Functional Differences Between 1956-57 And 70-71

So I have a question. Is there any functional (like weight carrying ability, towing capability, etc) difference between a 56-57 CJ-5 and a 70-71 CJ-5 given all other equipment like drive train is the same?

My Jeep is built on a Modified 56-57 CJ-5 Frame it has been boxed in the front and rear the rear cross member has been moved 2.5" forward (my tub is a 2A) I have the same springs and shocks as a 56-57 the Axles are a Dana 25 in the front and a 30 spline flanged Dana 44 in the rear (5.38 gears) I have rear E brake 11" x 2 Brakes from a 68ish Wagoneer. Cross over Saginaw 525 Manual Steering with all new steering shaft and column. So is there any reason that my useful load and towing capacity wouldn't be the same as a 70-71 given the same or better engine performance?

A 48 CJ-2A has a useful load of roughly 800 lbs the 70-71 CJ-5 with a 134F (rated 75 HP My 134L will have approx. 90 HP as built) has a useful load of over 1400lbs Just curious how what I have would compare to a newer version.

 

I've never considered a jeep as nothing more that a 1/4 ton vehicle . and might have towed maybe 450 lbs with a motorcycle trailer / 2 on trailer

 

That's nice but I am interested in their actual capabilities. Factory Specs are what I am interested.

The Military ratings for a M-38 is 1200 payload and a 2000lb hwy tow rating with a top speed of 60mph
The 1971 4cyl CJ-5 is rated at 1477 payload I can find no published towing ratings but again the factory lists top speed as 60 mph (its actually faster)

 

Doesn't really matter what someone thought was realistic 60 years ago if you have worn out springs and a motor that has a lot of miles and is putting out 30 horse power like most F-heads today.

 

My opinion is that 90 hp is a bit overly optimistic for an L-head. 90 hp from a heavily modified F-head could be done, but I doubt an L-head would ever approach that without spinning it to 6000+ rpm.
I know the racing Jeeps over in Naples, FL are running F-head power are a bit over 100-115 hp, but these are 10:1+ compression, big cams that won't idle under 2000 rpm, roller rockers, and straight headers. Oh, they are turning them to 7000+ rpm for this power. This type power is not useable for hauling loads or pulling trailers considering the power band starts above 4000 rpm.
I'll be putting one of these back together when I find another block and crank to build up, and I will have a dyno sheet.
-Donny

 

Well I would hate to think all that time I spent taking automotive tech in college was going to waste.

A 134L stock makes 60 BHP change the compression ratio to 7.2-1 increase the displacement 6cu in and you get 70-72 HP Computer spin balance the complete rotating assembly and you pickup another 3-4 HP change to a Tri Y Header type exhaust with a 2.25" pipe and a flow through muffler and you get another 3-4 HP Plus an increase in mid range Torque. Remove the fan and you pickup 5-6 HP. Change to a proper designed Aluminum intake manifold with a Weber DGV 32/36 progressive two barrel and another 2-3 HP use a Vacuum advance distributor with a Magnetic trigger and a MSD-6A spark box indexed spark plugs and a High output coil and you see 2-3 more HP Add in a ram air fresh air intake system and you see another 2-3 HP add them all up and pretty soon you get to 90 HP.

No I have a 134L with everything but the Block Rods and Crank. New with machine work done by a shop specializing in Willys flat heads and racing engines (some diversity there huh) Basically a NEW engine with all the above and a few more improvements. Everything in my suspension is new and much of it has been upgraded with stuff of my own design.

 

My Question was comparing a 56-57 NEW CJ-5 to a 70-17 NEW CJ-5 are there any functional differences as to load and towing.

 

I believe the differences/improvements in towing and hauling ability between the two model years would be mostly as a result of the improvements to the axles assemblies and the brakes. The 70-71 had the flanged rear 44 and 10" brakes vs the tapered 44 and 9" brakes.

Perhaps there were improvements to the rear drawbar design and the entire frame as well in terms of thickness of the metal. This I don't know.

More or better bring options in 70-71 may also be a factor.

3 speed vs 4 speed transmission could, and likely would, affect the manufacturer's advertised towing ability.

Whatever the case, whatever the year of the early cj, I, personally, would not be comfortable towing or hauling much more than the weight of the JEEP itself (and this would probably concern me a bit, actually) considering the short wheelbase, smallish brakes (even the 10s are small for towing) and the 4 banger. Particularly on the interstate or anywhere where speeds would exceed 40-45 mph.

We've all seen the pictures of the old 2As pulling a hay wagon. That was on the farm or maybe across town. Same with the CJ5 with a tow boom on the back pulling a Hudson across the service station parking lot. But I doubt nobody back then would have tried either of those tasks at highway speeds then much less at modern highway speeds where if you're not doing 70, you're getting passed by everybody.

