Should I change rear gears or tranny?

installer

installer

Active Member
I retired this year and it is finally time to do something about my Baby, so would love some thoughts on which way to go. Tranny, rear gears or both?



She (67 Olds) has a 330 runs about 360HP, original 2 speed was replaced before me with a turbo 350. rear end is a stock std 3.08 A posi might be nice, then I can wear out 2 tires instead of 1. :D



On the highway at 100Km she is screaming at about 3500 rpm. An OD would be wonderful.


ANy thoughts for a good combination would be much appreciated. :)
 
3500 RPM @ 100KPH with 3.08's???? Are you running wheel barrow or lawn mower tires??. When I was running 4:88's in my '57 I was @ 4000RPM @ 100 KPH. Something doesn't seem right. I'm thinking you have 4:11's in there.
 
Something wrong here?
From a internet calculator:

Enter the following values

Ring & pinion gear ratio 3.08
Tire height (in.) 30 (guess)
Engine RPM 3500
Transmission gear ratio 1

Vehicle speed in MPH 101.46
 
Wow 3:08's are a highway gear that rpm sounds crazy high. My thoughts are either your rpm are off (tack?) or you don't have 3:08's? or your running a 12" tire?
 
New tach, reads same as the old uglee one... rear tires measure 28"


I can't jack her up for a few weeks to double check until I've healed from this hernia operation. But possible they were changed from factory before I got her?
 
Yup, your speedo is likely out (likely because of the change from powerglide to TH350?)

I ran it through a calculator, and with 3.08 axle ratio & 28" tall tires, @ 3500 RPM, you should be going 94.7 MPH!!

Try it yourself, https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

It can only be one of several things:

>Speedo is out

>Tach is out (not that likely)

>Rear axle ratio is not the 3.08 you think it is

>Tire dia measurement is off? (again, not that likely)

**I ran the numbers, going progressively steeper with the axle ratio, trying to determine how far out on the axle ratio one would have to be to get the speedo to read 60 mph, and with 4.56 gears, you would be doing ~64 MPH @ 3500RPM


IIRC, my Mustang, when it had 3.55 gears and 24" tall tires was 70 MPH @ 3500 RPM.....

Anyways, you need to be checking some things:)
 
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I think all you guys are focusing on the wrong thing...HAPPY RETIREMENT. After working all those years just drive the wheels of her and never look back....eh
 
JohnnyBgood said:
I think all you guys are focusing on the wrong thing...HAPPY RETIREMENT. After working all those years just drive the wheels of her and never look back....eh
Click to expand...

MsOHlul.jpg
 
But seriously, there is one other possibility. Maybe it's not shifting into 3rd gear and is running in 2nd. This could be due to improperly adjusted TV linkage or the shifter linkage. Depending on how you want to use the car, the 3.08 ratio may be fine if it's mostly a daily driver. An OD automatic would give you more flexibility. There's a new tranny guy in town, Scott Anderson, just past Summergate Winery on Prairie Valley. Might be worth a chat with him.
 
Well, I don't believe TH350's use a TV, and I didn't mention not being in drive, as I was giving the OP the benefit of the doubt:)

But, now that you've mentioned it, I ran the numbers:

Ring & pinion gear ratio
3.08
Tire height (in.)
28
Engine RPM
3500
Transmission gear ratio (in second gear)
1.52
*Imperial Units of Measure
Vehicle speed in MPH
62.3

So, yah, it's plausible that the trans is in second, not drive

We've done all we can, now OP needs to do some investigation.........

GFaRT said:
But seriously, there is one other possibility. Maybe it's not shifting into 3rd gear and is running in 2nd. This could be due to improperly adjusted TV linkage or the shifter linkage. Depending on how you want to use the car, the 3.08 ratio may be fine if it's mostly a daily driver. An OD automatic would give you more flexibility. There's a new tranny guy in town, Scott Anderson, just past Summergate Winery on Prairie Valley. Might be worth a chat with him.
Click to expand...
 
Do you know for sure that your speedo is reading correctly?

Have you looked at the drive gear or driven gear? they could be mis-matched to your tire size and or rear gears.
 
definitely have all 3 gears, can tell by the 2nd chirp when she shifts :p


I have met Scott already, great guy. rebuilt my tranny for my work van.
(now my once in a while driver lol)


GFaRT said:
But seriously, there is one other possibility. Maybe it's not shifting into 3rd gear and is running in 2nd. This could be due to improperly adjusted TV linkage or the shifter linkage. Depending on how you want to use the car, the 3.08 ratio may be fine if it's mostly a daily driver. An OD automatic would give you more flexibility. There's a new tranny guy in town, Scott Anderson, just past Summergate Winery on Prairie Valley. Might be worth a chat with him.
Click to expand...
 
I actually use a GPS, speedo is out and in MPH, so rarely look at it.
Rear tires are also slightly larger than the front. I definitely need another gear for top end I'm afraid.




58chev said:
Do you know for sure that your speedo is reading correctly?

Have you looked at the drive gear or driven gear? they could be mis-matched to your tire size and or rear gears.
Click to expand...
 
Hmm, this is becoming quite the mystery. We are assuming that a single item is responsible for the high rpm @ 100 kmh. It's possible that there is more than a single discrepancy at work here. If it's the rear end ratio, it would be about 4.70, so are the gears 4.56 or 4.88? It is assumed that the tach is correct, but if it has a 4-6-8 selector switch and is set to 6 then that could be a factor. Then there's the converter which will have some slip depending or it's stall speed. Was the car modified for drag racing with a low gears and a high stall converter? It sounds like the engine has some mods if it's 360 HP as I think the stock rating is around 320 HP. However if it was set up for the drags, you would think that it would have a posi rear end.

If you would like help with checking your gear ratio (don't want to disturb your healing from the operation) I don't mind giving you a hand. Fourninefour fourteennintyseven.
 
Morning Lee, yes. you change change the setting in the gps for either MPH or Kph. My math ain't too good for converting on the fly. lol


Thanks for that link, I had seen one similar awhile back and was going to try that when I'm allowed to lift more than 10 lbs. :(


But when it warms up a bit (-6 right now) I will give GFaRT a call for an extra hand :)


Pretty sure the tach is accurate, car did have a stock 330 when I got it, my brother and I pulled it apart dropped a new Cam, timing gear, etc had the heads redone. added a new edelbrock carb and manifold and HEI

so tranny and rear end are the unknown right now.



Gave Scott a call yesterday to find me an Olds tranny with OD, I think that's the 1st place to start.




ratrig said:
Your reading KPH,not MPH on the Gps?
Here's a simple way to check your ratio:
https://tuning.americanmuscle.com/h...60743-How-do-I-verify-my-rear-end-gear-ratio-
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Putting on o/d in is the worst waste of time and money.
You built some performance in your motor and it won’t like cruising at 1700 rpm.
One of the easiast cures for the sound of a screaming motor at highway speeds is replace the fixed blade rad fan with a clutch fan.
Better cooling and quiet cruising.

Easy way to feel what an o/d is like is (in your case) drive at 45 mph (70kmh).
See how your motor likes it. Run a vacuum gauge in to where you can see it easily. The lower the vacuum the deeper into the throttle you are.
Try that at 100 kph too.
You might be amazed at the difference.
 
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I had a Nova with 3.73 gears and a 28" tire that was just over 3000 rpm at 60 mph. I just crunched the numbers on a 200R4 trans and the rpm would drop to 2300 at 60 mph
 
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