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3.33 Differential?

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533657 by Taco ...Nor am I with spitfire differential rebuilding experience obviously but the "flat" thrust washers were the ones I'm reasonably certain were replaced with fiber washers on the late models. That flaw and the substandard roll pin used to secure the cross pin negated much of the advantage of the stronger carrier & sun/planet gears added to late model differentials according to what I've researched.
..So swapping fiber for copper thrust washers is what some apparently have done. The weak roll pin... I don't know how or if that was remedied. I'm thinking without proper copper (better yet - bronze) thrust washers and a suitably strong securing roll pin for the pinion cross pin, the late model differential "should" of been superior but in actuality, wasn't...unless someone made the appropriate corrections

Thanks,
I had assumed that was so based on postings.

Here is the Rimmer link showing one:
https://rimmerbros.com/Item--i-ATA7039

Flat washers made of bearing bronze are something that any machine shop can make up, to any thickness.
In fact, you can buy the stock in desired thickness, and make washers using only hand tools.
Copper is better than fiber, but bearing bronze is by far the best.

As for the roll pin, it's only job is to keep the cross shaft from sliding loose from the carrier, there is no load imposed on it, no matter how hard the diff is stressed.
Staking the roll pin or peening the surrounding material can prevent it from coming loose.

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Taco Richard Dalrymple
Hope Mills, NC, USA   USA
In reply to # 1533674 by clshore Staking the roll pin or peening the surrounding material can prevent it from coming loose.
As far as the bad roll pin is concerned, it seems I recall they broke or fractured into pieces, but I'm not certain.
I do have a good variety of brass shim sheets on hand (Zoro), but not sure how suitable that is. Punch dies of that size I don't have.

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533678 by Taco
In reply to # 1533674 by clshore Staking the roll pin or peening the surrounding material can prevent it from coming loose.
As far as the bad roll pin is concerned, it seems I recall they broke or fractured into pieces, but I'm not certain.
I do have a good variety of brass shim sheets on hand (Zoro), but not sure how suitable that is. Punch dies of that size I don't have.

Fortunately, there is no requirement for the inner and outer edges of the washers to be precision machined, only that they fit.
They could be glued or clamped between two pieces of wood and cut out with a holesaw, jigsaw, coping saw, etc.
then smoothed with a file, sanding block, etc.

As a young man I had the luxury of working at a machine shop that had a punch press and large assortment of die sets.

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Taco Richard Dalrymple
Hope Mills, NC, USA   USA
I have read and viewed videos of cutting shim material by sandwiching the material between thin wood plates & cutting with a hole saw on a drill press. That I could do. I also have a small punch/die set that I could begin the inner hole of the donut with and finish with medic scissors or "penny cutters" as we called them in the Army. As you suggest, they don't have to be "pretty" they only need to be the correct thickness and remain in place. I have a very good selection of brass shim to choose from. Nice experiment for tomorrow..

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
The flat fibre washers (ATA7039) appeared in diffs from about 1973 onwards - the early Mk4 Spits had the original type copper/bronze washers. Canley Classics in the UK still sell the copper version, part number 134075, at £1.60 each. It might be worth considering a group buy to save on postage costs!

The pin retaining the cross shaft was originally a solid steel pin (about 1/8" diameter), but was replaced later by a spring steel roll pin, obviously easier to fit for the guys on the assembly line, but much weaker and more likely to fail in use. The solid pins are a fairly tight fit, and are retained by staking the holes in the casting. I've recently rebuilt a late US spec Spit 1500 3.89:1 diff, and found a complete spring roll pin plus half a broken one in place. As that diff was brand new when I bought it, it says a lot for the factory's build standard. That diff also came with only one fibre thrust washer, and no sign of the second one ever being fitted!

Apart from these two defects in the 'strongest' diff assembly, the crushable spacer on the pinion shaft is the other point of weakness, introduced to make it easier to get the pinion bearing preload set during assembly. The downside is that although the smaller pinion bearing inner race is firmly clamped between the input flange and the crushable spacer, the larger bearing's inner race is pulled hard against the shoulder on the pinion shaft, but is unsupported on the other side. All is OK until wear develops in the bearings, and the crushable spacer is free to rotate on the shaft - and maybe gets crushed a little bit more..... maybe one of the reasons that the late diffs get noisy. The earlier diffs (up to about 1973) had the pinion bearing preload set by a solid spacer and shims between the two inner races - much harder to set up, but this setup firmly clamps the assembly, and nothing moves!

It's perfectly possibly to fit the earlier solid spacer system to the late diff - the solid spacers are still available, although you may have to hunt for the shims. (I bought some general purpose shim washers from an online bearing stockist.). Ideally, the nyloc nut on the end of the pinion shaft should be replaced by the earlier castellated nut & split pin, but that means drilling the threaded section on the pinion shaft to take the pin. In reality, as long as a new nyloc nut is used, and it's fully torqued up, it won't move in service - especially with a few drops of Loctite or similar on the threads.

Timken bearings are reputedly the best for this application - I managed to get a couple of Timken taper roller bearings from a UK supplier, but sourced the others from Rock Auto in the US. Postage costs made them expensive, but still cheaper than those I could find in the UK!



