Birmingham Road, Pathlow
Stratford-Upon-Avon, CV37 0EP

3HA/3HU Alloy Diff Case & Internals for Aston Martin DB3, Lotus & Other 50's Cars Inc Many Specials

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Congratulations to Max Smith-Hilliard who came 1st in his Lotus 10 (and Longbrook Motorsport who prepare the car) at the 2024 Monaco Historic Grand Prix, class C 1952 to 1957 front engined cars.

Congratulations to Rick Bourne who came 6th in the same race, again with a Lotus 10,  Ian Grimes prepared this car, both cars used our diffs as described below



These Alloy Cased 3HA/ 3 HU diffs were fitted to the DB3, the Lotus 10 & a great many other cars including many specials of the 50s.             

PS It would even fit a Lagonda 2.6ltr & 3ltr from the 1950s which, if the right ratio were chosen with an overdrive kit, say 3.54:1 (optional Aston DB2 series ratio) would give it very long legs, especially with a torquey 2.750cc or 2.922cc engine.

The complete basic unit starts from £11000 + vat (May 24) , the price is then dependent on the individual specification from the std unit, ie, ratio needed, brake caliper / drum mounting brackets (the output shaft housings are different between disc & drum), output shaft spec, etc. this is a bespoke tailored fitment to suit the car in question.

The 1st 2 COMPLETE NEW DIFFS, 4.1:1 & 3.9:1 ratio's, were fully machined & fully assembled for a Lotus 10 in early May 2014, these had disc brake / caliper mountings, as of September 2018, last race of the season,  they have been successfully raced & proven with 2 minor problems which were easily rectified, the same customer had another complete new diff with a 4.27:1 ratio in 2019, all 3 diffs have only had oil changes & service inspections since manufacture.

2023/24 Another 2 diffs supplied to customer requirements, a 4.56:1 ratio & a 3.9:1 ratio, with this order we have uncovered a major problem which has resulted in a redesign of the LH driveshaft, we have 5 more casings & all of the associated parts for new build & ongoing service 

Basic diff unit comes with output shafts, back plate, etc of a known spec.

Various ratio's available 3.08:1, 3.54:1, 3.73:1, 3.9:1, 4.11:1, 4.27:1 & 4.56:1 ratios, some of these ratio's can be included in the STD basic price, some cannot.

After our 1st tests, all crown wheel & pinions are now Super Finished (unless otherwise asked) for an easier & quicker break-in and less overall heat in the diff unit due to reduced friction, also more strength as its like but not as good as shot peening.

We cast the batch of 10 casings & have now machined them all of (March 24) of the 3HA light alloy diff cases, the independent type as fitted to Aston Martin DB3, Lotus IX, (X) 10 & others, Lagonda 2.6 & 3 ltr if you are that extravagant, & a great many other 1950s cars, these diffs are capable of handling a considerable amount more horsepower that the original 3HA diffs.as the casing & internals are suitably beefed up.

The original casting was made by Perry Bar Metals in Birmingham in the early 1950s,our own castings are suitably strengthened over the original with extra ribs & thicker walls in certain places, the 1st casting has been sectioned & mods to the pattern then made a further 10.

/The 1st 2 'Lotus' cases were fully machined to take a proprietary diff & Crown Wheel - Pinion giving various ratio's stated above, this mean't that the genuine 3HA gears didn't fit any longer., this was a non STD item & incurred extra costs to the end user.

The case is designed to take a STD open diff, a special open diff which can take more ratio's, a special plate type LSD or a special Torsen Gleason locking diff, all three types are designed by & are available with an open diff from Four Ashes, the specials are at extra cost.

The newly designed HD output shaft, bearing support housing & easily available pair of bearings, seal, o ring &  nut for drum brake or disc brakes are available from Four Ashes.

We keep a full range of minor spares (seals, bearings, gaskets, shims, spacers) for these diffs in stock, the larger spares can be normally 'in stock' in working 5 days.

Note that these diffs do not fit any other Aston Martin's other than a DB3 sports racing car or a Lagonda.

Original Lotus 10 diff in lower photo's

If a casing is required to take genuine 3HA internals please contact us & we will machine a case to exactly 3 HA measurements.


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