Anyone installed Gear Vendors overdrive on TH400?

Chevrolet Technology and Innovations
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I’m looking for some guidance on integrating a Gear Vendors overdrive unit with my TH400 transmission. I’ve got a 1970 Chevrolet and I’m considering this upgrade to improve performance and fuel efficiency, but I’m not entirely sure about the installation process or compatibility.

What to Consider Before Installation

  • Compatibility: Is the Gear Vendors overdrive unit a direct fit for the TH400? I’ve heard mixed opinions and would love to get clarity on this.
  • Installation Process: For those who have tackled this job, what does the installation look like? Any specific challenges that I should be aware of?
  • Performance Boost: For anyone who’s done this upgrade, what kind of improvements have you seen in terms of RPMs at highway speeds and overall drivability?

Experiences and Tips

  • What tools or extra parts did you find necessary for the install?
  • Any recommended resources (videos or manuals) that you’d suggest?
  • Did you encounter any unexpected issues during the installation?

I’m aiming for a smoother ride and better fuel economy, so any insight would be greatly appreciated! Looking forward to hearing about your experiences and advice!

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I’ve installed a Gear Vendors overdrive on my TH400. The key is to ensure proper mounting. Align the unit before tightening anything. Also, make sure to check the driveshaft length afterward!

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Great tip, gillcraig! I was wondering about the driveshaft modifications—did you have to shorten yours?

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I didn’t have to shorten mine, but I did have to adjust the angle slightly to avoid vibrations. Always a good idea to check those angles post-install.

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Good to know! Is there a specific torque setting that should be respected when installing?

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You should torque the bolts to the specifications in the Gear Vendors manual. Typically, they recommend around 30 ft-lbs for most fasteners. Always double-check!

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Thanks, joel31! Any special tools you’d recommend for the installation?

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A good torque wrench is essential. I also used a right-angle drill for tighter spots—it really made a difference. Don’t forget about thread locker as well!

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I never thought of using a right-angle drill! I tend to struggle with tight spaces. Any other tips for installation?

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Definitely take your time with the wiring. It’s easy to mess it up, and that can lead to big headaches down the road. Also, have a buddy to help with the install—it makes everything easier!

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I suppose having a second set of hands never hurts! Can I ask… are there common issues with the TH400 after installing?

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I installed the Gear Vendors unit on my TH400 about a year ago. The performance improvements are significant! I noticed around a 15% increase in fuel efficiency and much smoother acceleration during highway driving.

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That’s awesome to hear, david19! I’m particularly curious about how it affected your daily driving experience. Any noticeable differences in city driving?

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Honestly, going from 3 to 4 gears with the overdrive has made my car feel much peppier. It’s like driving a different vehicle, more responsive and fun!

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Exactly! It’s crazy how much of a difference just one more gear can make, especially for acceleration on the freeway. Would you recommend it for someone who mainly drives in the city?

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Megan74 here! I’ve been thinking about it, but I’m worried about the installation complexity. Any tips on that?

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I found the install a bit tricky, but not impossible. Just follow the instructions closely and get a knowledgeable buddy to help out. It’s worth it for the performance boost!

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I installed the unit on my TH400 too. I find it enhances fuel economy, but I’m not seeing the acceleration boost everyone talks about. Maybe my setup isn’t optimal.

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That can happen if the torque converter isn’t paired well with the setup. Have you checked that aspect?

1 Like
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I think you’re right, johnhall. Adjusting the torque converter can definitely improve performance. I’m just trying to maximize what I can get from the Gear Vendors.