The Stovebolt Site Forums The Parking Lot Big Bolts 261+clark 5 spd

working on a 52 1.5 ton chevy. its already got a 235 transplant, I picked up a nice complete 261. I would like to swap in a a 5 speed OD. Will a clark be easier to install verses an nv 4500? If so what model should I be looking for. This is a working class truck and I am really wanting to wxpand the operating range without swapping rears.

A Clark is easier, but has its own issues. Clarks were used in a lot of the 50's and 60's 2 tons or larger GMCs. The bolt pattern on the bellhousing is the same as the sm420. Plan on cutting up the driveline to fit.

They are not sychronized transmissions, so plan on a lot of double clutching if you go that route.

Jeff

OD trans.' need to have an "O" in the MN, and the OD position will be FWD and right, if not, direct trans.

The Clark's do have a strange shift pattern, they take some unlearning to drive. A 207v is 1:1 in 5th. My 207vo is something like 1:0.86 in 5th and the shift pattern looks like this.
2 5 R
3 4 1
Luckily I only use 1st when heavily loaded. As mentioned, mine is also unsychronized, but to me that's not a big issue. Just like the shift pattern, it quickly becomes second nature.
Scott

Sorry Jeff but the Clark 5 spd. has a much bigger 6 bolt pattern than the SM420's 4 bolt pattern as is the pilot hole a half inch bigger.

Grant, I just gave one away a few months back and it shared the same bellhousing as the sm420. It came out of a 1953 GMC 450 series. I believe it was a 207VO model. It didn't use the SAE pattern. Maybe later models did, but not these ones.

Jeff

There are different size/model Clark transmissions, some are bigger than others.

Grigg

so should i be looking for a 207vo or a 264vo? or a new process 540go14? thanks for the replies by the way.

All in all the least intrusive swap would be a Clark 207vo or smaller if you can find one. The older overdrives are usually hard to near impossible to come by. The 207 should have a smaller retainer that I believe would work in your bellhousing, and there was one on ebay for a while..
Most of the np540 transmissions that I have come across had a different bolt pattern, larger and longer input shaft, and are 1:1 an od NP 540/541 trans is scarce today (like chicken teeth lol). Something to look into would be fitting the gear vendors over drive for the older Dodge NP435 to a 540 since they shared the size and spline on some of the output shafts like my 542GL.
Like the NP trans most of the larger Clark trans had the large 1 1/2 10 spline shaft, and the OD versions of those are also hard to come by.. not to mention parts are getting harder to find as well as support info.
I think you would be happier with a NV4500 trans for your swap. They are plentiful, parts can easily be found, shift nice, and have a higher O/D ratio than their older counterparts (.75) which would be nice with your current gear ratio. once again you are not going to have a direct fit swap, none of the NV4500 transmissions share a bolt pattern with any of the 4 speeds. 93 to 95 GM transmissions have the right input bearing retainer pilot diameter of 5.125" but I can't rember if the input shaft is long enough for an adapter plate to match it to your bell housing or not. Gotta do some measuring to see. Looking foward to see what you do!

Here is a good source for NV4500 info, I think may be helpful.
http://www.high-impact.net/transmission_and_gear/nv4500.htm

W/ an early GM 4500, don't need adapter, just redrill mount holes, w/ Dodge 4500, use Approx. 1" thick adapter Dodge/GM; Dodge has longer input shaft.

thanks for the tips. Ill weigh all my options and make a decision. It already has a brown lipe with about .85 OD. Im lookin to make a double OD. I see the gear venders unit is offered for the sm420. I might go that route.

Are you even sure a 1 1/2 ton pushed by a 235 can even handle a double overdrive? I would think with that much weight, the only way you could manage it would be downhill with a tailwind.

Jeff

DITTO. Not enough engine.

well I am upgrading to a 261. I run bobtail mostly I figured given the rpms with the .85, it would not be too much with a double OD but I have not done the math yet. I know it wont pull anything with a double OD. It did pull a 41 john deere model A in OD with a 235 which surprised the hell out of me. The .85 just is not high enough for me. I could always use the GV unit and remove the brown lipe if its too much.

Here's a gear calculator
http://www.onlineconversion.com/bigger_tires.htm
For double OD just put the second one in the "TransCas Ratio:" spot.

Another option that's a whole lot cheaper than a GV Overdrive is swapping the existing Auxiliary or just the gears inside for one with 0.73 ratio.

Also what about axle gears, do you have any faster choices there?

Grigg

not without swapping the whole rear axle. its currently got the original single speed with the 6.17 gear set. I recently built an AD chevy for a fella and swap the rear axle and added the front disc brakes per your recomendations. that particular truck was repowered with a 350, nv4500, and a dana 70HD. Thanks for the help with that btw. I am just not ready to tackle that swap again so soon after the last one lol.

An original 2 speed will have a faster ratio than that on the high side and could be an easy swap.

Did you put up any pictures of the work you did on the other truck, I'd like to see more about the front disc brakes, old I'beam and new P-30 spindles if I remember right.

Grigg

ill dig em up and try and figure out how to post them. Thats right I made some bushings as was suggested and used the factory king pins and axle with the p-30 spindles. easy to do and worked great.

Grigg, isn't the 2 speed high gear about 6.11? That amount is so negligable to not even count.

Even if you do add the 261, I still don't believe you'll have enough added power to push a double overdrive.

What is it you exactly want this truck to do?

A 235 or 261 can easily go the speed limit or a little more with an overdrive.

Jeff

I see no reason to put an OD in a 1 1/2 ton. A direct will go as fast as you want to go. Just step on the gas a little harder. These old engines will cruise at 3,000 RPM. If you are trying to get down to 2,000 like modern vehicles you will be lugging them.

well id like to do 65 with ease. right now its turnin and burnin to do 60. Ive been running a ford 2 ton with a two speed rear and 3 spd brown lipe. Im getting ready to take it down and repaint and repower with a 255 merc. so I am trying to at least get the same top end out of this chevy. when not working the trucks I really enjoy just driving them. Its nothing for me to drive 60 miles one way. So i like having enough gear to work them and when Im not loaded I want to do highway speeds. my ford can do 60 pretty easy but its got a 5.83 rear and .74 OD. Once it hits 2400 rpm it quits pullin. Its got plenty of throttle left just not enough torque. I figure a 261 should make a bit more power than even the 255 merc I am plnning on building

My info has the Merc 255 at 125 hp at 3700 rpm and 218 ft lb torque at 2100 rpm.

The Chevy 261 has 148 hp at 4000 rpm and 235 ft lb of torque at 2000 rpm.

Mike B

well according to the calculator grigg linked to, at 65 even with a double OD rpm will be 2400. thats still honkin n my opinion. according to the 261 power numbers above thats just above the sweet spot. It might work. Of course the faster you go th more air you gotta fight. Ill do some more number crunching or just get a brown lipe with a taller OD.

A gear calculator doesn't take into account rolling resistance and 5K pounds of weight on an unloaded truck, give or take. Just something to think about.

Jeff

right that is what i was refering to by fighting the air. these things have the air dynanics of a brick and given enough speed thats like pulling a load at a slower speed.