Th350 speed

[TJ1978]

My blazer is on 35's with a 350/th350

What is the top or ideal speed to keep the truck on the freeway? I was driving today and it felt better at 55-60mph any higher I felt uncomfortable.. not from anything the truck was doing but it made me think what's an ideal highway speed with this transmission in the truck I have.

 

[Bent77]

Drive it 60

 

[HankScorpio]

What axle gears? Tach?

 

[fourwheelerjeff]

drive it whatever makes you comfortable; sounds like 60.

 

[HankScorpio]

You should check your speed with GPS. With 35's you may be going faster than you think.

 

[Wes Harden]

Standard equip in 78 4x4 k5 was 4.11 with 35s should be able to 65 70 no issue

 

[TJ1978]

You should check your speed with GPS. With 35's you may be going faster than you think.

I have an app. When my gauge says 55 or whatever speed it's on the money

 

[TJ1978]

Standard equip in 78 4x4 k5 was 4.11 with 35s should be able to 65 70 no issue

I have 3/4 ton axles... somewhere on this site or pictures I posted what gears it has. I forget at the moment

Edit. Found it... not sure what it reads. 4:10 I assume

 

[tarussell]

That gear and tire combo ( 4.10 & 35” ) puts you at about 2,500 RPM’s at 65MPH-ish and if your speedometer appears to be correct your Blazer probably came with 3.42 gears originally with a 31” tall tire.

At that engine speed the motor would feel fairly good and responsive as opposed to leaning on the lugging side of the power band with all the resistance of highway speeds.

Your TH350 has a top gear of 1:1 just as a TH400 or a SM-465 does so the final drive on any of these trans will give you the same results.

 

[TJ1978]

That gear and tire combo puts you at about 2,500 RPM’s at 65MPH-ish and if your speedometer appears to be correct your Blazer probably came with 3.42 gears originally with a 31” tall tire.

At that engine speed the motor would feel fairly good and responsive as opposed to leaning on the lugging side of the power band with all the resistance of highway speeds.

Your TH350 has a top gear of 1:1 just as a TH400 or a SM-465 does so the final drive on any of these trans will give you the same results.

I was asking more so I know for piece of mind not from anything the truck was doing to make me think it's driving poorly.

Thanks for that detailed response.

 

[HankScorpio]

I was asking more so I know for piece of mind not from anything the truck was doing to make me think it's driving poorly.

Thanks for that detailed response.

I find myself hammering down the road at 2800 rpm plus sometimes, its fine, but when I let off and get it back under 2500 rpm everything just feels better. Trust your feeling.

 

[kennyw]

I have 3/4 ton axles... somewhere on this site or pictures I posted what gears it has. I forget at the moment

Edit. Found it... not sure what it reads. 4:10 I assume
View attachment 514474

41 ring gear teeth / 10 pinion teeth = 4.10 ratio
June 1976 production date.

 

[83ChevyK5Blazer]

I ran 37's and 4:10's for years on my 83, 2800 rpm is about 70, other than a drinking problem it was all fine.

 

[Stephen]

There's nothing in the trans or T-case to worry about, it's basically engine RPM that is sort of your limit. I say sort of because it's probably good for more time at higher rpm than you want to listen to.

You could be happy that it's not my dad's old cab and chassis K30 with a 454, 4.56s and SM465. That thing was running near 4K rpm at full highway speed. It was not comfortable.

 

[imiceman44]

There's nothing in the trans or T-case to worry about, it's basically engine RPM that is sort of your limit. I say sort of because it's probably good for more time at higher rpm than you want to listen to.

You could be happy that it's not my dad's old cab and chassis K30 with a 454, 4.56s and SM465. That thing was running near 4K rpm at full highway speed. It was not comfortable.

The last k5 I had with the th350 and 350sbc running at 3000 rpm to keep up 65mph it would overheat.
I could have put a bigger radiator or better fan, but I put 700r4 instead, best decision ever.
Dropped rpms, no overheating and picked up 3mpg savings

 

[Chickntrk]

I have driven all over in multiple trucks, none have had overdrive. Just returned from a trip to Maine which is about 11 hours of driving turning 2800-3000 RPM at 70-75 mph. Never had an issue and Id rather listen to a wound up engine than a lugging one.