8" to 9" rear end swap issues

[thehueypilot]

I just finished installing my new 9" Currie rear end with 4:11 gears and a Detroit Locker and Explorer rear disk brakes. For anyone interested in what hidden adventures await them here they are:

1. Drive shaft needed to be shortened 2 inches. $80.00

2. New special u-joint required to adapt Mustang drive shaft to bigger 9" yoke. $22

3. New u-bolts required which caused mtg plate to be modified to fit the bigger bolts. The under rider traction bar plate holes were not far enough apart so I had to cut the ears off and weld it directly to the mtg plate. (My labor for welding $0.)

4. Parking brake came with universal kit.....which did not work so I went back to the stock cables which do work. Wasted $110 on a part I did not need but can't send them back because you must cut them to fit. I actually have good functioning parking brakes for the first time in 10 years. (Yes they are not really needed but if you have a State or Military Post car inspections they are required to be functional.)

5. I had a drain plug installed ($50) but they installed it on the very bottom of the diff. housing. I should of specified that it be mounted slighly off center so the jack would not hit it everytime I have to lift the car.

6. Speedometer is about 10 mph off so I had to order a new gear. I hope it works because I have to adapt a early model gear to a late model AOD transmission. CJ Pony Parts had it under part number HW1295. $11

7. Since I already had disc brakes (SS Brakes = Junk (my opinion) The brake lines attached with no modifications. The stock rim would only work with one 1/4" spacer and slight grinding of the caliper. The SS brake calipers took two spacers and major grinding and the parking brakes never did work. (Yes it was a bad design to start with but why continue to sell them if you know they do not work!)


All in all it was not that hard to install just took longer than expected because of the unforseen issues. I have not been to the track yet to see the fruits of my labor as far as 1/8 mile ET improvments but will go this weekend if it does not rain.
Total cost = $3,207.00

 

[12sec67]

when i did my swap from 8"with 3.55's to 9" with 4.11's i didn't really gain anything because you have so much more rotating mass... disc brakes+ calipers, 31 spline axles, and heavy duty housing...wieghs approx 75lbs more than an 8" then add the rotating mass! keep that in mind when your at the track.

 

[steel1212]

I'm getting ready to bolt in my 57 ford 9 inch I wonder if I'll run into the u joint problem?

 

[68rustang]

when i did my swap to 4.11's i didn't really gain anything because you have so much more rotating mass... disc brakes+ calipers, 31 spline axles, and heavy duty housing...wieghs approx 75lbs more than an 8" then add the rotating mass! keep that in mind when your at the track.

Where is the extra rotating mass? A slightly larger OD ring gear, and slight larger OD axles are about all I can think of. Rotating mass-wise anyway.

 

[12sec67]

Rotating mass-wise anyway.

all i'm sayinging is that it is a big difference...8" to 9"...bigger heavier axles, housing, rotors, caliper drag, locker......... he will see.

 

[thehueypilot]

I do know my 8" with traction lock was not going to last much longer. I was really disappointed at how fast the clutches wore out. They lasted only two seasons.

 

[Dark Knight]

you probably could have told them what size u-joint you had and they could have put in the same yoke.. or had them change the end on the driveshaft when it was shortened..

 

[68rustang]

all i'm sayinging is that it is a big difference...8" to 9"...bigger heavier axles, housing, rotors, caliper drag, locker......... he will see.

Well then you are not talking about rotating mass

Anyway the 8" to 9" weight "problem" is over stated:

http://www.ultrastang.com/Rearinfo.asp?Page_ID=1

Well let me rephrase that. The is a weight penalty for going with a 9". But that penalty is outweighed by the strength advantages over a 8". There are pro's and con's to any swap.

 

[thehueypilot]

Well then you are not talking about rotating mass

Anyway the 8" to 9" weight "problem" is over stated:

http://www.ultrastang.com/Rearinfo.asp?Page_ID=1

Well let me rephrase that. The is a weight penalty for going with a 9". But that penalty is outweighed by the strength advantages over a 8". There are pro's and con's to any swap.

I did consider an 8.8" because the articles said they had a lot less friction and were almost as strong as a 9" rearend if built properly. I found out that built properly meant it would cost twice as much as a 9" rearend. Go figure?

