Ford guys: Differences between 8.8 and 9" for daily-driver usage

Birdie2000

Birdie2000

Club Member
So I have a 4th-gen F-body and need a new rear but my budget is limited and there's not much of a middle ground in terms of pricing for this application. I've been particularly indecisive about this because it's basically rebuild my stock 10-bolt for about $1k (which I am considering) or spend $3k+ on an aftermarket (I really don't want to spend much more than $2k). The car will have a twin-turbo setup and will likely be in the range of a 500rwhp with a T56 and I will be daily driving this car so I want it quiet and well-mannered. I don't need anything crazy but rebuilding my stock rear is a gamble at best with a manual at that power level even without taking it to the track. Also, the used market on aftermarket rears for these cars is basically non-existent unless you want something with a spool and steep gears.

I've found two options that come reasonably close to my intended price point and those are either a custom hybrid 8.8 setup or I've found one vendor that has a an affordable 9" housing/axle package that I could use to piece together a decent rear for similar money. Both would probably be fine for my power level.

I'm completely unfamiliar with Ford differentials and gearsets and this is where I need help: My main objective in all of this is that it needs to be dead silent and drive well since this is a daily driver application. My questions are as follows:

1) Are there any differences in the noise between the gears/etc. available for the 8.8 and the 9"? What gear manufacturer/type would you go with for my application? I'm looking at a 3.30-3.50ish ratio. I've heard a lot of people say that the 9" tend to inherently be noisy while the 8.8s are pretty quiet. What is everyone's experience on this?

2) People seem to think that the Ford Racing Trac Lok with Carbon clutches is more than adequate for that power in an 8.8 while still being quiet, etc. Does this diff also exist for the 9" and have the same noise/strength characteristics?

3) I've heard something about needing tapered bearings for frequent street use with the 9"? Can anyone elaborate on this?

4) Any other noticeable differences between the two I should be aware of for my application?
 
They are both great rear ends. With proper mods either one is a good choice. The 8.8s are plentiful and cheap to start with a used unit. The 9" will be hard to come by for cheap.

Im hoping the Motown resident gear expert chimes in on this one.
 
Thanks. My main concern is if a 9" can be made daily-driver quiet. Would make the decision easier.

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I cant speak on the 9" because I have no experience with that axle but I do with the 8.8".

I recently had mine rebuilt again and built up and it cost me close to $800 for parts alone. Moser 31 spline axles, FRPP Carbon T-lok diff, FRPP gears, new bearings, ARP wheel studs. I cheaped out and didnt get a fancy diff cover, maybe in the future.

1. Ive only gone with FRPP gears and have never had a problem with noise. Im sure thats all dependent on setup though. The price between different gear manufactures is pretty close so if you choose an 8.8", Id go with FRPP.

2. The carbon T-lok diff is a great diff for the price. Obviously its not as nice as a TrueTrak or other helical LSD but it gets the job done and for the power your car is making, would be fine IMO. Terminator guys run them all the time over 500hp and Ive never seen one fail.

I dont know if they make one for the 9", most likely not.

I can't answer the rest of the questions but Im sure someone on ls1tech could.
 
They make a TrueTrak for the 8 and 9 inch Ford rear ends.

the nice part about the 8.8s is that most come with disc brakes so there is no additional cost to upgrade from there. Not sure how that helps with a GM product.

Ill second the advice to go with FRPP gearsets. They make great products.
 
Have you called around for pricing? DTS can probably quote a 4th gen, built 10 bolt, 12 bolt, 9" over the phone. You might get into a 12 bolt cheap if you skip heavy duty parts. Sorry I dont have any real advice...i buy everything PROVEN....(Used...). :)
 
I forgot about DTS, I'll give them a shot. I'd happily buy used if anyone ever had a 4ch with 3.42 gears for sale, hah.

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mustangmike6996 said:
They make a TrueTrak for the 8 and 9 inch Ford rear ends.

the nice part about the 8.8s is that most come with disc brakes so there is no additional cost to upgrade from there. Not sure how that helps with a GM product.

Ill second the advice to go with FRPP gearsets. They make great products.
Click to expand...

I meant to say they dont make the carbon trac-loc for the 9", maybe the clutch packs can be upgraded though?
 
Couple things... First I think your HP estimations are a bit conservative. Depending on hp both housings tend to bend the tubes forward. The 8.8 they weld some additional tubing in place..... the 9" gets a gusset welded on the back. Without them they bend. The 8.8 will also need tubes welded (using Nickle) to the center section, and a TA or support type of rear cover (that or a billet left cap). Both are very strong...but you will need to use all 9" aftermarket parts such as the case/nose/yoke.
As far as ring & pinions go, ford motorsport for the 8.8. For the 9" US gear or Motive would be my choices. Both set up good. Noise..... how are you mounting the housing? Solid bushings or urethane? Solid transfers a ton of noise. You will hate it.
Forget about running clutch or cone type posi's.... quafie or true track are what you want. I'm sure Mosier can advise you on axle splines for your HP levels (31/33)
The tapered axle bearings..... this is a bit to type. I can explain this much faster to you on the phone. Your missing one VERY LARGE part of this equation. Brakes. What brake kit you choose are going to determine the housing ends required. Most people that assemble this type of housing go with the large 9" Ford Wheel bearings. They are available in both tapered or ball bearing. Most drag race guys run the ball bearing.... and for the most part this bearing (made by the Green Ball Bearing company on Ohio) will work..... how ever I can tell you of story's of my own customers that lost a axle shaft on the freeway from running these bearings, and how switching them from green to timken tapered bearing solved the problem 100%... but every application is different.
Your choice in brakes is going to kill your budget. Call me if you need help/advise. There are some local fabricators that may be able to help you.
 
The 8.8 seem ok if you get a good TA bracket and welder.
They cut the tubes off your 10 bolt and slide them into the 8.8 and reweld them but I would make sure they do some bracing
 
I am still planning on the 8.8 conversion for my car. Cut tubes off an 8.8, and a stock 10-bolt. Weld together and add any bracing, torque arm hardware, etc. I have the 2 donor housings. Will just need to order axles (f-body axles with ford Spline) and a gear set. So far I have $0 invested in this set-up. Found the housings people just wanted to get rid of. This method allows me to keep the stock brake set-up as well.

If you stick with the stock rear in your car, stay on street tires. The street tire will be your fuse to prevent gear issues. But even if those get warm enough, you WILL break a gear. I tore a tooth or two off of my ring gear after doing a bunch of burnouts on old tires to use them up before getting a new set. Found out the hard way the next morning when I had a strange noise back there..... :banghead:
 
Where would you guys add bracing?

I think I'm pretty set on going the 8.8 route. Not as cheap as I'd hoped but still a great option considering my budget. Just need to find an 8.8 donor housing. Get a Ford Racing torsen, Ford racing gears, custom axles, and I should be good to go. Just gotta decide who to fab it. There's a guy in OK that does these for $680+ shipping including powdercoating but I have to send him the donors. Think any one competent can do this locally for less than the $800 it would cost in total for that guy? Not sure what the rates are on rear end fabrication. They make a TrqArm bracket for like $50 that just needs to be welded on in addition to the axle tube swap. Obviously someone using a jig and truing bar.

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To your original post.......an 8.8 can easily handle 500 to the tire. There are guys running 700+ and still using the 03-04 Cobra diff (has the carbon clutch packs). The quietest gears are OEM Ford, so try and get a stock 3.55 (they are a dime a dozen).

If you find a crappy donor and want to rebuild the diff, the clutch kit you want is FRPP part number M-4700-C...
http://www.summitracing.com/parts/FMS-M-4700-C/


--Joe
 
The TA mount I need is specific to f-bodies and is welded on.

Are you suggesting reusing a set of stock gears? I thought that was a surefire way to get noise? I'm hoping to get a Torsen diff in this thing since it'll be driven a ton and possibly see a road course track day or two, but I'm not totally against a traditional posi.

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Birdie2000 said:
Are you suggesting reusing a set of stock gears? I thought that was a surefire way to get noise? I'm hoping to get a Torsen diff in this thing since it'll be driven a ton and possibly see a road course track day or two, but I'm not totally against a traditional posi.
Click to expand...

Yes absolutely. OEM gears are the quietest.

The Eaton TrueTrac is a great alternative to a clutch style diff too. If you really want to go nuts, get a Wavetrac, they are practically indestructible.

--Joe
 
Thanks, I'm sure they are. I could have sworn that it was risky to reuse because they would have already established wear patterns and it was difficult to set them up exactly the same when reinstalled, especially if they didn't come from the same housing.

If I wanted 31 spline and 3.55 or less gears, is there any OEM 8.8 I should be looking for? I know most of the ones I saw with 31 spline had 4.10 gears. Also, where is the cheapest place to find these, just a normal junk yard?

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Birdie2000 said:
If I wanted 31 spline and 3.55 or less gears, is there any OEM 8.8 I should be looking for? I know most of the ones I saw with 31 spline had 4.10 gears. Also, where is the cheapest place to find these, just a normal junk yard?

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Click to expand...

03-04 Mach 1's would be exactly what you want. 8.8 with 3.55 gears and they had the 31 spline axles and the Eaton diff with carbon clutches. You can probably get one in good shape from a guy who swapped the solid axle for an IRS.

--Joe
 
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