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Old 03-13-2004, 04:07 PM   #1
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7.4L 4L80E BB w/ 138K miles-tranny flush?

I have just made a deposit on a Suburban 2500 and the present owner from 110-138K miles has only changed oil.

No knowledge of tranny service work. My concern is dislodging sludge on tranny flush causing more problems. My transmission shop says only use synthetics if the tranny is near new- ie < 20K miles. He says dino after that. But others do put in synthetic with higher miles.

Any of you think putting an additive in for a couple days prior is a good idea? Dino or synthetic in tranny on flush with 138,000 mi.? Any particular brand better (like Mobil One)?

I plan to change ALL fluids - radiator, PS, PBrake back to differential.

I will be pulling my sig A/S 25' at 6-7K lbs hopefully for 2 years and then may get the 6.0L or 6.5 Diesel (scarce as hens teeth).

Steve
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Old 03-13-2004, 05:48 PM   #2
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If you go to search and search for "trans" pick the thread "trans - Your opinion" Lots of info here!!


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Old 03-13-2004, 06:01 PM   #3
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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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Old 03-13-2004, 07:15 PM   #4
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You may want to post this question over on the BITOG website. These guys cam also offer some expert insight into your questions.
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Old 03-13-2004, 08:29 PM   #5
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Kevin and Pick,

Thanks so much for your experience and referrals.

I have also been over to the Suburban forum #1 Son.

But Kevin you are the first one who really explained why to do the sequencial flushes. Actually that is why I was thinking of putting some additive pre-flush to help get the stuff in suspension. Someone mentioned a trade name & I forgot.

Also heard that using a synthetic may start a bleed-by leak vs the dino fluids.

Steve
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