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T98A and 7.5x16 tires |
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Joelweb 
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Joined: 31 Mar. 2022 Location: Missoula, Mont. Status: Offline Points: 76 |
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 Topic: T98A and 7.5x16 tiresPosted: 20 Sep. 2022 at 10:58pm |
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Lot's of stewing here over tire size on a CJ2a. I see people recommending against running 7.5x16 tires on L-head power Jeeps because the tall tire height robs power unless you upgrade from a T90A to a T90C tranny. As an alternative, anyone got thoughts on pulling power running a fresh
L-head and T98a tranny? The 2nd and 3rd gearing in the T98A is a
little higher than 1st and 2nd gearing in the T90A (although not quite as tall as 1st and 2nd with the T90C), and it seems that
might mitigate some of the challenges people are noting. thoughts? T98a 6.40, 3.09, 1.69, 1.00 T90a 2.79, 1.55, 1.00 T90C 3.34, 1.85, 1.00
Edited by Joelweb - 20 Sep. 2022 at 11:01pm |
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1947 CJ2A
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oldtime
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Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4178 |
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Posted: 20 Sep. 2022 at 11:08pm |
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IMHO the T98-A is golden for off-road applications where an extra low gear is desired.
That said it’s a very tight fit into an 80” wheelbase flat fender. The transfer case must be moved aft by 5-1/2”. The extra short rear propelled shaft angle is at absolute maximum when standard rear suspension is at full droop. In fact you must use the late transfer case rear companion flange yoke so that it does not impact the propeller yoke at full rear axle droop. Got that ? It’s pushing the propeller angle to its absolute max with standard suspension. Will not work if you have extra axle droop (longer than std. shocks). The T98-A gear steps are very nice.
Edited by oldtime - 02 Oct. 2022 at 9:05am |
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Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963) Zero aftermarket parts |
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Joelweb
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Joined: 31 Mar. 2022 Location: Missoula, Mont. Status: Offline Points: 76 |
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Posted: 01 Oct. 2022 at 3:18pm |
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Thanks, OldTime. I don't know if I have the later companion flange or not. My Jeep came with the setup already installed. I was looking at some parts suppliers and they don't distinguish between an early or late companion flange. Any more details you can provide would be appreciated. thanks
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1947 CJ2A
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oldtime
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Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4178 |
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Posted: 01 Oct. 2022 at 3:43pm |
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I don’t have any early companion flange yokes at this time for visual comparison.
Here is the later (deeper/ taller) one. It measures 1.15” from a flat surface to bottom of the journal. Early rear flange yoke = A-950 Late rear flange yoke = 807784  I could sell you a good use original Spicer late type if you need one.
Edited by oldtime - 02 Oct. 2022 at 9:05am |
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Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963) Zero aftermarket parts |
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smfulle
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Posted: 01 Oct. 2022 at 10:47pm |
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For what it’s worth, I feel like the issue with the Go Devil and large tires is not in the lower gears. To me it is in high gear, trying to make highway speeds. Every transmission is 1 to 1 in high gear so gear changes in the lower gears makes no difference at highway speed.
Your milage may vary.
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Beach Bum
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Joined: 21 Sep. 2019 Location: Seattle Status: Offline Points: 935 |
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Posted: 01 Oct. 2022 at 11:48pm |
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I have a stock L head motor and atv overdrive in my 48 2A. I can say for absolute certainty from my own experience that the stock flathead CANNOT pull an overdrive in high gear with 5:37 gears and anything taller than stock tires. Can’t do it, won’t do it (I wish it would believe me).
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oldtime
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Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4178 |
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Posted: 02 Oct. 2022 at 8:57am |
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I agree, the Go Devil is only 60 hp.
That’s why I gave up on them in 1983. Just would not suffice as a daily driver when the National speed limit was raised up from the previous 55 mph limit. At that time I switched to the 3B so I could get another 12 hp out of the 134 cubic inches. By the mid 90’s as people began driving faster and faster on the interstate; I could only see the writing on the wall for the Hurricane engine too. At least as a daily driver trying to tackle the steeper interstate grades. These days my daily drivers are all D-225 powered and I only have one Hurricane powered 3B that is designed for extreme off road recovery use. That’s the one with T98-A, Powr Loks and a rear PTO winch with recovery boom. I have 30” tall 6.50 x 16” STA super Traxions on that Jeep. I only run the 7.50” tires with the 155 HP Dauntless. I suggest you follow the Willys standards and go with no more than 7.00 x 16” military tires on any 134 engine having 5.38 final drive ratio. If uncertain then…. Ask Stan about that.
Edited by oldtime - 02 Oct. 2022 at 9:02am |
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Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963) Zero aftermarket parts |
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Joelweb
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Joined: 31 Mar. 2022 Location: Missoula, Mont. Status: Offline Points: 76 |
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Posted: 16 Oct. 2022 at 4:36pm |
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Thanks, Oldtime. I just sent you a private message about the companion flange. |
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1947 CJ2A
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Spinnas
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Joined: 24 Apr. 2018 Location: AZ Status: Offline Points: 375 |
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Posted: 17 Oct. 2022 at 10:11am |
There's about 7-8 local flatfenders that I know of that do 55-60mph cruising on the regular with L-heads, in OD, with mostly 7.00-16 and 7.50-16 tires, mine included. As Stan says, your mileage may vary.
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nivrat
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Posted: 17 Oct. 2022 at 12:46pm |
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I run 750-16 tires on my 46 2A with a fresh Lhead, T98, D18 with OD, and 538's. I can do 55 on flat ground most days (depending on which way the wind is blowing). Would I notice a performance improvement going to a 600-16 tire? Very likely. Why? The taller tire affects final drive ratio and more importantly the RPM that the engine is running at the given speed. Engine RPM at 55 will be higher with the shorter tire. The Lhead makes its max torque at 2000 RPM but max HP at 4000. The shorter tire will put your RPM's higher than what the taller tire will do.
So yes, the taller tire does have a detrimental affect on performance, but it is not just in OD. Their performance detriment is in all gears; final drive ratio and RPM are affected in every gear. 2nd gear in the T98 is a 3.09 (first gear T90C is actually lower at 3.34 as was mentioned earlier) but with the taller tire its performance is probably somewhere between the 3.09 and the 2.79 of a T90A. I live with the performance decrease of the taller tire because I like the tread design of the Deestone 503 (its the granddaddy of the Armstrong Trutrac, my all time favorite tire) I get a little more belly clearance but another important factor is they were CHEAP.  Everything is a compromise in the end; build them to your liking and get out and enjoy them. FWIW, Mike |
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Beach Bum wrote: