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Canadian Poncho Homepage -> Canadian Poncho -> Hillar's General 65-70 Full Size Forum -> 1969 4-speed, what gear would you choose
Post Info TOPIC: 1969 4-speed, what gear would you choose
ABC123


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1969 4-speed, what gear would you choose
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As you may have read, the differential spin test has revealed that my original 2+2 is fitted with 4.10s

001a.jpg

This is a 427, 390, 4-speed Quadrajet 

A good member has offered me a set of 331s at a good price but added this, below just so I can lose even more sleep over this car hmm

"Before you commit, have you thought about how the 2+2 427 390 will be driven?

Now even if you buy the gears, you'd always get that back for them. They aren't easy to find GM 331's.

But I thought I'd ask.

 

Highway, round town and backroad cruising, little rips, good all round gear but generally below the powerband. 3.08

Light highway, round town, backroads, decent street ripping, closer to the powerband. 3.31

Round town ripping, a little highway, backroads getting high now at 2800 rpm, in the powerband. 3.55

Round the corner. ripping. highway ramp to ramp rips only, quickly into the band. 3.73

Strip, always in the band. 4.10"

 

What do you think ?



-- Edited by ABC123 on Saturday 3rd of February 2024 09:02:31 PM



-- Edited by ABC123 on Monday 5th of February 2024 06:14:19 PM

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4SPEED427


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That member has summed up the gears perfectly.

If you want to get out on the open highways and put miles on, go with the 3.07's. I have those in my Strato Chief with a 15" tire to knock down the rpm a bit. With the stock size 14" tires even the 3.07's were borderline as far as I was concerned. Will 3.31 with an M20 work fine? Sure, it did way back when but that was in the days when 2500+ rpm on the highway was considered normal. Now anything over 2000 rpm on the highway is considered excessive.

Honestly, you're in an over 4000 pound car. If you want jaw dropping performance you bought the wrong car!

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1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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65 SD L79


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Randy, you say fitted with 410 and spin test, what is stamped on the tube for original gear?



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65 SD L79


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307 with a close ratio M21 ? whats your thoughts on using this Carl?



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4SPEED427


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65 SD L79 wrote:

307 with a close ratio M21 ? whats your thoughts on using this Carl?

 I suspect an M21 with 3.07 wouldn't be much fun at stop signs. The M20/3.07 combo is ok with a big block but I wouldn't want any less mechanical advantage.

 



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seventy2plus2


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This is an interesting topic.
My 70 LS6 Parisienne with wide ratio M20 has 3.07 rear gears. It's also running tall 15" tires (235/70R15). I'm using a 3 finger McLeod clutch which grabs pretty good.
The 3.07's are ok around town, but I'm buzzing 3000 rpm at 80 mph on the highway.


I've purchased another 12 bolt diff from a 70 Impala with 2.73 gears, have removed that carrier and have put the 2.73 ring gear on a posi carrier. I'm yet to drop that carrier into that diff yet - maybe this spring.
I'll experience more chatter around town with the 2.73's, but will drop my highway rpm's.






-- Edited by seventy2plus2 on Sunday 4th of February 2024 02:11:04 PM

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DonSSDD


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My 409 has a 3.08 rear, 28 inch tires, 2500rpm is 68mph, add bigger tires to the mix. Rims are 15 inch, 28x8 inch pie crust street legal drag radials. 

spicerparts.com/calculators/transmission-ratio-rpm-calculator



-- Edited by DonSSDD on Sunday 4th of February 2024 05:37:08 AM

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Canadian Poncho


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Keep the 4:10's and do this. Only you would know that's not a Muncie under the car. That's my 2 pennies. You'll have the best of both worlds. No compromise. 

https://www.moderndriveline.com/shop/solutions/gm-conversion-solutions/chevy/65-70-impala-5-6-speed-conversions/



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Prefectca


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I was talking to a guy at a show years ago with a nice Beaumont with a 396. He was running a Saginaw four speed with a 3:50 low gear with a 2:73 rear end ratio. He still had the original Muncie and rear end, 3:55 ratio I think. For going to cruise nights and shows the car was much more usable with the Saginaw and 2:73 gear.

