TeeLew
Well-Known Member
- Thread starter
- #1
TL;DR: I'm trying a taller rear gear, played with the diff, and put in soft rear springs.
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I spent last week on a rear-end project that I’ve been thinking about for probably 3 years (or 25+ depending on how you count). It was one of those deals where I wanted to do something simple and all hell ends up breaking loose. I have a real hard time leaving well enough alone, I guess, but taking my car apart and putting back together keeps me out of the bars, so it’s an overall win.
The initial thought was simple enough. My car is an Eco HPP, six speed with a 3.55 gear and a Torsen Diff. I do autocross stuff to entertain myself. I noticed I’m always between second and third. The faster corners are *definitely* faster taken in third because in second you’re just ringing the piss out of the engine, but anything slow has to be in second. You're constantly shifting, which is slow. Remember, Eco’s have about 1000 few revs than a Coyote and they fall off even before redline. However, Eco’s make really good bottom end torque, which I’d like to be able to better exploit. Also, my car is a daily, and the 3.55 gear is obnoxious with a torquey engine. I’m sure it’s fine with an auto, but it’s pretty bloody annoying to have to constantly a gear higher than you really want to be. First is useless for anything. Second is a little too fast in a parking lot and a little too slow in my neighborhood, and I end up skip shifting to 6th at 55 mph.
So I wanted to put a 3.15 rear gear in my car…and that’s where it all went wrong!
I like the Torsen diff and don’t want to change it, but the 3.15 ring gear is physically smaller than the 3.55 and can’t accommodate the same size diff. So, I can’t just swap ring and pinions. Apparently there is a Torsen made for the 3.15, but I don't want to spend that money.
All manual transmission cars have a cast iron housing to withstand launch abuse. With the Torsen, it’s about 32# heavier than the aluminum housing & Trac-Lok. I love to get weight off my car and that’s a *chunk*. Since the easiest way to change the gear is to swap the entire rear housing, might as well go AL. I’m not the redline/clutch drop type. I got the rear housing off the Marketplace here for not much more than shipping.
S550 rear ends are notorious for over-heating. While this hasn’t been an issue for me in a parking lot, I know it could be on track. I’m not interested in doing an entire pump cooler arrangement, but when I saw the Fluix finned rear cover, I figured that was a perfect middle ground for an Eco. Those rear cover external torx bolts suck. Studs and Kay-nuts with captives go on. The Fluix rear cover is 11# heavier than the stock cover, so my total weight drop is cut to 21# from the cast iron housing. To be fair though, that 11# is lighter than the corresponding cooler/pump combo and does the same job.
The diff that comes with 3.15 gears is the Ford Traction-Lok. It’s the same damned thing it’s been since the 60’s with very little change. There are a potential of 3 drive/driven plates per side giving a total of 12 friction surfaces. Each surface has a thin phenolic layer to reduce noise. If you really use a Trac-Lok, then you burn the phenolic completely off in about 2 weekends and lose all the preload in the diff. FP does make carbon fiber surfaced plates, but still 3/3 per side. This improves engagement and wear, but it doesn’t really help total locking and the torque bias that a Trac-Lok can provide is about 1.75:1. To be able to put power down as well as the Torsen, I know it needs to be tighter.
In the mid-90’s, I ran my Fox in E-Street Prep. I had a 3.27 gear/T-5 combo. It worked OK when new, but was a peg-leg in short order. I didn’t know how to fix it then, but over the years, I’ve thought about it. That’s how I came up with the idea of making my own plates. They’re water-jet cut, ground and hardened tool steel and I made them thinner, so I can fit 5 drive/driven plates on each side of the diff for a total of 20 friction surfaces. This alone accounts for a 66% increase in locking capacity. Besides that, the Ford pieces are crap, warped, stamped steel, so they don’t really make good surface contact. Having the plates ground flat means the surface contact is as close to perfect as I can make it. The holes in the floater plates are to carry oil for cooling and it also smooths engagement. Some smart and experienced people helped me out, here…I didn’t just pop them out my keester. So, I made these plates and part of this adventure is giving them a test.
I previously had the stock diff housing bushings with the BMR red pucks. These were my last stock bushings on the car and even though they were in good shape, I wanted to go to the Whiteline kit. The pucks just seem like a ½ measure.
I got Kell-Trac’s stud kit a while ago. They go in with the subframe.
