TH 350???

[baddawgcustoms]

My son got this transmission in a swap, and I'm 96% sure it's a th350 but I would love the confirmation before I use this to mock up my car. I'm sure I'll find a tranny that I know is good or have this one gone through, but just want some confirmation before I use it to mock things up. Thanks.

 

[RPM]

I don't think that is a turbo 350. It has an electric plug in. Might be a turbo 350c, which would have a lock up converter.

 

[Hotrod46]

I'm with Ron, TH350C. It's also a Buick, Oldsmobile and Pontiac (BOP) bellhousing and has the long tailhousing. There is a "short tail" version that will let you have a slightly longer driveshaft.

Be careful when looking for a TH350. There is a TH250 version that looks almost exactly like a 350, but it has different internals and a much lower torque rating. The 250 has a band adjustment bolt sticking through the passenger side in about the middle of the case while the 350 doesn't.

The TH350C is considered to be a little weaker than a regular TH350.

 

[baddawgcustoms]

I really didn't notice the bellhousing. thanks Ron and Hotrod. I did a little looking on craigslist for th350 and 700r4. 350's seem to be going for 150-300, and the 700's from 250-400. I know I read a lot that the 700's don't hold up well on big motors, but I'm running bone stock 307, and would love the overdrive. Anything costly about running the 700's? I believe the kickdown is electric? What about the speedometer hookups? Somebody educate me on the 700r4. Never had one in anything. thanks.

 

[RPM]

A 700 is a great transmission. They have a real low first gear ratio, about 3.10. Then they have the OD for hi speed cruising. Plus the lock up converter.

For comparison. The 700 with a 3.73 rear will leave the line like a turbo 350 with 4.56 gears. Then in OD it will be like a turbo 350 with 3.08 gears. So you have a real low ratio to leave the light with, but low rpms for high speed cruising.

The 700 would be a good choice with the 307 engine.

 

[Hotrod46]

I'm running a 700 in my bucket. The main issue with them is getting the throttle valve (TV)cable adjusted right. The arm that operates the TV cable needs to be the correct ratio and in the correct location. This is critical for the trans to live since the TV controls pump pressure. Get it wrong and you can toast a trans very quickly. The TV controls kick down. The only electric controls are for converter lockup.

Here is a link to a page with some good info about setting up the linkage and wiring the lockup.

http://purplesagetradingpost.com/sumner/techinfo/700R4p1.html

I like the one in my car. I get around 21-22 MPG with a 350 HP engine and 3.42 gears. The lower cruise RPM's makes the exhaust a little quieter too. I would run 3.73's or better next time around.

I wired mine to be selectable between locking up in 3rd and 4th or 4th only. I rarely use the 3rd gear lockup option and probably wouldn't include that next time. I have a trans temp gauge in my car and can confirm that the trans runs cooler with the convertor locked.

Mike

 

[Hotrod46]

I meant to add that all the cable operated 700's I've seen had mechanical speedometer drives. I'm running a VDO electronic speedo with a sender screwed onto the trans where the cable normally goes. I highly recommend electronic speedo's. No calibration hassles.

The best 700's are 89 and later. They have some internal upgrades that make them stronger. GM modified these transmissions several times over the years as problems showed up.

The 4L60 is a later upgraded version of the 700 and looks the same externally.

The 4L60E was electronically shifted by the drivetrain computer. You can get a stand alone control box that will shift the 4L60E behind your 307. They're pricey, but eliminate the TV cable and allow you to tune your shift points easily. The E versions came in mid to late 90's trucks.

 

[baddawgcustoms]

T

I meant to add that all the cable operated 700's I've seen had mechanical speedometer drives.

The 4L60 is a later upgraded version of the 700 and looks the same externally.

The 4L60E was electronically shifted by the drivetrain computer. You can get a stand alone control box that will shift the 4L60E behind your 307. They're pricey, but eliminate the TV cable and allow you to tune your shift points easily. The E versions came in mid to late 90's trucks.

thanks a lot for the help. That's what I was hoping was to find a 700 with mechanical kickdown and cable speedo. The gauge kit my dear wife got me for Christmas is for mechanical speedo. (Speedway 6 gauge discontinued set for $199).

 

[bobs66440]

I was originally going to use a 700R4, but it seemed like a big hassle with getting the TV cable mated to the carb and getting it adjusted correctly. Also, hooking up the lock-up switch/wiring seemed like a pain also. I was going to try to work through it because I already had one in a donor car, but when I ran it I couldn't get it to shift into OD even though I thought I had everything hooked up correctly. What a headache. I struggled with it for a while then finally landed on a TH350 for the simplicity...

 

[Hotrod46]

The TV cable isn't really that bad as long as you understand the angles. The link I posted explains it pretty well. I got lucky in that the kick down stud on my Rochester 2G was in an acceptable location. Most carb manufacturers offer kits that will put the cable in the right place.

The lockup wiring is pretty simple too. Just send 12 volts to the solenoid valve and it locks up as long as the trans is in 2nd gear or higher. There are kits that you can get that have all the correct parts, but most 700's already have usable parts in them. Some solenoids have one wire and some have two. All you really need is a pressure switch on the 4th gear pressure circuit and the correct electrical plugs for the outside. It's best to have a switch on the brakes to cut power to the lockup solenoid when the brakes are applied. That can be done easily with a common 5 pin automotive relay using any brake light switch.

 

[rcnurd]

I put a 700r4 in my bucket and since I'm dumbfounded on trannys, I had a friend of mine, who had a transmission shop that went out of business, rebuild it. He said he put in a shift kit, Corvette servos, and a 1/4" check ball in the valve body to lockup the converter, I wouldn't need the wiring. I put the tranny in and it does shift into overdrive at about 38 MPH. I had a turbo 350 in there but got tired of screaming down the highway at 70 MPH doing 3000 RPM. Now I cruise at 70 doing about 1800 RPM. If you do a google search on "lockup check ball 700r4" You'll get a page with all the 8x10 glossies with circles and arrows showing where the ball goes. I'm happy with it, I also put the geometry lever on the throttle linkage of the carb to get the right angles for the TV cable.

 

[2old2fast]

Why is it that some think 3000 RPM @ 70 MPH is "screaming down the road" ???
dave

 

[TriodeLuvr]

Why is it that some think 3000 RPM @ 70 MPH is "screaming down the road" ???

My wife screamed once at about 7500 rpm and 165.

 

[rcnurd]

Why is it that some think 3000 RPM @ 70 MPH is "screaming down the road" ???
dave

Because it's loud and obnoxious. I'd rather hear the low slow rumble and not the high RPMs.