Guys, I believe that my ST300 has some major issues and instead of trying to rebuild it, I would like to swap it out for a Powerglide or TH350. Part of the reason for my decision is that I believe the ST300 is a switch pitch and I don't think it's the original trans, nor is the switch pitch solenoid connected. The motor is the OHC 6.
Could you tell me if the Powerglide and/or TH350 is a drop-in replacement for the ST300? I know that I probably need the kickdown linkage in either case, cause the ST300 achieved the kickdown with electric solenoids inside the trans.
The reason I'm asking if it's a drop-in is because I've seen references to the TH350 that say "long tailshaft, short tailshaft" etc...
Powerglide is the Chev designation for the GM 2-speed transmission and is essentially the same transmission as the ST300 - other than the bellhousing bolt pattern.
A better more modern choice of transmission would be the 200-4R which features slightly wider gear ratios than the TH350 and adds an overdrive fourth gear for economy.
It is the same length as the ST300 and uses the same driveshaft. The crossmember from a TH400 will fit with minor mods for the trans mount. The 200-4R uses a cable to tell the transmission how much throttle you are using so it can shift at the right speed and with the right firmness, so you'll need to make a bracket to hold the cable. It also has a lock-up torque convertor for still better fuel economy and there are kits to make this functional in your car.
The better 200-4Rs are in cars produced after '86. The one that I have was in a 1987 Pontiac Grand Prix with a 4 bbl V-8 (Chev with the dual bolt pattern so it'll fit the OHC). It'll handle anything the OHC six can dish out with no upgrades needed. This is my choice for a cheap modern automatic to put behind the OHC. If you find a good used one you can use it as is and save yourself the cost of a rebuild/upgrade.
One thing to consider, the overdrive gear wouldn't be usable with really tall gears (2.56:1 for example) but you could use the money saved by buying a good used one like I did to upgrade your rear gear ratio to 3.55 - 3.90:1.
Here're the overall gear ratios with the 200-4R: first is 10.67:1 (2.74 x 3.90), second is 6.12 (1.57 x 3.90), third is 3.90 (1.00 x 3.90), and fourth is 2.61 (0.67 x 3.90).
The 200-4R with 3.90 gears would give the same off the line acceleration as a TH350 with around 4.30 gears but still have the same fuel economy as a TH350 with 2.56 gears! The best of both worlds, performance with economy. That's why I'll be using the 200-4R with 4.11 gears with my 250 OHC in my '69.
Great advice by TOHCan. To answer a part of your question; If you get a short shaft 350TH it will be a direct bolt in. The only thing that is a slight problem is the shift indicator doesn't have low 2 and low 1. This doesn't effect how the trans will work, just the indication of which lower gear you are in. It's not a problem when you get used to it.
If you choose a TH350 however, you will find that it is a direct bolt in replacement for the ST300. There's no need for a different transmission crossmember. There is no need for a control system for the lockup torque converter(required for the 200-4r). Make sure you get a BOP (bell housing) bolt pattern though. Lokar sells the downshift cable, and you can get throttle brackets as well.
I got my 200-4R with torque convertor, TV cable and cable bracket at the local pick-n-pull for $70. I pulled it myself so I could check the year (after '86), application (V-8 4 bbl car), and condition (mileage on car, fluid smell, amount of friction material from wear in the pan) before purchasing to make sure I got a good one. There is a tab on the back of the transmission that has the application info if you are wanting to buy one that has already been pulled.
You can leave out the lock-up on the 200-4R (same as the TH350 then) if you want to keep the cost down.
That just leaves the crossmember as the biggest difference. My car already has the TH400 crossmember so I didn't check any farther, but I'd suggest getting the crossmember from the donour car and doing a trial fit with that. Very likely the ends where it bolts to the frame will need modifying (width, fore and aft bolt placement, etc.) but if you take the new one to a good welding/fab shop with good measurements you should be able to get something usable for a reasonable price. I'd be surprised if they take more than 2 hours of shop time to do the job. And that way you can keep your stock crossmember as well!
Get a later low mileage 200-4R that's factory built for a V-8, pull the pan to see if there is any debris inside, change the filter and fluid while you're there, get the crossmember modified and bolt it in. That's about the cheapest way that I can think of to replace the ST300 with a better transmission; others may have better ideas!
I would advise against using a stock used 200R4. They are usually junk. They were junk when new. Not going to hold up with any hard use at all. These trannies need to be beefed up to handle a strong V-8.
I would advise against using a stock used 200R4. They are usually junk. They were junk when new. Not going to hold up with any hard use at all. These trannies need to be beefed up to handle a strong V-8.
On the other hand, since I believe you have an OHC6 the 2004R would be acceptable. These transmissions were used behind V8 Olds and Turbo Buicks. It should hold up fine in this case. The first gear is deeper than a TH350 and the overdrive is nice. If you're going to the effort of a swap, this would be the way to go.
I would advise against using a stock used 200R4. They are usually junk. They were junk when new. Not going to hold up with any hard use at all. These trannies need to be beefed up to handle a strong V-8.
On the other hand, since I believe you have an OHC6 this would be acceptable. These transmissions were used behind V8 Olds and Turbo Buicks. It should hold up fine in this case.