I’ve been on 750# rear springs for a while and they feel like a pretty good compliment to my 450# fronts, but I’ve been 950, 850 and 750. Each time I’ve dropped rates, I’ve like it, so I ordered the next two drops down. 650 and, since they didn’t have a 550 on the shelf, 500. The 500 is a 2.5 x 7 spring where all the others are 2.5 x 6. Just because I’d rather overstep the target and then come back, and the 1 vote poll, I decided to go with the 500# rear. I know, I know, I know…..I want to try it. I’m perfectly happy to put *any* of these springs on the car. I’m having as few a number of pre-conceived notions as possible. I just want to feel it. In general, I tend to run the rear spring rate of any car I happen to be playing with as soft as I can to improve exit traction and as stiff as I have to in avoidance of excessive understeer. With the 750, I have very little understeer right now and can always improve traction. It might not be great, but it’ll be OK.
It's important to take into consideration that my car is quite a bit lighter on the nose than a GT and I’ve got the battery in the trunk. Weight distribution is a big deal. My car will always be a little bit of an odd-ball in this respect.
OK, so everything went fine on the way out of the car. I got a cheapy 500# hydraulic table at Harbor Freight and it makes everything pretty straight forward. I had previously used a wide-base ATV jack, which was unstable and just not strong enough to handle the whole assembly. I am doing this all with the car on Quickjack lifts.
The AL housings were all auto cars, so you have to change the driveshaft flange for a manual. You get a roll-over torque reading and then match than with the new flange. It ended up about 100 ft-lb of torque on the nut to get the 15 in/lb roll-over. It’s not meant to deform the crush sleeve further or change the pinion position. The big nut is deformed on the shaft, so a PITA to take off.
Diff bushings came out with a Saw-all. That’s always fun.
I did find my vertical links were pretty much frozen in place. When I got these, I had thought about going to a class where you couldn’t run monoballs. When I decide to go CAM, that went out the window, but I figured these were ‘good enough.’ It turns out the Delrin had pretty much seized on the aluminum inserts and was causing a lot of stiction/friction. I freed up all inserts with emery cloth on a lathe, but I’m going to replace with monoballs soon. I don’t want to chase that, again.
I spent a lot of time cleaning and checking things. No real horror stories on the putting things back together. I position the table and go up. You end up having to do some side to side stuff, but it isn’t bad. Thread the studs in and put the nuts on. You know, there’s very little that’s rocket surgery on these deals. It’s just a whole lot of little things that have to happen in a very specific order. The deal is, you just have to keep working until it’s done.
I love the gearing in town. I’ve only had it for about a week, but all the gears are exactly where I expect them to be, now. First in parking lots feels right. Second in my sub-division is right. Faster city streets are 5th, not 6th. 6th is freeway only. It’s early days, but second seems to be just fine for a tight hairpin. I don’t feel like I’m driving a Honda S2000.
I had a 500-ish mile trip this week. I’ve made this drive over and over for the last 4 years. My best ever MPG was 29.1, but my average is less than 28.5. First trip, 30.3 MPG and that was doing nothing special.
The diff plates definitely have some parking-lot groan, but it’s not horrible. I haven’t really been in the position to get a read on how it acts in anger. Here is my issue, though, the rear end has a hell of a howl in it. I don’t know if it was there before I got it, but it’s there now. Maybe I messed up the snout torque? I don’t know. I don’t think the Whitelines are supposed to be particularly noisy. It will be coming out this summer for new bearings and R&P…goodie. I probably should have done this before, but I was hoping to avoid it.
The diff runs cool on the freeway. At 55 deg temps, I was seeing 131 deg rear temp and at 75 I saw 153. This was running a consistent 75-80 mph. Whatever is going on in the rear end isn’t making much heat, which is good.
The rear springs... It’s hard to say on handling. I haven’t been able to really hustle it much. It feels like I’ve probably picked up some understeer, but it doesn’t feel like I put Slinky’s in. It still has reasonable response on the street. The ride, though, that’s bloody great. This thing just soaks up rough pavement. Remember that softening rear springs was supposed to make the thing have some sort of pitching issue and that’s why the rear has to run stiff? It’s bullsh!t. OE guys are obsessed with it, so they sacrifice very primary considerations for a much less important 3rd order effect. It’s better connected to the road and feels more composed. I don’t know that I’ll feel the same way when I’m at speed. I’m concerned it won’t want to change directions well in a slalom and I think longer duration corners could particularly be an issue for understeer. All I can say to this point is so far/so good.
