Front axle swap?

This is an F134 Jeep. These Jeeps came with one of two axle ratios - 5.38:1 or 4.27:1. The amount of power available is rather low considering the aerodynamics of a Jeep. Wind resistance is a mighty barrier.

With the F134, your top speed will be limited regardless of what gear ratio you pick. With a high number (5.38) the top speed is enforced by maximum engine speed. With a low number (4.10) top speed is enforced when you run out of power.

Your top speed could be a little lower with the 4.10s than with the 4.27s or 5.38s. It's hard to predict exactly, and different owners will likely get somewhat different results depending on conditions and how hard they are willing to push the engine.

More technically, power is force times speed, or for an engine, torque times RPM. If torque were constant, higher RPM would always make more power. But it's not - torque starts to fall off as RPM increases. For the F134, torque starts to decrease after about 2000 RPM - look here
http://cj3b.info/Tech/EngineDyno.html
You can see that the Willys engineers only measured to 4000 RPM. It's all over by then - the torque curve is falling and the engine may go faster, but it's not going to make more power. And the very long stroke of the F134 means that the piston velocity is very high, along with forces on the rod bearings. Not good for long engine life.

But the central fact remains that you simply run out of power, regardless of the gearing. I have driven but never owned one of these Jeeps, but I gather that the best combo will be the 5.38s with an overdrive. When you are on level ground with no headwind, the overdrive will give you a little more top speed. And you can drop back to direct drive on a hill or facing a headwind.

 

Ask and you shall receive they say!

You guys are an abundance of information. I mean, holy smokes. I'm going to need so many more trips around the block to catch up!

 

That is the plan, as it sits.

 

Realize that a power steering pump is a parasitic load on the engine. Your engine does not have much power to spare.

Up to you - it can be done and has been done. But with your tires, I would go manual Saginaw. You get the tracking and precision improvement of a modern Saginaw steering gear, and with narrow tires, the effort is not excessive. You'd need to work a little more to parallel park, and on the trail in a cut-and-fill situation. Loose ground makes it a little easier. I would go with the Jeep bus wheel, which gives you more leverage than a passenger car wheel. Ratio of a manual Saginaw is slower than a power gear too.

 

Power steering is not really much load at all driving straight, but when you turn it will start taking HP away, probably up to 3hp at full turn. The generator probably takes nearly as much power when the lights and defrost are on.

 

I've swapped in a narrow D30 from a CJ7 under my CJ3A. It came with 3.XX gears, which don't work with my 5.38 gears in the rear D44. Since I've got an overdrive (which drops the revs 25%), I decided to stay with 5.38s. Just to be warned, 5.38 gears for D30s are not common and thus are expensive. New 4.xx gears would be maybe $150, but my 5.38 ring and pinion were $300.

I also threw on some aluminum spacers to make the rear D44 match the track width of the front, but it's not really necessary. Some old rigs have wider front tracks than rear for turning and stability.

 

I didn't even think about a power sag using a PS setup.

I'll search out a manual box and go that route, for sure.

Wowsa! Matching gears front to rear will be pricey but, it sounds like the proper setup. They say do it right the first time so, I'll pinch pennies and bite that bullet!

*so I won't need to add spacers to the rear to compensate for the inch and a half? It's perfectly safe?

 

For an old Jeep.

 

Lots of (nearly all?) cars have a wider front track than rear. Said to be intentional to improve maneuverability.

With a D30, the slightly wider front track makes your turning circle smaller, both because the wheel angle can be larger, and because of the narrower rear track. So it's an advantage, if the look does not bother you. Really, no one will notice unless they are another Jeeper or you point it out.

One exception is the J-truck, which has a slightly wider rear track.

 

Got it.

So, I'll hunt down a manual steering box. Do you suppose I'll have to modify anything in regards to the D30 with that or is it pretty straight forward mounting the box and ordering the proper pitman?

 

Wasting your time with a Manual Gear Box..........not much difference in force required to steer than what you currently have.

 

I disagree...made a HUGE difference with mine (I have 2.5" lift & 31" tires).

 

2x. The main advantage is about half as many places to develop slack even if the steering effort isn't that much less. IMO, the bell crank is probably the worst component and it's gone with the Saginaw. In short, manual or power, a Saginaw box usually points the tires in the direction you want them to go rather than needing a border collie to herd them there.

 

I had a 2a ross box and a v6 or m38 box. the v6 or m38 box was worlds better than the 2a box. I drove my present jeep around with a power saginaw box that was not hooked up to the P/S pump yet and it was not a lot of fun. I bet the manual saginaw box would bet quite a bit better than that. If OP didn't have the f head and had a couple free ponies like a v6 i would say go power and don't think twice. Since its the Fhead.....I would still go power.

 

I have also done several..........with D-27 axles......played with the geometry in all of the installs , Maybe a D-30 might help?...........Yes going down the freeway on pavement ....it's OK with small tires aired up.....once off Road in soft stuff or trying to park one on pavement , Not So........Never seen results that were worth the trouble and I also did my own years back and was disappointed.....great for upper body strength though!

"Steering effort" as John mentioned above is most important in my eyes!.....with the antiquated suspension not many go down the road straight anyway............Power is the only way!

 

My steering effort is much less than with the Ross box.
Another way to reduce steering effort is a 2 hole knuckle. The D30's already have that so you'd automatically gain that advantage.

 

Doug,

You may be on to something with the D-30 axle........my only conversions have been on the early closed knuckle axles..........not really sure if it's the steering arms and the two hole spindle or just the change over from the old D-27 version closed knuckle high friction balls and internal knuckle bearing cups to the later D-30 style open knuckle joints and more conventional ball joints they ride on.......but I can see where the D-30 would have less friction.

I just went and measured a D-27 spindle arm from center to center and it's 6.500" .........On a D-30 drivers side spindle at the steering arm it's only 5.750" that's .750 less mechanical advantage or leverage that should require more force.............on the Passengers side D-30 same 5.750" for the inside tie rod hole but the drag link is almost at 7.000"......so that 1/2 " would help some in the mechanical advantage department........but I'm really thinking the big help may be from not trying to turn that large spherical ball and seals and that heavy grease inside........notwithstanding the more modern ball joints the D-30 spindles swing on surely should help.............Interesting subject just the same!