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1922
United Kingdom
549 Posts |
 Posted - 25 Nov 2011 : 21:25:05
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Rapiers are 4.22, but H120 are 3.89 (actually 3.8888888....).
Don't think there is any way to see from the outside, other than turning the input shaft and counting how many times the hubs turn to calculate the ratio.
To be certain you need to extract the diff unit and count the teeth (Paul's listed all the numbers).
The 3.89 axle was also fitted to the Alpine (fastback), Humber Sceptre saloon/estate and some Hunter estates and Hunters saloons with overdrive.
The general rule for what ratio was used (for the mainstream 1725 engined Hunter/fastback range) is:
H120: 3.89 (all H120 are manual with overdrive)
Rapier: 4.22 for manual (overdrive is standard), 3.7 for automatic.
Alpine (I'm not certain here): 3.89 for manual, 4.22 for manual with overdrive, 3.7 for automatic.
Hunter saloon: 3.7 for manual and automatic. 3.89 for manual with overdrive.
Hunter estate: 3.89 for manual. Don't know about auto or overdrive.
Humber Sceptre: Same as the Hunter but the overdrive is standard on manual cars.
I've given a few of these axles quite a lot of abuse of the years and the only one I killed was the one I ran dry - the pinion bearing did not like that at all!
Given sufficient enthusiasm it is possible to twist the overdrive input shaft and it doesn't take much to destroy the rubber mount on the propshaft centre bearing. By "enthusiasm" I mean full throttle launches accompanied by blue tyre smoke and black stripes left on the road 
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Edited by - 1922 on 26 Nov 2011 20:32:21 |
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Paul
United Kingdom
60 Posts |
Posted - 23 Nov 2011 : 22:04:57
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Aren't they all the standard 4·22:1 (38:9) crownwheel and pinion set used on overdrive Alpines from 1959 or are any the 3·88:1 (35:9) non-overdrive version or the 3·7:1 (37:10) set used on some Arrow Range automatics?
The Yanks Our Colonial friends plonk Cologne V6s in Alpines and retain the gearbox but usually uprate the rear axle so, if you want further information, I would recommend the S.A.O.C.A. forum.
From personal experience, the main problem with the standard Rootes diff. is that the locking tabs compress over time leaving the crownwheel free to move backwards and forwards a bit. This has been known to lead to bolt failure and, hence, loss of drive. Mind you, Iran Khodro continued with the same construction even up to the Peugeot RD!!
Rare? Not in 4·22:1 (38:9) or 3·88:1 (35:9) and the 3·7:1 (37:10) are not yet too much in demand by those who want a better cruising gear.
My Alpine won't float!  I need one which does!! |
Edited by - Paul on 23 Nov 2011 22:13:17 |
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moditup
United Kingdom
83 Posts |
Posted - 22 Nov 2011 : 19:47:23
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Hi all just a few questions regarding the H120 axle,
1.How would i identify a H120 rear axle ?
2.How tough are they under tuning ?
3.How rare are they to come by nowadays ?
Any info much appreciated.
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H120 axle ID
