305.

[64nailhead]

An OD transmission is going to require a rear gear change to gain full effectiveness. If you're willing to swap the rear gear ratio, then put in an OD, if not, then the TH350 is a better alternative IMO. But I would highly recommend an OD and a gear swap - it will feel like you added 50-100hp.

 

[olds307 and 403]

I agree on the 700R4 for a 305, let others use the drying up supply of 2004R's for something else😉. Every shop will build a 700R4, few can build a 2004R properly. Use a 2000 stall and up the lame stock gearing to a 3.42 or a 3.73 gear with a 700R4. It means cutting the driveshaft to fit. If you don't want any improvement in performance, a completely stock TH350 or even a TH250 in a pinch. The stud by the cooler lines means it is the weaker TH250. Also the later TH250C/350C use a completely different and more expensive lock up converter. The 4 pin connector on the driver's side of the case means a lock up converter.

 

[Doug213xrj]

X2 Th 350 for ease of installation, 700R4 for a OD.

Doug

 

[Gonzo1970]

305 - 2004R - 3.73's

I ain't mad.

-Gonz

 

[69hurstolds]

I think it's drifting away from what is needed vs. what we all would do if it were ours. I think there are more questions to be asked of RoxanneThe79’Cutty first.

Guesstimating/Assuming a low numerical gear set like 2.41 or 2.73 at best and likely a toasted or soon to be toasted 200C transmission or 3-speed auto-something to start with, along with that 305, what is the end goal? What is the short-term goal? These questions need to be answered first. Is this to replace the transmission in your car or are you planning more upgrades in the future? Are you going to replace the 305 with say, a 383 stroker at some point? Or just leave it as is? If this will be a mod-rod, then sure, go with a 700 over a 200-4R only because of availability. The 200-4R, if built right, is a pretty stout transmission in its own right. But that's key with the 4R. You need to make sure it's built right. In pure stock form, the 305 could tear it up.

For your least amount of money, if you have the availability of a TH350 in front of you for cheap, it's a FINE transmission to live a long life behind a 305, cheap to rebuild and even modify a bit for long-term reliability. Keep in mind the TH350 uses a vacuum modulator where the TH200C does not. Also, the TV cable on the TH200C will be replaced with the kickdown cable on the TH350. There MIGHT be some bracketry by the carburetor needing to be changed. And probably cooler lines too. But it should bolt right in otherwise. While your driving habits may tear it up, the 305 shouldn't be able to. It will be comparable to what came in it stock as far as performance, but again, where are you going with this project?

Unless you know the history of ANY used transmission, it's always advisable to go through it first or have a trusted shop go through it to ensure it's in great shape. If you're just replacing your tired old transmission, this would probably be the easiest swap compared to any OD variant. No rear gear changing required.

 

[Clone TIE Pilot]

Any change to a different transmission will require the correct crossmember to match your transmission choice. A TH200 crossmember will not fit with a TH350 or either OD trans. Pre 84 G bodies will not have frame mounts for a TH2004R crossmember.

 

[69hurstolds]

Any change to a different transmission will require the correct crossmember to match your transmission choice. A TH200 crossmember will not fit with a TH350 or either OD trans. Pre 84 G bodies will not have frame mounts for a TH2004R crossmember.

I can't say for 100% positive about real world stuff, but my information shows a TH350 should mount up just fine physically on the 200 mount and crossmember. I believe they're the same length and share the same yoke, too. I don't know for sure, though.

But the parts book says the crossmember (referred to as a "support") for an M29 (TH200C) is the same part number as the 79 Hurst/Olds or 80 442 with a TH350 (M38). Same with the rubber mount. Same part number for each.

Totally agree about any OD transmission going to need a little more work to fit a 78-83 (exc. W40 in 83) frame.

Part number 472143 for the rubber mount. Superseded to 22188145. Fits TH200C and TH350.

The crossmember, aka support, is p/n 473721. There's no other part listed. In case anyone was wondering, 260F is gas, 260P is the short-lived diesel.

 

[carnutjw]

Any change to a different transmission will require the correct crossmember to match your transmission choice. A TH200 crossmember will not fit with a TH350 or either OD trans. Pre 84 G bodies will not have frame mounts for a TH2004R crossmember.

Sorry to be contradictory, but yes the TH200 crossmember will accept a TH350, at least my car did. Used same kickdown cable bracket, had to reshape trans cooler lines to attach to TH350, and had to make a vacuum line for TH350 modulator and Tee it into a port behind carb.

 

[Clone TIE Pilot]

Sorry to be contradictory, but yes the TH200 crossmember will accept a TH350, at least my car did. Used same kickdown cable bracket, had to reshape trans cooler lines to attach to TH350, and had to make a vacuum line for TH350 modulator and Tee it into a port behind carb.

Guess I was mistaken then. However, TH350s do come with different length tailshafts to watch out for. Also Monte Carlos and turbo Buicks do use different TH2004R crossmembers.

 

[69hurstolds]

Guess I was mistaken then. However, TH350s do come with different length tailshafts to watch out for. Also Monte Carlos and turbo Buicks do use different TH2004R crossmembers.

Yeah, that is a very good point about length. And 4R crossmembers- TB, MC, and Cutlass generally used different crossmember part numbers. What those exact differences were, I'm not sure.

But if you get a TH350 for an A-body, I think they're the shorties (6"). So if it's a 6", you're golden. They also have 9" and 12" tailshafts. You want the length to just about match the 200's length. On the El Caminos- did they use a different length tail shaft? They seem to have strange driveline dimensions from what I'm used to. I dunno.

According to parts info, for the 200-4R, if you have an Olds V8 in front of it from the factory, Y or 9, it used trans support p/n 14068895 from 84-88 in any G-body. That means every single V8 Cutlass from 84-88 (and 83 H/O) uses the same 200-4R trans support. Obviously you need to have the frame extension installed if your putting it in a 78-83 Non-H/O frame. Pontiac also used the same support behind the 305 w/200-4R in 84-87 GPs for whatever reason.