1989 blazer axle ratio swap - Chevrolet Forum - Chevy Enthusiasts Forums

K5 Blazer 1969-1994
While this model ended its run, it is not uncommon to see them on the road or off, years after production end.
Platform: Truck, GMT 400

1989 blazer axle ratio swap

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Old April 24th, 2017, 9:48 AM
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Default 1989 blazer axle ratio swap

I have a 1989 v10 blazer that has a 342 axle ratio and was wondering if going to a 373 would be better. Truck is all stock with tbi 350 700/r4 265 75 16 tires it is very sluggish of the line and on the interstate in overdrive shift to drive and I can cruise 85 no problem while towing rpm runs about 2000 in overdrive 3000 in drive it shifts in and out of overdrive at hwy speed going up hills not towing but it pulls high teens for milage on interstate in overdrive drop to drive and it sucks fuel. Also wanted to know what was standard equipment for gear ratios and what is special order. Why would their be such low gear ratio on a truck that only has what 150hp.
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Old April 24th, 2017, 1:53 PM
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Has it always been sluggish or is this something new? The 342 is better for all around driving with better economy. As the ratio gets higher the performance will improve but economy will suffer.
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Old April 24th, 2017, 2:22 PM
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Yes I have had it for a year and it has always been like this it has no hesitations or stumbles its just slow when towing and does shift out of OD when not towing on interstate I agree the higher ratio should lower economy but will it with the higher ratio it should stay in OD more and do less shifting. The 342 ratio probably was fine with the factory 235 75 15 wheels but I have never had those on always 265 75 16 and it looks like the 373 will only raise rpms by about 200 also then is the bigger tires on the 342 ratio dropping it to low and by having a higher ratio even if economy drops a little would it be a trade off for the wear and tear on trans.
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Old April 25th, 2017, 9:24 AM
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How does the transmission fluid look? Is it red or brown? Has the transmission filter been changed?
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Old April 25th, 2017, 9:21 PM
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Yes trans fluid is red I and I do not know when the filter was last changed. I am not a expert but I feel that it is not a mechanical problem but rather maybe a motor lacking power or a truck that is not set up right. One thing I do want to mention is that iam from south dakota and out interstate speed limit is 80 mph so I usually run between 75 to 85
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