independent rear suspension modification

[davidjonh]

I am new to the forum so I hope I am doing this correctly. I have a 1985 Avanti and I am looking for information on modifying the rear suspension to an independent rear suspension. I understand that a number of articles have been written in the Avanti Magazine but do not yet have access to these. Is there anyone out there who has information on doing this modification or has the back issues 89, 118, or 122?

David

[SBCA96]

Your post came through, so you did it correctly. If you are not a member

of AOAI yet, then I suggest you join up! I think that Lew might be able to

tell you if those back issues are available, or you can check the backorder

page on this site.

http://www.aoai.org/isell/results.php?acti...y=Back%20Issues

There are benefits of independent suspension, but also many negatives.

The Dana 44 in your Avanti is a very good unit, and if you are looking for

improvements in ride and handling, there are things you can do.

Tom

[davidjonh]

Tom, thanks for the reply, I am a member of AOAI and actually thinking of getting the five year membership on renewal. I checked the back issues like you mentioned, I had forgotten about this, and see that 118 is still available.

I sort of have a special need for having the rear end fixed with relationship to the frame but I understand the ride may be better with the independent suspension and I would also like to add disc brakes to the rear since I am starting with a bare frame. I had looked at changing the leaf springs to the composite type but that alone would cost about $400. I'm wondering what others ran into by making the modification. Any idea on the negatives?

Thanks again, David

[grobb284]

You can still have a Dana 44, and independent suspension as well, in your Avanti. Here is a Viper differential, which is a Super Dana 44. It is matched to aluminum half shafts, stainless cambers bars, and aluminum tie rods. The outboard knuckles are Corvette, with C5 dual piston calipers. The overall width is in the vicinity of 58/58 1/2" , same as the original Avanti.

Most high end rear drive cars have independent rear ends. Mercedes, BMW, Lexus. I'm unsure what the negatives are, unless you are an all out drag car. There are a number of postives, one of them being less unsprung weight.

If you want you can just purchase the Viper adapter plate, and do the work yourself.

It does require a modification to the floor pan under the rear seat for the 4 link attachment.

Here is the tag that we found under the sand cast rear housing after we polished it smooth.

[Ernie]

The new Mustang still has a live rear axle. With a Roush supercharger that developes over 400hp, the live axle is doing fine and still gives a very good ride.

For my money, the change to an independent axle is not worth it.

[SBCA96]

Front disc :

Rear disc on the Dana 44 :

Tom

[davidjonh]

"You can still have a Dana 44, and independent suspension as well, in your Avanti. Here is a Viper differential, which is a Super Dana 44."

I saw this Viper differential in another post and the first thing I thought was this was really nice. The next thing I thought was this must cost a lot of money. Where would you get the Viper components and the adaptor plate? Any idea on how much modification of the floor pan is needed?

I'm more interested in ride and reducing weight than in going fast. I did that when I was a lot younger. Some very interesting information here.

Thanks to all so far. David

Edited March 18, 2007 by davidjonh

[SBCA96]

Well ... when you take out that "heavy" Dana 44, and swap in your new IRS,

send me an email and I will come by and get it out of your garage.

Keep in mind that for most driving, and on most roads IRS & a live axle are

going to be almost impossible to tell the difference. The IRS shows its its

colors most on a turn with uneven surfaces. A live axle will skip, but the IRS

will hold the road. Unless you are a spirited driver, chances are you will not

ever see the benefits of an IRS. You might also notice a slight improvement

on straight line driving, but thats questionable.

I am looking into a way of modifying the live axle with coil overs (eliminate

the leafs) and trailing arms with a panhard bar and upper arm. Its in the

dreaming stage right now, but this is done fairly often in other makes. I feel

that a true "bolt in" 3 arm system might be fairly popular.

Tom

[Twnchgr]

You can still have a Dana 44, and independent suspension as well, in your Avanti. Here is a Viper differential, which is a Super Dana 44. It is matched to aluminum half shafts, stainless cambers bars, and aluminum tie rods. The outboard knuckles are Corvette, with C5 dual piston calipers. The overall width is in the vicinity of 58/58 1/2" , same as the original Avanti.

Most high end rear drive cars have independent rear ends. Mercedes, BMW, Lexus. I'm unsure what the negatives are, unless you are an all out drag car. There are a number of postives, one of them being less unsprung weight.

If you want you can just purchase the Viper adapter plate, and do the work yourself.

It does require a modification to the floor pan under the rear seat for the 4 link attachment.

Here is the tag that we found under the sand cast rear housing after we polished it smooth.

Now thats cool Twnchgr

[davidjonh]

Sorry to all, I have not been back on to comment and thank others for their comments. In the last few days I have been doing more research and ordered a back issue of the Avanti Magazine which is supposed to have some information on installing a Corvette rear independent suspension. I found a place within 15 miles of where I live which deals only with Corvettes and who actually has two mid 80 units. So far it appears that I may well be able to adapt the current 15 inch Lincoln Towncar Ford rims to the Corvette unit. These rims came with the car and cleaned up nicely. They have the newer Ford pattern of 5 lug on 4.5 inches. I picked up a number of the parts for the Corvette rear end and they do seem very light weight in that may are aluminum. If necessary the half shafts can be shorten.

I have also been talking to Flat Out Engineering about their kits which may allow you to almost bolt in a Corvette rear end but so far I don't have a final answer. I have some frame repair to do anyway and a bolt kit would save considerable time as some of the work will be done by someone I trust to do the job right. I have read the step by step procedure which can be found with a link on their web site and it really seems straight forward. I plan on eliminating the leaf spring for the original Corvette rear end and installing coil overs which are also available from Flat Out Engineering. Pictures are on their web site.

