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Old 09-18-2009, 03:59 PM
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T-400 3rd gear question??

I have a 69 Chevelle 305, a new TH400 (400 miles on it), with a 3200 stall and 3.73 running gear. 1st and 2nd gear shift fine and firm. Now 3rd gear I dont feel but I accelerate to 70 no problem on the Xpressway. Could it be there and I'm not be feeling it?

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Old 09-18-2009, 04:22 PM
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Quote:
Originally Posted by ss396si
I have a 69 Chevelle 305, a new TH400 (400 miles on it), with a 3200 stall and 3.73 running gear. 1st and 2nd gear shift fine and firm. Now 3rd gear I dont feel but I accelerate to 70 no problem on the Xpressway. Could it be there and I'm not be feeling it?
Not sure about the feel but you should be able to verify by the RPM difference in 2nd & 3rd at a common speed.
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Old 09-18-2009, 04:29 PM
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as the transmission upshifts from 1st to 2nd I can see the rpm's climb up and back down. When the car is in 2nd I see the rpm's just keep climbing. Would it help if i adjust the vacuum modulator?

Last edited by ss396si; 09-18-2009 at 04:54 PM.
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Old 09-18-2009, 06:39 PM
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What are your RPM's at freeway speed (70) then we can calc the 3.73 gear to see if your in second or third.
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Old 09-18-2009, 06:47 PM
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2500-3500rpm
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Old 09-18-2009, 07:41 PM
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Can you narrow it down a bit more than that? 1000 rpm swing is a broad brush for calculating a gear at 70 mph. And I forgot to ask what tire size you had?
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Old 09-18-2009, 08:59 PM
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Quote:
Originally Posted by ss396si
I have a 69 Chevelle 305, a new TH400 (400 miles on it), with a 3200 stall and 3.73 running gear. 1st and 2nd gear shift fine and firm. Now 3rd gear I dont feel but I accelerate to 70 no problem on the Xpressway. Could it be there and I'm not be feeling it?
Not to be a wise-acre ... but it's a 3-speed automatic.
If you feel it shift twice ... it's in 3rd, right?

(Starts in 1st, shifts to 2nd, shifts again into 3rd)

"2500 - 3500 RPM range" is too low a figure to be stuck in 2nd with 3.73's.

My '68 Torino had 3.50:1 gears, G60-14" tires, and used to run around 3200 RPM @ 65-70 MPH. My buddy had a 70-1/2 Camaro 4-speed car with 4.11's and 15" rubber. It also ran about the same RPM on the highway.

I can also understand why you mention a "range" ... it's due to that 3200 RPM stall convertor. On the flat land (or downhill) the RPM's will be much less than they would be pulling up a hill or accelerating.
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Old 09-18-2009, 09:21 PM
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I you have a 235 70r 15 which is roughly 28 inches tall the rpm's calc out to 3140 rpm on the th400 with 3.73 gears so if you are turning in the 3000 range at 70 you would have to be in third. Second gear with those tires is around 4700, and you would feel that.
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Old 09-19-2009, 03:39 AM
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Quote:
Originally Posted by Barn Owl
Can you narrow it down a bit more than that? 1000 rpm swing is a broad brush for calculating a gear at 70 mph. And I forgot to ask what tire size you had?
I'll have to drive the car again to get a more accurate reading on the tach. I have 235 60r15 in the back
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Old 09-19-2009, 09:14 AM
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Yeah, anywhere close to the tire size that I guiessed at and the rmp you stated and your in 3rd, just like 66 said if you feel it shift twice then your in 3rd.
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Old 09-19-2009, 02:37 PM
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Quote:
Originally Posted by ss396si
I'll have to drive the car again to get a more accurate reading on the tach. I have 235 60r15 in the back
When you are driving at 60 or so pull the gear selector into second and see if the rpms change. It sounds like you are in third from your numbers you posted
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Old 09-22-2009, 09:50 AM
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I just set the vacuum modulator screw 1/4 back and it worked, I feel 3rd gear!
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Old 09-22-2009, 09:57 AM
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Just out of curiocity, why the 305 in it?
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Old 09-22-2009, 02:36 PM
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I bought the car w/ a 305,TH350 and a 8.5 10 bolt. I upgraded the drivetrain w/ a moser 12 bolt and a TH400. The 305 hopefully will be scraped for a small block 406.
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