Ford 7 1/2" I.R.S.

[Old Jag Guy]

Good evening all.... Well i guess, while trying to save money, and for ease of availability, i bought a complete "rear suspension and drive" out of a late '90s Thunderbird. Now, I notice that the "pinion" is offset by about 35mm. Plus, the axles (WMS) will be app.724mm from the center of the frame, I think that will be o.k., but I will have to move the trans. tunnel that distance to the pass. side. I really don't want to move the tunnel and I'm not totally sure I can use this "rear end". I could buy custom axles, but quoted $450.00 is three times the cost of the rear end purchase!! Do you think I am wrong in trying the T-Bird? Maybe, give up the ghost, and look for a rear closer to the Sierra? Any advice is appreciated. Thanks, Don

[Not Anumber]

Could you get a local engineering shop to shorten one of the drive shafts ?

I would not advocate moving / enlarging the transmission tunnel to accept a propshaft that will run at an angle.

I once had an AC Cobra replica with IRS where the diff was way off centre and the propshaft/ torque tube ran at a sharp angle to the transmission. It broke UJs regularly.

[Old Jag Guy]

Originally Posted by Not Anumber

Could you get a local engineering shop to shorten one of the drive shafts ?

I would not advocate moving / enlarging the transmission tunnel to accept a propshaft that will run at an angle.

I once had an AC Cobra replica with IRS where the diff was way off centre and the propshaft/ torque tube ran at a sharp angle to the transmission. It broke UJs regularly.

Thank you for your reply! I didn't think of that. Just center the "pinion" then that would automatically make one axle short, then have the other one shortened! I will get an estimate for that. I think I was looking at it for so long I couldn't think....... Thanks again, Don

[H-L-Smith]

There are several people in the USA who have, or are, adapting the Thunderbird and Lincoln (similar mechanicals, but lighter aluminum case) IRS system to Locost chassis including the Haynes Roadster. If you have an interest, I can collect some links to their build logs and any discussions of the units accessible on the Internet.

Regards,

Lonnie

[Old Jag Guy]

Originally Posted by H-L-Smith

There are several people in the USA who have, or are, adapting the Thunderbird and Lincoln (similar mechanicals, but lighter aluminum case) IRS system to Locost chassis including the Haynes Roadster. If you have an interest, I can collect some links to their build logs and any discussions of the units accessible on the Internet.

Regards,

Lonnie

Thank you Lonnie. I did read one, I think it was a guy in Cali. around 2010(Bugeye)?, but he had axles made, and that's an expense i am trying to avoid. I cant remember if his is wider than the Haynes. I will keep looking, before I give up. Thanks again, Don P.S. I am on the "Locost USA" as Old Lotus Guy, do to the fact that my early Mech. career, I had worked for both Jaguar and Lotus

[H-L-Smith]

Originally Posted by Old Jag Guy

Thank you Lonnie. I did read one, I think it was a guy in Cali. around 2010(Bugeye)?, but he had axles made, and that's an expense i am trying to avoid. I cant remember if his is wider than the Haynes. I will keep looking, before I give up. Thanks again, Don P.S. I am on the "Locost USA" as Old Lotus Guy, do to the fact that my early Mech. career, I had worked for both Jaguar and Lotus

If you choose to run with your pinion offset and the stock axles, you'll be OK if you keep the total angle of the propshaft to 5 degrees or less. That's not just hearsay. It's based on some engineering equations used for years. Total angle would be calculated by how much the shaft is up or down looking at it fore and aft (side view) and how much right or left (top view). The math is pretty simple and I can give some references to it and the equations. I had to do the research because I'm using a Ford Mustang 7.5" live axle and it's offset as well.

Now, that does not tell you if you should change your tunnel to accommodate reasonable clearance around the offset shaft. You'll have to determine that based on the running gear you use and its position in the chassis. I laid it out on by build table surface for my components and you could easily do the same, I'm sure.

Cheers,

[Old Jag Guy]

Originally Posted by H-L-Smith

If you choose to run with your pinion offset and the stock axles, you'll be OK if you keep the total angle of the propshaft to 5 degrees or less. That's not just hearsay. It's based on some engineering equations used for years. Total angle would be calculated by how much the shaft is up or down looking at it fore and aft (side view) and how much right or left (top view). The math is pretty simple and I can give some references to it and the equations. I had to do the research because I'm using a Ford Mustang 7.5" live axle and it's offset as well.

Now, that does not tell you if you should change your tunnel to accommodate reasonable clearance around the offset shaft. You'll have to determine that based on the running gear you use and its position in the chassis. I laid it out on by build table surface for my components and you could easily do the same, I'm sure.

Cheers,

Thanks again. First I will correct myself, the guy that I had read about was in California, but his "Forum Name" is {dm2play} and he used, what he called, a Cobra rear end, which looks the same as my T-Bird other than the cover and rear mounts. Today I am re-checking all my dimensions, so I think I might be able to get by with getting one axle shortened, also I will call "7th Heaven" and get the diameter and groove count of the "short" Sierra axle. Thanks again for the "math", and your advice. I guess it would be esier if I had a "doner" but , where would the challenge be then? Don

[flyerncle]

One shaft should be longer than the other in any case,it will differ if you use a 7 1/2 in diff as opposed to a 7in diff by equall amounts the diff is offset.

There is a casting mark on the diff that is the center of the pinion and you can line this up with chassis center line.