 

[Edbert]

Huey, looking at your engine specs I would expect more rwhp output than that. The torque is impressive but that cam has HUGE lift and the 225s should get major top end HP figures I would think. Not that there's anything wrong with 340rwhp but it just seems low. Is it what you expected?

I for one am suprised your 8 lasted at all behind that monster!

 

[68rustang]

I did consider an 8.8" because the articles said they had a lot less friction and were almost as strong as a 9" rearend if built properly. I found out that built properly meant it would cost twice as much as a 9" rearend. Go figure?

I don't know about being twice as much $$$. I put an 8.8" out of a 95 GT under my 68. I got the 8.8 as part of a whole parts car. Other than that I have a few hours in cutting off the four link brackets and welding on spring perches and $12.95 for the actual perches. I know its not as strong now as a 9" but being into it for only $12.95 give me TONS of upgrade room before I approach even the price of an 8" much less a 9". 5.0 mustang parts are dirt cheap too.

 

[10secgoal]

Huey, looking at your engine specs I would expect more rwhp output than that. The torque is impressive but that cam has HUGE lift and the 225s should get major top end HP figures I would think. Not that there's anything wrong with 340rwhp but it just seems low. Is it what you expected?

I for one am suprised your 8 lasted at all behind that monster!

In his defense. Autos dyno like crap. I only have 275 to the rear. But I run a little faster that what I should for that little to the rear. AND you can't break parts without traction, which I am sure is a problem in that car.

 

[thehueypilot]

Huey, looking at your engine specs I would expect more rwhp output than that. The torque is impressive but that cam has HUGE lift and the 225s should get major top end HP figures I would think. Not that there's anything wrong with 340rwhp but it just seems low. Is it what you expected?

I for one am suprised your 8 lasted at all behind that monster!

I had a high speed miss on the dyno so I could not get a good full pull. It turned out to be spark plugs too hot and gap too big. I would like to go back to another dyno now that I got all the issues ironed out but I haven't found a good one yet that is close by.

 

[thehueypilot]

In his defense. Autos dyno like crap. I only have 275 to the rear. But I run a little faster that what I should for that little to the rear. AND you can't break parts without traction, which I am sure is a problem in that car.

Yes traction was a problem when your traction lock kicks in and out during a burnout and sometimes off the line. Early model Mustangs also have a size limitation when it comes to tire width when not tubbed out. I am running 9.5" wide Quick Time Pros which are not as sticky as a true drag slick. I am hoping for 1.60, 60' and 7:50's in the 1/8 mile.

 

[shotsy]

I don't know about being twice as much $$$. I put an 8.8" out of a 95 GT under my 68. I got the 8.8 as part of a whole parts car. Other than that I have a few hours in cutting off the four link brackets and welding on spring perches and $12.95 for the actual perches. I know its not as strong now as a 9" but being into it for only $12.95 give me TONS of upgrade room before I approach even the price of an 8" much less a 9". 5.0 mustang parts are dirt cheap too.

did you have to shorten the 8.8 or was it close enough to run without cutting it? What is the stock length of the 8.8 I guess would be a better question?

 

[Jester67]

did you have to shorten the 8.8 or was it close enough to run without cutting it? What is the stock length of the 8.8 I guess would be a better question?

Yes inquiring minds do wont to know.

 

[68rustang]

did you have to shorten the 8.8 or was it close enough to run without cutting it? What is the stock length of the 8.8 I guess would be a better question?

If you search by my user name or 8.8 you will find pictyures of my car with the rear end under it. Right now It is not shortened and I am using late model (95) sized wheels They BARELY clear the quarters. When the car is actually back on the road I will need to play with the backspacing a little.

 

[67GTCOUPE]

Huey, looking at your engine specs I would expect more rwhp output than that. The torque is impressive but that cam has HUGE lift and the 225s should get major top end HP figures I would think. Not that there's anything wrong with 340rwhp but it just seems low. Is it what you expected?

I for one am suprised your 8 lasted at all behind that monster!

CAMSHAFT. It is all in the cam, it most likely has too much duration.