The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 61 Apache Overdrive

Hey everyone,

I have a 61 Chevy Apache 4x4 with the 6cyl motor and the 3 speed trans with granny gear. I have red a post about adding a stock overdrive to the trans for extra gears. I was wondering if anyone knows of a part number or a way I could find one of these? I really need to find one for I cant really drive my truck until I find one! Any help would be great.

Why cant you drive it? Post some pics i love the 4bys

When driving it over 45mph the revs are WAY to high, the motor just screams. Ill drop some pics for ya soon.

Do you have a 3/4ton or a 1/2 ton

3/4 ton on another thread some said there was a over drive that bolted right up to the back of trans

Probably a Gear Vendors aftermarket overdrive. Very pricey. The only other options would be to go to a later 5 speed overdrive, like the NV 3500, NV4500, or T5, the MY6/A883 4 speed, or the SM318/SM326 or BWT85N with the BW overdrive. The SM318 would be the easiest swap, but will lose the low first gear.

just slow down. they were not made for highway cruisers, but work trucks. , if you are just going to use it as a pavement queen , put a t5 in it
ron

Yeah the problem I have is that my house is located on a highway where the speed limit is 55mph. I would like to use this beautiful truck as a "daily driver". So a trans swap would be the best option? Do you think that would be cheaper/easier than swapping out the gears front and back? Also there is not a stock overdrive add-on??? I had seen it in another post. That person had said that you could find those stock add-on overdrives for around $200.00 used. Hummmm what to do!?

Hey Longbox55 it was a thread that you posted on where you were talking about the add-on overdrive, you posted pics of the overdrive also. Would this not work with my application?

there is a stk 3 speed overdrive trans that will bolt in. they do show up on ebay once in a while. they were used more in cars . they were avail from 55 models and up.
there is an older and newer version (around 65-66) which are more desirable. either will do the job though
ron

Most likely, the trans pictured was the SM318 with the Borg Warner overdrive that's in my own '55 1/2 ton. The overdrive isn't so much of an add on as it is a slightly different transmission. The main transmission case has a few differences from the standard 3 speed, mainly a shorter mainshaft, extra oil return holes, and a provision for the reverse lockout rod. However, that trans is a direct bolt in for the standard 3 speed, and should work just fine in your application.

The stock 3 speed with overdrive is a T85. They came in an early model with a 4 bolt side cover that didn't have a synchro first and a later(post 1966) 7 bolt side cover that did have a syncro first. I have the later one that I put in my 1966 GMC with a 305 V6. The overdrive is a .7 to 1 so it will reduce your RPM's by 30%. Here is the original literature on the early model T85:

http://speedprint.com/deves50/overdriveindex.php

Read all about it!
Regards,
Steve

You say that you have a 3 speed w/ granny gear. That is a 4 speed, not a 3 speed. SM-420 in Chevrolet speak. As far as add on overdrives for $200 bucks, good luck. I've done it, but more by luck than by common availability.
The way I did it in my '61 K10 was to purchase a Spicer 2021 over/underdrive and put in in between the the trans and the transfer case. Super short driveshaft. It works nice. I bought 2 of them. The first was $300 bucks and it howled like Banshee when at speed. I found another one on eBay and paid $200 foir that one. They are not common. Go ahead and search eBay right now. I'll wait.

I didn't think so.:)
You could use a lever to engage, but I went with a PTO pull knob and cable as it was less destructive to my original truck.

The OTHER way to get overdrive with an SM 420, is to get a Ranger overdrive. this unit goes between the trans and engine. It moves your trans, and thus your shifter, back 7 inches.
Info here for Ranger OD.
Summit carries them for just under $1,400 bucks. Not cheap, but not terrible either.

Frankly, I don't think a T-5 or Borg-Warner is going to stand up to a 4x4 drivetrain. B-W's are not particularly strong. And t-5's are going to push your transfer case WAYYYY back. I not sure how long the NV 4500 is but I suspect that it's longer than the sm420.
Here's mine. Just in case you wanted to see. It will hit 90 mph pretty easily. All factory drivetrain other than the Spicer 2021. 6 cylinder.

