'69 C20 Change Trans vs Rear End, or Both

[chevyremod]

I've just bought a 1969 C20 camper special that is stock with a 4 speed trans with granny gear. Also 350, 4b carb (edelbrock, had to replace the original), long tube headers, stock ac, pwr steering and brakes.
I'm looking to paint it a color that I want, put some wheels on it i love (5-spoke cragers preferably), change out the interior to a split bench seat, and use it for a regular if not daily driver.
I'd love to improve fuel economy, especially on the highway. I have no way to measure rpms right now but it seems pretty wound up at 70 mph.
I'm looking for an economical way to better my situation with mileage and drive operation. I'd love to be automatic but I'm ok with keeping the 4 spd forever.
Can you give me some suggestions for changes? Manual vs Auto, rear axle change etc.?

[67chevy_hotrod]

I have a 69 c20 and I had the same issue. Mine has a th400 that works a fine. I found a NP 5 speed( granny 1, standard 2,3,4 and overdrive 5th!!!!) but the th400 worked fine. And Ho52's are hard to get parts for and expensive. Needless to say I found a post Dana 60 with 3:54's and now I'm Rollin 65 mph at like 2500 rpm vs 3300! Whichever route you choose you will just be pleased with results lol. Rearend is less work as long as you can weld and do math!!

[chevyremod]

Never learned welding but can do math. From what vehicle am I likely to find a post Dana 60 with a 3:54?
I've heard so many different options and some say that if I am going to obtain any real improvement that I need to get a 5.3 L with a 6 speed automatic overdrive out of a recent chevy half ton.
My truck is as original from the factory as it could be at this age. The "service parts identification" label is still on the glove compartment door. But nothing appears to tell me what my gear ratio is. I guess I'll have to open the rear end. It probably needs service anyways.

[LongBox]

You can calculate the rear gear ratio. Your truck apparently has an open rear end, so you can jack up one side of the truck. Put a chalk mark on the driveshaft, and one on the rear wheel that's in the air. Turn the wheel one complete turn. Count the number of turns the driveshaft makes. I'm dimly remembering that you divide the number of turns by 2, and the answer is the gear ratio.

If my memory is wrong, someone please jump in and correct me.

Now, it's probably not a bad idea to pull the cover off the diff, and do a fluid change. the ratio should be stamped on the crown gear.

[toolboxchev]

I can almost guarantee you have a 4.10 gear set in the rear by the options list. They may have put in a 3.73 but that was mostly left for the big block trucks.

[Ken B]

I have 4.10's in my 70 Longhorn with 350 and 4 speed. It sounds as though you have 4.10's as well because my truck is at about 3 grand at 70. I don't like to run it at 3000 rpm's other than quick little burst's etc. I generally try to keep it at 2600 rpm's when on the highway. I have just learned to live with it, the slower speeds on the highway keep me out of trouble and I like the power of the 4.10's when I need it. I do drive my truck every day in the nice weather. I even took it on a 12 hr. round trip this past summer, slow but steady..

[chevyremod]

I don't plan on using it for hauling a truckload of wood out of the forest. I'd like to take it on a couple of long trips per year to a TX A&M game or two.
Though we Aggies love Chevy trucks we don't like Longhorns or orange. LOL.
Speaking of the long time rivalry between the Aggies and Longhorns.

[jeffahart]

Originally Posted by chevyremod

I've just bought a 1969 C20 camper special that is stock with a 4 speed trans with granny gear. Also 350, 4b carb (edelbrock, had to replace the original), long tube headers, stock ac, pwr steering and brakes.
I'm looking to paint it a color that I want, put some wheels on it i love (5-spoke cragers preferably), change out the interior to a split bench seat, and use it for a regular if not daily driver.
I'd love to improve fuel economy, especially on the highway. I have no way to measure rpms right now but it seems pretty wound up at 70 mph.
I'm looking for an economical way to better my situation with mileage and drive operation. I'd love to be automatic but I'm ok with keeping the 4 spd forever.
Can you give me some suggestions for changes? Manual vs Auto, rear axle change etc.?

You need to know your rear end gears and your rear tire diameter and your rpm at some baseline mph. You can hook a cheap temporary tach to you steering column. You can get larger rear tires to get you near the 3.54 range. It's an inexpensive way to see if gearing will get you where you want to be. But you need to know where your at now.... gears, tire diameter, RPM.

Can you post a pic of your truck, we all like pics!

[my67c20]

Many options come to mind. First is to look into a 700r4. This will require only mechanical skills, and will net you an overdrive trans, and may improve highway mileage. If you like the stick, and you don't plan on abusing it, look into the NV3500. This may require fabrication skills. A more heavier duty version would be the NV4500, and again may require fabrication skills. A more expensive option would be a gearvendors overdrive and you can stab this onto what you have, but will require some mods. I would look at some online gear ratio and tire size calculators. You really need to weigh the cost of upgrades versus the cost of low mpg versus how long you plan to keep the truck to see if the numbers make sense. These things are rolling bricks, and there are many threads focused on fuel economy, so spend dome time and search and read. Lots of good options, and even a good cost breakdown.

