Ride Height of 1985 Avanti

[davidjonh]

I have decided to install an 84 Corvette independent rear suspension in my 1985 Avanti. Unfortunately before I took the car apart I had not made this decision and I only measured the ride height distance from the ground to the point on each fender well just above the centerline of each wheel. However, I did not measure the distance from the ground to any part of the frame in the rear and I am now trying to place the frame at the original ride height before I place the Corvette suspension for attachment. I was wondering if anyone out there might know approximately what the measurements might be to a specific point on the frame in the rear such as the center mounting bracket attached to the rear cross bar, or other points.

David

Edited April 15, 2007 by davidjonh

[SBCA96]

Thats an interesting situation. I think that answer will vary between cars, ride height is

going to be different depending on the condition of each persons rear springs, you will

get quite a few different answers. It will be difficult to decide on how to mount the rear

suspension since you need to load it down with the actual weight of the car. The final

height is honestly up to you, leaving the amount of tire to fender gap YOU want. Maybe

you want to lower it from where it was anyway. Or maybe you want to lower the front.

I would suggest mocking it up with the weight of the car on it, put sandbags into the

trunk to simulate fuel weight and passengers, and spare tire!

To give you a starting point, I measured MY Avanti, the lower front leaf spring eye bolt

on the drivers side is 9-3/8 inches from the ground. Thats with 245/45 R17 tires.

Tom

Edited April 15, 2007 by SBCA96

[davidjonh]

Tom, thanks, you are probablyl correct that it is going to vary between cars and condition. My 85 has 15 inch tires so I'm sure that can make a difference. When I back calculated the height at the top of the center mounting bracket that is attached to the rear bar I came up with 10-3/4 inches but the body is up in the air about three feet on saw horses and is not level. I discovered that makes a difference when you are trying to measure from the wheel well. My system for lifting the body is a very slow process which I ony want to do one more time when I lower it down on the frame The problem is that I what to install the Corvette rear before I roll the frame back under the body because I know some modifications may be needed to the trunk area.

From what I can remember and some pictures the rear leaf springs seemed to be mostly flat before I took the body off and the drive train out. I have some pictures of an 85 from an Ebay sale of a vehicle that was in like new condition and it looked like the springs were also flat.

Thanks again. Dave

[SBCA96]

This thread on SDC might be of interest to you .. someone photoshopped my

car and lowered it. It made the car look interesting, but realistically not road

worthy. Read all the posts, I put measurements into there of the tire center

to ground and frame measurements.

http://www.studebakerdriversclub.com/sdc_f...p?TOPIC_ID=8844

My rear springs had a REVERSE arc when I got it, I installed station wagon

rear springs (4 leaf) and was afraid it would sit too low, so I added a pair of

"add-a-leaf"s to it. The result was comical - live and learn :

Tom

[davidjonh]

Tom, that link is really interesting and a great help. I started looking back at all my information and found some interesting things. First my measurements for all three wheels, through the centerline of each wheel were 27-1/4 inches to the wheel well which is pretty much what others are showing. The funny thing is that on the front right side it was 26-3/4 and maybe I now know why. The wing on the radiator bracket which supports the front of the body was broken completely off on the right side and the fiberglass mounting piece on the firewall was almost cracked all the way around it, again on the right side of the car. Maybe that is where the 1/2 inch lower figure came in for the right front of the car.

I went out and measured the vertical distance from the top of the rear center frame support and the front leaf spring eye bolt hole (which in my case is the lower hole at the rear of the large bracket) and found it to be about 1 inch lower than the rear center frame support. If I assume I back calculated the distance from the ground to the top of the rear center frame support, the leaf spring eye bolt hole would be approximatey 9-3/4 above the ground. That is at least in the same general area as your dimension of 9-3/8. Of course my tires are 195/65 R15 and measure a little over 25 inches in diameter and the frame is not sitting level on the engine stands so I have to "adjust" my measurements. It looks like the X-member is about 4-5 inches off the ground from the link you gave me so I can see where mine will be once I get the frame off the engine stands.

