What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Gear Weirdness...Help!

SchnorrCS

SchnorrCS

1/2 ton status
Joined
Oct 11, 2005
Posts
368
Reaction score
0
Location
Loveland, CO
Ok....So I had no idea what gears my truck came with so I had done some math found elswhere on this site and somehow came up with 5:13.
Just got done taking the cover off to change the 90w and thought I'd count the teeth. 37 ring 9 pinion. Tha6t comes out to 4.11s. Then why the hell does my truck turn 3000 rpms while doing 60? I have 35s on it.
Also, I thought that 4.11s where a posi gear. As in I though gm only put 4.11s in with a posi rear. Yes? No? Bueller? It's a 74. Dana 44 front, 12 bolt rear. Thanks guys.
 
There was no gear that was exclusive to the Posi, being a 74 it may have been changed by a PO. I got a look at the option sheet for my blazer and 4.11s were an option (its a 73) If you doubt your count somewhere on the ring gear there should be numbers stamped on it. If there is not this is a pretty sure sign that it is an aftermarket gear set.
 
Are you going by the speedo?? Was it corrected for the tires?? If not then you are doing over 60. My old car had 4.10 with 27" tires, and that would do 60 at 3k.
 
I got 37s which are only about 36s on the truck and 4.10s with a 700R4 and I can turn 3000 at 60 when I am in 3rd so the numbers work out like yours.

Ira
 
Thanks guys. There are numbers stamped on it, and they match my count. Why is my truck so damn slow? I know I was doing 60, I checked it with mt gps.
 
SchnorrCS said:
Thanks guys. There are numbers stamped on it, and they match my count. Why is my truck so damn slow? I know I was doing 60, I checked it with mt gps.
Click to expand...

Horsepower is horsepower, gears won't make a weak engine a strong one.
 
38377k5 said:
Horsepower is horsepower, gears won't make a weak engine a strong one.
Click to expand...
True enough. If that's the stock '74 engine, it's rated at either 145 or 160HP (and about 270 ft lbs or torque), tasked to move two tons of steel.
 
and in 1974, wasn't that GROSS horsepower?

My '74 was a DOG before the 383 upgrade.

My 3.08 gears still suck though.
 
Motors not stock, but I hear ya. I was just thinking how the hell did people do road trips in the 70s when trucks were topping out at 60-65 mph. I'm getting ready to drive from Cali back to Colorado, and I am going to trailer my K5 behind the pops 1 ton Dodge Dualy, and when he's towing he goes faster than 65, ya know?
 
I think that they'd already started rating net HP back in '72. The mid-late 70s and most of the 80s were dark days, with the automakers scrambling to meet both smog and CAFE mandates while still using carburetors.

Adoption of EFI helped a lot to meet those dual mandates, while allowing some muscle to return and not blow those other two things out of the water. OD transmissions helped out a lot with mpg when they started showing up on vehicles.
 
Not sure what kind of math you did but 37/9 = 4.11

Like was already said, if you have not recalibrated your speedo after the tire size change then your speedo is incorrect along with the odometer.
 
Uh Yea...I know 37 r and 9 p is 4.11. Already said that. The math I was refering to is an equation for finding gear ratio without knowng exactly what you have. Has to do with speed tie size and rpm.
 
Sorry, thought you meant you did the math on the gear tooth and came up with 5.13.
 
The RPMs are still fishy Clint...

If you have 4.11s and 35 inch tires you should be pulling somewhere between 2200-2500 RPMs, not 3 grand.

What is the actual measured tire height sitting in the driveway? It will probably come out to 33-34 actual height.

But that still doesn't translate to such a high RPM.

I assume you are running a manual transmission? If it is an auto with a high stall that would explain the higher RPM, but with a manual, is the clutch slipping? Was 4th gear somehow replaced with an odd gear set?

I noticed on another post you stated the front axle had a different gear set, so with that logic, who knows what the PO did to that blazer.

Josh
 
Bullitt427 said:
If you have 4.11s and 35 inch tires you should be pulling somewhere between 2200-2500 RPMs, not 3 grand.

What is the actual measured tire height sitting in the driveway? It will probably come out to 33-34 actual height.

But that still doesn't translate to such a high RPM.

I assume you are running a manual transmission? If it is an auto with a high stall that would explain the higher RPM, but with a manual, is the clutch slipping? Was 4th gear somehow replaced with an odd gear set?

I noticed on another post you stated the front axle had a different gear set, so with that logic, who knows what the PO did to that blazer.

Josh
Click to expand...

Look in his sig he has a 350/350/203, I checked it on www.4lo.com and it works out to 5.13's w/ 35's, 3,000rpm, 1:1 (tranny) and 1:1 (tc) but as stated above it might not be a true 35" tire. My 38.5" MT Baja Claws inflated to road psi are only 37" and even shorter when I deflate for off-road so as stated, go out and measure the tire.

-Avery
 
Also, you're never going to get a true 1:1 ratio with a TH350. There will always be some TC slippage. Add in a little bit of tachometer error and you could easily have a 500 rpm discrepency.

To answer the question:
... how the hell did people do road trips in the 70s when trucks were topping out at 60-65 mph?
Click to expand...

Easy. The national speed limit was only 55mph and gas was cheap.
 
38377k5 said:
Horsepower is horsepower, gears won't make a weak engine a strong one.
Click to expand...

horsepower wont get a vehicle moving at all, but torque will. gears multiply torque, so they will make the truck quicker out of the hole.
 
Yea, I know it's not a "true" 35, it measures to about 34, but I'm kinda thinking it might have some lower gears somewhere. I thought I read about a "low geared" TH350, but I'll have to do some investigating.
As far as the axel, another member said something about it being the 1/2" tube, 3/4 ton axle. I think the difference between the gears is just that 4.11 and 4.10 is so close, they may have used them in the factory. Perhaps Dana doesn't/didn't at the time make a 4.11, and since the ratio is so close, GM just said F it.
Also, with the 1/2" wall tubes, is it possible that my Blazer could fall under the whole "Heavy Half" GM made?
Josh...You remember my 83? It was a Heavy Half. It was also an 83, and they stopped using the D44 in the Halfs, so maybe that's it.
Anybody know any web site or something that I could run my VIN or somejunk and figure this crap out?

Thanks again guys.


P.S.
Hey Josh, Shannon said to drop dead....:haha: :D :crazy: :doah:
 
You must log in or register to reply here.

Latest Posts

Top Bottom