Which trans to use?
Which trans to use?
- Thread starter dmiller
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pc79cj5
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- lake alfred,fl
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- 1979 cj5 amc 360, borg warner t18a, dana 20, 3.55 gears, acme hardtop
Which 4spd
Thats the question there. Most Cjs of that era used the T-18 4 spd. There were 2 different ones though. Earlier ones up to 75 used a close ratio T-18 . This Transmission had a first gear of 4.02. From 77 to 79 they used the wide ratio T-18a wich had a granny gear of 6.32 wich is great for nice slow crawling. You of course have a "76 wich could have eiter , or some swapped in Transmission as well.
Your in Allentown? Im in Slatington and work at the Nestle Purina plant on 309. Do you have the Transmission out?
dmiller
Jeeper
I don't have it out yet. Just picked up both this weekend. I am new to jeeps so I may have some novice questions. I'll have to check the Transmission numbers and let you know.
No problem. I pmd you my number. 
Saddle Tramp
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- 1978 CJ5, AMC 401, CJ T18, Scout Dana 300, 2-1/2" Lift, Locked
I assume of course that we are talking about a CJ T-18 . Sometime during the 1976 model year run, no one seems to know exactly when, Jeep switched from the close ratio (4.02) T-18 to the wide ratio (6.32) T-18 so hard telling which one you have. Everything on the drive train is interchangeable between the two jeeps with few exceptions. The 1979 bell housing will be drilled for both the CJ T-18 and the standard 3 speed T-150 and both bell housings will bolt to either the AMC I6 or V8 as will the clutch components.
The reason to swap in the T-18 behind the AMC 304 is crawl ratio. For example the stock T-150 /Dana 20 crawl ratio is: 2.99 (T-150 1st gear) x 2.03 (Dana 20 ) x 3.54 (most likely axle gear ratio if not changed from OEM for 1979 to 1979) = 21.49. Of course a lot depends upon how you use your jeep, and 21.49 may be OK for some but not for most of us. When I bought my 1978 CJ5 it had a T-150 /Dana 20 combo with 4.56 gears. The crawl ratio was 2.99 x 2.03 x 4.56 = 27.78; still not good making it uncomfortable to just idle along on a rocky dirt road. However if you install a T-18 wide ratio things improve dramatically: 6.32 x 2.03 x 3.54 = 45.42. There is no hard and fast formula for what the perfect “crawl ratio” is but I consider anything around 50 as decent. Rock crawlers probably want twice that but again it all depends upon your use of the jeep. The wide ratio T-18 is so much more desired over the close ratio because: 4.02 (close ratio low) x 2.03 x 3.54 = 28.89.
If you want a lower (numerically higher) crawl ratio the obvious option is to change gearing in the axles but the other option is to put a Teralow or JB Conversions gear lowering kit in the Transfer Case and keep the taller (numerically lower) gears in the axles to help the streetability on the asphalt; particularly useful if the jeep is a daily driver too. The Dana 20 kit reduces the low range to 3.15. With the Wide ratio T-18 - 6.32 x 3.15 x 3.54 = 70.47 crawl ratio. Even with the close ratio T-18 - 4.02 x 3.15 x 3.54 = 44.83; depending upon use, still not bad for many of us.
The reason to swap in the T-18 behind the AMC 304 is crawl ratio. For example the stock T-150 /Dana 20 crawl ratio is: 2.99 (T-150 1st gear) x 2.03 (Dana 20 ) x 3.54 (most likely axle gear ratio if not changed from OEM for 1979 to 1979) = 21.49. Of course a lot depends upon how you use your jeep, and 21.49 may be OK for some but not for most of us. When I bought my 1978 CJ5 it had a T-150 /Dana 20 combo with 4.56 gears. The crawl ratio was 2.99 x 2.03 x 4.56 = 27.78; still not good making it uncomfortable to just idle along on a rocky dirt road. However if you install a T-18 wide ratio things improve dramatically: 6.32 x 2.03 x 3.54 = 45.42. There is no hard and fast formula for what the perfect “crawl ratio” is but I consider anything around 50 as decent. Rock crawlers probably want twice that but again it all depends upon your use of the jeep. The wide ratio T-18 is so much more desired over the close ratio because: 4.02 (close ratio low) x 2.03 x 3.54 = 28.89.
If you want a lower (numerically higher) crawl ratio the obvious option is to change gearing in the axles but the other option is to put a Teralow or JB Conversions gear lowering kit in the Transfer Case and keep the taller (numerically lower) gears in the axles to help the streetability on the asphalt; particularly useful if the jeep is a daily driver too. The Dana 20 kit reduces the low range to 3.15. With the Wide ratio T-18 - 6.32 x 3.15 x 3.54 = 70.47 crawl ratio. Even with the close ratio T-18 - 4.02 x 3.15 x 3.54 = 44.83; depending upon use, still not bad for many of us.