Looking at a ‘76 how easy to add OD?

[Fishwater2002]

Are you saying that the transmission and transfer case have been changed ?
A Blazer/JIMMY in 1976 with a 400 engine would have only come with a TH350/203 combo - TH400/203 first year was 1977 and only in 3/4 & 1-Ton trucks and the TH400/205 setup wasn’t offered until 1980 ( and only in 3/4 & 1-Ton trucks ).

Since your JIMMY doesn’t specify a gear ratio code on that SPID that indicates that it has the standard gear ratio which is a 3.07 ( see pic of standard ratios ).

Adding an O/D to a 3.07 geared truck might put the RPM’s a little low and hurt the driving experience.

Take some good pictures of your trans & T-case and we can identify what you actually have and possibly explain the easiest route to a trans swap.

View attachment 533657

Serves me right, I googled it and the 1M40 came up as a T400 but I just saw the pics from the inspection and it’s definitely a T350 pan. The truck is getting shipped to me so I’m having to go off of google searches. I also didn’t see 3.07 listed for the standard ratio so that’s probably a pretty good gear with 33’s for highway cruising, I’ll be taking it to camp every weekend and it’s about 50 miles each way in two lane highway which as I mentioned above was not enjoyable with 3.23’s and 26” diameter tires…

 

[HankScorpio]

You need to forget about car ratios, 3.07 is the first thing to change. 33's on a carb V8 is going to feel very underpowered if that is the true ratio.

 

[HankScorpio]

Gear Ratio Calculator

Good gear calculator here

 

[tarussell]

Gear Ratio Calculator

Good gear calculator here

Great calculator !

 

[HankScorpio]

Great calculator !

Yeah, it's one of the best easily available ones.

 

[imiceman44]

Are you saying that the transmission and transfer case have been changed ?
A Blazer/JIMMY in 1976 with a 400 engine would have only come with a TH350/203 combo - TH400/203 first year was 1977 and only in 3/4 & 1-Ton trucks and the TH400/205 setup wasn’t offered until 1980 ( and only in 3/4 & 1-Ton trucks ).

Since your JIMMY doesn’t specify a gear ratio code on that SPID that indicates that it has the standard gear ratio which is a 3.07 ( see pic of standard ratios ).

Adding an O/D to a 3.07 geared truck might put the RPM’s a little low and hurt the driving experience.

Take some good pictures of your trans & T-case and we can identify what you actually have and possibly explain the easiest route to a trans swap.

View attachment 533657

You're forgetting something.
The 700r4 1st gear is deeper than the th350 1st.
It will be an improvement.
I still think a set of axles with 3.73 is a cheap way to helping with that.

 

[tarussell]

You're forgetting something.
The 700r4 1st gear is deeper than the th350 1st.
It will be an improvement.
I still think a set of axles with 3.73 is a cheap way to helping with that.

No doubt the 3.06 of a 700R4 ( if that’s what he will go with ? ) will feel much better than the 2.52 of a TH350 but all the remaining ratios will still feel lacking with such a low numerical axle gear combined with a 33” tire.
The drive ability will still take a hit after the initial help of the lower first gear ratio. Gotta keep that low power smog era SBC from excessively lugging too much.

 

[imiceman44]

No doubt the 3.06 of a 700R4 ( if that’s what he will go with ? ) will feel much better than the 2.52 of a TH350 but all the remaining ratios will still feel lacking with such a low numerical axle gear combined with a 33” tire.
The drive ability will still take a hit after the initial help of the lower first gear ratio. Gotta keep that low power smog era SBC from excessively lugging too much.

My point was that it wouldn't be worse but could offer some lower RPMs at higher speeds.
3rd would be the same as 3rd with the th350.
For a driver with 33" tires he definitely should have 3.73
If he gets a 700r4 then he could go with 410

 

[tarussell]

My point was that it wouldn't be worse but could offer some lower RPMs at higher speeds.
3rd would be the same as 3rd with the th350.
For a driver with 33" tires he definitely should have 3.73
If he gets a 700r4 then he could go with 410

With an appropriate final gear the 700R4 would be a very nice setup but if the 3.07 is kept ( I assume the O/P was going to keep it ) a 700R4’s 2ND gear to 3RD spacing is too much of a drop and a choked up motor will suffer in the top two higher gears in most situations.

I agree with ya’ that a 3.73/4.10 gear with adding a 700R4 would be a good driver.

Sadly most folks nowadays believe that lugging a motor is what’s supposed to happen instead of keeping the motor in a proper power band for efficiency.