The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1969 - 1972 Blazers and Jimmys Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 10-06-2010, 10:07 AM   #1
red71cheyenne
Back in the sticks
 
red71cheyenne's Avatar
 
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
Low Gears!

Oh my gosh, the Blazer is low geared! I drove it to work this morning. I'm guessing I was doing around 30-35 mph and my tach was running 2K! It has 35 inch tires and I'm thinking 4.11's in the rear. My spid never broke out what rear it had. But they are low!

Do you guys know if a 3.42 or 3.08 will fit in this carrier? All I know for sure is it has a 12 bolt cover on it. Not sure on what gear set is actually in there. Its gonna have to change if I ever hope to take it on the hiway though. Its fun though, kinda like driving a Tonka Truck!
__________________
1971 Cheyenne C-10 w/700R4 and Tuned Port Injection
1969 K5 Blazer w/Tuned Port
2010 2SS/RS Flaming Orange Camaro
2011 K1500 Suburban
2014 K1500 Pickup
2008 Nissan Altima? The wifes' hoopty
red71cheyenne is offline   Reply With Quote
Old 10-06-2010, 12:52 PM   #2
-Greg72
Registered User
 
-Greg72's Avatar
 
Join Date: Nov 2001
Location: Austin, TX
Posts: 308
Re: Low Gears!

You sure the transfer case in in 2HI???


-G
__________________

1972 K5 - 502BBC/4L80E/Magnum205/Mog-9s/5.26s/38" BFG KM2s


Find me on INSTAGRAM @MIGHTASWELLK5

'72 K5 - Greg's "Might As Well™" Build
-Greg72 is offline   Reply With Quote
Old 10-06-2010, 01:15 PM   #3
red71cheyenne
Back in the sticks
 
red71cheyenne's Avatar
 
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
Re: Low Gears!

I have it shifted all the way forward and my front drive shaft spins loosely, so I think so. Not sure what its doing internally, but if it were in 4HI or LO the front wouldn't turn freely right?
__________________
1971 Cheyenne C-10 w/700R4 and Tuned Port Injection
1969 K5 Blazer w/Tuned Port
2010 2SS/RS Flaming Orange Camaro
2011 K1500 Suburban
2014 K1500 Pickup
2008 Nissan Altima? The wifes' hoopty
red71cheyenne is offline   Reply With Quote
Old 10-06-2010, 05:03 PM   #4
jasons
not enough hours in the day
 
jasons's Avatar
 
Join Date: Jan 2009
Location: Axtell, NE
Posts: 550
Re: Low Gears!

If it is the 205 transfer case, which I believe came in all the Blazers, all the way forward is 4 low. From front to back the gearing is like this.

4 low
Neutral
2 high
4 high

If it is a different transfer case the pattern could be different.
jasons is offline   Reply With Quote
Old 10-06-2010, 07:59 PM   #5
-Greg72
Registered User
 
-Greg72's Avatar
 
Join Date: Nov 2001
Location: Austin, TX
Posts: 308
Re: Low Gears!

Quote:
Originally Posted by red71cheyenne View Post
I have it shifted all the way forward and my front drive shaft spins loosely, so I think so. Not sure what its doing internally, but if it were in 4HI or LO the front wouldn't turn freely right?
Are you saying that your 700R4 is in overdrive and still turning those kinds of RPMs...??? (or does your Blazer have a stock tranny like a TH350?)

I don't think there's a axle gearset on the planet that is deep enough to do that on it's own.

I'm going to go run a few numbers.


EDIT:

If you are accidentally in 4LO and have an NP205 there will be an extra 1.96:1 reduction in your gearing. If you had a common rear axle ratio like 3.73s the numbers would look like this:

2000RPM = 28MPH in top gear (non-OD)
2500RPM = 36MPH in top gear (non-OD)

Your overall gearing (transfercase and rear axle works out to 7.31:1)...so yeah, that's LOW!!!


If you're in high range in the transfercase and had the deepest gears possible in the axle (maybe 5.13??) you'd be running at 41 MPH at 2000 RPM and 51 MPH at 2500 RPM.... still quite a bit faster than what you're reporting.





-G
__________________

1972 K5 - 502BBC/4L80E/Magnum205/Mog-9s/5.26s/38" BFG KM2s


Find me on INSTAGRAM @MIGHTASWELLK5

'72 K5 - Greg's "Might As Well™" Build

Last edited by -Greg72; 10-06-2010 at 08:09 PM. Reason: Added calcs...
-Greg72 is offline   Reply With Quote
Old 10-06-2010, 08:15 PM   #6
red71cheyenne
Back in the sticks
 
red71cheyenne's Avatar
 
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
Re: Low Gears!

