Looking to change rearend... opinions?

[joker1626]

I purchased a base kit 5 years ago. Just recently got enough push to finish it.

I purchased a rearend from a 98+ mustang GT. I went through it a few years ago and it has 373s in it. I was planning on pairing it with a T5 WC (I already have this).

I'm curious if I'm going to need to change the gearing in it. I'm thinking the weight of the car my be to low for that combination.

The rear end is a four link setup.

Anyone have a similar setup or have an opinion? Any thoughts would be helpful.

[q4stix]

There are going to be a lot of variables like engine output, driving style, use, etc. and a lot of opinions about it.

I'd suggest just starting with the way it is so you can finish the car and then decided if it's an incremental change you want to make following getting it on the road. I've also got plans to change the ratio in my car for various reason, but I have to tell myself there's already a gear in there and I have plenty of other things that aren't done yet.

[rich grsc]

You don't say what engine you're using. I would say yes that is a less than ideal ratio for these cars. I believe the best ratio for a small block, lower HP, is 3:55. Jump to a big block, big cube, high HP and I'd look closer to 3:27, even 3:08 if you've lots of torque.

[joker1626]

Sorry, I didn't mention the engine. I have a 351w .30 over.

I figured I wanted 327 gears. I am not planning on racing. Just a cruiser. I know the 373s are going to be horrible on the highway.

[Jeff Kleiner]

The 3.73 won't be bad on the highway once you are in 5th gear but the other end is where they may be less than ideal depending on which first gear you have. Exactly which T5 is it? What is often referred to as "world class" is the OEM 5.0 Mustang spec version with a 3.35:1 first gear ratio. The T5-z has a 2.95:1 first gear. When coupled to a 3.73 rear the 2.95 ratio first nets an overall reduction of 11.0:1 which is not bad (in general I like around 10.5:1 for a street car). The 3.35 first gear along with a 3.37 rear results in an overall of 12.5:1; that's pretty short---great for pulling stumps or burnout contests but it will have you pulling for second gear before you get across the intersection. Which trans you have will make all the difference.

Jeff

[videodude]

The 3.73 won't be bad on the highway once you are in 5th gear but the other end is where they may be less than ideal depending on which first gear you have. Exactly which T5 is it? What is often referred to as "world class" is the OEM 5.0 Mustang spec version with a 3.35:1 first gear ratio. The T5-z has a 2.95:1 first gear. When coupled to a 3.73 rear the 2.95 ratio first nets an overall reduction of 11.0:1 which is not bad (in general I like around 10.5:1 for a street car). The 3.35 first gear along with a 3.37 rear results in an overall of 12.5:1; that's pretty short---great for pulling stumps or burnout contests but it will have you pulling for second gear before you get across the intersection. Which trans you have will make all the difference.

Jeff

So Jeff,

If I read what you wrote correctly, a WC T-5 (from my stock '93 5.0 HO) and the (optional, as ordered) 3.08 Trac-Loc (from the same donor) is actually a GOOD street combination, in your opinion? It is actually pretty peppy in a car that weighs twice as much as a roadster.

'Jus askin' . . .

Video

[joker1626]

Thanks Jeff. This is what I was thinking, also. My trans is not a "z". I think that my T5 with 373s and 300HP on this light of a car, is going to be hard to drive on the street.

[joker1626]

I will probably finish as is and replace the rear end after I've been in it completed.

[Jim Doak]

I think Jeff's nailed it.

I have a 302 with 3.73 gears. I shift into 2nd gear pretty quickly from a stop; however, the 3.73s are pretty good everywhere else and allow the engine to operate at a reasonable RPM (not too low) when cruising on the highway in 5th. (I do have the "Z-rated" heavy duty T-5 with the 2.95 first gear ratio.)

[Gromit]

X3 with what has been said. re geared my '86 IROC T5U tran with the 2.95 First to a 3.73 rear the tire circumference was 80.4 inches. that makes first overall 11.00 it woke the car up performance wise but in stop and go situations if the car is rolling and you put in the clutch you have to up shift to 2nd. as has been said that's as low a first / rear gear as I would ever want to go for street sized tires. I would expect in the lighter roadster it would be even more fun to drive and I would want to try it as is before changing anything. again assuming that your transmission is a 2.95 first.

Chris AKA Gromit

[NAZ]

I concur with Jeff's detailed assessment above, however, from a practical perspective why add more work and cost at this point when you've never tested the current combo? It's taken you 5-years to get to this point so why would you want to make modifications before even trying it? If the axle is already installed what advantage do you see to removing it now vs. after you test it. Sounds like this is a street toy so it's probably safe to assume gaining the absolute last bit of performance is not a goal.

Also, you say you "went through" the current axle but what does that mean specifically? A complete overhaul including bearings and seals? Do you have the knowledge, skill, and special tools to change the ring & pinion yourself or do you have to farm this work out? No it's not rocket science but it is not as simple as changing your spark plugs -- to do the job right requires tools that most hobbyists don't have. If you have to farm it out the cost just increased exponentially. These are the things you need to consider before pulling the trigger on a gear change. Especially if you haven't actually confirmed that what you have you can't live with.

[OVCobra]

Similar to Jim Doak, I have a 347 backed with the "T5 Z" and 3.73s in a four link...1st gear is short but keeps the exhaust note "quiet" on take off, do not need much gas.
Pulls like a bear even in 5th gear and is fine at highway speeds.
Overall I like it but just my 2 cents.

[joker1626]

I appreciate the input OVCobra. I think I'm going to try it out before I drop the rear end.

[CraigS]

Agreed, try it. I wouldn't choose it if I had no gears at all but it will be fine. 1st is too short but you get used to it. It also makes getting off the line in normal driving very easy- almost can just let out the clutch w/o any gas applied.