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4SPEED427


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That 3.50 first gear would sure make a difference.



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Prefectca


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4SPEED427 wrote:

That 3.50 first gear would sure make a difference.

 Exactly, and how many of use really abuse our cars. The Saginaw trans although not as strong as a Muncie would be fine for the type of usage our cars would see today. 



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4SPEED427


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Prefectca wrote:
4SPEED427 wrote:

That 3.50 first gear would sure make a difference.

 Exactly, and how many of use really abuse our cars. The Saginaw trans although not as strong as a Muncie would be fine for the type of usage our cars would see today. 

 Yes, the way I drive my car a Saginaw would never break. I only use a Muncie to make it correct, no other reason.



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ABC123


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I am trying to build the car as accurate as I can.

The M-20 is almost finished and there is no going back on that.

I will try to find a stamp but there is no tag on the differential.





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Canadian Poncho


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What about an overdrive?


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4SPEED427


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ABC123 wrote:



I will try to find a stamp but there is no tag on the differential.



 I assume you know it's on the passenger side axle tube on the front of the tube?



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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
ABC123


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Never assume biggrin



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seventy2plus2


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ABC123 wrote:

I am trying to build the car as accurate as I can.

The M-20 is almost finished and there is no going back on that.

I will try to find a stamp but there is no tag on the differential.



 The stamping should be on the passenger side axle tube, facing forward.   You likely need to get a wire wheel to really clean that area.



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seventy2plus2


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What's that diff out of? It's missing the bracket to hold the brake line flex hose. That bracket is unique to 69-70 12 bolts, the 10 bolt bracket is different.

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CdnGMfan


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You've got 3.31s waiting? Run them! They are a great compromise between launch-ability & highway livability. That is what a 4-speed big block '69 Big car would have come with originally by default anyway.

The nice thing about 4.10s and a hot engine, at 60 mph you will be at your torque peak and can generate rubber at that speed. As I like to say, "tell it to the judge..."


3.07 gears with a close-ratio M21 makes no sense for stop-and-go driving, but it is great for slice & dice at speed on a course where the close ratios give a smaller rpm drop between gears. It is a pretty specialized combination. We used to have options, until Fleet Average Fuel Economy hijacked the option list & cancelled things.

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cdnpont


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If only they had of made 3.23's...

But I agree that the 3.31 is the best available compromise. I had 3.08's in my 65 with the M20 4 speed, a little soft off the line, but all round pretty happy for the most part.



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ABC123


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seventy2plus2 wrote:

What's that diff out of? It's missing the bracket to hold the brake line flex hose. That bracket is unique to 69-70 12 bolts, the 10 bolt bracket is different.

 This is the tough part of a car like this.

We know these guys did a lot of swapping 40 years ago.

Historic value was never a consideration.

They may not even had known how rare the car was.

I'm trying my best with what I have and what I can find biggrin

 



-- Edited by ABC123 on Sunday 4th of February 2024 04:59:09 PM

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timbuk


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410s are low if your not going 90 miles an hour id go 331,if on highway lots 308 guess it depends what yer doing randy racing cruising or in between

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65 SD L79


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cdnpont wrote:

If only they had of made 3.23's...

But I agree that the 3.31 is the best available compromise. I had 3.08's in my 65 with the M20 4 speed, a little soft off the line, but all round pretty happy for the most part.

 When I think of your your choices I believe 3.31s is the way to go. If you want to go on the Highway take the white car with 273,s Auto and A/C . You have 2 cars and the best of city and highway cruisers



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ABC123


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canadianponcho.activeboard.com/t68581005/for-sale-very-rare-427-cid-69-pontiac-parisienne-excellent-r/

According to John, 3.42s in the white car.

Anyone ever heard of 3.42s in a GM ?

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4SPEED427


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Not in the 12 bolts car diffs but the aftermarket makes 3.42's for them.



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