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3.33 Differential?

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Taco Richard Dalrymple
Hope Mills, NC, USA   USA
"21H5478" is cast into the carrier. Rimmer says that carrier could belong to Spitfire MKIV/1500 up to FH106100 or GT6 MK3 from KE/KF200001 and or finally, as purchased, Triumph TR7 with 4 speed.



Edited 1 time(s). Last edit at 2018-05-15 08:43 AM by Taco.

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533169 by 14GPDJENGINEERING Yes, it is a live axle and to use in a Spit you will have to swap the Casing - Housing - Front Pinion.

https://rimmerbros.com/Item--i-GRID006128

Or, as noted, drill & tap the 4 holes yourself.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
I see no provision (bosses) to drill & tap therefore I will be needing another housing...

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533254 by Taco I see no provision (bosses) to drill & tap therefore I will be needing another housing...

In that case, you need a case …
(cheap buggers, how much metal was saved by deleting the bosses from the casting).
Lucky you, get to experience the joy & pain of fitting a crown&pinion set, shim packs, preload, (perhaps collapsible spacer), geartooth contact pattern, etc.
Be sure to obtain an assortment of pinion and carrier shims, perhaps the case donor diff will supply what you need, or some folks here will share.



Edited 1 time(s). Last edit at 2018-05-15 01:55 PM by clshore.

14GPDJENGINEERING Avatar
Silver Spring, MD, USA   USA
That case style without the front mount bosses goes back to the Standard 10. And that live rear axle was used in the early Lotus 7s.



Dennis smiling smiley

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
In reply to # 1533300 by clshore
In reply to # 1533254 by Taco I see no provision (bosses) to drill & tap therefore I will be needing another housing...

In that case, you need a case …
(cheap buggers, how much metal was saved by deleting the bosses from the casting).
Lucky you, get to experience the joy & pain of fitting a crown&pinion set, shim packs, preload, (perhaps collapsible spacer), geartooth contact pattern, etc.

I've been studying up on what's involved. The fiber shims should be replaced anyway, if they're even still there, one sun gear has a fair amount of "back & forth" play or "end float". First priority is a replacement casing, I've decided to keep the 3.89 diff intact. Any idea how much I should spend on a front case?

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533304 by 14GPDJENGINEERING That case style without the front mount bosses goes back to the Standard 10. And that live rear axle was used in the early Lotus 7s.

Master Foundryman to his mate:
"Hey Colin, go back into the storage shed, get that old wooden pattern, yeah the one we used to prop the doors open in the summer.
I hope the termites haven't gotten to it. They want us to make cases for something called a TR-7"

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grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1533219 by Taco "21H5478" is cast into the carrier. Rimmer says that carrier could belong to Spitfire MKIV/1500 up to FH106100 or GT6 MK3 from KE/KF200001 and or finally, as purchased, Triumph TR7 with 4 speed.

That's strange - the only carriers I've seen with the flat machined sides are the later RKC1983 type, apparently done that way to stress relieve the casting. (The information from Rimmers is correct, by the way.) The 21H5478 has no such machining, and is left 'as cast'. The later diffs (with the RKC1983 carrier) have sun gears with 15 teeth, the earlier ones have 16. Planet gears all have 10 teeth, it's just that the later ones have larger teeth. Note also that the taper roller bearings supporting the carrier were changed to suit the later version. Have a look at the serial number stamped on the TR7 front casting - if it's lower than CG51494, it should have the 21H5478 carrier, above CG51495 it should have the RKC1983.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
The serial number on the front casting is CG 31705 and the sun gears have 16 teeth. That should make it an earlier production according to your research.

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533306 by Taco
In reply to # 1533300 by clshore
In reply to # 1533254 by Taco I see no provision (bosses) to drill & tap therefore I will be needing another housing...

In that case, you need a case …
(cheap buggers, how much metal was saved by deleting the bosses from the casting).
Lucky you, get to experience the joy & pain of fitting a crown&pinion set, shim packs, preload, (perhaps collapsible spacer), geartooth contact pattern, etc.

I've been studying up on what's involved. The fiber shims should be replaced anyway, if they're even still there, one sun gear has a fair amount of "back & forth" play or "end float". First priority is a replacement casing, I've decided to keep the 3.89 diff intact. Any idea how much I should spend on a front case?

Given that Spitfire diffs commonly fail, and that most folks will simply replace them with a used part rather than pay to repair them,
used cases (those that have not been recycled as scrap) ought to be relatively plentiful.
You may have better luck finding an entire broken diff, and stripping it down yourself, since that's less work for sellers, particularly non-gearheads.
The bonus is you get some spare bits and pieces that may prove useful (shims, flanges, studs, etc.)
The downside is shipping cost. Best scenario would be a local seller that just want's to get rid of the old broken lump.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
Okay, trying to digest all of this, make some sense of it as best a novice can.
So.. if I want a complete 3.63 differential using the crown/pinion from my TR7 differential and preserve my good 3.89 differential intact and ready for spare use, my best option is:
Source a complete late model 1500 differential donor with 15 tooth sun gears and beefier planet gears. Replace all fiber shims with the "good" ones and go from there?

clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1533503 by Taco Okay, trying to digest all of this, make some sense of it as best a novice can.
So.. if I want a complete 3.63 differential using the crown/pinion from my TR7 differential and preserve my good 3.89 differential intact and ready for spare use, my best option is:
Source a complete late model 1500 differential donor with 15 tooth sun gears and beefier planet gears. Replace all fiber shims with the "good" ones and go from there?

You may have to gather pieces/parts from several sources to get all the goodies you want in one unit:.

3.63 gearset
strong carrier
strong sun & planet gears
metal thrust washers
Spitfire diff case with 4 front mounting holes.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
First of all, thanks for all the great knowledge Steve and Carter, I really do appreciate the education and guidance. The good news is the crown & pinion I have are in great shape and a matched set, both sharing the same engraved numbers. Now to find a FH106101 or later differential with RKC1983 carrier, stronger 15 tooth sun wheels & more robust planet gears plus some suitable, durable, shims/thrust washers. I believe any Timkins for the differential can be sourced new?
The 15 tooth sun wheel gears (UKC6281) and thin shims are the ones not available according to Rimmer. One question regarding this, is the RKC1983 carrier & heavier sun/planet arrangement actually proven stronger than the earlier productions or is it only "thought to be" stronger?

clshore Carter Shore
Beverly Hills, FL, USA   USA
Having never rebuilt a later model diff with the fiber parts, I'll just ask this straight up:

Are the fiber parts the flat ones or the spherical ones?

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
...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



Edited 2 time(s). Last edit at 2018-05-16 07:18 PM by Taco.

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