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Differential trouble

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moltenmetal Avatar
moltenmetal Paul Martin
Toronto, Ontario, Canada   CAN
1975 Triumph Spitfire 1500 "E-Fire"
Yep- definitely hopeful, which is better than despair...the only way we're going to know in my case is to get the thing out of the car and get it apart, so I'll let the local guy do that for me. If I'm in for a total rebuild, I'll know that soon.

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Igordiver Avatar
Igordiver Igor Duerloo
Kapellen, Antwerp, Belgium   BEL
1968 Triumph Spitfire MkIII "Thin Lizzy"
1977 Porsche 928 "The Shark"
Got back into it yesterday. With good results. smiling smiley
Have the diff out and there's little damage. The inner pinion bearing is broken, all other parts are intact.
Will be picking up parts tomorrow and refit. Getting ready for the slow proces of setting backlash.
Can anybody tell me what it is supposed to be and how much torque is required on the Dowel nuts and on the castellated nuts?

Kind regards













"Alterius non sit qui suus esse potest"

clshore Carter Shore
Beverly Hills, Florida, USA   USA
Bearing don't just spontaneously break apart.
Damage like that results from other hard steel bits getting ground up between the rollers and races.
All it takes is one piece of such debris to break a bearing, the resulting pieces circulate inside the case
and can cause the other bearings to break, as well as damage the ring/pinion gearset in a chain reaction scenario.

Even though the crownwheel bearings may appear undamaged, few of us possess eyes with micrometer
resolution needed to assess damage.

I'd replace all 4 of the roller bearings, unless you enjoy pulling and rebuilding the diff, and want more practice.

No matter what, you must thoroughly clean and purge the case and the components of all debris.
A powerful magnet is useful. Place it inside a Ziploc bag, and wipe it around every internal surface,
every nook and cranny. Plenty of solvent and compressed air to blow out holes and clear debris.
(the baggie allows you to easily discard any bits that stick to the magnet).

You really, really, really need proper directions from the Workshop manual to do this job correctly.
The pages are available from the web if you search.

Be patient, and be prepared to repeat the steps as many times as it takes to get the correct settings.
Getting 'close' is not close enough.

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Lizzard d id
san jose, ca, USA   USA
I'd not rebuild / work on that one . I'd find a nice used diff and buy it whole . That one has been run dry , I see dry parts that should be wet , I see sparkly metal where there shouldn't be any , I see funny looking gear faces , it will be a bad old diff no matter what you do . Do yourself a favor and buy a good used diff . They are not all that rare or valuable .

clshore Carter Shore
Beverly Hills, Florida, USA   USA
Yeah, 'metal sawdust' is always a bad sign ....

Azoth Shane G
Los Angeles, CA, USA   USA
You should buy the Bentley workshop manual and exhaust your google-fu searching for related information on how to do this.

If you're sticking with that diff, you have a fixed spacer that uses shims to set the pinion preload. This will be the first thing you need to get correct when rebuilding. Your shims look bent (and really thick?) from the picture, which is really strange. The best source I found for these shims was rimmerbros. There's another shim underneath your broken pinion bearing which is very important - keep the one you have and hope that it works out because finding replacements for these is not easy. You either need to have them made or buy them from ebay.

You will also likely need to replace the copper shims in the sun/planet gear cluster - there are two cupped washers (Moss carries them) and two flat washers (canley classics). The flat washers are a fixed size but the cupped washers come in multiple sizes and should be chosen such that there is zero backlash for the inner gear cluster. When properly assembled you may not be able to turn the gears by hand, but they will turn easily when you have the leverage the pinion gear ratio gives you.

The workshop manuals will have all the info you need on bearing preload numbers and backlash. Oddly enough they won't have all of the torque information for some of the interior fittings, but you can find that info here: http://www.triumphspitfire.com/Torque.html. If it's in the workshop manual use that information first though.

The basic process for rebuilding it goes like this: select proper shims to set pinion preload. You measure the preload with an inch-lb torque wrench (or metric equivalent). Remember to oil the pinion bearings before taking this reading. Also note that the important number is the preload once you're turning. I think the nut is something like 1 1/8". Once you have the pinion preload set, you can work on the backlash for the ring gear. This is done by shims between the carrier bearings and the case. The manual describes a formula for figuring this out, though in my experience it's more of a rough guide then an exact calculation. Your pinion preload will increase (something like 4-6 in-lbs) after you have the ring gear in place. Finally you should use a gear marking compound and paint a few ring gears to make sure you have your pinion depth set correctly. Worst case scenario you'll be taking the entire differential apart and changing the thickness of the pinion under the pinion bearing before doing this again (and again, and again...).

Don't rely on these rough instructions - get a book.

Igordiver Avatar
Igordiver Igor Duerloo
Kapellen, Antwerp, Belgium   BEL
1968 Triumph Spitfire MkIII "Thin Lizzy"
1977 Porsche 928 "The Shark"
Ok, thanx for the info.
I have found a manual. It says preload should be between 12-16 inch-lb. Converting this to Nm means between 1,35-1,80 Nm.
It also says : "One thousand of an inch shim thickness 4lb in torque"
So, common sense tells me that shim thickness should be between 003" and 004". But I got a feeling that common sense will not apply?
Can anybody shed some light on this?





"Alterius non sit qui suus esse potest"

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14GPDJENGINEERING Avatar
Silver Spring, MD, USA   USA
I think the meaning is a change of one thousandth of an inch shim thickness equals a change of 4 lb-inch in torque.
That is a decrease in shim thickness gives an increase in preload torque and an increase in shim thickness equals a decrease in preload torque.

As with transmission overhaul, all gears must be thoroughly cleaned for inspection.
All gear teeth especially on the pinion should be smooth and shiny -- no scoring, spalling, chips, cracks or broken teeth. If so the unit will be noisy and short lived.



Dennis smiling smiley



Edited 1 time(s). Last edit at 2017-11-06 11:00 AM by 14GPDJENGINEERING.

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Azoth Shane G
Los Angeles, CA, USA   USA
In reply to # 1496159 by Igordiver Ok, thanx for the info.
I have found a manual. It says preload should be between 12-16 inch-lb. Converting this to Nm means between 1,35-1,80 Nm.
It also says : "One thousand of an inch shim thickness 4lb in torque"
So, common sense tells me that shim thickness should be between 003" and 004". But I got a feeling that common sense will not apply?
Can anybody shed some light on this?

I would start at around 0.020" then add and subtract as necessary using that conversion as a rough guide.

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