I plan to remove the rear leaf spring on the Corvette rear end and install Aldan shocks and coils so I should be able to adjust some heights later. I want to put the rake back in the car and with what I am doing I should be able to remove most of the spacers in the front. In order to use my current rims and my new tires I did some more checking today and it seems like I can either use wheel adapters for about $100 or have the hub and rotors redrilled for maybe $300-$400. Problem is, if I redrill the hub and find out later the bearings in these sealed units are bad, I would not only need to buy new hubs/bearings at $180 each but also have to have the hubs redrilled. Talk about one thing leads to another.

Your results using the add-a-leaf are indeed interesting.

Thanks, Dave

[SBCA96]

I am confused about your wheels, the need for spacers, and the "sealed units".

Maybe my brain is not firing correctly at 3:21am ... but your Avanti still has the

Stude frame correct? If not, I just gave you a LOT of info thats useless.

Speaking of one thing leading to another ... I should tell you about when I had

bought my DVD player .. then I needed a new TV .. then a receiver ..... and ...

Tom

In order to use my current rims and my new tires I did some more checking today and it seems like I can either use wheel adapters for about $100 or have the hub and rotors redrilled for maybe $300-$400. Problem is, if I redrill the hub and find out later the bearings in these sealed units are bad, I would not only need to buy new hubs/bearings at $180 each but also have to have the hubs redrilled. Talk about one thing leads to another.

[grobb284]

Dave: The rake of the Avanti is built into the body. The frame is essentially level.

I doubt that you will have room for your wheels if you use adapters. The early C4 rear Corvette suspension is 62.5" wide, where the Avanti is around 58". Even if you narrow the rear, adding an adapter is taking up space that you can't typically spare.

If you narrow the rear assembly, are you still using the orginal C4 cast brace? Be sure to check for clearance if you do. Have you made cursory measurements to be sure this is doable? The reason I ask, we put a stock C4 independent rear in a 1955 Chevy, and the body is at least 4-5" wider than the Avanti, and we needed to use approximately 35mm offset to put a 9" rim inside with adequate clearance.

If you narrow the Corvette rear, the axles do not come out straight from the central carrier.

Tom: The "sealed units" are the rear bearing assemblies for the Corvette independent rear. They retain the wheel hub, and as they are 4 3/4 BC, they would need to be drilled for 4.5".

Edited April 18, 2007 by grobb284

[davidjonh]

Yes the 84 Corvette rear end has sealed bearing assemblies and they are at 4-3/4 rather than the standard Ford 4.5 inches. My rims are something like 6 or 6.5 and are not really deep like some of the newer rims. From what I understand they are off a Lincoln Town car and somehow got on the Avanti.

The frame on my 85 is the old Lark frame, again from what I can understand and looks in pictures just like the standard X frame from the earlier Avantis. I thought that 85 was the last year they used this frame. I understand the rake is in the body with the use of the spacers and as my Avanti sits level I can understand why there are lots of spacers in the front to raise the front back up to the level position and eliminate the rake. I have been told by Corvette shops that the 84-87 Corvette rear ends are 61.5 inches and the later ones are at 62.5 inches. I picked up the rear end when it was apart so I first need to get the wheels mounted and then put it back together and take some measurements. If it is actually 61.5 inches I would need to narrow it by about 1-3/4 inches per side which may cause some concern about the way the wheels contact the ground. Adding wheel adapters results in narrowing each side by an extra inch but also pushes the wheels out that same inch so it would seem that wheel contact with the ground would be about the same.

I'm not sure what the "C4 cast brace" is unless it is the "wing" which really can't be narrowed without a lot of modifications. I have been working with Flat Out Engineering in Orange CA and while it is possible to narrow the Corvette rear end, you have to be careful of components hitting each other and how the wing and other components are mounted. Flat Out makes very nice kits for installing the Corvette rear ends but this is the first time they are thinking of working with the Avanti frame which is different than the older trucks and such. Again, I need to get the rear end back together first to make some measurements but before I do that I have to get the wheels on, sort of like a catch 22. It would seem that if you narrow the rear end slightly and then lower it in the center the wheels will sit flat but that is something I need to work out.

