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| New 30% Overdrive | |
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| Tweet Topic Started: Sep 3 2012, 07:22 AM (2,464 Views) | |
| 8305 | Sep 3 2012, 07:22 AM Post #1 |
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Hi, I am ready to order an Overdrive, from Herm The Overdrive Guy. I can not decide if I should order it with the original 25%(0.75:1) ratio or buy the one with the new, longer 30%(0.70:1) ratio? Engine is a Hurricane with a T90 transmission. Anybody has any experience with this longer OD? |
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'60 M38A1 1/4 ton trailer | |
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| oldtime | Sep 4 2012, 10:44 AM Post #2 |
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I was not aware of the new 30% O.D. ratio so thanks for posting. As you know Gear Ranging is dependant on many factors. Engine torque @ RPM, transmission ratios, transfer case reduction ratio. the final drive ratio and the tire diameter plus ones intended useage for the Jeep. Please specify T90 A or C and your final drive ratio. What type of driving do you expect ? I'll crunch the new numbers and provide some Gear Ranging insight. Warning very indepth: http://z4.invisionfree.com/CJ3B_Bulletin_B...?showtopic=2427 Also fill in your SIGNATURE with basic information on your Jeep. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| Daryl | Sep 4 2012, 01:04 PM Post #3 |
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I was at Herm's on Friday and was able to look at his new mainshaft for the 30% overdrive. At first look it appears to be much more stout then the original shaft. I have not been able to drive one yet, but will post when I get a chance to get one. |
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Lotsa Jeeps, and a few extra parts In Bonney Lake, Washington Always willing to look at a Jeep for you BEFORE you buy it to check it out. | |
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| scott | Sep 4 2012, 11:12 PM Post #4 |
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Hi guys I have a 30% OD on my jeep now. I have had it for the summer and I love and hate it at the same time. I love having 2 gear in OD. It gets the shifter away from my fat legs and is still powerful. 3rd gear with any incline is really tough. I'm sure 3 gear OD on the freeway would be great but I don't go on the freeway with my B. Or have I used the OD in low range in the woods. I have only used 3 gear OD on the main roads where the speed limit is 45 and mostly down hill Or flat grade. My though is if you had a v6 with moderate tirers I would take the 30% OD any day of the week. my jeep is a typical worn out jeep. it has a tired engine and 30x9.5 bfg's Maybe a fresh rebuilt f head would be a different story. but I can only speak from my experience. If you live near or visit cleveland Ohio please feel free to give it a drive Best of luck with your decision Scott |
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| Bob | Sep 5 2012, 06:52 AM Post #5 |
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Hey Scott, if you're near Cleveland, Ohio, please consider coming to my show! Northern Ohio Flatfender Gathering |
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Bob 1953 CJ3B 1965(?) CJ5 1949 Jeepster 1947 Cj2A 2004 Kubota l3400 | |
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| oldtime | Sep 5 2012, 07:31 PM Post #6 |
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I have driven decades in Wilys Jeeps being totally dependant on them as daily drivers. I can assure you that it's mandatory to harness every bit of power from the meager 134 Willys engines. Harnessing mainly entails having a drivetrain system that is fully compatable to the selected engine. While it's true that a 1% change may not be noticable, it is certain that a 5% change will be noticed and a 10% change will be blatantly obvious. Mathmatics reveals certain facts that may not be readily percievable to the senses. I have tested my jeeps and the mathmatics always verifys the observations. In this case I have done extensive math using various charts and I am absolutely convinced of the results. The Warn 25% O.D. is by far the most useful ratio that is currently available. It is my opinion that the 30% O.D. provides only a very limited benefit and only under certain conditions. 30% O.D. provides zero benefit for a Hurricane powered CJ as compared to 25% O.D. 30% O.D. vs. 25% O.D. is only sensable for use with larger engines such as D225. 