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Do you ever drive your ULTRA 4 Rock Racer In Reverse?
Are your Diffs Mounted Upside Down?

  • What happens to your diffs in reverse?

  • Are they as strong in both directions?

  • Are some diffs stronger in reverse?

Typical passenger vehicles, 4WDs', Suv's and Trucks all spend 99% of their life running in the forward direction and engineers go to great lengths to ensure the Differential Gears are the strongest, lightest, and most efficient when running in the Forward Direction.

Differentials are designed to be strongest when driven in ONE direction. Differentials gears are typicaly Hypoid (Pinion is lower than the centre of the Ring Gear) or Amboid (Pinion is Higher than the centre of the Ring Gear) and the gears are cut in a direction to allow the pinion to be loaded correctly when the vehicle is driven in the forward.

For more than 50 years, competitors in all sorts of motorsport disciplines have known that a Ford 9 Inch (9") Diff gear is much stronger than other Diffs on the market. Much of the strength of the Ford 9" Diff comes from it's unique gear profile where the Driven Side of the Ring Gear is almost "Vertical" compared to other diffs.

This is fantastic if you ONLY drive your vehilce forward all the time and if you have NOT mounted your diffs upside down. Ultra 4 Rock Racing, Rock Crawling and Rock Bouncing require competitors to drive BOTH forwards and backwards up incredibly difficuly rocky terrain at times in first gear low range under full throttle to be competitive.

ULTRA 4 Vehicles that have Mid or Rear Engines are forced to run their diffs upside down because the tailshaft is running completely backwards compared to a conventional vehicle. This results in the rear diff running on the WEAKEST, coast side for 99% of the time which is of course not ideal. The whole reason competitors install a $10,000, $20,000 or even $30,000 10 Inch Custom made Tubeworks, Spider Trax, Currie, Strange, or other brand of diff in an Ultra 4 Racer is to increase the reliability, but running them backwards, on the coast side is just silly.

Diff Operating Direction - Most Diffs are Designed to operate 99% in One Direction

The super low range transfer cases can place incredibly high loads on differentials, much much higher than can be found in Drag Racing, where the 9" made it's claim to fame so we need to very careful when the vehicle is in reverse or when the diff is mounted upside down.

if you are looking for new diffs for your new vehicle or project and you will be applying heavy loads in reverse at ANY time, please consider diff gears that have a design and Gear Profile that is more suitable for being driven in Both the Forward and Reverse Direction. While the 9 inch and 10" gears are great in One Direction, they can be much weaker than other diffs when driven in reverse.

If you are 100% convinced that a Mid Engine is for you, perpaps look into a Custom Transfer Case or Vee Drive that will reverse any tailshaft direction that is running the wrong way to ensure your diff is operaring on the Drive Side as much as possible.

If you cannot get all your tailshsfts to run in the correct direction to drive the Diff Gears on teh Coast Side all the time, then perhaps the 10" gears are not for you. There are plenty of diff Gears such as DANA that have a more traditional Gear profile that has very similar Drive Side and Coast Side gear profiles, resulting in a diff that is almost as strong in the reverse direction as when it is being operated in the forward direction.

10" Gears are great for Drag Racing, and Trophy Trucks when they are driven on the Drive Side, In the correct dorection ALL the time, but please be careful when selecting your next Diffs.

Dont just follow the flock and do what everyone else is doing:

  • Stop

  • Think

  • Ask yourself:

  • Is this really correct?

  • Are we creating another problem?

  • Is this a "band aid" and not a real solution?

  • Dont be a Sheep

  • Dont follow the Flock!!!

If you need some advice, please contact us at Proformance and one of our Imagineers would be more than happy to talk to you about your concept vehicle, your driveline and concerns you may have.

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