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Username Post: 69 GMC geared too low        (Topic#357521)
Original58 
Contributor
Posts: 522
Original58
Loc: Manitoba, Canada
Reg: 10-30-13
08-05-19 03:57 AM - Post#2772438    

Hi,
Normally post in 58 section but just picked up a 69 GMC with 4 speed. Its geared low...pulling tree stumps low. Im thinking ithas a sm465 with 4 series gears.
Im wondering if a rear gear change would be enough to be more driveable or should I look at a 5 speed?
Anyone been down this road?

Thanks
Jeff

1958 Biscayne 283 Turbo-Glide 31,000 mi (now 35,000 and counting) driven daily
1966 Mustang Inline 6- C4 57,000 mi and growing daily
1929 Graham - Paige 612- the eternal headache that I will never sell


 


bobb 
Super Senior Member
Posts: 5496

Loc: paradise
Reg: 09-05-03
08-05-19 02:32 PM - Post#2772472    
    In response to Original58

how tall are your tires?

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
Original58 
Contributor
Posts: 522
Original58
Loc: Manitoba, Canada
Reg: 10-30-13
08-05-19 05:52 PM - Post#2772488    
    In response to bobb

Pretty tall already. Its 3/4 ton with 16 in rims.
Ill have to check the size when im back in town.
I could maybe go with 31s but it wouldnt reduce revs by much. Was just curious what others have done.

Jeff

1958 Biscayne 283 Turbo-Glide 31,000 mi (now 35,000 and counting) driven daily
1966 Mustang Inline 6- C4 57,000 mi and growing daily
1929 Graham - Paige 612- the eternal headache that I will never sell


 
JimKshortstep4x4 
Chevytalk Moderator & "15th Year" Silver Supporting Member
Posts: 5104
JimKshortstep4x4
Loc: Muskegon, MI, USA
Reg: 03-28-02
08-07-19 03:58 PM - Post#2772651    
    In response to Original58

My son has a 70 GMC, 3/4 ton truck with a TH-350 in it so we understand why you are looking into a fix.

I picked up a 700r4 that we are looking at replacing the TH 350 with. We looked at changing the rear end to one from a C-10 but then addressing the front end and what to do with it is needed. Lower ratios for the 3/4 ton differential were looked into but the choices are limited.

Jim

65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/TH 350
71 Snow plow, 4x4, 350, TH 350
72 GMC Shortbed, stepside, 427/TH 400


 
Original58 
Contributor
Posts: 522
Original58
Loc: Manitoba, Canada
Reg: 10-30-13
08-07-19 06:24 PM - Post#2772662    
    In response to JimKshortstep4x4

Thanks for the information. I may need to look at a complete diff and / or a 5 speed.
Once I get more time I'll have to do some calculations on different combinations.

Jeff

1958 Biscayne 283 Turbo-Glide 31,000 mi (now 35,000 and counting) driven daily
1966 Mustang Inline 6- C4 57,000 mi and growing daily
1929 Graham - Paige 612- the eternal headache that I will never sell


 
64K10 
Member
Posts: 77
64K10
Loc: Cali
Reg: 06-25-04
08-09-19 07:11 AM - Post#2772797    
    In response to Original58

Do you know what diff and gear ratio are currently in truck? Dana 60?

Probably 4.10 or 4.56 gears depending on engine option (V8 or 6). Gear set may be deeper like 4.88's but that would have been a special order option.

For starters look here for gear sets:
https://www.randysworldwide.com/chevrolet-drivetra...

64K10


 
Original58 
Contributor
Posts: 522
Original58
Loc: Manitoba, Canada
Reg: 10-30-13
08-09-19 11:58 AM - Post#2772822    
    In response to 64K10

Hi. Thanks for the link.
Its a Dana 60. Time to do some calculating.

Jeff

1958 Biscayne 283 Turbo-Glide 31,000 mi (now 35,000 and counting) driven daily
1966 Mustang Inline 6- C4 57,000 mi and growing daily
1929 Graham - Paige 612- the eternal headache that I will never sell


 


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