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Spitfire Rear Diff, Spitfire Questions

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pjsmetana

pjsmetana

Jedi Warrior
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I didn't go surfing today, because my wife has a sunburn. You married guys understand. So, I finally got the back end up in the air and turned the rear while inspecting the Prop-shaft. Prop-shaft is fine. I don't know if this is a good or bad thing, as the noise is from the rear differential. It is amazing how rear noises can transfer up a tube and make you think its something else. At least I think its the diff, as when I grab a wheel and turn it back and fourth, or grab the prop-shaft and turn it back and fourth I get some solid low-pitched clanks from the diff.

This leaves me with a few questions. Mind you, this is my 1st and only RWD car that has the engine in the front, so bear (bare?) with me.

What is the factory ratio on an 80 Spit? Mine is labeled 3.63 on the underside with yellow paint.

If I get a new one, what ratio should I change it to for FL highway speeds? We have 70+mph, and figure a 3.5k to 4k revs at speed would be great. OD on of course. I don't know what it is atm, as I've never taken her over 55mph.

How hard is it to change the diff? I hear of people swapping them out for racing all the time, so I assume its a doddle, but I've never done it.

Is the diff heavy enough that I will need a 2nd person to help me? I've only got about 18 inches of room to work with mind ya. Ground to frame. Plus, I don't have any buddies that around here that know their rump from their elbow, when it comes to cars, so its gotta be something I can do myself, or I gotta have a station do it. Unless one of ya is willing to come help in exchange for some free surfing lessons :laugh:

What does rebuilding the diff consist of? Again, 1st RWD car that is not Mid or Rear Engined, so everything for me has been transaxles.

Any words of advice or cautions before I dive into this mess?
 
3.63 diff is available in u.k., but pretty rare around here. if someone marked it with yellow, maybe it came from a salvage yard? small chassis ratios were 3.27(GT6),3.63(U.K.),3.89, and 4.11. if you have a 3.63 rear, might be worth saving?
3.27 would give you good milage, but be slow off the line. 3.63 or 3.89 would be best in a spitfire.
diff probably weighs around 60lbs, maybe?
 
Not really a "home job" to set up a ring and pinion as there are clearance and preload issues. Best approach would be to get it out, relatively simple, and take it to a shop for bearings. Very unusual to whip the gears, they are probably salvageable. Doable even with the limited space available, take it slow and plan ahead. Don't get your hands between the pumpkin and the floor ! Possible to balance it on a floor jack to monkey it into position for the reinstall. Bob
 
It is now 10:40pm eastern time, and I've been under my car for a couple of hours installing my diff.
You will need to get the car up on jackstands... it makes it much easier. Next, you must have the diff on a hydraulic floor jack. Find a friend to operate the jack up/down, in/out at your command. I was under the car positioning the diff to get it lined up with the 4 mounting studs. It's not fun, but doable.
Safety first, keep clear of the diff... it weighs about 70lbs give or take. If it drops it could spoil your whole day.... be careful!

<span style="font-style: italic">edit: oh yeah... I have a TR6... don't know the setup for a Spit, but I assume they are similar.</span>
 
Pete,

while you are checking things out, check the u-joints in the halfshafts. you could have a joint going bad and hearing it in the rear. From what I hear the Spits can be pretty hard on the halfshaft ujoints.
 
Moderate clunks when you turn it back and forth aren't necessarily a reason for rebuilding the diff. It might just be some backlash, which is more or less normal.

This gets us back to running the drivetrain with the car up on jackstands, which I think we discussed before. That's what I did with my Stag, to establish it's diff was duff. Turned out to be two broken teeth on the ring gear.

Then the "rebuilt" diff I purchased turned out to have issues as well, so I went through it myself. Definitely "4 wrenches", but can be done. I would definitely suggest having a press, though, as you'll be doing many trial assemblies to get the gear mesh just right.

DSCF0065.jpg
 
Consider too,the flange bolts from the differential to the axles. The bolts may loosen and then bolt holes on the flange become egg shaped. That happens if the wrong bolts are used. T.T.
 
Don_R said:
Pete,

while you are checking things out, check the u-joints in the halfshafts. you could have a joint going bad and hearing it in the rear. From what I hear the Spits can be pretty hard on the halfshaft ujoints.
Click to expand...

My shafts all look brand new. I've had this car for about 14months, and it only has 22k miles on it.

Trevor Triumph said:
Consider too,the flange bolts from the differential to the axles. The bolts may loosen and then bolt holes on the flange become egg shaped. That happens if the wrong bolts are used. T.T.
Click to expand...

I don't think they are eggshaped, but I did check torque to make sure they arent trying to become eggshaped... and I'll be darned, every one of them needed about a 1/2 a turn. I pulled one out to make sure its the right size, and its very tight... as in, the threads just touch the hole all the way around. Good bolts too. Grade 8.