They didn't hold up with the V-8 Olds or even the wimpy deisels. I've swapped countless 200R4's for people. I believe the Buick Grand Nat's had the beefed up version. I had a 78 Turbo Buick and the trans puked on that too and it was just a 6 cylinder.
im with fbody! ive done the same for alot of people around here. they were behind v-6's and they still got smoked! i would go for the higher hp applications gm had if your not going to rebuild it. otherwise i would go with a new one. if you dont connect the lock-up on the 200r you'll regret it seriously! it wil;l go bad in a hurry! id go with a th350 with 400 guts. you'll get the stouter clutches and gears in doing this. as the others have said it a direct fit.
Andy
due to budget cutbacks, the light at the end of the tunnel has been disconnected for non payment.
I would advise against using a stock used 200R4. They are usually junk. They were junk when new. Not going to hold up with any hard use at all. These trannies need to be beefed up to handle a strong V-8.
On the other hand, since I believe you have an OHC6 this would be acceptable. These transmissions were used behind V8 Olds and Turbo Buicks. It should hold up fine in this case.
They didn't hold up with the V-8 Olds or even the wimpy deisels. I've swapped countless 200R4's for people. I believe the Buick Grand Nat's had the beefed up version. I had a 78 Turbo Buick and the trans puked on that too and it was just a 6 cylinder.
The wimpy diesels still put out plenty of torque which is what kills a transmission. No doubt the later 200s are stronger than the earlier ones (just like the 700R4s), although the 2004R was not available until '81, so I don't know how you had one in a '78. I believe the only difference between a stock 2004R and the GN was the valve body.
Jim, the 200-4R will handle the output of the OHC just fine in stock form. The later ones have the factory upgrades needed to survive behind a V-8 without problems; the earlier ones had some issues as did the 700-R4.
200-4Rs are used behind just about everything now, including 572s. The 200-4R is easier to mod to handle that kind of power than the 700-R4 and has the dual bolt pattern so it can fit anything. Plus it's lighter, smaller, takes less power to run, etc.
Your '78 Turbo Buick would have had the TH350! And turbocharging tends to add to the output of even a puny six cylinder!
If you want to read up on the 200-4R here's a link:
Yah, you are right it was the earlier 200R. All the 200's are stock junk. Very light duty trans. That's why the high performance people have a good business building them up. Steer clear of any used trans unless you know the history AND it's a 400. Acurate sells a nice new 3 year waranteed 350 for around $400. It's a 'no-brainer' for someone on a budget.
They're easier and cheaper to build for high performance, which is why the high performance people build them! They wouldn't use a transmission that would break and give them a bad reputation!
Buying a used transmission has the same stigma that buying a used engine has. That's why I picked mine when it was still in the car so I could check a few things. Not too hard to find a good one if you know what you're looking for.
Seriously, there has been some really good 4 speed auto conversion advice over the years on this site and all the good advice comes with the most important part; Buy a new high performance 4 speed auto trans to start with. TCI and Bowtie(LINK: http://www.2004r.com/trans/level2.shtml ) have them for around $1100 or a mild street version for $940. After you get all the other parts to convert you will have around $2000 into the conversion. Acurate will sell you the 350th for $435 with a 3 year warantee. If you go the 350 route you can get by with just buying the trans.
You mean you don't need a new shifter adapter, torque converter, trans kickdown setup, or driveshaft with the Th350 switch?
There is about $500 delta with everything considered. Considering the deeper gear, reduced engine wear at highway speeds, and improved gas mileage, it's worth it.
Shift adapter is optional. Driveshaft is the same. I do recommend a new torque convertor. The kick down is different but cheap.
I don't believe you have your math correct at $500 difference. The difference is at least twice that. If you are talking just savings in gas it's going to take 20000 miles of highway driving(in overdrive) to even come close to breaking even.
I'm not an advocate of either. I see the good points of both. Since the original question asks about the 350 I'm leaning that way for this thread for obvious reasons.
QUOTE: Guys, I believe that my ST300 has some major issues and instead of trying to rebuild it, I would like to swap it out for a Powerglide or TH350.
I finally got around to pulling out my OHC6 to do the ST300 to TH350 transmission swap. SURPRISE!...the bolt pattern on the transmissions are not the same. The one on the left is the ST300 trans that was in the car. The one on the right is the TH350.
Now, can someone tell me if there are different variations of the TH350 bolt pattern? This was supposed to be a "direct swap".
The one shown on the right is a Chevy pattern bellhousing. It's easy to tell BOP from Chevy transmissions; see the valley between the top bolts on the BOP trans?
They do not interchange. JRosetti noted this early in the thread:
Quote:
If you choose a TH350 however, you will find that it is a direct bolt in replacement for the ST300. There's no need for a different transmission crossmember. There is no need for a control system for the lockup torque converter(required for the 200-4r). Make sure you get a BOP (bell housing) bolt pattern though.
Last edited by Yellowbird; 09/03/0702:34 PM.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
too bad you are not closer.i have alot of firebird th-350 tranny's here.you need a bop bolt pattern on the bellhousing like vikki noted and a short tail shaft for f-body
I would advise against using a stock used 200R4. They are usually junk. They were junk when new. Not going to hold up with any hard use at all. These trannies need to be beefed up to handle a strong V-8.
i agree with jim on this one.go with an original tranny.you will save the next owner of that car alot of grief when he needs to order parts for it and they are worth more if original.if you want late model technology,buy a late model car
Claus, you are the man and you probably saved me a major pain in the arse.
You are welcome..
Remember to measure the thickness of the adaptor, and insert washers (same thickness as adaptor) between the flexplate and converter.-and remember to use loc-tite on the (3) bolts..
