make for better mileage but that's not a concern. I'm trying to avoid a massive change as I want to keep the column shifter in place. I think the "BOP" core might be the deal.

But before I seek out a core, lemoldsnut, what do you run in your 442? The ST-300 indeed is kind of cool and seems healthy. Does anyone know where the mystery leak may be coming from? It is not the pan gasket which I changed or the rear seal. I've had it up on a lift for hours but only leaks when I'm not looking! Could it be evil?

oldsmobiledave

No matter how well the ST-300 is working once you swap out to a T350 you will never want to go back to a boring 2 speed again.

lemoldsnut

I agree once you swap you won't go back. I run a TH-400 in my 67 442 and a 4 speed in my 66. Your leak could be the vacuum modulator they have an o ring that could be the leak, or the diaphram of it could be the leak, that usually causes a shift issue. It could be the o ring on the fill tube, or a front pump seal or rear seal, It could also be that the vent tube is plugged and causing it to not vent and push the oil past the seals when under pressure. The shifter shaft seal could be leaking too. I assume you drive it now and then and are looking for something reliable and that works a little better. I agree that a 200r4 would be nice. It would cost more and really, fuel mileage is not that much of a consideration in a car that might get 5-8 tanks of fuel run threw it a year. I would run the th-350 in your case. It is a very simple bolt in swap.
Of course that is just my opinion. Others will have their point of view as well. I think you can do a th-350 the cheapest and get the most results for your dollar. A good rebuild and a mild shift kit.

You did not complete your registration so can't tell where you are located.

Hope that helps.
Larry

oldcutlass

Generally when this question is asked, one of us always states that the trans must be from a Buick, Olds, or Pontiac, a BOP trans is the only direct bolt on. Chevrolet trans will not bolt up without an adapter.

If you are hell bent on changing, the easiest most economical swap is a T350. You will also have to replace your torque converter.

joe_padavano

There are three different TH350 cases, Chevy-only, BOP-only, and unisex. The Chevy-only will NOT bolt to an Olds (or any BOP) motor. The other two are complete bolt-in replacements for the Junkaway, assuming you have a short-tail TH350.

White_Knuckles

"JunkAway"! LOL.

Okay, thanks to all - I get it. I looked last night for a replacement pan thinking even though it looks fine, it's not sealing. There isn't a pan to be found on the Intraweb - anywhere! These things are indeed history.

Yeah, not a daily driver by any means. So, a BOP, TH350 with a mild shift kit is on the radar. I want to install it and forget it type project. I think the column linkage should work to access 1st gear? If not sloppy enough, perhaps there's something in the column that can be tweaked for more throw? Really don't want to mess with a floor cable shifter.

So we all agree I need a "short tail-shaft" to retain the existing driveline? Anything with U-joints or something to consider for fitment?

You guys are great, thanks for the assistance!