So here is some numbers to consider. For every inch in diameter your tire grows you gain 2 mph at a given rpm. For every inch your tire grows you reduce your rpm by 100 at a given speed. An overdrive transmission will reduce your rpm by 600. Changing rear gears to 3.42 drops rpm by 250, and 3.08 by another 250. Assuming these are available for your axle. Estimate gears to cost 1k per axle, or tires 1k per vehicle, or transmission 2k per vehicle, best bet is to go the tire route. Might be a dog off the line, but you have the granny gear, but you gain on the high side. Also with the gear ratio of the SM465, this may give you more range in 2 and 3rd. So @ 2500 rpm the max speed in 1st is 9, 2nd is 16, 3rd is 35, and 1st is 55. With 6" (34") taller tires @ 2500 rpm the max speed in 1st is 11, 2nd is 19, 3rd is 43, and 1st is 67. Just my 2 cents

[jocko]

You won't "solve" your fuel economy or rpm concerns with tire diameter. You get mathematically closer to what you'd want - but it's almost unnoticeable. With a stock 4.10 rear that came in C20s with small blocks (I do recommend confirming what you have. 4.10 would not be on SPID as that's standard for your configuration and absence of 4.10 or presence of a different ratio will let you know what it was born with - but do the tooth count or rotation method to get a feel for whether or not it's been monkeyed with over the years), you have two main options (and there is always a gv o/u as mentioned above, but they are quite pricey, so will focus on the two below)- and while either is sufficient, both would be overkill. Depends on what you are willing to sacrifice.

1) swap to o/d automatic. This is what it sounds like you prefer. Recommend a built 2004R. Check out Bow Tie Overdrives - and read the info on their website, even if you don't buy from them. If they are still in business. This option adds the o/d gear and a deeper 1st. Off the line accel improves slightly (not that you need that with 4.10s - but at least you retain hauling torque IF you ever need it) and you get about a 30% reduction in highway rpm.
In other words,you don't give up anything.

2) swap in a 3.54 Dana 60. There is no 3.73 route for C20 (ring & pinion swap only) that I'm aware that is easily obtainable. 3.73 is a C10 12-bolt thing. They (3.54 D60s) came behind this era's big blocks. Decent cruising rpm reduction at highway speeds - but you lose your inherent low end torque multiplication. You might not think you care, but it is what a C20 was made for and you might miss it, even on a trip to Home Depot.

I don't believe cragar ever made 8 lug 5-spoke s/s wheels.

[chevyremod]

I have LT235/85R16 tires and have done the count on my rear end.
For 10 rotations of tire the drive shaft rotated 19.75 times. So, what is my ratio?

[chevyremod]

Originally Posted by jeffahart

You need to know your rear end gears and your rear tire diameter and your rpm at some baseline mph. You can hook a cheap temporary tach to you steering column. You can get larger rear tires to get you near the 3.54 range. It's an inexpensive way to see if gearing will get you where you want to be. But you need to know where your at now.... gears, tire diameter, RPM.

Can you post a pic of your truck, we all like pics!

I have LT235/85R16 tires and have done the count on my rear end.
For 10 rotations of tire the drive shaft rotated 19.75 times. So, what is my ratio? And, here are some pics:

[jeffahart]

Originally Posted by chevyremod

I have LT235/85R16 tires and have done the count on my rear end.
For 10 rotations of tire the drive shaft rotated 19.75 times. So, what is my ratio?

I think you've made a mistake, this shows a 1.97:1 ratio, super tall gearing. Once you figure your rear ratio then we can use the tire size to figure your effective ratio.

OH, and... Nice Truck!

[chevyremod]

Originally Posted by jocko

You might not think you care, but it is what a C20 was made for and you might miss it, even on a trip to Home Depot.

I don't believe cragar ever made 8 lug 5-spoke s/s wheels.

I really don't want a heavy hauler so I doubt I'll miss it.
I've not been able to find a cragar SS 5 spoke or look alike for an 8 lug but I do love the look. I actually didn't know that before I bought it but if there is a route to get the SS 5 spoke when I change a rear end, I'd take it. The next best look is the 2010 chevy 5 spoke with 8 lug. I like that look too.

[chevyremod]

Originally Posted by jeffahart

I think you've made a mistake, this shows a 1.97:1 ratio, super tall gearing. Once you figure your rear ratio then we can use the tire size to figure your effective ratio.

OH, and... Nice Truck!

I did it twice. 20 rotations of the drive shaft for 10 rotations of the tire.
I'm headed to buy some rear end fluid to do a change and actually eyeball the inside. Looks like its leaking anyway. Here's some pics of the rear end and numbers on it.
OH, thanks. I plan to paint it Aggie maroon. LOL. I'm also planning on removing the side trim. I just like the sleek look without the trim.

