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Old 11-17-2011, 01:05 AM
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Issue with 1980 Camaro burning lots of gas, high rev

Hi all, On my 1980 Camaro Coupe,, We finished working on it, after putting a replacement rear end, 3.08 gears, When testing on the highway, we noticed, after the tranny shifted to 3rd gear, the RPM was up to about 3500, and when letting off of the gas, a Major reduce of speed, causing your body too shift forward,, Like we were in a LOW gear, but the tranny shifted through all 3 gears,,, We spend lots of money on gas on one weekend.. I am not sure what is going on,, but in the 80's, I drove a 1978 with a 350 , mild cam, 3.40 gears I think,, I had many changes,, but Never had that problem,, After cruising, letting of the Gas, seemed to just gently reduce speed, this 80 Camaro is Reducing Way too fast,, Engine is a 305, Edelbrock Intake, 2701 I think, and Edelbrock Carb, I don't think it has to do with the engine,, Please if anyone can help me,, How do I test this car, what do you recommend to test, and how,, Please help.. Much appreciated..

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Old 11-17-2011, 06:24 AM
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Sounds like the rear end ratio is higher than 3.08. Did you check the actual ring and pinion or go by the number stamped on the housing?

To check rear end ratio jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. With the tranny in neutral (block the front tires first) rotate the jacked up tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 turns, you have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.
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Old 11-17-2011, 08:12 AM
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Quote:
Originally Posted by Juicer28
Hi all, On my 1980 Camaro Coupe,, We finished working on it, after putting a replacement rear end, 3.08 gears, When testing on the highway, we noticed, after the tranny shifted to 3rd gear, the RPM was up to about 3500, and when letting off of the gas, a Major reduce of speed, causing your body too shift forward,, Like we were in a LOW gear, but the tranny shifted through all 3 gears,,, We spend lots of money on gas on one weekend.. I am not sure what is going on,, but in the 80's, I drove a 1978 with a 350 , mild cam, 3.40 gears I think,, I had many changes,, but Never had that problem,, After cruising, letting of the Gas, seemed to just gently reduce speed, this 80 Camaro is Reducing Way too fast,, Engine is a 305, Edelbrock Intake, 2701 I think, and Edelbrock Carb, I don't think it has to do with the engine,, Please if anyone can help me,, How do I test this car, what do you recommend to test, and how,, Please help.. Much appreciated..
What transmission is in it. Are you sure it is shifting into drive.
How fast were you going at 3500 rpm.
How tall are the tires
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Old 11-17-2011, 10:56 AM
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Being you only mentioned 3rd gear I'm going to stick my neck out and guess it's a 350-400-TH tranny. If that's the case the first thing I would look at is the vacuum modulator and the vacuum ports the hose is connected too.
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Old 11-18-2011, 09:22 PM
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Sorry, I did not post what tranny,, it is a 350 tranny.

We were on the highway, and cruising at about 75 mph, The RPM, was at about 3500, and when letting off of the gas, It slowed down a lot.. Tires are 14 inches, Will soon be 15.
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Old 11-19-2011, 01:43 PM
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Quote:
Originally Posted by Juicer28
Sorry, I did not post what tranny,, it is a 350 tranny.

We were on the highway, and cruising at about 75 mph, The RPM, was at about 3500, and when letting off of the gas, It slowed down a lot.. Tires are 14 inches, Will soon be 15.
That's what my 350/350TH and 4:10 rear gears turn at 75 mph and I have 31' tall tires.
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Old 11-19-2011, 01:57 PM
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Quote:
Originally Posted by Juicer28
Sorry, I did not post what tranny,, it is a 350 tranny.

We were on the highway, and cruising at about 75 mph, The RPM, was at about 3500, and when letting off of the gas, It slowed down a lot.. Tires are 14 inches, Will soon be 15.
Check the rear gear ratio!
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Old 11-19-2011, 06:34 PM
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Tomorrow, we will be testing it to see what gears we have in that rear end, where is the Tag located, if it is still there, and what type of info will be on the Tag..
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Old 11-19-2011, 06:48 PM
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There is a tag held in place by one of the bolts retaining the diff cover, BUT...

Check the link in Cobalt327's post above and check that out first. The tag could be long gone or not applicable. Your gears can't lie when you are counting driveshaft revolutions!
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Old 11-19-2011, 09:53 PM
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If the replacement rear end is the same corporate 8.5" as it came with, the only tag that might be there originally is one that would say posi lube only, they're not like some Ford, etc. rears that have a tag w/the ratio.
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