In a Ford, yes. But not in a Chevrolet. GM used their own transmissions, the SM318 and the SM326, with the same overdrie tailshaft that was used with the T85N. The only GM application of that trans was the "Dearborn transmission" option on the mid '60s Pontiacs.

thanks everyone i think i will just change the gears in the rear ends i have a winch that works on a p.t.o off the transfer case so if i had to move the transfer case it would be a pain

Rick

You may run into some issues with changing the gear ratios in the differentials, mainly the rear, if they are the factory axles. The front shouldn't be too much of a problem, as it is the closed knuckle Spicer/Dana 44. Plenty of gear choices available for that one. However, the rear will be an HO52. There are no aftermarket gearsets avaialbe for that differential, the only option is to find the third member from a '68-'72 C20, usually with a 350 and automatic, which has the 4.10 gear. The only other choices are a 4.56, which is most liley what you have, or a 5.13, usually found in 1 tons.

either that your upgrade your axle assemblies, gives you disc brake and p/s. not a difficult job
ron

how do i tell what rear end i have i know it is a 10 bolt. so i cant just change ring and pinion gears?
Rick

how do you do that
Rick

You have to change both of them obviously, but what's not so obvious, is that the factory did not put the SAME ratios in both the front and rears. My '61 for example has a 3.90 in the rear and a 3.91 in the front. Look at GM specs through the years and you'll find the same situation on them all.
I hope you don't start to change the whole mess around just because it's "easier". Originality WITH functionality isn't easy, cuz everyone would do it. Like having your cake and eating it, too! I hope you get it to where your satisfied.

These trucks were not made for speed. The only good way is for you to upgrade to newer axles and if you do ill buy your original 1s

are you sure it is not 3;90 in the frt and 3;91 in the rear. you want the little higher gear in the frt
ron

Yup, I'm sure. 3.91 is higher.

3.91 is higher numerically but lower in ratio and you want a higher ratio in the frt
eg 4:10 frt, 4:11 rear
ron

OOOps! you're right . I was wrong. It's actually a 3.92 in the front and a 3.90 in the rear. I told those idiots at GM not to do that, but they went ahead and did it anyway. Who knew?
This information provided to you from the 1960/61/62 ST-9 Service manual supplement for tilt cab/ 4 wheel drive/ and Powermatic transmission.Section 16-16.

I realize that I am only a wrench fetcher compared to you being a shop shark.
are we talking apples to apples or to oranges.
it apperars that you are talking meduim duty truck-(tilt cab-4 x 4-powermatic trans, which in this application would be a napco)

"
4WD high/Low (locked) forces both front tires to turn the same rotation. Thus you get axle binding when making turns (outter tire turning faster than inner tire on the same axle). Also, on some older generation 4x4's (not sure if this still applies today), the front axle has a slightly higher gear ratio than the rear axle, thus causing a bind in the transfer case. So you can imagine that you can have one or two areas where binding can occur and shorten the life of the drivetrain if you were to drive your vehicle in 4WD locked mode on normal dry surfaces. When driving in snow or wet surfaces, this allows you the drivetrain to have some slippage but still maintain traction. But this mode should only be used for short term as binding on your drivetrain components still exists. I am sure you have experienced your D doing its jerky jerky motion when trying to make a turn from a standstill. The jerky jerky motion is caused by the front tires as the inner tire is spinning same rotation as outter tire. As the inner tire has a shorter distance to travel, it is trying to outpace the outter tire."

in our trucks K10-20 the ratios for these vehicles were as listed
3.73:1 frt 3.73:1 rear
4.10:1 frt 4.11:1 rear
4.55:1 frt 4.57:1 rear
ron

i have been told i can not change the ring and pinion gears on my 1961 k20 they don't make gears for it is there a full rear end from another year that will bolt up