[zosoppp]

Originally Posted by jeffahart

I think you've made a mistake, this shows a 1.97:1 ratio, super tall gearing. Once you figure your rear ratio then we can use the tire size to figure your effective ratio.

OH, and... Nice Truck!

If the other tire was on the ground then multiply result by 2. that would be about 3.94.

[jeffahart]

Let's assume now you have 4.10s. With 32" tires. Stock I think was around a 29" so I think you may be effectively at around 3.55 or there about, but you can run it through a calculator on the internet. But verify again you have 4.10s for sure.

Once you get your highway RPM at say 65mph, then you can start playing with the numbers and try to figure a tire and gear combo. And maybe you can get where you want without transmission swap. But your tires are already tall. Use the converters on the internet; there are Ratio RPM charts available.

[chevyremod]

Based on the stamp on the gear in the rear end, I believe I have 4.10.
5 08 73 DANA 30360 B3D83X 41-10

[jeffahart]

Yes 4.10. 41-10 is 41/10=4.10 41 ring 10 pinion.

Now you need a tach, I use column mount tach myself. And then you can intelligently proceed with your analysis on your desired highway RPM. Example is: you like the sweet spot at 55MPH and wish you had that RPM at 65MPH... what gearing will it take you to get you there. You could work it out on paper but, if you have a tach you know for sure.

[jocko]

So, here is what you're lookin at for keeping your 4.10s or for swapping to a 3.54. (235-85-16 is a 31.7" dia tire) with various trans swaps:

Note - for highway cruising speed's sake - just use the TH400 numbers to represent your granny 4-speed. Your 4-speed and the TH400 (and the TH350 or a factory 3-speed manual) all have the same final drive ratio of 1:1 - so the cruising rpm is accurate. Also, keep in mind that the mph shown on your speedo may not be accurate since you've changed tire size slightly from stock. Use a gps to know your actual speed when assessing your rpm.

Also note that changing to 3.54 (only) still puts you are 2439 rpm at 65 mph on the highway (2814 at 75 mph) whereas 4.10s with a 2004R swap puts you at 1893 rpm at 65 mph (2184 rpm at 75 mph). This makes a strong case for a trans swap over just a rear end swap. And if you did both, you'd be cruising at only 1634 rpm at 65 mph - which is probably starting to get TOO low (numerically) and you'd risk lugging the engine. I think the 2004R or 700R4 swap without a rear gear change is your most desirable option. But, if someone handed you a 3.54 rear end for free, well, you be the judge.

Stock tire size was 29.8" for a C20 - changing to a 31.7" tire only changes effective final drive ratio to approx 3.85:1. Anyway, regardless of what it does for you - if you liked it, you wouldn't be asking these questions, so a 31.7 dia tire (which is 1.9" larger in dia than stock) doesn't buy you much - it only drops your rpm by 180 at 65 mph when you go from a stock 16.5x8.75 tire to a 235-85-16.

Also note!!! bLah blah BLAh blah. Enough info - go make that trans swap!

[chevyremod]

Originally Posted by jocko

I think the 2004R or 700R4 swap without a rear gear change is your most desirable option. But, if someone handed you a 3.54 rear end for free, well, you be the judge.

go make that trans swap!

I'm sold on the stats. I should switch out the Manual trans to an automatic and go to the 2004R.

I'm good mechanically. There's not ever been much I haven't been able to figure out or do. I'm completely comfortable changing out a rear end. However, I've never removed or installed a transmission.

What would you recommend?
1. Purchase a rebuilt 2004r from a reputable dealer? If yes, who do you recommend? or Buy from a salvage yard? If yes, how do I identify a good transmission? If I am to install, I would love to have a step by step or video. Do you know of one?
2. Have someone else do it?

[RustyBucket]

"OH, thanks. I plan to paint it Aggie maroon. LOL. I'm also planning on removing the side trim. I just like the sleek look without the trim.".....

just one old guy's opinion.... AND it IS YOUR truck, but .... so many of 'em got worked hard and beat up and that's a nice straight truck with good trim. Seems almost sacrilegious to pry it off and plaster or weld up the holes. It's been on there nearly 50 yrs. They put it on the year I graduated from high school, when dinosaurs roamed the earth and Moby was a minnow.

[Bigdav160]

Nice to have the Dana axle.
Most Chevrolets came with the Eaton. Not much for parts with the Eaton.
Plenty available with the Dana 60.

[Ken B]

Originally Posted by chevyremod

I don't plan on using it for hauling a truckload of wood out of the forest. I'd like to take it on a couple of long trips per year to a TX A&M game or two.
Though we Aggies love Chevy trucks we don't like Longhorns or orange. LOL.
Speaking of the long time rivalry between the Aggies and Longhorns.

oh. ok.

[RustyBucket]

P.S. you don't have the original blue steering wheel in nice shape, do ya?