Which differential for a scratchbuild?

[john chesnut]

I used a C5 Corvette Diff in my Cobra. The C5 uses a transaxle but I had an aluminum front plate made that bolted in its place that has an input shaft so that a driveshaft can be used. I used the C5 upper and lower control arms as well. The set up works very well.


I had several adapter plates and input shafts made at the same time. I was thinking that I would use them for future projects. I think I'm done with new builds. I would sell a set up for $500. I know they cost me 3 times that much.

[Three Peaks]

Originally Posted by 120mm

Aaaand..... Look what fell in my lap today!

https://www.ebay.com/itm/113051509277

Did you also get the axles and uprights?

[120mm]

Originally Posted by Three Peaks

Did you also get the axles and uprights?

Nope, just that. Axles appear to be stupid easy to get (assume will need to be shortened anyway) and I am unaware of what an "upright" is.

The entire purpose of getting the diff now is to ascertain the location of the cross-member. I'll get the rest of it when I am at that point in my build.

[Three Peaks]

The uprights are the part that hold the brake calipers, rotors, and hubs/bearings and connect to the control arms. You'll need them to position your parts, build your control arms and pick up points, and measure the lengths of your axles so you can have them shortened, along with deciding what backspace of wheels you will need or want, where to position your trailing link, and where your shock mounts will be located. They are kind of important at this stage of the build IMO.

As for mounting the differential, I used a 2 x 3 rectangular tube coped to fit the round chassis tubes on each end at the correct height for the differential flange to be located. You need to determine the center line of the axles from the center line of the wheels with the frame at ride height. There will be a lot that will go into this stage of the build compared to the rest of the scratch build. There aren't a lot of blueprints to help you with this part of the build or the uprights you will probably need to build to fit the Tbird/Explorer IRS uprights. You can use original style uprights and adapt them to your differential if you have the ingenuity and ambition. Or, you can get the Jag/Dana 44 type rear and use the same system Kirkham uses with adapters to the stub axles and Porsche 930 axles to go with their machined uprights. Pretty expensive option but plug and play.

Sounds like a fun project. Post pics as you go along- BTW, how far along are you at the moment?

Bob

[LMH]

FYI, original style rear cast steel uprights (hub carriers) are pretty big money! Around $2000 per side when you include drive hub/stub axle and bearings. That doesn't include brakes.
Larry

[120mm]

Originally Posted by Three Peaks

The uprights are the part that hold the brake calipers, rotors, and hubs/bearings and connect to the control arms. You'll need them to position your parts, build your control arms and pick up points, and measure the lengths of your axles so you can have them shortened, along with deciding what backspace of wheels you will need or want, where to position your trailing link, and where your shock mounts will be located. They are kind of important at this stage of the build IMO.

Are they also referred to as "knuckles" or "spindles?" I can't find a picture anywhere of something called an upright, though my plans refer (obliquely) to them. Am assuming they are called spindles or knuckles in other automotive terms.

As for mounting the differential, I used a 2 x 3 rectangular tube coped to fit the round chassis tubes on each end at the correct height for the differential flange to be located. You need to determine the center line of the axles from the center line of the wheels with the frame at ride height. There will be a lot that will go into this stage of the build compared to the rest of the scratch build. There aren't a lot of blueprints to help you with this part of the build or the uprights you will probably need to build to fit the Tbird/Explorer IRS uprights. You can use original style uprights and adapt them to your differential if you have the ingenuity and ambition. Or, you can get the Jag/Dana 44 type rear and use the same system Kirkham uses with adapters to the stub axles and Porsche 930 axles to go with their machined uprights. Pretty expensive option but plug and play.

On the originals with Salisbury diffs, there is a hinged, cushioned plate that bolts directly to the diff "nose". I am assuming that because the Explorer diff is cushioned, this can be stiffly mounted otherwise to the cross-member. If so, I was planning to do exactly what you describe. Do you have a picture showing this detail on your build?

Sounds like a fun project. Post pics as you go along- BTW, how far along are you at the moment?

Bob

I have purchased plans and am disposing of the 1938 Dodge Sedan that is sitting in the space I will use for the build. I am in the process of collecting tools and materiel. I have yet to build my jig table.

I am recording the build on this thread: 289 Plans Build

There are two things that describe me best. I am a researcher and a sharer, so I plan on providing a detailed build thread, to include mistakes I make on the way. I think there is a greater good that makes recording a build of this nature.

Thanks!

Drew

[MAStuart]

Drew The best advise is come and see me. It should take you about 3 hours or less to get here . I am located 12 miles north of route 80 in Mendota Il 61342. Bring your diff along for a ride . You will be able to see if it would fit in an original style leaf spring chassis. I am building 2 of them. You will see the tools I am using. I am building in a home shop.But beware the place is a mess. Meanwhile Check out my build thread . You will see how close of a fit that an original style diff is. The thread to my build is located here scratch build

[120mm]

Originally Posted by MAStuart

Drew The best advise is come and see me. It should take you about 3 hours or less to get here . I am located 12 miles north of route 80 in Mendota Il 61342. Bring your diff along for a ride . You will be able to see if it would fit in an original style leaf spring chassis. I am building 2 of them. You will see the tools I am using. I am building in a home shop.But beware the place is a mess. Meanwhile Check out my build thread . You will see how close of a fit that an original style diff is. The thread to my build is located here scratch build

I will do that very thing.

[Three Peaks]

Great advice to see a build in process. It would have saved me huge amounts of time in my scratch build. The Explorer diff won't mount in the same way the Jag rear with adapters mount. Also, most guys who use the 8.8 rear take the rubber bushings out of the front ears and make up or purchase solid aluminum bushings for the front to hard mount the front of the diff. Since the rear of the diff won't have the soft mount like in the car it came out of, it will be hard mounted also. If the front moves, the rear brackets can also break off so hard mounting is the only way to insure a solid mount.

