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  #1  
Old 01-23-2001, 12:32 AM
River Beast River Beast is offline
 
Join Date: Apr 18, 2000
Location: Lakewood, Calif
Posts: 11,642
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I read your post on Veepster's thread about the 18...I assume it has a pass/pass output due your stating your going to use a offset QT rear end. This has got me thinkin'.....

...This could be a LONG thread... sorry.

I like to do alot of research before jumping into a project... so here goes:

1. you said the D18 guts will fit a D20 case... as long as the locating bore diameters are the same, will it work.

2. I know I would need to find an output shaft to swap into my TH400 to get away from the QT 10 spline shaft, so is there a particular tailshaft for the 18 for a TH400? Or will an outshaft of the same diameter for a d20 output shaft work with the D18?

3. What years/vehicles are there to choose from to find the "right" D18" if there is a particular one to get for our FSJ's?

I am looking into this for a couple of reasons that bother me.... strength of the chain in the QT with a P/T to withstand the torture of turning 39.5's with 4.89 gears and the overall driveline slop that P/T kits amplify due to the 10 spline shaft wear on the mating gear. I don't mind it too much but it does pose some concern. Having no front shaft right now and locked in E-Drive tends to lead me to believe that the slop will be there even after the P/T kit install. I figure if I'm going to spend around $400 on a P/T... why not look into a gear driven case that may benefit me more in the long run with more strength from the start and longevity.

Thanks for taking the time... I appreciate it... any links to info and good gouge you may have would be a serious "added bonus" for me to "educate" myself in this potential swap in the future..
BEFORE I go further with my driveline mods.

Much thanks again....

------------------
Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
39.50x15x15 Super Swamper TSL's
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/spazz4life
My E-mail: monster_fsj@hotmail.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[This message has been edited by River Beast (edited January 23, 2001).]
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  #2  
Old 01-23-2001, 02:09 AM
scotty's Avatar
scotty scotty is offline
 
Join Date: Jun 12, 2000
Location: dayton,oh,45431
Posts: 6,627
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1) the spicer 18 case was used from about 1942 to 1971 and came in 3 basic types: 1)from 42 to 45 the shaft that the intermediate gear spins on was small-3/4 of an inch. 2) from 45 to 53 the intermediate shaft was bigger at 1 inch. 3)from 53 on up most cases used the biggest shaft at 1.25 inches,which is the same as the intermediate shaft in a dana 20,and whay you must use this case for purposes of swapping 18 guts into a 20 case. it possible to find a medium shaft in some post 53 cases,so double check before handing over any non refundable cash. you can measure the intermediate shaft easily without case disassembly,as you can see it on both sides of the case.on one side it is retained by a bolt and small piece of flat metal. the 20 shaft is retained the same way,if youve ever examined a dana 20,then hopefully you know what im talking about.

ok,other than that,the indexing bore on the front of the case is one of 2 diameters.prolly most 18s out there use the "small" 3 inch indexing hole.with this case,the input gear must be pulled from the rear before the case is removed.in this style,the locating bore in the xfer also doubles as a bearing retainer. the dana 20 and supposedly some later versions of the 18 use a "large" 4 inch locating bore.in this style,the gear remains bolted to the tailshaft and fits thru the hole when the case is pulled. if you were lucky enuff to find one of these,it is a direct interchane with the 20,and no case swapping would be needed.pretty much the only reason to swap 18 guts into a 20 case is to get the large bore,so if you happened upon an 18 with a 4 inch bore,you should be able to swap the input gear,and bolt it right on to the the factory th400/20 adapter.

the other ting to remember is that the 18 uses a different input gear,so you must get the input gear with the xfer case.in a jeep application,the dana 20 uses an input gear with 6 internal splines. all 18s also use an input gear with 6 internal splines,except for those attached to a t14 tranny.for some reason,the t14 used a 10 spline shaft,instead of the 6 spline. my 18 came from a t90,and the input gear was a direct swap onto my t18 tranny.

*********

2) for case swapping,it doesnt matter which index hole the case has. what is important is to find a post 53 case with a 1.25 inch intermediate shaft,as this is the size the dana 20 uses. it is just like rebuilding an 18,except put the parts into a freshly cleaned 20 case instead.no wierd machining or anything. the one thing that i did learn the hard way: if your case has the drum e brake on the output,you must drill and tap a hole on the side of the 20 case for the fill plug before case reassembly. with the e brake style output,the speedo and rear bearig retainer are in the way of the stock fill plug on a dana 20. i noticed this little bit of info AFTER i got it all back together,and am still debating if i should take it apart again to fix it,as right now ive just a rubber plug stuffed in there. i think it will work,but im not real happy with it.

one other rebuild tip,leaving out the interlock pill between the shift rails in the front bearing retainer will let you access low range while in 2wd.

an 18 case that comes from a cj will likely have the drum e brake on the output.i have seen 18s that do not have the drum brake,supposedly they came from willys trucks,wagons,and some wagoneers.

you will need to find a factory dana 20 adapter and tailshaft.the 18 and 20 both share the "texas" bolt pattern,so they are both compatible with the factory 20 adapter.

you will need to count the internal splines on a factory th400/20 input gear before you can go any further.i assume it also has 6,so an 18 input gear should swap right on. maybe someone with a factory th400 and 20 can verify-kenall,used to have a factory 20/400,maybe hell know.

