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| Gearbox Ratio's | Rating: 
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| Posted: 08-26-2005 09:00 am |
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1st Post |
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Tony Hollart Member
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I have been told that the Hillman Hunter gearox is the same casing and internal workings as the the Rapier H120 gearbox. From the outside of the gearbox it does look the same but it does have different ratio's. Has anyone fitted the Hunter gearbox and what where the ratio's like ? ......H120/Jensen...........Hunter.............Hunter GB + JH Diff Diff..JH 3.73...............HH 3.89 1st---11.6 to 1 (3.11)-----13.04 to 1 (3.35)----12.49 2nd---7.42 to 1 (1.99)-----8.32 to 1 (2.13)----7.98 3rd---4.81 to 1 (1.29)-----5.41 to 1 (1.39)----5.21 4th---3.73 to 1 (1.00)-----3.89 to 1 (1.00)----3.73 Top / 4th is obviously the same, all the other gear are lower, would it make that much difference? Comments welcome.
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| Posted: 08-26-2005 03:14 pm |
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2nd Post |
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Judson Manning Member 
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Tony, Your comparison of ratios confirms the good news we've know for years in that the stock JH 4sp is a fairly close ratio transmission. When combined with h/c pistons and a 'torquey' cam like the E or 107, the stock transmission and rear end provide a great driving experience. A stock (i.e. non-torquey) JH could easily benefit from a lower 1st gear to help it get moving from dead-stop (much like every 4cyl BMW, where you have to shift to 2nd before you cross the intersection!). However, stock or modified, the 907 doesn't exactly have a lot of low-end torque or a wide torque-band. Consequently, a wider ratio gearbox could result in a fairly frustrating driving experience around town and definately on the track. Even with all the flack it receives, the stock JH 4sp transmission (when rebuilt properly) is a regular 'rock-crusher'. It uses the same Borg-Warner style synchros used in the current Corvette, Viper and Mustang transmissions. Getrag used Porsche-style synchros on the JH 5sp and later tried Moly-style synchros in the 1980s BMW transmissons. http://www.metricmechanic.com lampoons both of these 'innovations' on their website. In my opinion, the stock 4sp is fantastic with a mildly warmed-over 907 engine. If you want to grab another gear, the W58 Supra transmission has very similar ratios plus an overdrive. If your budget is unlimited, and if you can find a bellhousing from the early Eclat 2.2, you could use the BMW M3 Getrag 265 transmission modified by http://www.metricmechanic.com into their 'Ultimate Transmission'. Quite possilby the last transmission you'll ever need! Judson
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| Posted: 08-26-2005 04:16 pm |
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3rd Post |
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Mark Rosenbaum Member 
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I agree with Judson, the stock 4-speed has excellent ratios. The ideal in most applications is to have the ratio between adjacent gears equal to the ratio between engine rpm at peak power and engine rpm at peak torque. For the stock JH, with its power peak at 6500 rpm and its torque peak at 4800 rpm, this ratio is 1.354 to 1. Playing with the numbers (a scurrilous vice, to be sure) we find that a JH would be best served by a 5-speed with ratios as follows: Gear Theory 5 1.00 : 1 4 1.35 : 1 3 1.83 : 1 2 2.48 : 1 1 3.36 : 1 As you can see, for the top three gears, the stock 4-speed comes quite close to this theoretical ideal.
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| Posted: 08-27-2005 03:03 am |
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4th Post |
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Tony Hollart Member
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Thanks for the feedback about ratios in the gearbox. What has happened is the PO rebuilt the box but did not leave suffcient clearance for the roller on the input shaft. They have rubbed on the thrust washer and damaged the hardening on the output shaft. The symptoms were in neutral with clutch out there was a rumble from gearbox, push clutch in the noise would stop. I hope to use the output shaft from a Hillman Hunter as a replacement in my own gearbox. The Hunter gearbox does not appear to be a straight swap item as the input shaft is shorter than the Jensen, this means I will swap over all the gears and layshaft into my own gearbox to retain normal Jensen ratio's. For Mark Rosenbaum who seems to like collecting data on car things, the Jensen gearbox has the following numbers cast into the outside of the box U 71981060 4DA 21055 11 F 4 The Hillman Hunters ( 1978 registered ) has U 15M 7 A ( not actually an A but a triangle ) 71981060 More photos to follow if I have success in the rebuild. Attachment: DCP_0001.JPG (Downloaded 36 times)
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| Posted: 08-30-2005 03:31 am |
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5th Post |
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Tony Hollart Member
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Differences between H120 and Hunter gearbox continued. The input shaft housing on the Jensen has the shaft that the clutch release bearing slides on, the Hunter gearbox ( on LHS of photo ) does not have this shaft. The other difference that I wish I found out about earlier was that the tip of the Input shaft that goes into the roller bearing in the fly wheel is approx 15 mm diameter for the Jensen but is 16 mm diameter on the Hunter. I will get the machine shop to take the replacement from the hunter gearbox to fit the flywheel. In photo you can see the similarities on the bell housings also. Attachment: input shafts1.JPG (Downloaded 28 times)
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| Posted: 08-30-2005 01:38 pm |
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6th Post |
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Judson Manning Member
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Tony, The input shaft pilot bearing size is actually standard Chevrolet 0.590" diameter. I found this out when I had my transmission rebuild shop modify my Supra W58 input shaft so I could swap transmissions more easily. I know shipping would be realativley expensive, but I'm sure there are a number of clubbers with 'spare' 4sp parts that wouldn't mind donating to your cause. Why don't you post what you think you need, and we'll see what we can do to help. Judson
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| Posted: 08-30-2005 09:15 pm |
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7th Post |
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Tony Hollart Member
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Thanks for your offer. The cost of machining the shaft down is going to be about $30, which gets the problem sorted out again. We all know that the Jensen has been called a "parts bin special", but it still works very well. I have posted the information about the Hillman Hunter gearbox to make others aware that this is a potential source for gearbox parts. When you have a rare or unusual car you get used to being told " parts for those cars are rare as rocking horse poo" which is not actually the case for us, as Hunters / Viva's were very common up untill 10 years ago.
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