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Discussion Starter #1
First, many thanks to DonL for finding River City Differentials.

I received my rebuilt diff this week from RCD and it was installed Friday.

A very nice match to the 7MGTE.

First gear is actually usable, highway cruising is very nice.

The pesky rear end whine is gone, but some residual, as I suspect it's
now the drive shaft, or just the noisey W58 resonating through the driveshaft.

Next project: 3" stainless exhaust.
 

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How much did your rebuild cost and what did you have done?


-Ken
 

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Jim, now you will need to invest in a nice stiff front sway bar (to keep that rear end planted), and coilovers in front to adjust the front/rear weight distribution. Really, you are gonna love that rear diff ! With that turbo power, it will be a massive improvement over whatever you had, but first time you notice inside wheel spin, remember what I said :)

Don L.

Should be sending you some stuff this week.
 

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Discussion Starter #4
MK2Racer said:
How much did your rebuild cost and what did you have done?


-Ken
I shipped a set of relatively new ring and pinion to Sean.

He had an extra case.

So, a full rebuild, a TrueTrac installed. $550 Shipped from CA to MA.

Personally, I think this is a very good price.
 

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Discussion Starter #5
Don L. said:
Jim, now you will need to invest in a nice stiff front sway bar (to keep that rear end planted), and coilovers in front to adjust the front/rear weight distribution. Really, you are gonna love that rear diff ! With that turbo power, it will be a massive improvement over whatever you had, but first time you notice inside wheel spin, remember what I said :)

Don L.
My first MK2 had stock springs, Koni Adjustables and Addco's.
The Addco's made a big difference, reducing that rear diaganol squat.

On this MK2, I have Eibach's, NOS Illumina's and stock sway bars.

I'm currently pleased with the factory sway bars for regular spirited driving. Though since you are our resident expert on MK2 suspension,
I will put this on my every growing list of to do items.

Another side note. A local boat fabricator just bought a CNC mandrel bender. It has the mimic feature, which if I supply a donor, it
can calcuate the bends and angles. Hmm, hollow sway bars. Hmm...
 

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Jim,

Hmmm, hollow front bars.... THAT would be very interesting. Just my opinion that for very agressive driving, including getting that rear end planted on power out of turns, a much stiffer front bar is needed. I had a custom bar made that is about 50% stiffer than the Addco front. Really helped. People say it looks like a GM F-body front bar. 1 & 1/4" I believe.
Hollow bar would be great cuz my bar is soooo heavy. My main concern though would be the center bar mounts. A hollow bar would need to be bigger in outer diameter right ? Not sure it would be easy to make a center U-bracket that big.

Keep me posted on how that TruTrac works for you.

Don L.
 

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[quote="jdk_ii]
Another side note. A local boat fabricator just bought a CNC mandrel bender. It has the mimic feature, which if I supply a donor, it
can calcuate the bends and angles. Hmm, hollow sway bars. Hmm...[/quote]

Jim, do you think he could make em for less than what Addco charges?

Second question, is that the same type of mandrel bender used to make SS exhausts?
 

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Discussion Starter #10
82Spearco said:
Jim, do you think he could make em for less than what Addco charges?



Second question, is that the same type of mandrel bender used to make SS exhausts?
Unknown. I'm going to bring a prototype to him to get an idea of pricing.

Different guy, but he can bend stainless tubing (ie, exhaust).
 

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Re: re:

jdk_ii said:
Crocket said:
how did you correct your speedometer with the new rear end (3.73s)?

Sonny
Not done yet. I have the parts. Just need to play "Operation".
Jim-I'm interested to see what you come up with on the speedo fix. I've had the 3.73 when the gte went in. Lewitz and I looked at all the speedo gears and long story short I concluded - the inner tailshaft drive gear needed to be changed along with the outer nylon gear - this was for the '85 P-type.. So, used a GPS and calculated that I'm off 10%.. easy # to add to the speedo.. Jay B
 

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Discussion Starter #12
Re: re:

Suprajayaz said:
jdk_ii said:
Crocket said:
how did you correct your speedometer with the new rear end (3.73s)?

Sonny
Not done yet. I have the parts. Just need to play "Operation".
Jim-I'm interested to see what you come up with on the speedo fix. I've had the 3.73 when the gte went in. Lewitz and I looked at all the speedo gears and long story short I concluded - the inner tailshaft drive gear needed to be changed along with the outer nylon gear - this was for the '85 P-type.. So, used a GPS and calculated that I'm off 10%.. easy # to add to the speedo.. Jay B
I have all the correct parts. Just there is two install methods.

Pull the rear tailshaft housing off (ugh), or test my surgeon skills.
 

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Uhh, Don, I don't know where you are getting your info but I have a couple questions. How can you adjust front/rear weight distribution with a set of coil overs, and how will he get inside wheel spin with a LSD? As far as I know the coil overs can only be used to adjust cross weight and not F/R balance. Sorry, just noticed those and have to ask. Oh, and if you have a front bar that's to stiff won't you just lose traction on the front and understeer instead of actually gaining traction on the rear?
 