30% O.D. absolute best application would be for use with D225, T-15 and 5.38 final drive. And even under those specific conditions I consider it as an inferior system to a properly sychronized drivetrain having the appropriate final drive ratio to begin with. In other words it is my opinion that one should not correct the final drive ratio by use of an O.D. The O.D. is mainly used to evenly split transmission gear ratios otherwise the O.D. is only good as an extra gear. The absolute best available drive train combination for road use with a Hurricane engine is T90 C transmission with 25% O.D. and 5.38 final drive, on narrow 30" to 31" tall tires. The 5.38 and 25% O.D. yeilds a 4.03 compounded final drive ratio. Final drive ratios above 4.03 are simply too steep for the little Hurricane engine. This specifically means that an overgeared Hurricane cannot maintain nor accelerate on anything but flat land or downhill. Downhill and flatland use only is just not acceptable. Minor grades must use O.D to maintain acceptable speed for interstate hiway travel. If you was to add the 30% O.D. to a 5.38 final drive the compounded final drive becomes 3.76%. That's simply too high for a Hurricane engine. The 3.76 % compounded final drive could only work for a larger engine such as the D225. But 30% O.D. will never be optimum for any jeep because it is not directly proportionate to the gear span of any Jeep nor any truck transmission. Jeep and truck transmissions range from 16% half span to 26% half span. They do not half span at 30%. Early standard gear ranging = 5.38 final drive to 37/1 crawl reduction Late standard gear ranging = 4.27 final drive to 35/1 crawl reduction Early 25% O.D. gear ranging = 4.03 compound final drive to 37/1 crawl reduction Early 30% O.D. gear ranging = 3.76 compound final drive to 37/ 1 crawl reduction Late (4.27) O.D. gear ranging is never recommended I do have transmission, O.D., transfer case, final drive and tire diameter charts for those who might need to know more about gear ranging applications. GEAR RANGING is Jeep science itself ! |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| 8305 | Sep 7 2012, 01:24 AM Post #7 |
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Thanks for everybody for their help. Placed the same question on other forums as well, but received replies only here. Ordered the 25% or 0.75 ratio OD from Herm. I did some calculations and computer simulations too. The longer 30% ratio looked good on paper, but simulations can not replace actual, real world driving. The high speeds forecasted by the calculations, may exist only in theory, because as some of you stated from experience the Hurricane is not capable even in good condition. But if it was able to go over 60-65mph, I do not really want to go that fast with no belts, no roll bar etc. I appriciate your thoughts and help and looking forward to drive my jeep with the overdrive next spring. |
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'60 M38A1 1/4 ton trailer | |
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| ziv | Sep 8 2012, 12:39 PM Post #8 |
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Oldtime, after reading your full explanation about O.D. ratios, let me ask some basic questions to make it clear (for me, as my english is poor): 1. You wrote "The O.D. is mainly used to evenly split transmission gear ratios otherwise the O.D. is only good as an extra gear". What do you mean ? 2. When start driving with 1st gear+O.D. - the engine isnt very happy to get to the road, it feels weak. Is it more logical to get the O.D. out before i stop (traffic lights and so) ? 3. Any good from using the O.D. when off-road with 4*4 Low ? (my jeep has the T90, Dana 18, 700*16 and the 5.38 ratio, all standard). Thanks Ziv |
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1974 CJ-5 F-134 T-90 Dana18 1:5.38 1979 CJ-6 258 T-150 Dana20 1:4.10 (export model) 1956 Willys S.D , 1960 Maverick 1960 CJ-5 F-134 T-90 Dana18 1:5.38 (belongs to my father) zivjeep@yahoo.com | |
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| oldtime | Sep 8 2012, 05:33 PM Post #9 |
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An O.D. has the ability to perform two distinct tasks. It can simply function as an extra gear by increasing the final drive ratio after 3rd gear is wound out. When used merely as an extra gear the O.D. compounds the existing final drive ratio. (axle ratio) 5.375 final drive x .75 O.D. = 4.03 compound final drive The O.D. can also function between all existing transmission gear ratios. This second useage is termed "gear splitting". Gear splitting provides the distinct advantage of allowing the engine to operate near its maximum efficient crankshaft velocity. Gear splitting is especially beneficial if the engine provides marginal power. Gear splitting allows the marginal engine to perform near its peak operating RPM. When used as a gear splitter the ideal O.D. ratio is relative to the specific gearing of the transmission. Obviously.... A typical Jeep 3 speed has 3 gear ratios plus reverse. The gears are 1st, 2nd, 3rd plus reverse. A typical jeep / truck type 4 speed has 4 ratios plus reverse. The gears are Low, 1st, 2nd and 3rd. Low gear is normally not used and is generally not synchronized. 