Technical => Drivetrain Tech => Topic started by: sum_weirdo on January 08, 2006, 07:46:26 PM
Title: More info on differential gears
Post by: sum_weirdo on January 08, 2006, 07:46:26 PM
I'm just starting to put thought into changing my differential gears higher but I'm having a hard time finding solid info on the subject. The Chilton manual doesn't tell me squat but I've come to expect that from them. For starters what precisely are the stock gears for an 83 5.0? 2.73 or something? And about what gear size would you guys recomend I go to for a street/maybe strip car? Basically I like squealing the tires at every light but I don't want to have a seriously negative impact on fuel economy, the car sucks enough gas already. And finally where would I go to buy new gears and what else needs to be modified? I believe I've heard the speedo gear needs to be changed. I've been on Summit looking for these things but haven't had any luck. Tips?
Title: More info on differential gears
Post by: CougarSE on January 08, 2006, 09:41:11 PM
My Sled has 3.27 but that was part of the Tow Package. I think your guess is pretty close. I have a ranger with 4.10's and it feals much faster than the cougar, and they have similar hp rating. The Ranger seriously is suprising with those gears.
Title: More info on differential gears
Post by: Haystack on January 09, 2006, 06:35:27 AM
get 3.55's, and you will lose MPG no matter what you do with gears probably. get a turbo coupe rear end, and upgrade to better brakes at the same time.
Title: More info on differential gears
Post by: sum_weirdo on January 09, 2006, 12:41:01 PM
That would be worthwhile. What are the stock gears for a turbo coupe?
Title: More info on differential gears
Post by: t-bird85 on January 09, 2006, 02:25:32 PM
My 85 came with 2.73 On the pumpkin there will be a tag get the numbers and post them I can tell you what you have, I put 3.45 in mine took about an hour.. If your tring to save a little cash the gears in an 86 ranger are 3.45 and can be found in most junk yards.
Title: More info on differential gears
Post by: sum_weirdo on January 09, 2006, 03:08:09 PM
Pumpkin? You mean the differential casing? I don't plan on jacking the car up today to look but thanks for the tip on the Ranger gears. I may just go after those.
Title: More info on differential gears
Post by: CougarSE on January 10, 2006, 05:20:24 PM
Quote from: t-bird85
My 85 came with 2.73 On the pumpkin there will be a tag get the numbers and post them I can tell you what you have, I put 3.45 in mine took about an hour.. If your tring to save a little cash the gears in an 86 ranger are 3.45 and can be found in most junk yards.
4x4's with a v6 and an auto have 4.10's with a 5 speed, 3.55's unless its a 4x4 later than 89 are 8.8.
Also almost all ranger 7.5s are a limited slip. even 2x4's unless its like a no options base model.
Title: More info on differential gears
Post by: SLEEPER T-BIRD 87 on January 10, 2006, 06:39:49 PM
i would go with a 3.55 or a 3.73 gear
Title: More info on differential gears
Post by: 1WLD BRD on January 10, 2006, 09:37:28 PM
I have 4.10's in my 5.0L stang, and love them. getting 450kms to the tank on the highway too! (still haven't figured that one out yet)
It is actually too high for a light car though (but it is fun going sideways in 3rd gear on dry pavement:cool:.). I bet they would be well suited to the bird and cougars. I have a brand new set of 3.55's that have been sitting here for 2 years. I would like to either install them in the stang and put the 4.10's in the bird. Or just sell them.
Title: More info on differential gears
Post by: sum_weirdo on January 10, 2006, 10:47:16 PM
Hmm. I'm debating to myself whether to change the gears or go with the whole turbo rear end. The general consensus around here seems to be that the 7.5 is no good if you plan on putting alot of power to it, which I am planning in the future. Decisions decisions.
Title: More info on differential gears
Post by: CougarSE on January 11, 2006, 05:15:25 PM
Quote from: sum_weirdo
The general consensus around here seems to be that the 7.5 is no good if you plan on putting alot of power to it, which I am planning in the future. Decisions decisions.
Wow I don't know where you got that? I've heard that the 7.5 can take you into the low 12's. Now thats alot of power.
