7.4L 4L80E BB w/ 138K miles-tranny flush?
Greetings Steve!
When I approached a similar situation with my '75 Cadillac Edlorado (the Executor of the estate had absolutely no maintenance records and knew nothing of the car's history other than it was a one owner - the title verified that fact), and it had just short of 100,000 miles. The method that we followed for the first transmission service was to change the fluid and replace the filter (that was a little more than a year ago), my mechanic's suggestion was to drive if for six-months or at least 3,000 miles then change again using the flush, then fluid and filter change. When I take the Cadillac out of storage in a few weeks its first stop will be at the mechanic's for a fluid flush and new filter/fluid.
The reasoning given by mechanic was that he didn't want to circulate the very old and dirty fluid around any more than necessary - - his thought was that by doing a normal change followed by a few thousand miles of normal driving the new fluid would have a chance to pickup and "suspend" any dirt that wasn't removed in the first change and that it would then be acceptable to flush then change filter/fluid.
In the past few years, I have purchased several older GM cars and followed this service methodology with various varieties of the TurboHydramtic 400/425 transmission. So far the only part that I have had fail was one modulator - - something that was replaced inexpensively and didn't impair the general operation of the transmission once the defective part was replaced.
Good luck with your Suburban! I hope that yours is as dependable as mine has been - - I am up to nearly 125,000 miles with absolutely no problems other than the finicky electronic transfer case module that was replaced multiple times under GM's warranty. So far it has been regular service every 3,000 miles with transmission service every 30,000 miles.
Kevin
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Kevin D. Allen
WBCCI (Lifetime Member)/VAC #7864
AIR #827
1964 Overlander International
1978 Argosy Minuet 6.0 Metre
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