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1970 Eldorado 1990 Brougham 5.7
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7 Posts
Discussion Starter · #1 ·
I need to replace the axle seals on my '90 Brougham. While I was in there, I was considering a Eaton TrueTrac posi and 3.42 gear change. My only concerns were the 3.42 may be too steep when combined with the low first gear of the 700R4/TBI combo. Also, do you flash the PCM to achieve the correct MPH on the speedo? Anyone done it? old posts? Thanks in advance...
 

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2014 ELR
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10,425 Posts
3.42s will certainly not be too steep. The 94-96 trailer package came with 3.42s stock, while the 93 trailer pack got 3.73s stock.

Your car doesn't have a re-writeable PCM like the LT1 cars. It uses replaceable PROM chip. However, it might be as simple as changing the speedo gear in the trans for your year.
 

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1970 Eldorado 1990 Brougham 5.7
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7 Posts
Discussion Starter · #3 ·
Thanks, I will look further into setting up the speedo. I am leaning towards the 3.42 to retain good highway cruising although it seems some of the LT1 cars do go for the 3.73 or 4.10 to compensate for large tires or stoplight brawls:sneaky:
 

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Super Moderator
2014 ELR
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10,425 Posts
I've got 4.10s behind one of my LT1s. However, in front of the gears is a T56 manual 6 speed trans. More fun, and better gas mileage...
 

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1970 Eldorado 1990 Brougham 5.7
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7 Posts
Discussion Starter · #5 ·
The six speed must be a hoot to drive:D. The LTI cars have a much wider powerband than the TBI to boot. It would be nice to get the car close to LTI specs with Vortech heads, cam, Holley TBI, exhaust, etc...I would never go with a carb. I may just leave it stock and do a gear change:annoyed:
 
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