Gears

[fnny6770]

My 1980 GMC 1 ton truck came from the factory with four 10 gears 400 engine and a th400 tranny, my brother put a 454 in it with a three speed manual transmission and it seems like the differential gears are too high, my question is what size differential gears would have came with a manual transmission?

 

[idahovette]

You are gonna have to define "too high".....too high engine speed(RPMS)? or it lugs the engine?..(doubtful) Please, more info

 

[Rusty Nail]

And pix or nobody will believe you...this  is the internet, after all!

 

[nvrenuf]

@fnny6770 there is no set ratio with auto or manual transmissions, a 3/4 ton (or 1 ton) could have come with 3.73, 4.10 or 4.56(rare). What actual ratio came in a truck is dependent on the options ordered.

 

[Shorty81]

My 86 3/4 ton 3:73, 208 transfer, 31" tires with the sm465 manual runs 2000 rpm at 55. I'm really happy with my gearing, I rarely get over 60 mph. If I need to creep around the woods I have low range and the creeper 1st gear.

 

[Old Guy Bill]

As previously posted we need more info..
Is it “Too high” when traveling in high gear, or “Too high” when trying to take off in low gear?
Please elaborate

 

[nvrenuf]

It should be said out loud that ratios that are high numerically are considered low and conversely ratios that are low numerically are considered high.

3.08 = high
5.13 = low

 

[fnny6770]

I misspoke, it seems like the gears are too low I haven't driven it in many years but it seems like at 50 or 55 mph the tack is anywhere between 25 and 3,000, my father ordered this from the factory so I remember the Gear ratio is 410, but pictures will have to wait because my truck is at my daughter's house 60 mi away or I might could possibly find some older ones to post but it just seems to me that 410 differential gears was because of the automatic transmissions gear ratio, it's a camper special

 

[fnny6770]

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[fnny6770]

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[fnny6770]

It's very Rusty and all of the factory badging has fallen off or been removed, did I mention it is a 4x4?

 

[fnny6770]

It's the only truck I've seen that came with shock absorbers, from the factory mounted in the bed of the truck that mount to the cab

 

[Camar068]

maybe drop a 700R4 or 4L80 transmission in it? It'll give you a 4th gear.

[edit] nevermind, you said it was a 3 speed manual.

 

[Rusty Nail]

Omg! Dude that's AWESOME ! Congratulations!

 

[Ricko1966]

maybe drop a 700R4 or 4L80 transmission in it? It'll give you a 4th gear.

[edit] nevermind, you said it was a 3 speed manual.

Actually,not a bad Idea. It started life as a th400.A 700r4,leave the pedals as is just a spring to return the clutch, the column probably wasn't changed. Then he'd have gearing for work and decreased rpm on the highway. But @fnny6770 any mods you make to slow the highway rpms down are going to be expensive and you will still have to buy gas. You will have to put a lot of miles on this truck to break even in gas savings.