TR3driver said:
Moderate clunks when you turn it back and forth aren't necessarily a reason for rebuilding the diff. It might just be some backlash, which is more or less normal.

This gets us back to running the drivetrain with the car up on jackstands, which I think we discussed before. That's what I did with my Stag, to establish it's diff was duff. Turned out to be two broken teeth on the ring gear.

Then the "rebuilt" diff I purchased turned out to have issues as well, so I went through it myself. Definitely "4 wrenches", but can be done. I would definitely suggest having a press, though, as you'll be doing many trial assemblies to get the gear mesh just right.
Click to expand...

Against every safety conscious bone in my body, I ran it on jack stands with the front on wheel stands, facing into my garage. No odd noise. This was after torque checks mind ya. I then took it off the stands, rolled it out to the driveway, started it again, then took it for a spin with no tranny cover. I whipped it around, and shook the snot out of my car. The noise is gone. I'm amazed that so much noise can come from a few bolts just needing a little more torque.

Also, it is amazing to drive like this. Driving with the tranny tunnel off is a blast! You hear everything! You see everything! You even feel the heat of the exhaust! But, Man! Does it suck when you get up to speed! All the old dirt and grime comes off as the wind blows up and into your face! I want to spray a cleaner on it, or at least hose it off, but with all my interior being 'right there' I think I'll wait and do it from the underside when the tunnel is on :smile:

Thanks again for everyones support. I still have a hard time trusting it was just retorquing everything, but I'm sure time will tell me. I sure hope thats it! :smile:

One thing odd I did find though... when up on the jack-stands my Drivers Side Rear Wheel turns a whole lot easier than the Passenger Side Rear. Both turn by hand easy enough. Just seems odd to me that one side spins easier than the other. I don't think its brake drag, as I know what it sounds like after an adjustment, and its not like that.
 
FWIW, on my TR3A I got tired of those bolts always loosening up even with new Nyloc nuts (which BTW should be replaced every time); so I converted to what MMC calls "Oval lock with conical top locknuts" https://www.mcmaster.com/#catalog/116/3185 . Never had one come loose again.
 
Pete,

My halfshafts looked good, but after I pulled them I found that 1 of the ujoints was rough (rollers going bad).

Glad you found your noise, Back to happy motoring
 
This is encouraging news Pete!!! Mebbe there's a day-trip to Tampa in the near future?

This trap is baited with CAB, BTW. :wink:
 
DrEntropy said:
This is encouraging news Pete!!! Mebbe there's a day-trip to Tampa in the near future?

This trap is baited with CAB, BTW. :wink:
Click to expand...

Does "CAB" mean "Couple-A-Beers"?

A trip over to the wess-sie-eed of Fl may not be in the book for my Spit. Least not yet. I ain't been able to trust her over a few miles at a time, as she's shut-down on me twice in the whole 40 miles I've done on her since move'n back to my Home State of FL. I do love my Triumph dearly, and its just so much fun to drive, but if I have an appointment of any sort that has a time requirement on it, I drive my Honda. Plus, 55 on a 70+ highway is just darn scary! I don't like the idea of being rear-ended at speed, but I hate to think that it could be some generic car, like a Kia or a Hyundai, that ends up in my boot... as my car just deserves better than that! It could at least be name brand!
 
"Cheap Arse Beer" in point of fact. But I'd lay in somefin' special with a bit o' lead time.

I understand about the Spitty. No sense riskin' it to stuff like Interstates.
 
Pete,

I take mine out on the interstate. No problems and no overdrive yet.

I only put 3,000 miles on it last year.
 
I agree with Don. I understand your hesitation in terms of "trusting" the car (especially trusting it not to shut down), but these cars honestly WERE meant to run all day at 3000-4000 rpm or better. If a 40hp Herald 1200 with a 4.11 diff can run all day at 65 mph or better (that roughly works out to a bit over 4000 rpm) -- and mine has done just that -- a 1500 Spitfire with a 3.89 or 3.63 should do just fine!
 
right on Andy,

My Spit has no prob doing 3500 rpm on the interstate (3.89 diff). Most of the shows in my area are a bit of a trip for me. Even took it to Nazareth, PA on a whim to do the Martin Guitar tour.

Pete,
what shutdown issues you havin?
 
Don_R said:
Pete,
what shutdown issues you havin?
Click to expand...

None at the moment, but SHHHHH she might hear you!

Well, I took a bit of that "drive'r fast'r" advice today... and I got up to 'bout 57mph before I started getting a slight vibration, then backed off to 55. There may be an alignment in her future. Drives straight as an arrow though. I'll get that done, get the tires balanced, have a tuning shop adjust my carb and timing for higher RPM on the Dyno, and if its still there I'll finally get that prop-shaft balanced.

Ya know... for a while there I was complain'n that I didn't have enough to do...
 
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