All in all, a hell of a project and I’ll keep you up on where it goes from here.
______________________________________________________________
I spent last week on a rear-end project that I’ve been thinking about for probably 3 years (or 25+ depending on how you count). It was one of those deals where I wanted to do something simple and all hell ends up breaking loose. I have a real hard time leaving well enough alone, I guess, but taking my car apart and putting back together keeps me out of the bars, so it’s an overall win.
The initial thought was simple enough. My car is an Eco HPP, six speed with a 3.55 gear and a Torsen Diff. I do autocross stuff to entertain myself. I noticed I’m always between second and third. The faster corners are *definitely* faster taken in third because in second you’re just ringing the piss out of the engine, but anything slow has to be in second. You're constantly shifting, which is slow. Remember, Eco’s have about 1000 few revs than a Coyote and they fall off even before redline. However, Eco’s make really good bottom end torque, which I’d like to be able to better exploit. Also, my car is a daily, and the 3.55 gear is obnoxious with a torquey engine. I’m sure it’s fine with an auto, but it’s pretty bloody annoying to have to constantly a gear higher than you really want to be. First is useless for anything. Second is a little too fast in a parking lot and a little too slow in my neighborhood, and I end up skip shifting to 6th at 55 mph.
So I wanted to put a 3.15 rear gear in my car…and that’s where it all went wrong!
I like the Torsen diff and don’t want to change it, but the 3.15 ring gear is physically smaller than the 3.55 and can’t accommodate the same size diff. So, I can’t just swap ring and pinions. Apparently there is a Torsen made for the 3.15, but I don't want to spend that money.
All manual transmission cars have a cast iron housing to withstand launch abuse. With the Torsen, it’s about 32# heavier than the aluminum housing & Trac-Lok. I love to get weight off my car and that’s a *chunk*. Since the easiest way to change the gear is to swap the entire rear housing, might as well go AL. I’m not the redline/clutch drop type. I got the rear housing off the Marketplace here for not much more than shipping.
S550 rear ends are notorious for over-heating. While this hasn’t been an issue for me in a parking lot, I know it could be on track. I’m not interested in doing an entire pump cooler arrangement, but when I saw the Fluix finned rear cover, I figured that was a perfect middle ground for an Eco. Those rear cover external torx bolts suck. Studs and Kay-nuts with captives go on. The Fluix rear cover is 11# heavier than the stock cover, so my total weight drop is cut to 21# from the cast iron housing. To be fair though, that 11# is lighter than the corresponding cooler/pump combo and does the same job.
The diff that comes with 3.15 gears is the Ford Traction-Lok. It’s the same damned thing it’s been since the 60’s with very little change. There are a potential of 3 drive/driven plates per side giving a total of 12 friction surfaces. Each surface has a thin phenolic layer to reduce noise. If you really use a Trac-Lok, then you burn the phenolic completely off in about 2 weekends and lose all the preload in the diff. FP does make carbon fiber surfaced plates, but still 3/3 per side. This improves engagement and wear, but it doesn’t really help total locking and the torque bias that a Trac-Lok can provide is about 1.75:1. To be able to put power down as well as the Torsen, I know it needs to be tighter.
In the mid-90’s, I ran my Fox in E-Street Prep. I had a 3.27 gear/T-5 combo. It worked OK when new, but was a peg-leg in short order. I didn’t know how to fix it then, but over the years, I’ve thought about it. That’s how I came up with the idea of making my own plates. They’re water-jet cut, ground and hardened tool steel and I made them thinner, so I can fit 5 drive/driven plates on each side of the diff for a total of 20 friction surfaces. This alone accounts for a 66% increase in locking capacity. Besides that, the Ford pieces are crap, warped, stamped steel, so they don’t really make good surface contact. Having the plates ground flat means the surface contact is as close to perfect as I can make it. The holes in the floater plates are to carry oil for cooling and it also smooths engagement. Some smart and experienced people helped me out, here…I didn’t just pop them out my keester. So, I made these plates and part of this adventure is giving them a test.
I previously had the stock diff housing bushings with the BMR red pucks. These were my last stock bushings on the car and even though they were in good shape, I wanted to go to the Whiteline kit. The pucks just seem like a ½ measure.
I got Kell-Trac’s stud kit a while ago. They go in with the subframe.
