HT350 and Overdrive Question

[mrghostwalker]

I'm running a 350 engine in front of my ht350 tranny in my K20/K10 and was wondering if anyone has used an overdrive unit with the HT350? If so how strong are the overdrive units?

 

[85K304SPD]

Do you mean a Gear Vendors bolt on overdrive unit behind the T-case?

 

[Vbb199]

I assume you mean a th350 paired with a gear vendors OD unit.

 

[Bextreme04]

The gearvendors units are great for just highway cruising. If you do any towing, you are going to be better off just getting an overdrive trans to replace your TH350. The easiest replacement would be to just slap a 700R4 in there. If its built right and you have a BIG external cooler, you shouldn't have any issues with a 700R4. The overkill upgrade if you do any kind of heavy towing or have big power would be to put a 4L80e in. Your biggest issue with a GV unit would be that you are 4wd. I dont think they make a version that goes between the trans and T-case and if they did, you would definitely need new driveshafts.

 

[mrghostwalker]

Yeah, my research shows that a build 700r costs a little less than a Gear Vender unit!

 

[Vbb199]

Yeah, my research shows that a build 700r costs a little less than a Gear Vender unit!

That's correct! What's under the hood? What sort of power? Gear ratios? Tire size?

 

[mrghostwalker]

I'm running 33inch tires with a 350 engine. It looks like I'll just get a heavy duty 700r and do a tranny swap.

 

[82sbshortbed]

I was looking into this when I was debating on a 700r4 or gear vendor od on the th350. $1,800 for the 700r4 and 3k for gear vendor od. I went with 700r4.

 

[1980 Big Ten]

Similar to @mrghostwalker, I have an original TH350 and am looking to upgrade so that I can use overdrive on the interstate and save on gas. Mine is a 1980 C10 Big 10 with a CBC 350, 4-bbl Q-jet, and P235/75R15 tires. No idea what the gear ratio is or how to find it.

I want to tow a simple 18-foot outboard boat, so I guess my question for @Bextreme04 and other experts is whether I need to upgrade to a transmission cooler if I upgrade to a 700r4. I don't think I even have a stock transmission cooler.

Also, it's my understanding that I shouldn't tow in overdrive. Is that correct?

 

[NickTransmissions]

Similar to @mrghostwalker, I have an original TH350 and am looking to upgrade so that I can use overdrive on the interstate and save on gas. Mine is a 1980 C10 Big 10 with a CBC 350, 4-bbl Q-jet, and P235/75R15 tires. No idea what the gear ratio is or how to find it.

I want to tow a simple 18-foot outboard boat, so I guess my question for @Bextreme04 and other experts is whether I need to upgrade to a transmission cooler if I upgrade to a 700r4. I don't think I even have a stock transmission cooler.

Also, it's my understanding that I shouldn't tow in overdrive. Is that correct?

No towing in OD if you can avoid it...trans coolers are always recommended, esp in heavy duty applications like towing/hauling.

There's a few other things Id do to the transmission specifically for towing, let me know if you need a quick list of them.

Main thing you need to know with the 700R4 is proper set up and adjustment of the throttle valve cable. If not done correctly, you'll smoke the 3-4 clutch pack in as little as a few miles of driving...

 

[Bextreme04]

Similar to @mrghostwalker, I have an original TH350 and am looking to upgrade so that I can use overdrive on the interstate and save on gas. Mine is a 1980 C10 Big 10 with a CBC 350, 4-bbl Q-jet, and P235/75R15 tires. No idea what the gear ratio is or how to find it.

I want to tow a simple 18-foot outboard boat, so I guess my question for @Bextreme04 and other experts is whether I need to upgrade to a transmission cooler if I upgrade to a 700r4. I don't think I even have a stock transmission cooler.

Also, it's my understanding that I shouldn't tow in overdrive. Is that correct?

100% what Nick said. The big benefit of the 700R4 over the TH350, especially when towing(even outside of OD) is the ability to have the converter locked up. Locking the converter will GREATLY reduce the amount of heat you are generating during normal driving. I have a Tru-Cool 40k on my 2011 Suburban that we regularly use to tow. Adding the stock external cooler dropped my normal towing trans temps to ~100 degrees above ambient, unless pulling hard up a steep grade at which point the cooler couldn't keep up and it could climb to 120-140 degrees above ambient. Upgrading from a stock sized external to the 40k dropped my normal trans temp to ~60 degrees above ambient and I've never seen it go above 185... even when pulling a long steep grade at 65mph in 100 degree ambient temps.

You will want to keep the radiator cooler and run the external cooler in series after the radiator cooler. This will help stabilize the trans temp and warm it up enough in colder weather. Above about 130 degrees trans temp, the radiator cooler will actually add a significant cooling effect to the trans temps as well.

For a squarebody, it is hard to fit a Tru-cool 40k because of the way the structure is laid out behind the grill. Lots of guys run an M7B(Tru-Cool 24k PN: LPD4589) or a 26K LPD4590 cooler instead. It is almost as good and it fits well on the passenger side behind the grill. The smaller 24k is 8"x11" and the bigger 26k is 11"x11".