| Author |
 Topic  |
|
moditup
United Kingdom
83 Posts |
 Posted - 22 Nov 2011 : 19:47:23
|
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.
|
|
|
Paul
United Kingdom
60 Posts |
Posted - 23 Nov 2011 : 22:04:57
|
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 |
 |
|
|
1922
United Kingdom
549 Posts |
Posted - 25 Nov 2011 : 21:25:05
|
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 
 |
Edited by - 1922 on 26 Nov 2011 20:32:21 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 27 Nov 2011 : 13:42:39
|
| Thanks guys, there is one in a scrap yard near me but its a really rusty back axle that apprantley has come off an H120 rapier, just wondered if i can use the diff has the rest of it is scrap its been outside that long even the wheel studs have rotted, but i assume the that the diff will be ok has its filled with oil and i can just swap it over ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 27 Nov 2011 : 14:30:02
|
Yup - you will need remove the hub back plates and pull out the axle half shafts a couple of inches to disconnect them from the diff.
Normally you use a slide hammer for this connected to the wheel studs - you might have to improvise a bit if it's very rusty!
Once the half shafts are disconnected the diff unit can be unbolted from the axle and removed.
If you are lucky you can just clean it and bung it in, if you are very lucky it won't whine or leak passed the front oil seal.
Don't be tempted to change the oil seal unless you have to, from past experience this will upset the pinion setting and cause the axle to whine.
|
Edited by - 1922 on 27 Nov 2011 15:05:58 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 27 Nov 2011 : 14:57:39
|
| I have just run down and bought it, i plan to strip it tommorow but how do i work out the ratio ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 27 Nov 2011 : 15:03:35
|
Just count the teeth on the crownwheel - 35 is a 3.89, 37 is a 3.7 and 38 is a 4.22.
If you are fitting this to a Rapier then try to get the speedo too.
You might also need the speedo drive off the gearbox (just one bolt to remove), I can't remember if those are different or not.
If not your speedo will read 8% low - not a disaster but a bit of a nuisance.
|
Edited by - 1922 on 27 Nov 2011 15:04:56 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 27 Nov 2011 : 15:38:21
|
| Yes i am fitting this to a fastback, is there any other rootes cars i can maybe get the speedo drive from ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 27 Nov 2011 : 16:26:29
|
I've checked the part number - it looks like all overdrive equipped cars use the 15 tooth speedo drive so you already have the correct one.
So it is the speedo you should change, the only one listed with the same part number in the 1971 parts book is the Humber Sceptre. You will need one from a pre '73 car as they change over to a clip on speedo cable after this.
Or they are companies that advertise in the classic car mags that can recalibrate them.
|
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 27 Nov 2011 : 18:18:03
|
| Thanks for the info, you mentioned the propshaft rubber center section failing under quick take offs, i beleive there is a one peice prop i could use but what car is this from ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 27 Nov 2011 : 20:55:06
|
Hunter saloon.
My first Rapier I used one from a '74 Hunter GLs, and my current one has the prop from a '75 Hunter 1500.
These are rubber damped and wider than the Rapier prop.
I think the idea of the split prop on the Rapier is that they are smoother, but the rubber mount is easy to destroy. Once the mount is ripped, each time you pull away the propshaft hits the inside of the tunnel and goes "clonkity clonk".
The Hunter prop fits straight on with no problems.
|
Edited by - 1922 on 28 Nov 2011 00:20:39 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 27 Nov 2011 : 22:49:40
|
| So is the Hunter prop a one piece job ?, and from what you mentioned is the gearbox weak if the engine is tuned to any degree ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 28 Nov 2011 : 00:00:19
|
Hunter props are usually one piece.
The Sceptre, Rapier, Alpine & H120 and some Hunters are split with a UJ, bearing and rubber mount in the centre.
The gearbox itself is strong, they were also used in Ginetta G21 and the Jensen Healey (this had a 144bhp Lotus twin cam).
The end of the gearbox mainshaft where the gearbox joins the overdrive is thinner than the rest of the shaft. I found a small twist in the shaft on one of mine at the point that it connects with the overdrive. I put this down to dropping the clutch at 6000 rpm a few times and smoking the back tyres.
Since then I've driven thousands of miles with an 130bhp Holbay Marathon engine and had no trouble. Howard Johnson claims 160bhp with his H120 (I think he has nitrous) but I don't remember him reporting any gearbox trouble.
I'm hoping for 150bhp or more when I get my Rapier back on the road but gearbox, overdrive and axle will be standard H120/Hunter GLS.
|
Edited by - 1922 on 28 Nov 2011 00:06:21 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 28 Nov 2011 : 17:48:19
|
Thanks for all the info much appreciated, i stripped the axle down and it doesnt look like its covered many miles, you was right about using a slide hammer it woudnt budge !
The idea i had in mind was to convert the rear suspension to a 4 link similar to the group 4 mk2 escort set up with coil overs has it looks like alot of parts are generic between the 2 cars, ive decided to convert the rear to disc brakes using the axle i bought so will post any progress on here.
I remember a build in a magazine about using bigger pistons and volvo inlet valves for the engine to get more power, i do have a seized holbay engine i bought a few months ago so may have it rebuilt, by the way whats the top spec you can go on one of these BHP wise ? |
|
|
|
1922
United Kingdom
549 Posts |
Posted - 29 Nov 2011 : 20:43:53
|
That depends on how driveable you want it to be and how much you want to spend.
120+ is possible at 1725cc and still be easy to drive on webers.
130+ is possible at 1840cc and still be easy to drive on webers.
160/170+ was done for racing back in the '70s. I've been told that it was cheaper to get this power from an 1725 Hunter/Rapier than a 2 litre Ford pinto engine.
I seen pictures of an Alpine two seater somewhere in the states with a turbo. See http://www.myturboalpine.com/
If you have some cash to burn I recommend that you talk to Richard Coles at Coltec (formerly Holbay) and/or Chris Draycott.
When I was at Coltec deciding what cam to use in my new engine, we discussed what RPM I wanted peak power at. Richard said that 7000rpm or more is possible with these engines (I've gone for mid-range and peak at 6000 ish). He tells me that the standard factory bottom end (crank, rods etc) are very good quality and very strong.
I don't know of any bits in common with any Ford but I was looking at an MGB GT V8 recently and the brake calipers and servo look exactly the same.
|
Edited by - 1922 on 29 Nov 2011 21:23:38 |
|
|
|
moditup
United Kingdom
83 Posts |
Posted - 29 Nov 2011 : 21:11:59
|
| Just after reading about the Marathon engine build if you knew the spec, i thought it might be worth while to buy the bits and let somebody else build it, i have read that this uses avenger pistons and liners but what cc engine and where would i get them from, thanks for your help. |
|
|
|
Topic |
|
H120 axle ID