3rd gear for both the 3 speed and the 4 speed transmissions is straight through drive at 1 / 1 ratio. The transmission provides what is called a Range. The full range is between it's lowest and its highest gear ratios. The individual range from one gear to the next gear is called the Gear Span. No jeep nor truck transmission will provide a perfectly uniform gear span throughout the entire range. Some transmissions range more uniformly than others. The 2nd to 3rd gear span is ideal to use for determining the optimum compatable O.D. ratio. This is because the 2nd to 3rd gear span generally requires more power from the engine than does the 1st to 2nd gear span. Ideally the O.D. should split the 2nd and 3rd transmission gears right down the middle. Ideally the O.D. should provide a ratio that is equal to 1/2 the span from 2nd to 3rd gear. Transmission gear ratio charts must be studied to fully understand transmission ranges. I also developed charts to convert various O.D. percentages into numberical "half spans ". These charts used together yeild ideal gear splitting formulas vs. actual transmission ranges and gear spans. I'll add my charts later if requested. All jeep and truck transmissions provide a 2nd to 3rd gear half span of 16% to 26%. A wide range (WR) transmission will benefit more readily from gear splitting than a narrow range (NR) transmission. The T90C has the greatest 2nd to 3rd gear span of all Jeep / truck transmissions. The T90C can potentially benefit from more from an O.D. than any other transmission. The ideal O.D. for a T90C would yeild a 26% half span increase. For this reason alone there is no advantage to any O.D. going beyond 26% O.D. The NR T18 has the smallest 2nd to 3rd gear span of all Jeep / truck transmissions. The ideal O.D. for a NR T-18 would only yeild a 16% half span. I just can't see having the gears span that closely together. Not even for marginal powered engines. So the NR T18 transmission is a very poor choice for use with any O.D. Yet the NR T18 can be ideal for certain drivetrain combinations without O.D. My figures includes the T90A, T90C, T14, T15, NR T18, WR T18, T98, WR T19, NP 435, SM 465 and SM 420 transmissions. Of all these transmissions the T90C provides the most uniform span ratios. The Ford WR T19 also has rather uniform span ratios that are very near 25% half span. Yes, for your particular drive train you should not be starting out in 1st gear x O.D. When I shift on the road I typically shift 1st gear.... 2nd gear.... 2nd gear x O.D. ....3rd gear .... and finally 3rd x O.D. Sometimes I just skip 2nd gear x O.D. and go straight from 2nd to 3rd. When the jeep is starting out on the road it is at an increased reduction ratio. I specifically call this the Take Off Ratio. This is normally 1st gear. Remember truck type 4 speeds have an extra gear called low that is normally not used for "take off". When the transfer case is shifted into it's low range the 1st gear is often much too slow for starting out. For this reason one can benefit from knowing the ideal "take-off ratio" for their particular vehicle. The common standard ( 2.798 x 5.375) take off ratio for a Willys 134 engine is right at 15.04/1 reduction ratio. For standard CJ's 1945-1979 the take off ratio will vary anywhere from 10.5/1 ratio to a 15/1 ratio. The ideal "take off ratio" for any vehicle is mainly relative to the engines power output. As previously stated.... The O.D. allows one to better control the RPM and power output from the engine while allowing greater variation to the foreward travel speed. When driving offroad a slow speed and low power is usually sufficient so the O.D. is not often needed for off road use. But under two certain conditions ample power may be required. Those two conditions are deep mud bogs and steep / slippery inclines. Under these conditions one may want to maintain the engine RPM nearer its maximum torque velocity. And yes the need increases as the engine power diminishes. In other words an O.D. its especially practical with meager engine power. The O.D. allows one to better control speed vs engine RPM. In this seemingly uncharted realm of engine RPM, torque output and gear ranging some untold concepts emerge such as idle crawl stall vs. gradability. Do you guys know your jeeps gradability @ idle crawl stall ? Do you understand why it matters ? |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| Daryl | Sep 8 2012, 07:16 PM Post #10 |
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Ken you have left out the "it is just cool to have 4 shifters" part of the equation. Thanks for putting this into terms that most can understand. These overdrives didn't really become all that popular until it became commonplace to swap a sbc into a Jeep. The overdrive was then added to be able to reach highway speeds by changing your final ratio to about 4:10s. In stock configuration, most universal Jeeps have a very good power to weight ratio and simply do not NEED an overdrive. |
