blank 05/29/14 02:32PM Clutches, Q&A, Transmission Repair, U Joints

Q&A with Midwest Transmission Center

I own a 1970 Pontiac Firebird with the 455 engine and automatic transmission.

Question:  I need to replace the positraction and install new  gears removing 2-56.  The firebird has the TH400 transmission, 8.2 10 bolt Pontiac differential. I need a gear ratio with additional power and still be comfortable to drive on freeway. 3,08 or 3.36 ?   The care originally had a TH350  but 455 with  60 over mild camshaft, destroyed them! I installed a TH400 now lost some pull in 1st and 2nd gear. what to do and how much?

Answer:  You can figure you RPM at whatever MPH you want to drive with this formula RPM = MPH X Gear Ratio X 336 then divide this by the tire diameter in inches.


Replacement for GM Stock Posi

Here are possible gear options we suggest:

  • Eaton positraction part # PFEA19674-010 $526.27
  • Motive Ring and Pinion set 3.55  #PFMWBP882355 your cost is $262.85 also available is a  Yukon 3.36 Gears set #PFYG GMBOP-336 cost for this gear kit is $294-55
  • You will also need a bearing rebuilt kit part number PFR-10-82 your cost is $ 116.41 plus S&H. These are all High quality aftermarket parts.

If you have additional questions, to place order or need help give Lance a call at 800-444-0755 he can help you. Installation is available in our shop in Maple Grove MN, just give us a call to schedule.

Transmission             Midwest 
Transmission        Clutch and UJoint, 
Tranny Conversions

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