rear diff - Page 2

feadam · #21 (**permalink**) 02-26-2020, 08:44 AM

The rep told me that they designed it after the original cobra (i think Lister also) 4HU case and that they came with the holes in top drilled. I looked at some photos of an original cobra diff and it had the holes on top drilled.

bcrumpley · #22 (**permalink**) 02-26-2020, 09:38 AM

Quote:

Originally Posted by feadam

gonna try, haven't done one before but I bet I can figure it out

I just installed an Auburn traction lock carrier & 3.54 gears in a Jaguar Salisbury 4HU differential and it was pretty straight forward, though not quite as easy as a Ford 8"/9". The only issue that I ran into was that the new carrier has a larger body than the original open one and it rubbed on the housing when shimmed to the spot that it needed to be in. Once I realized that, 30 seconds of grinding on the housing solved that.

feadam · #23 (**permalink**) 02-26-2020, 11:03 AM

The company I bought the diff from said its pretty straight forward, I think the bearings may be larger, but everything else interchanges.

feadam · #24 (**permalink**) 02-29-2020, 12:34 PM

This looks like color in the few I've seen painted original, now just letting it dry

feadam · #25 (**permalink**) 03-01-2020, 02:57 AM

better picture untaped

MAStuart · #26 (**permalink**) 03-01-2020, 07:38 AM

I did not ask. What are you building? After thinking about it I haven't seen any original rears with the holes drilled on top. You should have painted that area too. Hey it looks good that color.

feadam · #27 (**permalink**) 03-01-2020, 10:06 AM

So I have a book with original AC factory build pictures and it shows holes on top, the new reproduced cases dont have them because they really aren't needed. Somebody will probably correct me but the cases were used in Aston Martins and maybe listers and I think the top holes were needed. Ive seen black and the red color on them but not sure which cars used what color. I think 427s used the red, not 100% sure. Gonna try to do an original type car at some point, first have to move back from England. Was gonna buy one from the many manufactures cars over here cant get it back to states

Tom Kirkham · #28 (**permalink**) 03-01-2020, 10:27 AM

I would encourage you to look at two upgrades:

Change the original 19 spline stub axles to the 30 spline stub axles.
Drill the holes for the diff cooler.
Drill a hole for a temp sensor.

For a street car I would look at using a Eaton TrueTrac diff unit. Very reliable, and almost maintenance free. Also available in 30 spline.

I have not had much luck with Auburn diff units.

feadam · #29 (**permalink**) 03-01-2020, 10:43 AM

Tom
I might upgrade, but not planning on hammering this one as hard as I have in past with my other three cobras I've had. What did the originals come with, was it 19 spline and did they break easily? Do the rears have heat issues, is that why you recommend a cooler and sensor? I've wondered about heat being an issue but wasn't sure if I should put a cooler on it. Thinking about just cruising with this one, but I always think that and then I get in and back to driving the same again.

Tom Kirkham · #30 (**permalink**) 03-01-2020, 11:04 AM

Original Cobras had 19 spline axles.
Lots of 19 spline axles have broken.
If you are lucky the axle will have a ductile failure and just grind itself down.
If you are unlucky and have brittle failure the break will be a spiral and wedge the case apart. Remember, today's Cobras make more power, and have a lot more grip. The 19 spline axle is the weak link in the chain.

Most of the Shelby Team cars had diff coolers.

How can a limited slip be consistent, if the temperature is varying?

I am not saying you need a diff cooler for the street. Just that the mods are easy to do now and you can plug the holes. That way in the future, if you change your mind you can just remove the plugs and install the cooler.

rsk289 · #31 (**permalink**) 03-01-2020, 02:16 PM

On the subject of colour for differential casings, are you sure they were finished in red primer?
As a Brit with wide experience of sixties British sportscars of various makes, I know that many mechanical components were often finished in Glyptal. This looks like red oxide primer, but is very much tougher and resistant to chipping, wear etc. My Jag XK engine has the internal surfaces painted in Glyptal, which is still available. My Cobra's Kirkham diff is also painted with it.

https://www.electro-wind.com/glyptal...can-361-g.html

LMH · #32 (**permalink**) 03-01-2020, 02:50 PM

Quote:

Originally Posted by rsk289

On the subject of colour for differential casings, are you sure they were finished in red primer?
As a Brit with wide experience of sixties British sportscars of various makes, I know that many mechanical components were often finished in Glyptal. This looks like red oxide primer, but is very much tougher and resistant to chipping, wear etc. My Jag XK engine has the internal surfaces painted in Glyptal, which is still available. My Cobra's Kirkham diff is also painted with it.

https://www.electro-wind.com/glyptal...can-361-g.html

Roger, is it gloss for the sheen?
Larry

rsk289 · #33 (**permalink**) 03-01-2020, 02:58 PM

Semi-gloss to Satin, Larry. Photo attached prior to fitting - you can even see the tin behind!

LMH · #34 (**permalink**) 03-01-2020, 03:41 PM

Very cool! The darker color makes me initially think you're correct. Going through a couple Dave Friedman's photos, the differential looks black in the photos but his photos are black and white, so color doesn't show well. The red oxide is close to what Ford was using on the 9" center sections of the time but yours fits better with Daves photos.
Hmmm?!

Larry

rsk289 · #35 (**permalink**) 03-01-2020, 04:07 PM

I'd have thought the diff was painted before shipping to the US - probably?
I doubt AC would have been using Ford finishes on chassis/engineering parts.

It's tough stuff - much more resilient to damage etc. than a normal red primer. Used a lot here at that time for machine parts.

LMH · #36 (**permalink**) 03-01-2020, 04:42 PM

Our thinking at the time was more along the lines of industry wide usage of the red oxide, not just Ford. I asked a concours judge a few years ago about it and he said they look for a red differential. So that told me nothing!
I’ll post a couple photos later but I’m thinking you’re right here.
Larry

LMH · #37 (**permalink**) 03-01-2020, 07:18 PM

So I took Rogers photo and removed the color to better compare it to Dave Freidman's photos. The sheen looks right on. Color is hard to tell because of the B/W photo of course, so I looked at an unrestored XKE differential. Color looks pretty good too IMO. What do you guys think?

Rogers photo:

Daves Original:

XKE Differential:

Larry

feadam · #38 (**permalink**) 03-01-2020, 10:47 PM

rsk289, I see your in Cambridge, I'm on Lakenheath AB.

feadam · #39 (**permalink**) 03-02-2020, 06:18 AM

rsk289
Looking at your diff, were the rear covers the red or are they black? I thought they were all black

rsk289 · #40 (**permalink**) 03-02-2020, 06:36 AM

Hi feadam, yes, I'm north west of Cambridge. The rear cover that diff has fitted is one from a Jag diff, as I decided not to use the finned aluminium cover with breather take-off the Kirkham came with. The side covers are obviously different from originals as Kirkham use a different bearing arrangement.

The rear plates may well have been black on original cars, I didn't go into that much detail when I was putting this one together.