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Lotsa Jeeps, and a few extra parts In Bonney Lake, Washington Always willing to look at a Jeep for you BEFORE you buy it to check it out. | |
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| gianas | Sep 9 2012, 03:46 AM Post #11 |
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Even though I know substantially less than 1/5000th of what Oldtime and Daryl know about overdrives, there are a few things about ODs not mentioned here that could save someone considering an OD some money, pride, and frustration, especially if you think you already know all you to know, like a 3B owner described below. This appears to be what happened to the previous owner (PO) of a 3B I've owned. He has a PhD and views himself as quite talented in auto mechanics, referring to himself as "doctor," and not jokingly. Thinking he knew all he needed to know, the PO didn't call Herm to ask questions about the right number of teeth for the OD he bought from Herm to match the 3B's transmission. As a result, the PO installed the wrong OD for his transmission and exploded both the OD and the transmission, requiring a rebuild of both the OD and the transmission—expensive and humiliating. Keeping that situation in mind, anyone buying an OD might want to keep "teeth-count matchup" in mind. If you buy a stock 3B with this OD history, and the previous owner didn't properly install the required gaskets or tell you about the mistake he made, you'll be driving a jeep that leaves a distinct, tell-tale trail of gear oil that Hansel and Gretel would appreciate—at least a cup a week, if you drive the jeep every day. Since I'm no mechanical wizard, I always ask mechanical wizards what I should do and, most importantly, what I shouldn't do with valuable, mechanical stuff. I asked Herm those questions regarding his ODs, and he gave me answers based on often rebuilding what careless and overconfident jeep owners have done to the ODs Herm builds and sells. Herm advised me not to use the OD in four-wheel drive, frequently going in an out of a wide variety of gears, because he said I'd wear out the OD in no time doing that. The implication (unspoken message) I believed I was "receiving" from Herm was that ODs—on old, stock, Willys jeeps—were intended, primarily, to use as Oldtime described using his OD—to help an old, stock Willys go at highway speeds on relatively flat highways. Hotdogging an OD in 4WD—especially for someone with an engine larger than a Hurricane 134—is for people who can afford to be careless with money ... was the distinct impression I was getting from Herm. Experts like Oldtime, Daryl, and Ratchet can confirm whether what I "translated" from Herm is correct or not. Another piece of advice Herm gave me, when I asked him to tell me more about the "nots to do," was to check the oil in the transfer case and not let it ever get low because of the mechanisms involved in ensuring that the OD's gears are well lubricated. Failing to keep enough oil in the transfer case, he told me, would ruin my OD. I also got the impression from Herm that he would not sell you something carelessly, just to make money. In addition, I got the impression he would stand by what he sells, even past the warranty, because that's what he told me. I'd also say that you should get everything he promises in writing. And, I found, even when Herm makes some serious mistakes, he quickly, nearly instantly, makes amends. Also had an interesting discussion with the chief tech. person at Saturn who, surprisingly to me, gave me an honest and objective assessment of the differences between the Saturn OD and the Warn OD, plus the advantages and disadvantages of each OD. Simply put (in my "translation") each OD is stronger where the other is "weaker"; at least, that's what I gleaned from what the Saturn tech told me. He gave examples involving technical aspects of the "top ends" and "bottom" of both ODs, most of which, unfortunately for me, I didn't understand. Both Herm and the mechanic Herm recommends to install Herm's ODs in the Puget Sound area of Washington state would not tell me, categorically, which OD to choose, between the Warn and the Saturn. When I continually pressed both men to give me hints that wouldn't upset their seemingly divided allegiance between the Warn and Saturn, a Warn OD appeared (to me) to be recommended by both men for a stock 3B, when originality is a concern (which was and is for me). Since I wasn't using a tape recorder to validate what any of the people mentioned here said to me, I'll leave it to you to do your own investigation. I just wanted to mention some stuff I needed to hear before buying and installing an OD. What Oldtime wrote about the 16-26% and how and why a 30% OD isn't the unquestionable greatest for a stock 3B, I found fascinating and welcomed. greg |