Edited 1 time(s). Last edit at 2018-05-17 06:13 AM by grumpicus.

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533687 by Taco I have read and viewed videos of cutting shim material by sandwiching the material between thin wood plates & cutting with a hole saw on a drill press. That I could do. I also have a small punch/die set that I could begin the inner hole of the donut with and finish with medic scissors or "penny cutters" as we called them in the Army. As you suggest, they don't have to be "pretty" they only need to be the correct thickness and remain in place. I have a very good selection of brass shim to choose from. Nice experiment for tomorrow..

As well, the 'shims' (they are actually thrust washers) don't have to be one piece.
To achieve the needed thickness, 2 or more thinner ones can be combined.
Probably best to avoid extremely thin ones though.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
Again, your wealth of information is greatly appreciated gentlemen. Steve, it's probably a good thing we have an ocean separating us or I'd be knocking on your door daily.

There is no rush on this project. I passed on a complete, sealed, mid 75' differential yesterday because the FH production number preceded the RKC1983 carrier designation. Don't know, maybe I let a good deal fly, a 150 mile round trip and $200 probably could of put it in my truck. No longer available so one less thing to fret over I reckon.
Best probably to wait and find a known good RKC1983 carrier including sun/planet assembly, front cover and matching caps. Then I should have a pretty good idea of what I'm buying.
I can then replace the shims and crush ring with a proper spacer. Do it right a not look over my shoulder, always wondering if I made the right choice.

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wfrmkr Doug Hackler
Boise, ID, USA   USA
I converted my '78 1500 to a 3.63 gearset from a TR7. The car and I am much happier at highway speeds. It was also nice to be able to replace the speedometer gear with a stock part and maintain a reasonably accurate speedo. My understanding is that the 3.63 was standard Spitfire equipment in some European markets. It works great and I highly recommend the conversion.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1533774 by wfrmkr My understanding is that the 3.63 was standard Spitfire equipment in some European markets. It works great and I highly recommend the conversion.

Correct! - All UK and most Euro Spit 1500s had the 3.63:1 ratio, with or without overdrive. The exception was the Swiss version, which had the 3.27:1 ratio to satisfy local emission regs, apparently.

The rumour was that the UK Spit got the 3.63:1 ratio in order to achieve 100mph (just!) at around 5,500 rpm, making it a 'true 100mph sportscar' as the marketing guys at Triumph claimed at the time......

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533786 by grumpicus
In reply to # 1533774 by wfrmkr My understanding is that the 3.63 was standard Spitfire equipment in some European markets. It works great and I highly recommend the conversion.

Correct! - All UK and most Euro Spit 1500s had the 3.63:1 ratio, with or without overdrive. The exception was the Swiss version, which had the 3.27:1 ratio to satisfy local emission regs, apparently.

The rumour was that the UK Spit got the 3.63:1 ratio in order to achieve 100mph (just!) at around 5,500 rpm, making it a 'true 100mph sportscar' as the marketing guys at Triumph claimed at the time......

USDM owners should not expect that fitting the 3.63 in place of the 3.89 will make their cars capable of 100 MPH.
You would also need the Euro engine configuration, cam, carbs, manifolds, ignition, etc.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
Another question folks if you don't mind, does an "FH 10620" differential, qualify as a "FH 106101 and up" differential? In other words, is it likely if in stock condition, to have the RKC 983 carrier and 15 tooth sun wheel gears?

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spitfire50 Paul Mugford
Rochester, N.H., USA   USA
Richard,
No it could be around 95k units too early. 106101-10620=95481 There may be gaps in the sequence, but the numbers were used in order. Triumph didn't skip some then use them later.
All the best,
Paul

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
If the stamping of the numbers is anything like that on my FH107XXX unit, where the numbers were badly stamped and out of line, it's possible the last digit is very faint and difficult to see. I'd give the casting a scrub with a wire brush, to see if there are any more digits lurking in there!

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
I appreciate the confirmation folks. Steve, if I cannot locate an FH 106101 and up diff what is the next best differential to build my 3.63 ring/pinion around? Thanks, Ric

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1534509 by Taco I appreciate the confirmation folks. Steve, if I cannot locate an FH 106101 and up diff what is the next best differential to build my 3.63 ring/pinion around? Thanks, Ric

Ric - all the diffs fitted to the Spit Mk4 and 1500 up to FH106100 use the same carrier (21H5478), so that's what you'll be using if you can't find a later diff! The early Mk4 diffs (up to around 1973) used the solid spacer and shims on the pinion shaft, and the copper/bronze thrust washers, so the sun & planet gears may have survived better - but that's about it. If you're using the 3.63:1 pinion, they all came with the nyloc nut, as they originally used the crushable spacer. As I said previously, you could possibly use the earlier castellated nut and drill through the threaded part of the pinion shaft to fit a split pin if you really wanted to, but a new nyloc nut and a drop or two of Loctite will be fine.

To improve the survival chances of the 21H5478 carrier, it may be worth smoothing/filing the surface to remove any slight nicks or depressions where cracks may possibly start, but if you do that, remove as little material as possible.

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