I’ve been on 750# rear springs for a while and they feel like a pretty good compliment to my 450# fronts, but I’ve been 950, 850 and 750. Each time I’ve dropped rates, I’ve like it, so I ordered the next two drops down. 650 and, since they didn’t have a 550 on the shelf, 500. The 500 is a 2.5 x 7 spring where all the others are 2.5 x 6. Just because I’d rather overstep the target and then come back, and the 1 vote poll, I decided to go with the 500# rear. I know, I know, I know…..I want to try it. I’m perfectly happy to put *any* of these springs on the car. I’m having as few a number of pre-conceived notions as possible. I just want to feel it. In general, I tend to run the rear spring rate of any car I happen to be playing with as soft as I can to improve exit traction and as stiff as I have to in avoidance of excessive understeer. With the 750, I have very little understeer right now and can always improve traction. It might not be great, but it’ll be OK.
It's important to take into consideration that my car is quite a bit lighter on the nose than a GT and I’ve got the battery in the trunk. Weight distribution is a big deal. My car will always be a little bit of an odd-ball in this respect.
OK, so everything went fine on the way out of the car. I got a cheapy 500# hydraulic table at Harbor Freight and it makes everything pretty straight forward. I had previously used a wide-base ATV jack, which was unstable and just not strong enough to handle the whole assembly. I am doing this all with the car on Quickjack lifts.
The AL housings were all auto cars, so you have to change the driveshaft flange for a manual. You get a roll-over torque reading and then match than with the new flange. It ended up about 100 ft-lb of torque on the nut to get the 15 in/lb roll-over. It’s not meant to deform the crush sleeve further or change the pinion position. The big nut is deformed on the shaft, so a PITA to take off.
Diff bushings came out with a Saw-all. That’s always fun.
I did find my vertical links were pretty much frozen in place. When I got these, I had thought about going to a class where you couldn’t run monoballs. When I decide to go CAM, that went out the window, but I figured these were ‘good enough.’ It turns out the Delrin had pretty much seized on the aluminum inserts and was causing a lot of stiction/friction. I freed up all inserts with emery cloth on a lathe, but I’m going to replace with monoballs soon. I don’t want to chase that, again.
I spent a lot of time cleaning and checking things. No real horror stories on the putting things back together. I position the table and go up. You end up having to do some side to side stuff, but it isn’t bad. Thread the studs in and put the nuts on. You know, there’s very little that’s rocket surgery on these deals. It’s just a whole lot of little things that have to happen in a very specific order. The deal is, you just have to keep working until it’s done.
I love the gearing in town. I’ve only had it for about a week, but all the gears are exactly where I expect them to be, now. First in parking lots feels right. Second in my sub-division is right. Faster city streets are 5th, not 6th. 6th is freeway only. It’s early days, but second seems to be just fine for a tight hairpin. I don’t feel like I’m driving a Honda S2000.
I had a 500-ish mile trip this week. I’ve made this drive over and over for the last 4 years. My best ever MPG was 29.1, but my average is less than 28.5. First trip, 30.3 MPG and that was doing nothing special.
The diff plates definitely have some parking-lot groan, but it’s not horrible. I haven’t really been in the position to get a read on how it acts in anger. Here is my issue, though, the rear end has a hell of a howl in it. I don’t know if it was there before I got it, but it’s there now. Maybe I messed up the snout torque? I don’t know. I don’t think the Whitelines are supposed to be particularly noisy. It will be coming out this summer for new bearings and R&P…goodie. I probably should have done this before, but I was hoping to avoid it.
The diff runs cool on the freeway. At 55 deg temps, I was seeing 131 deg rear temp and at 75 I saw 153. This was running a consistent 75-80 mph. Whatever is going on in the rear end isn’t making much heat, which is good.
The rear springs... It’s hard to say on handling. I haven’t been able to really hustle it much. It feels like I’ve probably picked up some understeer, but it doesn’t feel like I put Slinky’s in. It still has reasonable response on the street. The ride, though, that’s bloody great. This thing just soaks up rough pavement. Remember that softening rear springs was supposed to make the thing have some sort of pitching issue and that’s why the rear has to run stiff? It’s bullsh!t. OE guys are obsessed with it, so they sacrifice very primary considerations for a much less important 3rd order effect. It’s better connected to the road and feels more composed. I don’t know that I’ll feel the same way when I’m at speed. I’m concerned it won’t want to change directions well in a slalom and I think longer duration corners could particularly be an issue for understeer. All I can say to this point is so far/so good.
All in all, a hell of a project and I’ll keep you up on where it goes from here.
[TL1]
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