I did send an email to Electro-Dynamics and received a very nice email back along with a price list for the Viper adaptor and a lot of other components. I am looking this over to see what I might be able to use and the note indicated that I might want to just purchase the Viper adapter and make the remainder of the parts myself. They have beautiful stuff including a stainless steel Avanti frame but for $13,000 I'll have to wait for a while. It sure would be tempting to purchase some of their products as the end result would be very nice.

Tom, I don't know where you live but I think that I will have a Dana 44 which will not be needed sometime in the future. The Corvette, as I understand it has either a Dana 36 or a Dana 44 rear end but some of it is also aluminum so again it helps me with a weight reductioin. I had looked at the composite leaf springs which are about $200 each but since I need the rear end fixed to the frame that idea went out the window. As things progress I will come back and note what I find out.

David

Edited March 25, 2007 by davidjonh

[SBCA96]

David,

I am in Santa Barbara, California.

Have you looked into the 03/04 Mustang Cobra rear end? Its an IRS and will

keep the factory 5 on 4.5 bolt pattern that Stude has. If you get the whole

rear end, you can hit me up for the Cobra front disc brackets I designed to

have the matching front disc setup. Actually, the Vette uses the same rear

brakes, so my setup will match those as well. Chances are the Mustang has

a width similar to the Avanti - or at least closer than a Vette.

Just a thought.

Tom

[davidjonh]

Tom, yes I did look at the newer Mustang Cobra rear ends and was thinking about buying one. The width is in the 61-62 inch range, mounting surface to mounting surface and from what I could determine from wrecking yards and Ebay they were at least as expensive as the Corvette 80's rear end. Like the mid 90s T bird and Lincoln Mark VIII the Mustang is sort of in a sub frame and is going to be heavier than the Corvette as well as most people I talked to indicated you probably could not narrow them to the 58 inches of the Avanti. With the Cobra and others you not only have to modify the half shafts but the sub frame and probably the control arms which is not really practical according to those people I have talked to.

Are you saying the Corvette bolt pattern is the same as I now have? Where did you get the discs in the pictures? Will they fit on the Corvette?

David, in Fairfield.

[SBCA96]

Sorry, I thought that might be a little confusing. Cobra uses the same 5 on 4.5

bolt pattern as Stude, Corvette uses 5 on 4.75. To use Vette rotors on a Stude

you have to redrill the pattern - then they have that swiss cheese look. What I

was getting at is the calipers are the same between Vette and Cobra, at least

the C5 and the Cobra. You are mentioning "80s" so thats a C4 I believe, and it

would have smaller brakes. I use the 13 inch Cobra front discs, the ones I got

were from StangSuspension.com. My third article will be in the next issue of the

Avanti Magazine - which should answer most questions. Keep in mind that if you

can get the weight low, the Avanti is 60/40 weight distribution, so lightening up

the rear end might not get the desired effect. That extra weight from the Stang

subframe might be a welcome addition once the heavy leafs are gone. Unsprung

weight it what you want to limit. With some Bilstein shocks & a larger rear sway

bar you can control over 4000 pounds pretty easily.

Tom

[grobb284]

I did send an email to Electro-Dynamics and received a very nice email back along with a price list for the Viper adaptor and a lot of other components. I am looking this over to see what I might be able to use and the note indicated that I might want to just purchase the Viper adapter and make the remainder of the parts myself. They have beautiful stuff including a stainless steel Avanti frame but for $13,000 I'll have to wait for a while. It sure would be tempting to purchase some of their products as the end result would be very nice.

Thanks for the kind words.

We often work with Corvette differentials, but with the narrower Avanti, the Viper differential already has a narrower mount vs. the much wider Corvette mount. Both are internally the same (speaking of the Dana 44's), the Viper having a crush sleeve on the pinion, the Corvette shims. Also, the Viper differential is often less expensive to purchase used, as compared the the Corvette C4 Dana 44.

Something we haven't discussed: How about a Champ quick change rear end with independent suspension? Here is a photo of one where we made an isolated mount for it, narrow enough to fit the Avanti (27" mounting)

[davidjonh]

Thanks for the clarification, that really helps. From some of the information I have it seems the later model Corvette rear ends like the C5 present issues with smaller wheel sizes like the 15 inch rims I currently have along with new tires. Thus the 80s C4 rear ends I have been looking at. This fits with what you are saying about the possible smaller brakes as I think the calipers in the later models cause interference with the smaller wheels.

Actually I am trying to get the weight down as much as possible and with the modifications I am making I plan on trying to balance the car more like 50/50 which is what the tag on the car shows. When I first had the car weighed I was a little shocked that the distribution was about 60/40. I guess when you put three passengers and some stuff in the trunk you might get back to the 50/50. But to me the Avanti seems too heavy in the front, thus the need for power steering? (something else I would like to get rid of)

I just got my back issue of the Avanti Magazine #118, those guys are fast. The article I was looking for was written by Gene Ester. It appears that the C4 Corvette front and rear suspension was used to update the Avanti suspension. If I keep trying to keep up I'll have to install the front suspension and updated steering. Since this is a 2002 article I doubt that the email is the same for Gene and I could not find him in the 2007 roster. Would have liked to see more photos and maybe talk to him because it doesn't look like the rear portion of the frame was modified at all from what I can see.

I would love to add all this new stuff but I have a lot of other expenses to getting this Avanti back on the road so for now it looks like I will stick with the C4 rear end.

David

Edited March 27, 2007 by davidjonh