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Hi Darin:

I have read a number of books on susp design, setup my autox car so many different ways its embarrassing to describe some of the weird handling I've caused, autoxed on a number of surfaces at all levels of competition. Really, it's a learning process, and I've learned from my trials and errors. I have coilovers in front only, and while you are right that crossweights can be adjusted (I've done the cornerweighting thing too) it still comes down to how well the front of the car sticks vs. the rear, on the road, not at the alignment shop. I change the f/r balance by raising BOTH front corners of the car. Many people forget about that option. I once dropped the rear, raised the front a bunch, hit the autox course, and promptly understeered (pushed) right off the first corner. It was awful. Great extreme example. Get the cornerweights balanced, but the whole front end can go up or down. I get my rear up and down via different springs or spacers.
As for the inside rear wheel spin with a LSD, unless you have a fully locked rear end, if the LSD is original and worn out (most are) the inside wheel will spin (just like an open diff). The stock LSD units had a fairly low % of lockup anyway. Get a aftermarket clutch unit, or helical gear unit like a Quaiff or the TruTrac, and they will work great as long as there is some resistance on both tires. If the inside tire lifts off the ground, it will spin like an open diff too (I've done this with the TruTrac). Not a fault of the LSD, its working as intended. So, the goal is to have the rear tires stay in contact with the ground on corner exits under extreme power. Not an easy task with our cars. Eibach and such maintain a fairly "nose down" balance. There are many that want the front down even more. Thats fine for drag racing, ok for street, but won't give you the best handling in turns. Selection of sway bars is again a balance of front to rear grip. Terms like understeer and oversteer get tossed around like passengers in my car. Keep in mind that if your car is at max grip in front, yes, a stiffer bar will cause understeer. I am still looking for max grip in front. Two things I focused on when trying to solve the rear traction problem: 1) decrease outside front corner compression on corner exits. It causes the inside rear tire to lift. 2) lower the rear relative to the front, or in my case, it was easier to spin my coilovers one turn higher on both front corners. There is just so much front susp stuff going on in turns, camber, toe, static or at speed. We have nose heavy cars, and despite a f/r weight balance of approx 53%f/47%r , I have had to really tweak the susp setup to get improved competitive handling.
Most folks won't get the full enjoyment of the TruTrac LSD until the traction problem is addressed. Better than stock, yes, but so much more is available. Ok, I've rambled enough. Just my opinion, another $0.02

Don L.
 

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Thanks for the quick reply, I didn't realize that raising or lowering the front together would give that much of a difference, I guess I just haven't played with it to the extremes you have. I've been helping set up a friend's RX7 and we've been playing with the suspension a lot. It's funny, I had completely forgotten that most LSDs require some friction, thank you for bringing that up, I guess it just means either get a full locker or make sure the suspension is tuned correctly. Just out of curiosity do you have any favorite alignment angles for toe and caster. I know running more caster will give more stability at high speed but if you go to much you lift the outside of the tire off the ground on sharp turns. I have access to an alignment rack at work and can do whatever I want with it so I can play with my car that way. Any hints will be appreciated.
 

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Well, you probably will dread driving a full locked rear end on the street, terrible when turning, not recommended. I don't believe alignment settings are adjustable on Supras except for toe in front, toe in rear. Camber and caster are fixed I thought. I have no great suggestions for street settings, just manuf settings. Autox alignment settings are fairly extreme and not the best for street or high speed.

Don L.
 

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I think you can also adjust front caster, if it's like my car then there are two big nuts on the strut rod that allow you to move it forward or backwards to change the amount of caster by a pretty good amount. In case anyone else is curious I've found running front and rear toe at about 0, instead of pretty far positive which is stock, and caster around 4.5 degrees instead of the stock 3.5 degrees works pretty well. I'll let anyone that is interested know for sure after I run Willow Springs at the end of the month.
 

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Darin,

I think you are correct. The two strut rods attached to the susp arms in front can pull the arms a bit. I run 4 degrees caster in front, haven't played with it much. I would never run any toe out in the rear as the cars are pretty tail happy already, some amount of toe-in for the rear seems like a good idea, maybe 1/16" per side. I run almost 1/4" per side toe-in for the rears to minimize oversteer and increase stability.

Don L.
 

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Don,
You are right about the rear toe and I may set it back in towards stock specs. I'm just experimenting right now and I need to go out and drive it hard to see what it really does. I'll probably get a chance to do that friday and I'll let you know how it goes. I'm not running toe out, it's right at 0 degrees, it's just farther out than stock. I think I had it at about 1/16" per side before and it was very neutral. I'm talking to a local shop about making a rear suspension that allows camber adjustment, it's slow going because I have finals coming up but hopefully over summer I can get somewhere.
 
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