 

I'm usually more concerned with what's going to tow my Jeep, not what my Jeep can tow...

 

I will be towing a 800-1200 lb GVW two wheeled trailer equipped with the same tires and wheels as on the Jeep and electric brakes. The "truck" under the trailer will be adjustable to get the proper balance and tongue weight. The trailer will only be about 3-4" wider then the Jeep tub (including the Tires which will be the same track as the Jeep) the body of the trailer will be 60" wide 40" tall and 72" long. An off road-able travel trailer of sorts I have designed.

I am looking at 450lbs of people 75-80lbs of extra fuel and spare tire maybe 150-200lbs of gear and then a 150-200 lb tongue weight. For a total Jeep load of 850-950lbs Well under the 1971 spec's of 1477lbs useful load for a CJ-5.

The Jeep will also have a structured Aluminum hard top. Which will have the added benefit of improving the drag co efficient especially since the little trailer will just about hide behind the jeep. I estimate the hard top and roll bar as well as structural improvements that have been made to the Tub will increase the Curb weight by 200 lbs

All my weight estimates are on the heavy side (sadly except for the People weight we are both FAT LOL)

I plan on taking some very long trips 3-400 mile type days on the road. Some freeway mostly state hwys and lesser roads. I drive dump truck 8-10 hours every day for work so being over taken and slow acceleration combined with a kidney killing ride is normal for me.

Virtually everything that could matter in my Jeep is either New, Upgraded, Or completely rebuilt. And everything was done with the final goal in mind.

 

With the 134F it lists 4.27 Mine will be 5.38" with a 30% ATV (from Herm the OD guy) Overdrive which with 29" tall tires will give a 2600 rpm at 60mph

 

I hate to be negative but thinking that you are going to achieve 60 mph with an F head towing that much weight is incredibly overly optimistic.

 

All up Jeep and trailer will be in the 4200lb ball park

A 62 Wagon with the 134F has a curb weight of 3400 put 4 adults and a couple suitcases and you have the same 4200 lbs Are you saying a 62 Willys Wagon powered by a 134F with a HP rating of 75 would not be able to run down the hwy at 60mph? And yes I know towing requires more HP then Hauling.

I have some experience towing everything from flat towing with chains, ropes towbars, and tow dollys I have pulled trailers from a 1000 GVW harbor freight flat bed to doubles 40' and 28' and 53ft chip trailers Baja bugs and every POS car or truck we had as kids to running low boys with huge equipment loads. I've driven everything from a lil Indian Mini Bike to 96' long 105,500 GVW Hay semis and currently make my living driving a 2016 Kenworth T-800 Columbia Dump truck and 4 axle pup trailer also at 105,500GVW

The first truck I ever drove on the road was a 1946 Ford 2 axle farm truck hauling 16 tons of Pole beans to the cannery when I was 14 and working on farms. It had the most worn out 239 Flat Head V8 you can imagine having been in constant farm duty since bought new in 46 I was driving it in 1973-74 And while it was only slightly over loaded (about 3 times what it was supposed to haul) it made it to 50 mph just took a while.

 

OK this went way off track all I wanted to know was how a 56-57 would compare to a 70-71 I wasn't looking to get into bench racing.

 

Your trailer sounds like the modified teardrop trailer I have in mind for a future build.

My M100 trailer weighs around 500# unloaded. I have filled it (and then some) with green fir rounds (filing in the spaces with limb wood) and the Fhead in my A1 tows it nicely. fully loaded, the trailer weighs around 1500#. On flat or rolling roads, I can drive as fast as I do when the trailer is not hooked up. But with the extra load, I slow down for safety reasons. I can "feel" the trailer while driving- but that's to be expected, as the trailer weight is around 2/3rds of the jeep's weight. But it's not really a big deal. I stop the whole thing with 11" drums in front and 9" in the rear brakes along with a bit of compression braking. No brakes on the M-100.

I live on an island where the top posted speed is 45mph. I don't routinely drive interstates and only exceed 50 when I am off island, so I don't think in the way most people do about getting places in a hurry. We don't need overdrives, big horsepower, etc. So I sorta see your situation out there towing a trailer with a jeep the same way; you won't be fast, but so what if you get passed by everybody else? So what if it takes you 5 hours to get to that day's destination instead of 3.5 hours? It's the journey you're after

I think you need to be mindful of the jeep's short wheel base. The rest you'll just work around. Take the lesser traveled roads, including the graded ones.

Edit: Tim's comment further on got me thinking- I'll be going with a 1 piece, flanged full floater on the A1. with that improvement, I'd never worry about a load taking out the rear wheel bearings. I'd want that upgrade prior to going long distances with the jeep, trailer in tow or not.