gear swap or IRS?

[rhyne]

finally have my ‘67 on the road after a 4 year restoration. my dilemma now though is this: at 55mph i’m running about 3k rpm. both are correct. i’m using the 352 slightly modified, hd-mx tranny, and 8.8 rear end from an explorer with 4.10 gears. i believe to lower the rpm so i can run highway speeds would be to swap to something closer the 3.25-3.55-3.70 range. cost wise i could put in an IRS from a mark viii, for about same price as purchasing gears because i still need a compressor etc. for the air bags that i wouldn’t need if i went IRS. would IRS be worth it, would the truck stance be as low as it is now? or is the high rpm even a fearing issue. seems a 3 speed tranny and 4.10 rear not really a good mix. any thoughts?

[Ohiotinkerer]

IMHO I would just swap the gears - I am building a Thunderbird IRS for my '67 build and you'll have WAY more money and time in swapping a Tbird/Mark VIII rear end in........and since you just finished the restoration a gear swap will get you back on the road alot faster than a IRS swap - you'll have frame cutting and welding to do, fabrication or purchase of mounts, and if you're like me and doing a CV front swap you'll need to change the hubs on the IRS because they used a 4 1/4 bolt pattern and the CV is 4 1/2 and that will run you $325 right there to buy those......you'll be money and time way ahead with gears unless that's what you really want to do.......

[rhyne]

thanks for the info. i’m not thrilled about any of it. i just despise having to rework anything. so ill back up and punt.

[DuckRyder]

with tire size info and such figuring out the proper gear to swap should be no problem, and i agree i'd just change the gears...

Or not worry about it... are you gonna be buzzing it on the interstate for hours?

What is your RPM @ 70?

[Ohiotinkerer]

with tire size info and such figuring out the proper gear to swap should be no problem, and i agree i'd just change the gears...

Or not worry about it... are you gonna be buzzing it on the interstate for hours?

What is your RPM @ 70?

If he's turning 3000@55 mph he's really gonna be up there at 70 - mine was turning 3000@70 with the stock tires and 3.25 gears but I got mine down with just swapping out to a set of 15X8 rims and 31-10.5 tires.....that dropped it down to just a shade over 2500 on the interstate......

[rhyne]

it’s about 4k at 70. it’s not a daily driver and i don’t foresee hours of hwy miles in the future. but a trip into nearby cities and towns that are 30 minutes to an hour away i would like to at least keep up with traffic without fearing the worst. i’m thinking drop in 3.27 gears. that will get me to 3k at 70mph. 3.08 would only drop to 2900. that should suffice i think. somethings gotta give so i guess the gears lose.

[DuckRyder]

based on your 55 numbers 3000 at 55 with a 1:1 high gear is about a 25.3" tire.

This puts you at 3800 at 70

3.55 gears would drop you to 3300 @70...

Those are real short tires do you love them? because if you threw something around 29" on it it would have the same result as a swap to 3.55.

Unless its a highway cruiser I'd advise against anything less than a 3.25, 3.55 or better preferred.

[rhyne]

i didn’t think about a taller tire. the ones i have now are 25.75 height. it is a low profile and i’m not crazy about them but they are new. i definitely wouldn’t go lower than 3.27 but if i could find a set of taller tires for about the same price or a little more than a gear kit it would be easier and quicker fix.

[zainyD]

I don't know if you have any junkyards in your area, but in my neck of the woods Explorer 8.8's are a dime a dozen. I would just look for one geared closer to what you're needing/looking for. I would wager it would be cheaper to get another complete rear end than it would be to regear or convert to an IRS.

Try car-part.com to find a JY close to you that might have what you're looking for.

[rhyne]

zainyd that makes sense for sure but they’re picked over around here and i paid as much as the gears cost. plus i’d have to rework all the 4 link and airbag brackets. for that matter i would put the 9” back under it. i only went with the 8.8 because of disk brakes. the rear end was cheaper than converting the 9 over. no sense crying over spilt milk tho. i’m out some cash anyways i was just trying to get the most out of this lack of planning.

[zainyD]

One other thought, you might check one of the Mustang forums. I imagine someone might have a used 8.8 OEM ring and pinion for cheap.

[Ohiotinkerer]

I picked up a used set of 2.73 8.8 gears for my Tbird rear end for $80........3.27 gears for those are fairly common used also because most guys go numerically higher when they do any work on mustangs......

[rhyne]

i will look to ebay...new set is like 132$ rock auto. but if i can save 40 or 50 with a good used set that’s a win for me. ill get em swapped in next week or 2 and post the results for those interested. thanks everyone.

[rhyne]

finally got the 3.27 gears installed. couple trips down the road, my mph are spot on with the speedometer again. at 55mph the rpms are about 2250 which is much better.