Front and rear end questions

I was planning to use these in my M38A1 - photos posted at: http://s1267.photobucket.com/albums/jj542/p38l5/front and rear ends/

They were on one of my parts jeeps. Both have 11" drums. The front housing has 27A on it. The rear has 44. The small ID tag from the rear has the following: 924486 4.27 47-11

I have not removed the tag from the front, and have not pulled the covers.

What are they and are they worth using?

Thanks,

g

 

Those are stock axles for the CJ5. 11" brakes would be an upgrade. The 44 would be a 4.27 gear ratio. You will need to verify the ratio for the front. Needs to be the same. IMO both are very good axles for light to moderate wheeling.

 

Thanks Mortten. ID tag on the front says 47-11 4.27. I pulled the cover off the rear - numbers confirmed. I haven't pulled the front. Light to moderate will suffice for me.

I will be running stock M38A1 F head, tranny/transfer, and adding a warn overdrive. Will the 4.27 be too high?

 

There will be opinions all over the place on this. With the F-head you will not get over 60 MPH. The OD is best in the 40 to 50 MPH range as it cuts your RPM's. After 50 any advantage is decreased by the lack of power to overcome wind resistance. OD gear ratio will put you at about 3.20. I bought one for my 3B but it has 5.38's. I haven't put it in yet so I have no results but I like the idea of having it. You might want to see how the 4.27's do before sinking the money into the OD. They my work fine for you. OD can be installed at any time.

 

To increase Jeep's potential road speed the 4.27 final drive ratio became the standard for CJ's in November of 1962.
The T90 1st and 2nd gear ratios were simultaneously lowered so as not to drastically effect the take off ratio and crawl potential.
As of September 1st 1964 the now famous "Warn Overdrive" became ...
Approved "JEEP" Special Equipment"
According to Willys Motors Inc. this is recommended equipment for 5.38 and 4.88 to 1 axle ratios only.
According to Willys Motors do not use both speed increasers.

I fully agree with that claim.
The available hp of the Hurricane engine is not sufficient to hande the increase of overdrive resistance in addition to the higher axle ratio.
So either increase your Jeeps maximum speed with the 4.27 axle ratio or use the 5.38 with an overdrive.

Of these two choices my opinion is that the overdrive easily rates more efficient than the 4.27 axle alone because of the compound geariing advantage that allows one to better maintain optimum engine velocity for the work load.
The 4.27 with O.D. is geared too high (3.20 reduction ratio) when considering the Hurricanes meager output of mechanical force and lack of stability a higher speeds.
With Hurricane engines and O.D. I recommend 5.38 final drive.
With D225 engines and O.D. I recommend 4.89 final drive.

The 4.09 and 4.27 final drive ratios are compromise ratios.
They are not the best for street use nor are they the best for off road use.
The 4.09 and 4.27 final drive ratios are ideal for use without an overdrive.
These ratios allow decent road speed without excess crankshaft velocity yet they remain low enough for decent crawl ratios and big tires.
The 4.09 and 4.27 are IDEAL for use with D 20 transfer cases when the Jeep is to be used both on and offroad.

 

Thanks guys, this is great info. I had an idea the 4.27s would be too high. I like the idea of lower gears - 5.38 to maintain crawl and od to decrease rpm in the 40-50 range. I am not a serious off-roader, no hill-climbs, no rock-climbs, no air UNDER the tires, and I stay off the freeways. If I get the bug to do something more serious - I'll trailer it to wherever I need to go. I am assuming 5.38s will interchange with the 4.27s?

 

For both axles the 4.27 and 5.38 gears use the same case. You would need to replace the ring and pinion and have it set up properly.

 

Thanks Doug. I have 2 more sets of fronts and rears - I'll check to see what they have for gears. Would the ring and pinion from a 1953 M38A1 work, or would it need to be more recent?
Ken, If I change to 5.38s and add the OD, what gear ratios should I run in the the trans? I have a new/rebuilt trans/transfer sitting in my shop but I don't know what gear ratios were installed. I assume they are whatever is appropriate for a stock 1953 M38A1.

Thanks,

g

 

If you have a T-90 A1 made from 46 to 62 the ratios will be 2.79, 1.55, and 1.00. If you have a T-90C made from 63 to 71 the ratios will be 3.34, 1.85, and 1.00. With interchangability the best thing to do is count the teeth on the input shaft and cluster gear to be sure. T-90A1: 18 tooth input, 33 tooth cluster. T-90C: 16 tooth input and 35 tooth cluster. I think they lowered the gears ratios in the later transmissions becase they went to 4.27 as standard over the 5.38. Either one would work. A 1953 would have a Dana 25 axle, not a 27. The ring and pinion is different and will not interchange. You would have to use the entire Dana 25 axle or get a ring and pinion for the 27.

 

Thanks Doug,

I brought both the 27 and 44 into the shop this morning. They are going to pull them apart, clean them up and see what's good or not. I found powr-loks for both the 27 and 44. We should know soon if I will need new axles, I seriously doubt what's in there are the correct splines for the powr-loks, and they are going to order 5.38 gears for me. The drums are 11" and look good, but they have not been inspected very closely. I spoke with McRuff this morning and got a good education on steering and axles. My thanks to all of you guys for your willingness to help and share information. If you ever have an airplane question - run it by me - I'll see if I can answer it.

 

Beyond structural integrity the main difference between transmissions are the various reduction ratios.

Here are some basic general concepts for you to review:
A three speed transmission provides 3 gear ratios identified as 1st, 2nd and 3rd.
A truck type four speed transmission provides 4 ratios identified as Low, 1st, 2nd and 3rd.
All 3rd gears are a straight through drive inferring a 1 to 1 ratio.
This means all transmissions provide the same basic potential for top speed.
With various transmissions installed there is no difference of engine RPM when attaining top speed.

The Warn O.D. yeilds a 25% velocity increase. This is noted as a .75 to 1 ratio.
The engaged .75/1 ratio O.D. does effect the engine RPM in 3rd gear.
When engaging the O.D. multiply the selected transmission ratio, the transfer case ratio and the final drive ratio by .75 to get the overall drivetrain reduction ratio.

When driven on road 1st gear is used for TAKE-OFF.
A truck type Low gear is not normally used on the road for TAKE-OFF.
Depending on specific engine installed the TAKE-OFF reduction generally ranges from about 10/1 to a 15/1 ratio.
The standard TAKE-OFF reduction ratio for the Hurricane engine is approximately a 15/1 ratio.
Here is the early standard TAKE OFF ratio for use with Huricane engines.
T90 A 1st gear ratio x the final drive ratio = 2.798 x 5.375 = 15.039/1 TAKE-OFF RATIO.

A Jeeps CRAWL RATIO is the ratio providing the greatest reduction.
Low gear or 1st gear reduction ratio x transfer case reduction ratio x final drive reduction ratio = CRAWL RATIO
The optimum crawl ratio is mainly effected by the engines harnessed force and it is also dependant on several other factors.

 

Do you fly or wrench? My Dad had 2 Globe Swifts and a 180 HP Comanche.

 

A little of both, airline, airshows, some instructing. I had to quit a year or so ago for medical reasons. My last personal airplane was a 450hp Stearman.

g

 

Any updates?