Rpm to high?

[Sspirawk]

72 c10 long bed 4 speed muncie. Like 3500 rpm at 65. Does it seem high? No idea on the rear end gears, 350 mild build. Any help is appreciated.

TiA

[ga-stepside]

Originally Posted by Sspirawk

72 c10 long bed 4 speed muncie. Like 3500 rpm at 65. Does it seem high? No idea on the rear end gears, 350 mild build. Any help is appreciated.

TiA

Assuming your tires are about 28" looks like you have a 4.56 rear gear...yeah too high for highway cruising IMHO.

http://www.advanced-ev.com/Calculato...ize/index.html

[davepl]

If you're going to be doing any amount of highway driving like that, you'll want different rear gears or an overdrive transmission.

Cheapest solution is to swap the whole axle, as setting up gears isn't easy.

[jocko]

What size tire do you have?

[HO455]

Welcome aboard.
I suggest you verify your tachometer's accuracy with a separate unit. (The factory tachometer in my Burban reads about 800 rpm high).
Post your rear tires size. If possible verify your speedometer's accuracy too.

[Sspirawk]

1. Thanks so much for the replies.
Ok tires are 275/60/15., appears to be a 12 bolt w/coils, thought stock were leaf?.

Also there is a massive splined pulley hanging on the end of the crank, guessing a blower belt pulley.

[rjs53]

275/60/15 is about a 28" tire. You could go with a 5 or 6 speed trans, but a 3.73 or even a 3.55 rear gear would be the least expensive way.ur the truck on a jack stand, spin the wheel one revolution and count how many times the driveline spins. If it goes around 4.5 times to the wheels one its 4.56 if it goes just over 4 its 4.11. I'm sure you get the idea. Its nice being able to run thru the gears sometimes, but not when you just want to cruise.

[jocko]

assuming your speedo is accurate (I'd confirm with a GPS before doing anything else), ga-stepside is spot on, it's a 4.56.

Red dashed line below is your config - even if you have a different muncie, and not a granny 4 speed, they all have 1:1 4th gear, so highway rpm is as shown. Chart below shows what you'd be looking at for RPM with multiple different overdrive transmissions - or if you changed to a 3.73. Or both. A couple notes -
- I wouldn't go with a T5 unless you were just cruising with it. They are great transmissions, I've installed one, but they aren't built for burnouts in a heavy truck or for trailering or heavy loads.
- If you want to stick with a manual trans, google on here for some NV4500 (or even 3500 if light duty use only) swaps.
- If you want to take the leap to an O/D automatic, most go 700R4 or 2004R. I only showed the 700R4, they are similar enough that you get the idea. Goods/others to both transmissions - but the swap is very common.
- Rear gear swap "only" will help highway rpm - but you will definitely feel the difference in the seat of your pants - as in, the thrill is gone. You will lose acceleration in 1st gear. O/D transmissions are great for keeping your bottom end acceleration snappy (most will increase it) and reducing highway rpm. In your case, however, a 4.56 is SO deep that an O/D trans will only do so much for you - AND, probably more importantly, it will almost render 1st gear useless (or even 2nd gear if you have a granny 4 speed) - you'll need to shift at around 5 mph into 2nd (or third in a granny 4 speed!) if you retain the 4.56 rear. Lots of things to consider. The sweet spot is, of course, the most expensive - i.e. O/D trans with 3.73 rear. Best of all worlds and why GM used this combo so often in later years.

So, a lot depends on what you want to do with the truck. Hope this helps! (oh, and by the way, coils were standard for your truck, leafs optional)

[Sspirawk]

Jocko:
Thanks so much, since I'm pretty much doing a frame off on it. I'm going to swap out the gears for a 3:73. I've always like a 4 speed. ThaT combo should still peel the rubber of the rims. I may consider a 5 speed will have to see a little further down the road.

Ss

[Barnfind46]

I had 4.56 gears in mine when I bought it. Difference is mine had a TH 400 trans. Engine ran 4,000 RPM at 55MPH with 28" tires.I now have a 2002 Silverado 14 bolt with 3.73's and 30" tires. Engine runs around 2200 RPM with same trans.Big improvement!

[70 shorty]

As others have said, make sure your speedo and tach are accurate before proceeding further. That being said, I run my Corvette at 3500-4000 rpm for hours at a time on the interstate and haven't had any problems. Granted, that puts me btwn 70-75mph and I have a 3.70 gear.

[jocko]

Originally Posted by Sspirawk

Jocko:
Thanks so much, since I'm pretty much doing a frame off on it. I'm going to swap out the gears for a 3:73. I've always like a 4 speed. ThaT combo should still peel the rubber of the rims. I may consider a 5 speed will have to see a little further down the road.

Ss

You bet. I think you'll be very happy with the 3.73, and it's the perfect step to an O/D combo down the road if you choose. Good luck!