You should be able to use the axles front and rear from the '73-'87 K/V20 or '77-'91 K/V30. Use caution when looking the mid '80s K/V20, some of them used the 9.5" ring gear 14 bolt, which is a semi float light duty. Ideally, the K/V30 axles woild be best combo for overall strength, as they are a Dana 60 front/ GM 14 bolt full float rear (some used a Dana 70 in the rear, usually duallies and tow truck package). The 3/4 tons used the same rear, but wiht a Dana 44 up front, simlar to what you already have but with open knuckles and disk brakes. Going to either front axle will gain you a tighter turning radius in addition to the disk brakes. You woul need to swap to a dual circuit master cylinder, preferrably with power assist, if you use the disk brake axle.
If you only want to swap the rear end, the 14 bolt from the years mentioned will do, wouldn't have to be from a 4x4, 2wd will be fine. You will want to consider swapping gears in the front to match, which shouldn't be a problem as they are still available fro the front diff.

I am not talking medium duty. This is for the 60 61 and 62 half ton 4 wheel drive trucks. After '62, you are certainly entitled to your opinions and facts, but pre '62, and NOT Napco, the 1/2 tons were the ratios specified above, namely, 3.90 and 3.92. rear and front respectively. I guess I'm going to have to send you a copy of the manual's page , cuz so far, you're not believing me.

I don't.as there is a rule with p/time 4 x4s.
full time 4 x 4s are different ratios are the same frt and back
you did mention tilt cab and they don't make a tilt cab in light duty and any above a 1t was a med duty and would have been a Napco application

3:90 ratios were more common from 73 and up I believe

http://public.bay.livefilestore.com...T9720D9mZr-Kg/Truck%20Axle_ID.jpg?psid=1

there was a 3:90 listed from from 60-63 for rear axle but no mention of frt axle
ron

http://www.6066gmcguy.org/DriveAxle.htm
this link shows that 60-62 K10s had a 3.92:1 ratio. which way it was it didn't say. the rule of thumb was though that the frt diff was higher geared (lower numerically) than the rear diff
ron

for those years will they bolt right up to my truck

I ran into similar issues with my '61 K10 when I started restoring the driveline a few years ago. I had the original Eaton rear and closed knuckle Dana/Spicer 44 in the front. I ended up just replacing them with 10-bolt corporate axles out of an '88 K10 Suburban with 3.55 gears. As others have mentioned, you get a tighter turning radius and disc brakes in the front with that type of conversion. The axles themselves are the same tube diameter and hub-to-hub width as the originals. However, you will need to cut the spring perches off the rear and weld on new ones at the correct width and angle for your truck. I mainly made the swap for the disc brakes, but the taller gears should help with drivability. I'm not too worried about acceleration with the SM420 and T221 still intact. I went with the 10-bolt axles due to their availability and lower cost, but you have other choices, like the Dana60/14-bolt full floating combo, if you're concerned about durability and strength. Of course, your milage may vary.

Regards,
Matt

thanks Matt do you know what other year rear ends that would work besides 1988

It's my understanding that any axles from our era on up to the late 80's/early 90's (with the caveat that they're from a similar grade vehicle) will be more or less a bolt in swap. I wouldn't call myself an expert on it by any means, but anything from the mid 70's on up would still fit the truck and give you better choices for gearing. Be sure to double check the track width on any axle you're thinking about using. You also may need new U-bolts to mount the axles. I don't remember the name of the company, but I had a firm in Canada make me new bolts to replace the originals. The front axle from the '88 had the same tube diameter, but the differential casing was forged a little differently and required a change in U-bolts. A minor setback, but still something to be mindful of. Usually if you pick axles from the eras I mentioned above from similar grade vehicles you won't have much trouble with the swap. Just be prepared to change the spring perches in the rear and perhaps some of the U-bolts up front. Hope this helps!

Matt

'87 would be the last year you could use axles from a Pickup, the '88s went IFS and have a wider rear axle. Blazer and Suburban, as well as 1 ton Chassis cab/Crew Cab models, up to '91 can also be used. They went IFS in '92.