I'll try to get some pics as soon as I can- may be a few days. I do have some work to do on mine to discover and cure a clunk I've developed, so I'll be under there this week. Do you have plans for the control arms as part of the drawings you got?

Bob

[eschaider]

Bob's point about the IRS housing mount front and rear is significant. For best results you need to mount both the front and back of the diff with mounts of similar hardness or the give of the softer mount will damage the more solidly mounted, mount.

Delrin is somewhere between a polyurethane mount and a solid mount. The ring and pinion meshing sound and ever so slight vibration is an undesirable side effect (for some) of a solid mounted IRS unit. These folks usually go to a polyurethane mount that, while quieter will unfortunately deteriorate with age. A better choice is Delrin. Delrin is a much more robust material with good life expectancy and relatively easy to machine.

The other choice is UHMW polyethylene (UHMWPE). Don't let the polyethylene part of the name scare you off. The UHMW part of the name means Ultra High Molecular Weight. UHMWPE is a type of polyolefin. It is made up of extremely long chains of polyethylene, which all align in the same direction. It derives its strength largely from the length of each individual molecule chain and the chain to chain overlap. The molecules are very long allowing for large overlaps providing the ability to sustain larger shearing (and compressive) forces molecule to molecule.

Outside the scientific community UHMWPE is used for composite plates in personal and vehicular armour. It will provide impressively good mounting strength while also attenuating some of the vibration and gear meshing sound that possibly delrin (If you are sensitive) or solid mounting with steel, might transfer to the drivers ears or seat of the pants.

Although it is not inexpensive, it is readily available. Amazon sells it in both sheet, rectangular bar and round bar form. You can also find it in most industrial and scientific supply houses.


Ed

[map]

Explorer 3:70 gear convert the CV stub to a 4 bolt flange using RS200 shafts..

https://photos.app.goo.gl/HjB8ZBx3pRX41bex7
https://photos.app.goo.gl/6VV6GCVhWLhMHuJB8
https://photos.app.goo.gl/Kih9GnuJiBx4eRQC7
https://photos.app.goo.gl/L44q8y8oKDZ6yKJo9

[MAStuart]

Drew I know you want to build a FIA style car. You also said it did not have to be exact. My question is why leaf spring? This will make it a lot harder finding uprights that will be of use. In my case I am building leaf spring car because I want the experience of driving an original type car. If I ever get one of the chassis to the roller stage using original style parts I will try to make parts for the second chassis using parts from easily available cars. I want to do this in a way that if I can ever afford to get a second set of original style uprights and brakes it will bolt on without any mods to the chassis. Not sure if this is possible but it is my goal.

[cycleguy55]

Originally Posted by 120mm

Aaaand..... Look what fell in my lap today!

https://www.ebay.com/itm/113051509277

Is that an open or limited slip differential? If the former, what LS option are you considering and why? Clutch pack? Torsen / helical gear?

[120mm]

Originally Posted by MAStuart

Drew I know you want to build a FIA style car. You also said it did not have to be exact. My question is why leaf spring? This will make it a lot harder finding uprights that will be of use. In my case I am building leaf spring car because I want the experience of driving an original type car. If I ever get one of the chassis to the roller stage using original style parts I will try to make parts for the second chassis using parts from easily available cars. I want to do this in a way that if I can ever afford to get a second set of original style uprights and brakes it will bolt on without any mods to the chassis. Not sure if this is possible but it is my goal.

My goal, which I put in my build (actually pre-build ) thread, is to learn about the process of building the car by actually doing it, while ending up with a car that roughly replicates the characteristics of a leaf-spring car. (While looking sexy as all heck.) Since the rear diff doesn't add materially to that experience, I'm willing to economize there. I'm still exploring my options about uprights. I believe I've seen a set of welded uprights.

Originally Posted by cycleguy55

Is that an open or limited slip differential? If the former, what LS option are you considering and why? Clutch pack? Torsen / helical gear?

Those are good questions I haven't asked yet. Though it gives me something else to think about.

[Three Peaks]

PM Sent

[eschaider]

Just pull the rear cover and you can see what it is in a NY minute.


Ed

[Mark IV]

Originally Posted by 120mm

My goal, which I put in my build (actually pre-build ) thread, is to learn about the process of building the car by actually doing it, while ending up with a car that roughly replicates the characteristics of a leaf-spring car. (While looking sexy as all heck.) Since the rear diff doesn't add materially to that experience, I'm willing to economize there. I'm still exploring my options about uprights. I believe I've seen a set of welded uprights.



Those are good questions I haven't asked yet. Though it gives me something else to think about.

The tag number on the diff will tell all.

[120mm]

[Mark IV]

8.8" , 3:73 open diff

[120mm]

Well, the verdict is back from the jury in my head, and the answer is: I am going with a reproduction Salisbury diff.

When I really looked into my own reasoning for doing a) a 289 leaf spring Cobra and b) building from scratch, I realized that it mattered to me that the rear diff should mount just like an original car, and the Salisbury is the most elegant solution for that.

There are three sources for reproduction Salisbury rear diffs that I have discovered. Kirkham, Hawk Cars and Mike McCluskey. The price for these items are somewhat steep, but that is just the cost of building a leaf spring Cobra, imo.

In the end, I live just down the road from Hurricane Motorsports, and if I really wanted a coil spring car using modern adapted parts, I could just buy one of their kits and build it out a lot quicker and cheaper.

Thanks for all the advice; it really helped me discover what I really wanted in my build.

Drew