Differential Decisions

[Chris01573]

Hi All,

So after some general advice.

I have the diff that came in my project car which is the correct 3.7:1 for a manual gearbox.

I also have a second diff that i purchased as a spare becuase it felt very smooth and tight... However it turns out that this is a 3.45:1 Diff with the 4 stud backplate to suit a stag. Having examined both, the 3.7 is OK no damage but has too much backlash on both the crown to pinion and on the sun&planet gears.

TD fitchett will charge me £500 for a recon unit or I strip both the diffs I have and build up one that is good for a lot less.

Does anyone know what the value of the 3.45:1 Diff might be if I were to sell it. ? Some pics below...

diff1.jpg Diff2.jpg

[MikeParker]

Hi Chris,

I would recommend trying to fix the backlash in your original diff if you fancy doing the job. I did mine without too much trouble. There are two sets of thrust washers that go and generally cause the backlash. There are some fibre washers on the sun gears (from memory) which, as you might expect, are prone to a lot of wear and some phosphor bronze cupped washers on the planet gears which had worn quite a bit on mine. I changed both sets and ended up with a diff with virtually no backlash. You can do the job with the assembly in the casing, so no need for special tools to pull the casing apart. You just need to drive out some pins that hold the axels in place. Just note where everything goes! One of the more satisfying jobs to do on a Stag!

Mike

[mole42]

On the other hand, several people use 3.45 diffs to lower the engine revs at motorway speeds. It's a popular conversion.

[Goldstar]

You might get £100 for a good diff on a good day (see eBay sold prices). As Richard says no harm in fitting the 3.45:1 unless you’re trying to leave rubber on the road at the traffic light grand prix - you could then does as Mike suggests at your leaidurenand change it over if you don’t like the 3.45

[NeilR]

Excess backlash between Crownwheel & Pinion requires shimming & meshing adjusting.
Very time consuming & you need some shims + possibly a new collapsible spacer.

The Sun/Planet backlash is relatively easy & quick to sort. As previously mentioned, can be done without removing crownwheel assembley for casing and can even be done
with diff still on the car, although it's far easier with it removed.

[sujitroy]

I've messed with a few different but not taken completely apart. I have a few YouTube video I made. I recall early and late diffs. early diffs use a collapsed something. use it once. This one is a bit more involved to work on I recall. some size shims are not available for the sun gears. Getting the contact point t between pinin and crown is critical and time consuming. a fellow in USA rebuilt his. He had it in and out of his car a few time and eventually got it running right. He reduced the whine. This guy has energy and patience. There are many documents floating around on how folks have rebuilt them. I have time but no strength to get that heavy diff in and out of the car.
Also, you many not want to mix and match gears between the two diffs.
Sujit

[Chris01573]

So looking at both diff inputs one has a castellated nut the other has a nyloc. I assume the nyloc indicates a crush spacer that would have been used to set preload ?

[mole42]

So looking at both diff inputs one has a castellated nut the other has a nyloc. I assume the nyloc indicates a crush spacer that would have been used to set preload ?

If they have been assembled correctly that will be the case. The nut castled for a split pin will indicate that the pre-load is set with shims, and bear in mind that the early diffs used different pinion bearings. Don't turn the diff with a spanner on the Nyloc nut - you'll likely upset the pre-load!

[Chris01573]

Ok thanks Mole if the preload is no longer as high as it is stated in the ROM should the nyloc be tweaked to increase it ?

[jbuckl]

It’s ok to tweak if you can measure the torque to turn.
If it exceeds the spec, you may well have to disassemble to get back to within spec.

imho the most important thing is to try and keep the diff at the correct oil level…. They have a habit of self emptying

[mole42]

Ok thanks Mole if the preload is no longer as high as it is stated in the ROM should the nyloc be tweaked to increase it ?

My understanding (bearing in mind that I've only rebuilt a few Triumph diffs) is that it is only possible to reduce the pre-load by tightening the Nyloc, and thereby squeezing the collapsible spacer a bit more. If the pre-load is lower than specified, then a new collapsible spacer is recommended and a new Nyloc....because loosening the nut will not increase the pre-load.

[Chris01573]

Thanks All, Just trying to get my head around how you would lock the pinion shat in order to nighten the nut ROM shows a flange and special tool that I assume fits over the shat with a hol in to tighten the nut through, any way of doing this without the tool ?

[trunt]

I’m going to do a Drew..

Tech section…

https://www.socforum.com/forum/forum/stag-owners-club/technical-section/powertrain/769336-diff-overhaul-from-don-kennedy

[jbuckl]

Thanks All, Just trying to get my head around how you would lock the pinion shat in order to nighten the nut ROM shows a flange and special tool that I assume fits over the shat with a hol in to tighten the nut through, any way of doing this without the tool ?

sent a pm

[richardthestag]

On the other hand, several people use 3.45 diffs to lower the engine revs at motorway speeds. It's a popular conversion.

Agreed for automatic transmission cars however it is a right royal pita with the manual gearbox. Clutch engaged at idle speed and the car is rolling at nearly 10mph. Fabulous for motorway speeds, ****e for crawling traffic.

have the t-shirt for this one gents. I have a 3.45 in mine that will be coming out very soon. If I ever manage to get any workshop space that is