Difference in Gear ratios

[jcondo]

I have stock 3.07 gears in my 77 k10, it sounds like its reving high at 50 mph.
Would higher gears allow it to not rev as high?
also since its full time 4x4 im assuming I have to change the front gears, but is there anything I need to do to the transfer case?
From what I can tell I have a TH350 that's a 3 speed.
Thanks in advance

[AcampoDave]

Have you confirmed your suspicions with a tach? I would want to know the actual rpms before all else.

[mongocanfly]

3.07s is a fairly high gear...meaning your rpm would be low at highway speed...is the trans slipping?...like Dave said...check the rpm...
And yes ...if you change the rear gears you'll have to change the fronts....the transfer case won't affect rpms...
What size tires are you running?

[jcondo]

Originally Posted by mongocanfly

3.07s is a fairly high gear...meaning your rpm would be low at highway speed...is the trans slipping?...like Dave said...check the rpm...
And yes ...if you change the rear gears you'll have to change the fronts....the transfer case won't affect rpms...
What size tires are you running?

I’m just doing some research atm. We are supposed to get a foot of snow today and tomorrow.
I don’t have a tach available currently but I planned on using one to check it.
Tires are 30x9.5r15.
I can feel it shift at about 25 and 35 mph but I’m not very knowledgeable when it comes to transmissions.

[mongocanfly]

With 3.07s/t350/30"tire you should be turning 1612rpm at 50mph
1612 is not high rpm...

[jcondo]

Originally Posted by mongocanfly

With 3.07s/t350/30"tire you should be turning 1612rpm at 50mph
1612 is not high rpm...

Thanks for the info. Once I get a tach and have a chance to confirm it I will let y’all know. Happy holidays.

[sweetk30]

what you think is high rpm has a lot to do with air cleaner and exhaust system mods cause they change the sound of the engine a lot .

as said best to confirm with a tach . if you want a good cheep small tack i have run this one for years and no problems. https://www.autometer.com/2-3-4-tach...ini-black.html can be had 10-15 bucks cheaper on auction sites all day long .

hose clamp to the column and she be easy to see and not block the speedo or fuel gauge .

also can you count the gears as it shifts ? maybe your not hitting 3rd gear and that's the problem ?

axle gears need to match all axles in the setup . t-case don't care what they are except they match each other . some axle combos wont match 100% but thats fine . example older dana 44 axles could be 4.09 or 4.10 and the rear could be 4.11 this is fine . what is NOT good at all is 3.07 / 3.73 or 4.11 / 3.42 like these combos would be very bad to try and not have huge problems.

[jcondo]

Originally Posted by sweetk30

what you think is high rpm has a lot to do with air cleaner and exhaust system mods cause they change the sound of the engine a lot .

as said best to confirm with a tach . if you want a good cheep small tack i have run this one for years and no problems. https://www.autometer.com/2-3-4-tach...ini-black.html can be had 10-15 bucks cheaper on auction sites all day long .

hose clamp to the column and she be easy to see and not block the speedo or fuel gauge .

also can you count the gears as it shifts ? maybe your not hitting 3rd gear and that's the problem ?

axle gears need to match all axles in the setup . t-case don't care what they are except they match each other . some axle combos wont match 100% but thats fine . example older dana 44 axles could be 4.09 or 4.10 and the rear could be 4.11 this is fine . what is NOT good at all is 3.07 / 3.73 or 4.11 / 3.42 like these combos would be very bad to try and not have huge problems.

yea I have an add on tach in my 80 Malibu, but I hardwired it in and mounted it more securely then with just zip ties, so ill purchase another one here soon.
There is nothing modified on this truck other then the exhaust heat pipe going to the air cleaner and the electric choke conversion kit when I removed the divorced choke. The exhaust is factory manifolds to glass packs and missing tail pipes from being rusted off. its a little louder then I want but im not to that stage yet.
As I said im still in the gathering information stage, so thank you all for the info and tips.

[cadillac_al]

People that are used to overdrive cars will think old vehicles rev too high. That's normal. My K10 with 3.08's will rev to around 3k rpm at 75 mph. 55 mph should be more like 2500 rpm. I took the tach out of my truck because I hardly ever looked at it after a couple months. When I robbed the tailpipes off my plow truck the drone was so terrible I had to put some tail pipes back on it. That was just moving it around the yard. I could never stand that drone while racking up miles.

[sweetk30]

glass packs + missing tail pipes = 10x more rpm than you are turning in your tach in your brain .

get them swapped out and also get some tail pipes on . if you can atleast do side exit it helps a TON on in-cab droan / noise levels . i learned this my self the hard way years ago . i didnt think it was bad untill all i did was add in a tail pipe to the same muffler and got it out from under the box and O..M..G.. what a difference that made in the driving of the truck for me .

[jcondo]

got the tach set up but noticed my front transmission seal is leaking, so I may just have the transmission rebuilt while I have it out. the P.O. said he has never had the transmission out of the truck, or the transfer case for that matter.
When I got the truck up to normal temp it was only at bout 6-700 rpms at idle in park.

[sweetk30]

700ish is fine in park . i have my fuel injected set up for 750 in park . butthats just me and my combo .

[Chevyrestorerman]

Originally Posted by jcondo

got the tach set up but noticed my front transmission seal is leaking, so I may just have the transmission rebuilt while I have it out. the P.O. said he has never had the transmission out of the truck, or the transfer case for that matter.
When I got the truck up to normal temp it was only at bout 6-700 rpms at idle in park.

At 50 MPH, what was the RPM with the new Tach ?

Was the transmission low on fluid causing the transmission to slip in 3rd giving you a bit more RPM ? Now a rebuild with a front seal/bushing failure.

[jcondo]

I didn't drive it, just started it up and let it run as I had the door sealed up for the winter. I had noticed the leak after I posted this question originally.

This truck is all stock, including the original a/c unit and w/e that coil thing is on the passenger side exhaust manifold.
After the holidays I plan on dropping the transmission and transfer case for a rebuild.
Thanks for all the help so far everyone.

[Chevyrestorerman]

Originally Posted by jcondo

I have stock 3.07 gears in my 77 k10, it sounds like its reving high at 50 mph.
Would higher gears allow it to not rev as high?
also since its full time 4x4 im assuming I have to change the front gears, but is there anything I need to do to the transfer case?
From what I can tell I have a TH350 that's a 3 speed.
Thanks in advance

Is this the same vehicle that had the vacuum line disconnected at the intake manifold that went to the modulator on the transmission. If this vacuum line is not connected and proper vacuum is not present at the modulator the transmission will not shift correctly causing the vehicle to "reving high at 50 MPH".

[jcondo]

No I never had an issue with a vacuum line issue.
I have found that the transmission has a front seal leak, so I’m gonna remove it and have it rebuilt after the holidays.
Thanks for the response tho Chevyrestoreman.