Title: More info on differential gears
Post by: slowfoxbird on January 11, 2006, 06:20:05 PM
7.5 will handle 400hp to the ground, and are a couple of pounds lighter than an 8.8. Plus, less rotational mass to get spinning and keep spinning. I have now idea why I am putting in an 8.8 in my car. Oh well.
Title: More info on differential gears
Post by: 1WLD BRD on January 11, 2006, 06:59:57 PM
HAHAHA!!! 7.5" handling 400hp. NOT FOR LONG!
You guys have obviously never driven your cars hard with a 7.5 diff. under it. I broke 4 of them, in the past 3 years. (once in the burnout box at the track.can you say "EMBARASSING!") Do your self a HUGE favor. Swap for the 8.8"
First hand experience here guys from someone who drives his cars harder then most. 7.5 diffs would be better boat anchors then under your car.
PS. my car MIGHT of had 130hp AT the wheels when it broke them.
Title: More info on differential gears
Post by: slowfoxbird on January 11, 2006, 07:45:45 PM
I have seen stock axles break, but not the housing or the trac-loc break at 400. All you need is a set of good after market axles.
Title: More info on differential gears
Post by: sum_weirdo on January 12, 2006, 01:16:14 AM
Lol. Glad to see everyone in agreement. Well I do like to drive my car fast but burnouts don't interest me. If the axles are the weak point I'd gladly replace them before pulling the whole rear end. Right now I'd estimate my car's horsepower in the neighbourhood of 200 probably on the low side. I'm gonna want to push it into the 300s but I'll probably never make 400 with this car, when I want something really insane I'll probably build a serious muscle car :)
Title: More info on differential gears
Post by: 1WLD BRD on January 12, 2006, 08:36:01 PM
My axles and housing never broke either. Everytime it broke it was because one or both of the spider gears grenaded. LITERALY. there was so much carnage the last time that I even split BOTH the bearing caps into 3 peices each. Never did find all the peices to those gears either.
Trust me. Take this thread as a warning my friends. the stock 7.5" WILL NOT handle alot of abuse for long. I know. I will post some pics later (if I can find them) of one of the diffs.
Title: More info on differential gears
Post by: SLEEPER T-BIRD 87 on January 14, 2006, 04:07:17 AM
Quote from: 1WLD BRD
My axles and housing never broke either. Everytime it broke it was because one or both of the spider gears grenaded. LITERALY. there was so much carnage the last time that I even split BOTH the bearing caps into 3 peices each. Never did find all the peices to those gears either.
Trust me. Take this thread as a warning my friends. the stock 7.5" WILL NOT handle alot of abuse for long. I know. I will post some pics later (if I can find them) of one of the diffs.
agreed
the axles will take you deep into the 6's in the 1/8 mile they are the same as the 8.8.
the weak point of the 7.5 is the ring gear/spider and the bearing cap area.as stated above
the are good for about 200 FLYWHEEL h/p
ive had alot of bad experiance with them including broken carrier on a STOCK 86 gt i had .
if you dont plan on abusing the car or using sticky tires and drag racing it may last you for a while.
Title: More info on differential gears
Post by: JAMEZILLA on January 14, 2006, 08:05:50 PM
My 1988 Tbird 5.0 came with 2.73s, and they were the only V8 gears mentioned in the owners manual section on towing. I bought an 88 turbo coup parts car 5speed and the gears in it are 3.73s.As soon as I get my garage( I'm building) done I'm gonna swap the rearend disc brakes & all(can't wait). I did find a pretty good selection of rearends available through junk yards on line, average price $300. But If you can get a whole car you'll have the proportioning valve, rear calipers, etc, too.
Title: More info on differential gears
Post by: fordfanatic67gt on January 14, 2006, 11:44:03 PM
I agree with 1wld brd. It is pointless to build that 7.5. You will have to buy new axles to handle power and then gears. Just find a 8.8 out of a thunderbird turbo coupe. They came stock with 3.73's if the car was an automatic and 3.55's if it was a manual. Not only do you get the gears it is also a posi loc, and rear discs. ya its more work but its better to that kind of job right the first time around rather.