********

3) other than that,look for a post 53 case with the big shaft(1.25").assuming the th400 20 tailshaft is a 6 spline,look for the 18 on a tranny other than a t14.if you do not want a drum e brake output, look for it in a bigger rig. if a case is out of a vehicle,all you need is to verify the internal splines on the input gear,and the intermediate shaft diameter.

i think thats about it.as long as the th400 uses a 6 spline output, it should be an easy way to get a gear driven xfer that matches your rear axle. the hardest part will honestly be swapping tailshafts in the tranny,and the hardest parts to find will defiantely be the th400 adapter and tailshaft.18s were use in alot of jeeps from 53 to 71.so you should not have any prollem finding an 18, or a 20 case to swap guts into.

any other ques?

scotty


[This message has been edited by scotty (edited January 23, 2001).]
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  #3  
Old 01-23-2001, 07:23 AM
River Beast River Beast is offline
 
Join Date: Apr 18, 2000
Location: Lakewood, Calif
Posts: 11,642
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Thanks a million Scotty... a wealth of info I really needed to continue my research in this area... I wanted to make sure of something:

Is there a strength issue between the 18 and the 20? My goal is to keep the driveline in line with the offset axles I have for my QT.... my angles are extreme enuf the way it is now! With this in mind I "assume" the 18, from what I have read so far has the same passenger side offset outputs for front and rear ...is this corect?

Also, Dave sent a link to this site: http://www.novak-adapt.com/

I read alot of good info in the site including the Novak #124 adapter kit to go from the TH400/QT to a TH400/D18/D20...all is included with the adapter kit to incl the tailshaft needed.

Take a look at it if you have time and see what you think... it's $495 but may be worth every penny if the right case can be found...

thanks greatly...

------------------
Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
39.50x15x15 Super Swamper TSL's
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/spazz4life
My E-mail: monster_fsj@hotmail.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"
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  #4  
Old 01-23-2001, 03:50 PM
scotty's Avatar
scotty scotty is offline
 
Join Date: Jun 12, 2000
Location: dayton,oh,45431
Posts: 6,627
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in theory,the 18 will be noisier and gear wear alittle faster,since in 2wd the gears are transfering power from the outputshaft over to the rear output,unlike the dana 20,which couples the rear sliding gear directly to the input gear for "straight flow" of power thru the case.

on the noise issue-a trasfer case would haev to be REALLY loud for you to hear it over 39 inch swampers

on the strength,alot of guys at gravelrama,and other mud bog/sand drag type events run an 18 behind 1000+ horsepower engines.the dana 300 is rated at 600 ft-lbs of input torque,and i assume the 18 and 20 to be not far off from that.alot of people that ive talked to have extra 18 cases because they swapped in a small block chevy,and figured the an xfer that came behind a flathead 4 popper wuld not last,so they collected extra ones. some of these guys have been trail riding flatfenders with 350s and 383s with 33s and 35s for over 2 years with no prollems whatsoever from the xfer.tri county gear does make a steel girdle that bolts onto the bottom pan,and rear cover to strengthen the case,wihch is really the only week link.18 and 20 cases ive heard are prone to cracking in this one certain area where there is not alot of metal between the bottom oil pan hole and the hole on the rear of the case,tho ive never actually talked to a person that this has happened to. i would have gotten one for mine,but i think it prevents me from using my PTO,so i didnt really bother with it. if you want to check it out their website is: www.tricountygear.com if you can dig up the dec 99 issue of 4wd and sport utility,there is an excellent article on installing the 3.15 tera gears into an 18. also the june 2000 issue of petersons 4wor has a good article on the 18 called "the best transfer cae ever" both of them helped to convince me this was the way i should go,instead of the standard dana 20.

i do not want to offend anyone running a QT,but in my honest opinion,i think an iron case,gear driven xfer will hold up alot better infront of 39 inch tires. i think that $495 spent on an adapter is better spent than $400 or more on a part time kit.

the novak kit looks like a good deal,and considering that youre unlikely to find factory stuff for less than half of that,its prolly not such a bad way to go. i have heard that the factory adapter between a th400 and 20 is a week link,and likely to crack or break. i dont know how true it is,but aftermarket kits from AA or novak supposedly have addressed that issue and are stronger than stock,so that may be one other thing to look into and consider.

from the looks of the kit,it may even work with a small hole case,so you wont have to worry about guts swapping. tho,from a strength standpoint,youll still want to use the later case with a big intermediate shaft,as these are definately the strongest version.

the only other thing to consider is where the shifters may come thru the floor,dont know if there would be seat interfearance or not behind a th400. if it came down to it,i could tell you how to modify the shift rails slightly so that you could use the currie twin stick dana 300 shifter to move the shifters forward to a more favorable spot.i wont really know if ill doo this,or use the stock 18 levers,until my tranny is actually in. i think my levers will be pretty far back,but mostly because im using a long t18 with a six. yours prolly wont be back as far as mine,and even still,i dont really think ill have a prollem if i bend the levers straight up,instead of how they bend alittle backwards in stock form.

let me know if theres anything else...

oh-almost forgot-yes,both outputs are offset to the passenger side,rear directly behind the front im really looking forward to the offset rear. i have alot of faith in the strength of my amc 20,but the diff is BIG.i should be able to cruise thru alot deeper ruts with an offset 44 than i could a centered amc 20.
------------------
scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

T18/dana-spicer 18 with drum E brake and PTO,and offset dana 44 swap very soon
BIG tow truck PTO winch and full roll cage install shortly thereafter
searching for jeep 4.0 six engine

now we can do some 'wheelin!


[This message has been edited by scotty (edited January 23, 2001).]
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