Differential rebuild

[rogerguzzi]

Hello Learned Friends

                                    Roger two times numpty here!

The story begins at Stoneleigh on Sunday when I spotted a Spitfire Differential priced at £60

and marked as a 3.89!(now part of my brain said mine is a 3.63) but looked in a couple of books on sale and they said Spitfire used 3.89!(I thought the old brain is going and perhaps I was thinking of the TR6 one I rebuilt)

So I bought it for £50 as it seemed to have less slack in it than mine (worn inner shafts and sun wheels)

But when I got home and checked my books (B******r they are 3.63)

But then I thought (dangerous process!) I run a 28% overdrive so what would the overall ratio be? As Spitty is a bit sluggish at times.

So after a bit of Mathematics and brain ache I came to the conclusion it would be ok.

Standard Spitfire is 18mph @ 1000rpm and 22.6 mph @ 1000rpm in o/d

My Spitty is 18.5mph @ 1000rpm  and 23.2 mph @ 1000rpm in o/d (175 x 70 x13 tyres & 28% o/d)

Standard Spitfire is 3111rpm @ 70mph

My Spitty is            3017rpm @ 70mph

With a 3.89 differential fitted it would be  17.3mph @ 1000rpm  and 21.73 @ 1000rpm in o/d

So @ 70 mph @ 3221rpm

So 204rpm more than now or 110 more than standard

So I stripped it and decided to fit new Timken bearings (numpty 2 coming)

Trawled fleabay and found all six from 3 different suppliers for £58

The 2 pinion ones arrived today and guess what this numpty had ordered the wrong one for the pinion head it is the right o/d but the i/d is 1 3/16” and not 1 1/16”(B*****r)

So I looked at the one fitted and it looks pretty good but then I thought (dangerous) what about if I sleeve the pinion? And maybe incorporate the spacer shim as part of the sleeve? (can anyone see anything wrong with this idea?)

This bearing is £14.90 as apposed to £50/60 and is a Timken!

So what do we all think? (you can tell me I am an idiot I will not be upset much)

Roger

ps I used this site for gear/speed calculations(Minty Lamb is down) If the results are correct it is a great and easy site to use!

http://endtuning.com/gearratios/

 

[Pete Lewis]

the main problem with any pinion bearing change is getting the conical mounting distance correct the very accurate dimenesion from the head of the pinion to the centre line of the crownwheel ,

you can fit the old outer ring and measure the height of the pinion  then replace and replicate this dimension, its might or might not be the same 

have you got a spreader for the bearing caps, if the preload on these two bearings is low then they will shift under load and alter the mesh , thats why they are pre loaded , so  the assembled pinion height must be exact, the backlash set to whats etched on the crown wheel and the pre loads up to scratch

then you can have a cuppa

never mind if the ratio's are slightly different ......or the diff will whine more than i do !!!

Pete

[dave.vitesse]

I agree with Pete's comments.  For Ref - The Mk4 Spit, 1300, used a 3.89. Prefix FH. The later 1500 Spit used 3.63. Prefix FR.

Dave

[rogerguzzi]

Hello Pete

                 I have already measured the pinion height, I could not see any etching on the crown wheel or pinion?

I thought I would make a loose sleeve first so I can mess about and get the height right then make one that is tight on the pinion and lock tighted and finished off between centers so I know it is true!

That should keep me quiet for a while?

Roger

 

[Pete Lewis]

whats  whats normally on the end of the pinion is the best run position variance from the cross over of cone projection and crownwheel centre lines

as + or -   number of thou

 

if nowt etched on the crown wheel take it as whats in the WSM.

you only need to sit the inner bearing ( pressed on the pinion) on a height block and run a vernier + dti over the head

what fits between it and the overun outer race doesnt matter apart from pre loads .

 

 

[rogerguzzi]

On 11/9/2017 at 1:44 PM, Pete Lewis said:

whats  whats normally on the end of the pinion is the best run position variance from the cross over of cone projection and crownwheel centre lines

as + or -   number of thou

 

if nowt etched on the crown wheel take it as whats in the WSM.

you only need to sit the inner bearing ( pressed on the pinion) on a height block and run a vernier + dti over the head

what fits between it and the overun outer race doesnt matter apart from pre loads .

 

 

Hello All

               I am slowly rebuilding this differential!

I have made a sleeve to fit over the pinion so I can use the cheaper Timken bearing(identical except the bore size)

I pressed it into place with bearing loctite (for belt and braces) and incorporating the spacer then did the final maching between centers so I know it is true.

Now I am setting the preload and according to the WSM without the oil seal it should take 15 to 18 inch/pounds to turn(now I have done 2 before this one but the old brain is going!)

If I hang a 1lb weight on a bar 15" long from center of pinion is that 15"/lbs? (I have shimmed it and tightened it to 90ft/lbs and it only takes 10/12oz to turn it) but by hand it feels tight!

What do you all think?

Roger

[Pete Lewis]

12 oz is  not that far off 16 oz  I would go with it