Title: More info on differential gears
Post by: sum_weirdo on January 15, 2006, 12:55:36 AM
Hmm. I've scanned online for the complete rear end, they're not that plentiful in Canada. None even close to my area and between the shipping costs and possibly duties that's a considerable cost. I could always keep an eye to Pickn' pull, they'd probably be cheaper but I'm not sure I've ever seen a turbo coupe there. Just about every Tbird I've seen sped was a 3.8. If I were to guess I'd say the turbos had a relatively short life, followed by the 3.8s and sometime soon probably the 5.0 birds will show up there in greater numbers. But I digress, I guess I've got some thinking to do.
Title: More info on differential gears
Post by: slowfoxbird on January 15, 2006, 11:46:32 AM
Well, others may have had problems with a 7.5, but I put a set of gears in a 2000 V6 Mustang, built it with a stock Ford Trak-Loc, and a set of 3.73s, no breaking. By the way, that car ran low 13s on a warm night, and high 12s on a cold night due to a supercharger. Now, I am not good with math, but to make a 3500 pound car scat down a racetrack that fast, sure takes a heck of a lot more than 200 flywheel horsepower.
Title: More info on differential gears
Post by: 1WLD BRD on January 15, 2006, 12:56:03 PM
Ok. A 2000 7.5" has WAY less wear and tear on it and has not seen the mileage that one from say an '85 has. Just keep your fingers crossed. Eventually it will give out.
Plus if it was centrifigally SCed it wont give that instant hit of torque that even a stock 5.0L can give it. The power doesn't come on as aggresive with a 3.8L
Title: More info on differential gears
Post by: CougarSE on January 15, 2006, 01:55:56 PM
Quote from: slowfoxbird
Well, others may have had problems with a 7.5, but I put a set of gears in a 2000 V6 Mustang, built it with a stock Ford Trak-Loc, and a set of 3.73s, no breaking. By the way, that car ran low 13s on a warm night, and high 12s on a cold night due to a supercharger. Now, I am not good with math, but to make a 3500 pound car scat down a racetrack that fast, sure takes a heck of a lot more than 200 flywheel horsepower.
Slow fox what was your 60 foot time with a 12 second et?
Quote from: 1WLD BRD
Ok. A 2000 7.5" has WAY less wear and tear on it and has not seen the mileage that one from say an '85 has. Just keep your fingers crossed. Eventually it will give out.
Plus if it was centrifigally SCed it wont give that instant hit of torque that even a stock 5.0L can give it. The power doesn't come on as aggresive with a 3.8L
I'm betting he did have as much torque down low as a stock 5.0. Also if mr weirdo is going to be changing gears he will be replacing worn components. Rearends break because of slop in the gears. He will be taking care of that slop hopfully.
Title: More info on differential gears
Post by: slowfoxbird on January 15, 2006, 07:19:06 PM
Not my times, that was a rear end that I built for someone else, but still, he was cutting 2.0s and 1.9s on drag radials. CougarSE, you are correct about things breaking from slop. Ford calls for .008-.013 inches of backlash on a ring and pinion set, but when I build them for performance I make sure they are .008-.010 inches of backlash.
Title: More info on differential gears
Post by: TurboCoupe50 on January 15, 2006, 07:48:39 PM
A newer 7.5" will live with 1.9-2.0 sixtys IF they are in good condition. Older ones with wear are gonna pop just as wildbird says... And if the car will pull 1.7-1.8 60s you better have a 8.8".
Title: More info on differential gears
Post by: 5.8fastcat on January 15, 2006, 10:23:04 PM
Hey guys the 7.5 and the 8.8 has the same axels. The diff's are the weak link. I've seen 8.8 trac-loks blow with 4.6 G.T. with spray on them. The slicks or drag radials will take there toll on any stock diff with 275RWHP or better. Stick cars harder on the rears. My car has a 1.60 60 ft time on drag radials, Currently has stock axels and diff. I've got new axels on my list of needed parts. Along with the Exploer 31 spline trac-lok