The Stovebolt Page Forums Home | FAQ | Forum | Swap Meet | Gallery | Tech Tips | Events | Features | Search | Hoo-Ya Shop
Work those trucks!




Share what you're up to this summer!

Stovebolt Site Search
 
Old Truck Calendars
Months of truck photos!
Nothing like an old truck calendar

Stovebolt Calendars

Check for details!


Who's Online Now
5 registered members (DaveV, 3800GUY, MikeE, 5 Window 9434, 1 invisible), 369 guests, and 3 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums48
Topics116,443
Posts926,239
Members42,439
Most Online940
Apr 5th, 2017
Image Posting Policy
Previous Thread
Next Thread
Print Thread
Page 1 of 2 1 2
SM420 - Swap or Gear Vendor Overdrive #1324447 Mon Sep 02 2019 04:16 AM
Joined: Sep 2018
Posts: 38
N
Noonan Offline OP
Wrench Fetcher
I would like to ask for input on the options that are available when replacing an SM420 and maintaining the strength and durability if not exceeding it while increasing highway speeds at a suitable RPM.

At this point Differential Gearing is not an option that I am ready to explore.

The first thing on my list is purchasing a Gear Vendor Overdrive unit. Although I would like to explore the options of a newer 5 or maybe even 6 speed Manual Transmission?

Right now I have a Small Block Chevrolet (SBC) mated to the original SM420 in a 1955 2 ton truck. I am working towards building a truck that will do long highway runs with a goose neck hauler (Even if it happens to be at a slower pace than the heavy haulers that are coming out now 60 years later.

I did find a bit of information regarding someone installing an Eaton 5 speed transmission behind a SBC which came out of a 1984 chevrolet C something or other.

Anyone familiar with any model of old truck I should be searching out/researching for a good manual transmission to snag as an alternative to the Gear Vendor Overdrive unit?

Thank you !






Last edited by Noonan; Mon Sep 02 2019 04:20 AM.
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324454 Mon Sep 02 2019 11:30 AM
Joined: May 2005
Posts: 9,133
G
Grigg Offline
.
What truck and engine?

I haven’t used a Gear Vendors unit but some friends have and won’t again. In their experience a lot of money for not a terribly robust OD if using a truck as a truck. They thought failure was brought on by holding back with the engine on down hills.


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324465 Mon Sep 02 2019 01:06 PM
Joined: Jun 2011
Posts: 2,846
E
EdPruss Offline
Shop Shark
NV-4500 should give OD. Be careful, normal 5 speed trans' that have OD added where 4th gear was located, NP-540, Clark, IHC, etc., do so by removing that gear, thus leaving a large gap in ratios just under direct. A two speed rear helps sometimes.

Eaton makes several OD trans, however many use SAE mounting systems. There are, however, bellhousing adapters that go from SAE engines to conventional flat trans' mounting systems. I have several if you would like a px.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324471 Mon Sep 02 2019 01:42 PM
Joined: Jun 2005
Posts: 155
W
whateverpratt Offline
Shop Shark
Don't use gear vendors. It's way overpriced for what it is, and it won't hold up if you are actually going to be hauling like you say.

The simplest old school swap will probably be a clark vo transmission which will be a 5 speed overdrive. They are kind of rare, but they turn up every now and then. I'd like to hear from someone who has experience with the older ones because I'm curious if they will bolt to an sm420 bell.

One obvious choice is an nv4500. You can find these in '90's to 2007 chevy pickups, and they will bolt right up to a small block, but you will need to remove your bellhousing crossmember. If you want to keep your bellhousing crossmember, you will need an adapter plate to mate the transmission to the original bell housing. I did my swap this way nv4500 with sm420 bellhousing

Another option is the spicer 3053a which is an overdrive 5 speed. I've seen those transmissions adapted to chevy motors. Again, bellhousing crossmember removal

I just posted a transmission in the parts for sale forum. It's an eaton fuller fs4005b with all the factory parts to bolt it to a big block. It would be a good choice except for the lack of an overdrive and bellhousing crossmember removal

If you want an overdrive fuller transmission (apart from some of the newer units they've been putting out), you need to step up to a 6 speed, but that makes the weight go up as well. Their smaller 5 speeds weigh 230lbs which is in the nv4500 range as far as weight goes. The 6 speed overdrives weigh around 350lbs which is in nv5600 territory, but I would choose that over an nv5600 any day.

Another option would be to try and adapt a g56 or zf6 to your motor. Those are both 6 speed overdrive transmissions that are reasonably light.

If you are still reading, haha, I would suggest swapping your sbc for a 12 valve cummins (you should have room in there), and mating it to an fso6406 or fso8406. If I couldn't find a decent fso trans, my second choice would be a g56. Both of those transmissions will bolt to the cummins with factory parts, and you would end up with a simple, reliable, and strong drivetrain.

Last edited by whateverpratt; Mon Sep 02 2019 01:42 PM.

'66 c10 rust bucket, 350 nv4500 stock bellhousing, '85 c30 front suspension, h072 rear axle with 3/4 ton rear coil springs
'67 cj5 225 oddfire motor, time for disc brake conversion, offset rear dana 44, intermediate pedals and steering upgrade
'48 3804 frame and bed + '52 6400 cab and front clip + 4bt, need to put them together
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324475 Mon Sep 02 2019 02:12 PM
Joined: Dec 2015
Posts: 1,986
69Cuda Offline
Big Bolt Forum Moderator
Advance Adapters sells the Ranger Torque splitter. It gows in front of the transmission, between it and the bellhousing. Your speedo and park brake remain intact. I just put one in my 58 2 ton. I am running a 327 that was in the truck when I got it. I dropped from 3600rpm @ 60 mph down to just under 3000rpm.

