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Old 02-01-2007, 07:20 PM
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Re: '91 caprice classic tranny

A "4L60" is a redesignation of the TH700R4. It is said to be easier to determine what it is to be used in with the 'new' designations. The way this works out is:

First digit is number of forward speeds
Second digit is design - L for Longitudinal mount (front engine rear drive) and T is for Transverse mount (front engine front drive or mid engine rear drive [Fiero]).
Third and fourth digits are the weight capacity (60 is 6,000 lbs GVW etc).

So, in 1987 (yes this happened in 1987 - look it up), GM redesignated their transmissions. The transmissions that didn't get a redesignation are the TH200C and 4R models.

TH400 became 3L80. TH700R4 became 4L60. TH125C became 3T40.

Much of the paperwork on the cars continued to call the TH700R4/4L60 a TH700R4 into the 90s, but the fact is the official redesignation took place for the 1987 model year.

TH700R4 and 4L60 are interchangeable terms beginning with the 1987 model year.
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