Spitfire & GT6 Forum

Yes, I know, I'm lucky. By now, I've been through pretty much every inch of my '66 and this is really the first find that I've had where the PO can be called a DPO.

At some point, the leaf spring was removed and somehow 2 of the 6 studs that go into the diff case were misplaced. Instead of ensuring an adequate replacement, it looks like the DPO used two bolts, of the wrong length and maybe of the wrong thread pitch and screwed them into the empty holes. Both did not fully thread into the diff case and therefore were not fully tightened against the retaining plate, providing the ability for movement.

So, over however much time the car was driven like this, those 2 poor holes became rounded out and the threading stripped. So, while this may be repairable, it probably isn't by me (weld buildup and re-tap is the only thing that I can think of) or I would have to use a bigger stud...after finding (or making) one of the correct length and all that. Fortunately, I have another diff still on the '64's frame, thought it's rear mounting bolt is seized in good. Given that the frame has already been hacked up pretty good, I may just be cutting it out and using it instead.

All that being said, I do consider myself lucky in the PO/DPO department overall.

Cheers,
Chris

The first pic shows the 4 studs (correct) and two bolts (not so much)
The second pic shows one of the bolts in the hole...I didn't have to screw this down. I just pushed it a bit. Nice.

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I learn something new every day...especially if I am working on my LBC!
Please visit my blog and website at http://www.roundtailrestoration.com
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Edited 1 time(s). Last edit at 2016-06-11 09:02 PM by cmfisher4.

The good news is that you don't absolutely NEED the two "middle" studs to hold the spring, but you would need to at least block off the holes somehow.

I'm sure there are others here who know much more about helicoils and other thread insert processes; the diff case might be saved, after all!?

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http://www.fairpoint.net/~herald948/database/

Oh, yeah, helicoils. Forgot about them. I've used them in my navy career. They may just be the ticket! Thanks, Andrew.

Besides, I would never trash this thing. I looked on Rimmer's just to see if the studs were available and rebuild diffs are close to $1000, including core charge.

Chris

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I learn something new every day...especially if I am working on my LBC!
Please visit my blog and website at http://www.roundtailrestoration.com
and my YouTube Channel at https://www.youtube.com/channel/UC8LASST0WuNG0-po4hK0Maw

When I was a Heavy Equipment Mechanic, I had a senior mechanic show me how to drive in track bolts with a sledge hammer when the holes get rounded like that. According to him, you first have to ask does the car "deserve better or not"! That old D6 did not by the way.

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Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace
2018 jaguar XE

Besides the obvious, it looks that perhaps the studs were in upside down as well, or, they are the wrong ones. The stock ones should end up with only about enough thread sticking up above the nut to hold about 3/4 od another nut.
Dan

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Dan Aycock
Walla Walla, Wa.
Yellowhawk Valley Spitfires
69, 69, 72, 75, 78, 79 Spitfires

Dan,
Surely not upside down, the holes aren't blind. They go through into the inside of the diff, so long threads would hit something in there. I think those are for a lowering block, though why so much thread is still open to question.
All the best,
Paul

Yeah, that was sort of my thinking about them just being the wrong ones. Obviously the other 2 are wrong.
Dan

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Dan Aycock
Walla Walla, Wa.
Yellowhawk Valley Spitfires
69, 69, 72, 75, 78, 79 Spitfires

Chris, I am no expert here but I can say and show that my 79 only has 4 in the setup. I just recently replaced the leaf spring and had great fun re outfitting the new with the old housing unit. Extra fun when the nipple of the center bolt did not nest...learning everyday that you should always check first in-spite of enthusiasm. Cheers, Jeff

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79 Spitfire (Barn find / Survivor)
Enjoying every minute of it

Jeffory,
The newer design leaf springs used four studs instead of six. Probably had something to do with letting the spring slide inside it's housing a bit, a means to correct the horrible jacking the rear of the car would experience under hard cornering. Here's an interesting article I found, along with others, on the subject.

Cheers,
Chris

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I learn something new every day...especially if I am working on my LBC!
Please visit my blog and website at http://www.roundtailrestoration.com
and my YouTube Channel at https://www.youtube.com/channel/UC8LASST0WuNG0-po4hK0Maw

You do not need the two inner studs.
To fill the two stripped holes, I suggest a couple of corks.

Seriously, a couple of corks is all you need, to prevent debris from entering the diff case.

Or, you could get all fancy and use a couple of molded caplugs.

But a couple of small rags, or even paper towels stuffed into the holes will do just as well.

The 4 outer studs do look a bit iffy, but as long as the nuts tighten down the top plate to firmly clamp the spring into the pocket, all is well.

45 ft-lb, ( == a good 90 lb tug with a 6" wrench)



Edited 1 time(s). Last edit at 2016-06-14 06:25 PM by clshore.

I have a whole other differential, with all 6 studs/nuts. I'm not sure the shape it's in, but I'm sure I can make one good one out of two okay ones.

Thanks,
Chris

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I learn something new every day...especially if I am working on my LBC!
Please visit my blog and website at http://www.roundtailrestoration.com
and my YouTube Channel at https://www.youtube.com/channel/UC8LASST0WuNG0-po4hK0Maw

Chris,
It is a relatively simple job to swap the rear case if the two diff units are the same. If they have different input flanges it may not work. If you are working with diffs for your cars and not swapping in one from the 1970s you only have to be aware of the change that occurred at diff number FC120 000. Units after that number aren't compatible with ones before it.
If the units are compatible you just undo the side plates and pull the output shafts out. Then unbolt the circle of bolts holding the rear case to the front. A new gasket and bolt things back together using the other rear case. Beware this is a time when "while I'm at it" can strike. I would take advantage of the opportunity of installing new output shaft seals though.
All the best,
Paul

Got it. Thanks, Paul. The diff is off of a '64, so it should be a simple swap.

Chris

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I learn something new every day...especially if I am working on my LBC!
Please visit my blog and website at http://www.roundtailrestoration.com
and my YouTube Channel at https://www.youtube.com/channel/UC8LASST0WuNG0-po4hK0Maw