Quote:
Originally Posted by -Greg72 View Post
Are you saying that your 700R4 is in overdrive and still turning those kinds of RPMs...??? (or does your Blazer have a stock tranny like a TH350?)

I don't think there's a axle gearset on the planet that is deep enough to do that on it's own.

I'm going to go run a few numbers.


EDIT:

If you are accidentally in 4LO and have an NP205 there will be an extra 1.96:1 reduction in your gearing. If you had a common rear axle ratio like 3.73s the numbers would look like this:

2000RPM = 28MPH in top gear (non-OD)
2500RPM = 36MPH in top gear (non-OD)

Your overall gearing (transfercase and rear axle works out to 7.31:1)...so yeah, that's LOW!!!


If you're in high range in the transfercase and had the deepest gears possible in the axle (maybe 5.13??) you'd be running at 41 MPH at 2000 RPM and 51 MPH at 2500 RPM.... still quite a bit faster than what you're reporting.





-G
I think I confused everyone. I have an SM465 and T221 transfer case. After driving it home this afternoon, it seemed a little better in the daylight. I think maybe I was guestimating a little off as my speedo may or may not be correct. It does a lot of bouncing!

G, I think you are close to being right on the 4.56 or 5.13 gears as the 221 has the same final as a 205. I'm going to try the chalk mark on the drive shaft and tire to see about what it looks like for rear end ratio.
__________________
1971 Cheyenne C-10 w/700R4 and Tuned Port Injection
1969 K5 Blazer w/Tuned Port
2010 2SS/RS Flaming Orange Camaro
2011 K1500 Suburban
2014 K1500 Pickup
2008 Nissan Altima? The wifes' hoopty
red71cheyenne is offline   Reply With Quote
Old 10-06-2010, 08:18 PM   #7
-Greg72
Registered User
 
-Greg72's Avatar
 
Join Date: Nov 2001
Location: Austin, TX
Posts: 308
Re: Low Gears!

Big tires will throw your numbers way off too.

Borrow a GPS or a phone with a GPS app that can give you actual speeds, you might be surprised to learn that the only thing wrong with your truck is the speedometer calibration.


-G
__________________

1972 K5 - 502BBC/4L80E/Magnum205/Mog-9s/5.26s/38" BFG KM2s


Find me on INSTAGRAM @MIGHTASWELLK5

'72 K5 - Greg's "Might As Well™" Build
-Greg72 is offline   Reply With Quote
Old 10-06-2010, 09:13 PM   #8
red71cheyenne
Back in the sticks
 
red71cheyenne's Avatar
 
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
Re: Low Gears!

Quote:
Originally Posted by -Greg72 View Post
Big tires will throw your numbers way off too.

Borrow a GPS or a phone with a GPS app that can give you actual speeds, you might be surprised to learn that the only thing wrong with your truck is the speedometer calibration.


-G
Whoa, good call! I should have thought of that, but I can't even spell GPS. Speaking of which, how would you cal the speedo? Different gear in the transfer case?
__________________
1971 Cheyenne C-10 w/700R4 and Tuned Port Injection
1969 K5 Blazer w/Tuned Port
2010 2SS/RS Flaming Orange Camaro
2011 K1500 Suburban
2014 K1500 Pickup
2008 Nissan Altima? The wifes' hoopty

Last edited by red71cheyenne; 10-06-2010 at 09:14 PM. Reason: Question
red71cheyenne is offline   Reply With Quote
Old 10-06-2010, 10:00 PM   #9
SeventyOne
Registered User
 
Join Date: Mar 2007
Location: Oakland, Ca
Posts: 1,381
Re: Low Gears!

Yes - There are different speedo gears you can swap in to achieve a closer to reality reading.

Don't remember really where to get them but run a google search.
SeventyOne is offline   Reply With Quote
Old 10-07-2010, 06:18 AM   #10
Blazer1970
Registered User
 
Blazer1970's Avatar
 
Join Date: Dec 1999
Location: Old Mission, MI, USA
Posts: 2,510
Re: Low Gears!

Your tach is not reading correctly.
__________________
Tim
Blazer1970 is offline   Reply With Quote
Old 10-07-2010, 07:14 PM   #11
red71cheyenne
Back in the sticks
 
red71cheyenne's Avatar
 
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
Re: Low Gears!

That may be true too. I'll have to check on that too when I check the rear end ratio.
__________________
1971 Cheyenne C-10 w/700R4 and Tuned Port Injection
1969 K5 Blazer w/Tuned Port
2010 2SS/RS Flaming Orange Camaro
2011 K1500 Suburban
2014 K1500 Pickup
2008 Nissan Altima? The wifes' hoopty
red71cheyenne is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 10:58 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com