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Greg Gianas Redmond, Washington 1954 3B, daily driver; old, beat up but still strong, last vehicle I'll probably ever own, purchased May 2012; first vehicle and jeep owned: back in 1965-66 (1965 CJ-5, Hurricane 134 engine); no better memories | |
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| williams3b54 | Sep 9 2012, 03:11 PM Post #12 |
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I don't udestand why not to use the OD in 4WD and off road? I have a Husky unit, rebuilt, by Herm, behind my F-Head, T-90, model 18 transfer case and I use the heck out of the OD off road and on road to get to the trails. My brother has a "Warn" OD in his 69 CJ-5 with the D225 and he uses his OD all the time off road too. Don't abuse them though. This OD has been behind the drive train since 2003. We usually get to take it to jeep trail events three to four times a year. I use the OD to split the gears between first and second all of the time when four wheelin. With the T-90 not being a syncro tranny, I leave the tranny in first gear and go into OD to up the off road speed and to be able to get back out of OD if I need to get a lower gear with out 'double clutching' the tranny. What a boon to the little jeeps back when "Warn" came up with the design for the OD and for un-locking hubs for them also. And don't forget the work horse the "Warn" winch. Dick W. Spokane Wa. |
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1954 CJ-3B Semi-modified for trail riding in the Northwest. See photos on CJ-3B page owners photos 1954. 1968 CJ-5/1975 231 odd fire V-6/ many other mods. ordered new from Toledo 1968. | |
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| Daryl | Sep 9 2012, 05:47 PM Post #13 |
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The key to using off-road is the relative term of "abuse". While they are stout little units on the highway, when putting lots of horsepower in front of them they can easily face challenges under rough use. Any time a clutch gets dumped with axles getting lots of traction, there tends to be an upstream desire in the drivetrain to find a fuse. You have to remember that the people on this board running nearly stock setups are a tiny minority in the Jeep community. So anyone giving advise on the use of an overdrive is most likely grouping you together with the crowd running motors with lots of HP, lockers and big tires. Common sense isn't always common to people who like to stomp on the skinny pedal. |
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Lotsa Jeeps, and a few extra parts In Bonney Lake, Washington Always willing to look at a Jeep for you BEFORE you buy it to check it out. | |
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| Duffer | Sep 10 2012, 09:45 AM Post #14 |
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Herm Tilford, IMO, is a VERY knowledgeable guy and a HUGE resource for anyone working with old Jeeps. That said, I have used Warn OD's very liberally in low range for over 40 years with absolutely no ill effects in both sbc and 225 Buick powered Jeeps. If you don't get carried away with the tire size (33" or less) and keep a relatively light foot on the throttle, the OD will be up to the task of splitting gears in low range and is considerably more convenient than shifting to 4H for short stretches of trail. Just about every destroyed OD I have seen is the direct result of lubrication failure. They literally cook if you let the transfer case get too low or if there is a problem with the oil scoop that is damaged or improperly installed. About the "Dr" that somehow fits a 26 tooth OD to a 29 tooth case or vice versa-no cure for that. I keep this one on the frig door http://search.dilbert.com/search?p=R&srid=...er=type%3acomic |
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John, SW Montana 55 CJ 3B, transmake, fiberglass/aluminum tub/hood/fenders, 381 sbc, AGE M22W trans, "super" D18/Teralows & Warn OD, D44/ARB/Dutchman front & full float D44/Powrloc rear axles-4.10's, Holbrook springs, 4 wheel power discs, Saginaw PS, Warn 8274 68 CJ5, stock 225, T86AA, D18w/ Warn OD, D27A & stock D44 (heavy duty housing)-4.88's, 11" brakes, stock Ross box, Belleview 6000 (a close to stock vehicle, including the Whitco top) | |
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| ziv | Sep 12 2012, 01:52 PM Post #15 |
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Ken, Thank you for the full information and answers to my questions. Ziv |
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1974 CJ-5 F-134 T-90 Dana18 1:5.38 1979 CJ-6 258 T-150 Dana20 1:4.10 (export model) 1956 Willys S.D , 1960 Maverick 1960 CJ-5 F-134 T-90 Dana18 1:5.38 (belongs to my father) zivjeep@yahoo.com | |
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