th350 questions... - Pirate4x4.Com : 4x4 and Off-Road Forum

Tyler C · 11-20-2008, 04:03 PM

So I just picked up a 77 chevy 1/2 ton, 350/350/203 drivetrain, 3.73 in the axles, with 35" tires. Im hitting 3000 rpm at about 55 mph, Im thinking that should be a little lower with the stock gears. Tranny doesn't feel like its slipping when Im accellerating, but could it still be when Im up to speed?

And second question- the damn thing wont upshift till about 4000 rpm, wtf is that? Once it gets there, it shifts fine, but as far as i can tell itll stay at 3500 all day without doing anything. Would a shift kit fix this? That can't be normal. Supposedly the tranny was rebuilt about 30,000 miles ago, but I know its been low on fluid a couple of times in the last few years. I don't know much about transmissions, so Im really not sure where to start, and the search didn't turn up anything.

Oh yeah, if this should be in the newbie section, let me know. Figured Id get more advice here though.

jenks21 · 11-20-2008, 04:58 PM

You should be around 1970 in rpms at 55. Check the modulator that has the vacume line attatched to the side of the tranny, and the vacume line for cracks, and see if you have vacume.

later
jenks

abig84 · 11-20-2008, 07:03 PM

yeah either its not shifting out of second or your speedo is all jacked up. i ran 410s and 33s and around 55 i was at like 2500

jenks · 11-20-2008, 07:18 PM

Quote:

Originally Posted by jenks21

You should be around 1970 in rpms at 55. Check the modulator that has the vacume line attatched to the side of the tranny, and the vacume line for cracks, and see if you have vacume.

later
jenks

x2 thats exactly what I would check first. If the line is disconnect or the module is bad that would cause a shifting problem. I had the same thing in my old truck and at 50 I was about 2000 rpm and at 70 it was 3000 rpm

Tyler C · 11-20-2008, 09:40 PM

Thanks guys. Unfortunately I won't be needing that advice anymore, just wrecked the truck

Just bought it too... oh well.

11-20-2008, 04:03 PM	#1 (permalink)
Tyler C Wheeler Join Date: Mar 2008 Member # 111714 Location: Petaluma, CA Posts: 467	th350 questions... So I just picked up a 77 chevy 1/2 ton, 350/350/203 drivetrain, 3.73 in the axles, with 35" tires. Im hitting 3000 rpm at about 55 mph, Im thinking that should be a little lower with the stock gears. Tranny doesn't feel like its slipping when Im accellerating, but could it still be when Im up to speed? And second question- the damn thing wont upshift till about 4000 rpm, wtf is that? Once it gets there, it shifts fine, but as far as i can tell itll stay at 3500 all day without doing anything. Would a shift kit fix this? That can't be normal. Supposedly the tranny was rebuilt about 30,000 miles ago, but I know its been low on fluid a couple of times in the last few years. I don't know much about transmissions, so Im really not sure where to start, and the search didn't turn up anything. Oh yeah, if this should be in the newbie section, let me know. Figured Id get more advice here though.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

11-20-2008, 04:58 PM	#2 (permalink)
jenks21 Registered User Join Date: Jan 2008 Member # 106427 Location: Central Illinois Posts: 391	You should be around 1970 in rpms at 55. Check the modulator that has the vacume line attatched to the side of the tranny, and the vacume line for cracks, and see if you have vacume. later jenks

11-20-2008, 09:40 PM	#5 (permalink)
Tyler C Wheeler Join Date: Mar 2008 Member # 111714 Location: Petaluma, CA Posts: 467	Thanks guys. Unfortunately I won't be needing that advice anymore, just wrecked the truck Just bought it too... oh well.