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Triumph Repair/Mk IV 1972 1300CC Spitfire


QUESTION: The differential on my car is making a whining noise and I think it needs a rebuild. Can you help with shimming/spacing data or any other information I would need?

ANSWER: Hi Albert,

The pinion bearing preload is 15 to 18 in lbs (0.17 to 0.21 kgf.m)(set with shims and be sure to put the chamfered end of the spacer toward the drive flange.)
Ring gear back lash is .005 in (0.13 mm)

To set the preload on the carrier bearings you need the manual because Triumph has made a puzzle of it. The earlier Spitfire manual makes no sence at all but if you get a manual get the later 1500 manual which is easier to follow. (same procedure) If that is not possible let me know and I will post that procedure on my web site for you to copy.

They have used the shimming and preload of the carrier assembly to set back lash between the ring and pinion and achieve carrier bearing preload in one operation without moving the pinion forward or aft.


---------- FOLLOW-UP ----------

QUESTION: Hi Howard,

thanks very much for your quick reply and the information. I have checked my manual, but do not make any sence as you said, please, please, please send me your procedure

I put 3 pages up on my web site for you to copy. Page 1 & 3 are of some use. Page 2 is just about setting up the pinion with the factory tools and you are not going to have them. All of this is easier when you have all these special tools. But it is not necessary and can be done without them. I rebuilt a lot of differentials of MG, Ford and other brands and only a few of the dealerships that I worked in had the special tools to set up a differential. I learned to use White Lube on the teeth to see the pattern for setting pinion dept. In your case I would not change the pinion dept by leaving the first spacer between the pinion gear and the bearing as this it what sets the pinion dept. If you are replacing the pinion bearings, only set the pre-load with shims and don't change the pinion dept unless you see a poor wipe pattern on the gear teeth using white grease.

If you don't have a spreader you may need to make one which is not hard if you have fabricating equipment. Even in dealerships I had to make one when I had a job that needed it and the dealership was going to take too long to get the one they were suppose to have.

I have not done a Spitfire but from what the book says it looks like they get a base line figure to start with, labeled "A" on page one and then taking into account the .005" gear back lash they add figures to arrive at a pre-load on the carrier bearings by math listed on page 3 of my papers. Just keep in mind as you spread the differential case don't spread it more then .008" so as not to damage the case.

I have rebuilt differentials on odd import cars that no manuals were available so I would just guess what to set everything at. But in reality most differentials set close to the same. I rebuilt a heavy duty Ford truck for a Ford dealership one time and I was surprised to see the specs almost the same as an MGB.

Some differentials were easy to do because they had the pre-load shims on the outside of the outer bearing races like yours, thus making it easy to set. Others put the shims under the inner bearing race so you have to continue to press off the bearing which was a pain.

You will need to purchase several extra shims for the carrier bearings to arrive at the correct pre-load and set the carrier assembly right or left to have the correct back lash.

On other differentials I found it easier to do by them quoting a .002" to .004" pre-load. So I just adjusted the side shims so that I had no pre-load and no side to side movement. then I added what ever they said was the correct pre-load (.002" to .004") and then checked back lash and if the back lash was over .005" (very common on most differentials) I just removed shims from one side of the carrier assembly to the other side thus keeping the pre-load I had set and moving the carrier closer or further from the pinion gear to get the .005" back lash required. Then a final test of white lube on the teeth to see that the pattern was correct and it was finished and I could expect it to perform well for a long time.

The Spitfire is basically doing this in one step with their math but when you read it, especially in the older shop manual it makes no sense at all. This is from the 1500 shop manual which is a little better but still confusing. Since you know you are not to spread the case more then .008" then you know the end result of the pre-load has to be less then .008" and you know that they set back lash with the side to side position of the carrier assembly it boils down to my old method of setting (ZERO) pre-load first and then add shims to get a preload and I often use .002" to .004" on other differentials then after I have that, I check back lash and if it is wrong I simply move shims from one side to the other to get the correct back lash and a final test of white lube will tell if the gear pattern is correct.

You can use the Triumph math way if you like but I just wanted you to see what I did.

Let me know,
Howard       Go to my web site at and change the ending to page2.jpg and page3.jpg  

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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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