That said, mine is an older cast iron one (no idea how old, or what shape the insides are in, I just put it in along with the trans that was attached when I bough it!) Mine added some noise and vibration but, I believe a lt of the noise is the transmission. One of these days, I will pull it back out an pull it apart to replace bearings in both trans and OD. We hauled our 35' vintage travel trailer about 7 hours away in July with it and had no problems. We are heading a couple hours north of here with it later this week.

https://www.advanceadapters.com/pro...overdrive-27-with-a-4686-retainer-index/


Mike

1955 Chevy 6400 ex-flatbed (no bed now!)
In the Stovebolt Gallery


1958 Chevy 6400 flatbed W/dump
In the Stovebolt Gallery

1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
In the Stovebolt Gallery

Sufficient unto the day is the evil thereof
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324483 Mon Sep 02 2019 03:09 PM
Joined: Feb 2004
Posts: 19,025
H
Hotrod Lincoln Offline
Boltergeist
The Gear Vendors unit is basically the same Laycock OD that was installed in 1950's and 60's European and British cars like the Jaguar, Austin-Healey, Volvo, etc. It's not terribly rugged, and it's very expensive to repair. It uses a cone clutch to engage the OD and it has its own small hydraulic pump built into the unit to provide pressure to apply the clutch. It didn't work well 50 years ago, and I haven't seen much evidence that any upgrades have been made to the 1950's technology. Run, do not walk away from that one!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: SM420 - Swap or Gear Vendor Overdrive [Re: EdPruss] #1324526 Mon Sep 02 2019 09:05 PM
Joined: Sep 2018
Posts: 38
N
Noonan Offline OP
Wrench Fetcher
Thank you all for the information ! Wow !

I will do a bit of research on the NV4500

@Edpruss

Can you explain this a bit better for me I'm not familiar with these terms

"There are, however, bellhousing adapters that go from SAE engines to conventional flat trans' mounting systems"

I actually have a Corporate 2 speed rear in place right now that I will most likely lock in high gear.
I also have a spare set - Eaton 2 speed rear with the proper 6 bolt pattern that I will swap in when I am ready to purchase updated rims and radials.

@Whateverpruss

Do you happen to know what vehicles used the overdrive fuller 6 speed transmissions that you had mentioned above ?

Who makes the g56 or zf6 transmissions? What vehicles might have run these?

I definitely wont be going to a diesel engine anytime soon.

@69Cuda

I am looking into the "Chevy Ranger Torque Splitter Overdrive" that you have sent me as well. Looks like it could be a cost effective method of doing things until there is no way around a swap.

It would be nice to have an updated gearbox moving forward.

There is a a lot to think about here

Thank you all again




Last edited by Noonan; Mon Sep 02 2019 09:10 PM.
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324538 Mon Sep 02 2019 10:39 PM
Joined: Sep 2018
Posts: 38
N
Noonan Offline OP
Wrench Fetcher
Has anyone come across the addition of some sort of E-brake assembly when running a NV4500 ??

I am really liking what I have read so far regarding the NV4500.

Readily available. Relatively inexpensive to purchase Re-manufactured.

All sorts of online support on swaps and tech !

Has anyone come across the addition of some sort of E-brake assembly when running a NV4500 ??

Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324585 Tue Sep 03 2019 01:53 AM
Joined: May 2005
Posts: 9,133
G
Grigg Offline
.
An NV4500 from a 90’s GM 3500hd or a step van (both with 10 lug wheels and therefore disc brakes rear) come with parking brake on the transmission.


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: SM420 - Swap or Gear Vendor Overdrive [Re: Noonan] #1324596 Tue Sep 03 2019 02:32 AM
Joined: Jun 2005
Posts: 155
W
whateverpratt Offline
Shop Shark
Grigg is spot on with the ebrake applications. I've only seen one for sale that has the ebrake on it, but they are out there.

Those fuller 6 speeds came in all kinds of trucks. A lot of guys will buy a used '90's fl70 (freight liner) just for the drivetrain (cummins 12 valve and fuller 6 speed). Otherwise, hit the medium duty junkyards.

ZF makes the zf s6-650 and s6-750 (zf6 for short). These were used in ford trucks, but they were also used behind the duramax and the chevy 8.1 (496 big block) until 2007. The chevy versions are more rare, but they can be found. A chevy zf6 would bolt right up to your motor and only weighs around 230lbs.

The g56 is a Mercedes transmission that Dodge has been putting behind the cummins in their trucks since 2005. It weighs about the same as the zf6 and is constructed similarly as well.

Easiest swaps will be nv4500 and Chevy zf6 since they will both bolt up to your small block without adapters.

The main advantage of a 6 speed is that you don't have the bad 3-4 split that you see in all the 4 speeds as well as the nv4500. It's not a real bad split unless you are really hauling a lot of weight.


'66 c10 rust bucket, 350 nv4500 stock bellhousing, '85 c30 front suspension, h072 rear axle with 3/4 ton rear coil springs
'67 cj5 225 oddfire motor, time for disc brake conversion, offset rear dana 44, intermediate pedals and steering upgrade
'48 3804 frame and bed + '52 6400 cab and front clip + 4bt, need to put them together
Page 1 of 2 1 2

Moderated by  69Cuda, Grigg 

Home | FAQ | Forum | Swap Meet | Gallery | Tech Tips | Events | Features | Search | Hoo-Ya Shop
Powered by UBB.threads™ PHP Forum Software 7.7.3