The conversation here is really helpful and hopefully as things progress I can get this figured out. Flat Out suggested I place the Corvette rear end under the frame and make the half shafts level and then place the frame at the standard ride height to make the other measurements. Thus my quest for ride height position.

Thanks all, Dave

Edited April 19, 2007 by davidjonh

[grobb284]

I have been told by Corvette shops that the 84-87 Corvette rear ends are 61.5 inches and the later ones are at 62.5 inches.

No, we have not found them to be the dimensions you are mentioning.

If it is actually 61.5 inches I would need to narrow it by about 1-3/4 inches per side which may cause some concern about the way the wheels contact the ground.

This does not affect how the wheels contact the ground. It does effect how the universals are angle limited and the overall suspension travel.

[SBCA96]

Oh ok ... I was thinking front wheel hubs, not rear .. somehow I switched gears

and was thinking front suspension. Lowering the body on the frame you must

make sure you have the engine clearance. Oh the fun of modifiying! I would

have been interested in the 4th Gen Cobra IRS install into an Avanti. Keeping

the same bolt pattern is nice, but I can say I want to go the Vette route myself.

I have considered an IRS, just seemed like too much trouble. Then many have

said the SAME thing about my Cobra brakes.

Tom

Edited April 19, 2007 by SBCA96

[davidjonh]

Well I started looking back at the information I have been gathering on the C4 Corvette rear ends and find that I have conflicting information about the width. I even found an article which indicated the earlier models, 84-87 measure 61-1/2 but other information says 62-1/2. So I decided to put the pieces back together as best I could, not exactly knowing what I was doing, and Grobb is correct, it measures 62-1/2 inches. So I guess you have to be careful about what you read in writing.

I also talked to Flat Out Engineering and discovered that another Avanti owner was just sent one of their kits for a standard width of 57 inches, which I if used in my case with the current wheels and re-drilled hubs and rotors will put the wheels within 1/4 inch of what they originally were. So I am not the first in using their kit. Modifications will probably be needed for some of the kit components or the frame but this looks like a pretty good solution.

The problem now is do I use wheel adaptors, aluminum or steel, or do I try to have the hubs and rotors redrilled to the new pattern? I have been calling around and it is hard to find anyone who will redrill the hubs and rotors and some people say use wheel adapters and others say no way. Anyone know how you clean up the aluminum components of the C4?

Moving forward, often confused, Dave

Edited April 20, 2007 by davidjonh

[grobb284]

The problem now is do I use wheel adaptors, aluminum or steel, or do I try to have the hubs and rotors redrilled to the new pattern? I have been calling around and it is hard to find anyone who will redrill the hubs and rotors and some people say use wheel adapters and others say no way. Anyone know how you clean up the aluminum components of the C4?

Would suggest drilling the hubs and rotors. Provides a factory style solution without "add-ons", and keeps the halfshafts and cambers bars longer. We can drill them for you if you wish.

To polish the aluminum, use finer grades of scotchbrite (sheets, drums, pads), followed by Simichrome or Wenol.

To accomplish your Avanti project you will need at a minimum:

1. A rear differential mount

2. A front differential mount.

3. Shorter half shafts.

4. Shorter camber bars.

5. New tie rods.

6. Reversed tie rod mounts at the knuckles.

7. Lowered inboard tie rod mounts.

8. New 4-link front mounts.

9. New lower shock mounts for the coil overs to clear the half shafts.

10. New upper shock mounts.

You can design those yourself, or I can help you with any of the above individual items.

If you want, this could be set up as a kit.

By the way, go here and see some of the brake kits we have available for the C4 front and rear suspensions. Corvette brakes for C4 suspensions

Edited April 20, 2007 by grobb284

[davidjonh]

quote grobb284'

Would suggest drilling the hubs and rotors. Provides a factory style solution without "add-ons", and keeps the halfshafts and cambers bars longer. We can drill them for you if you wish.

Grobb, thanks for the information, who would I contact to drill the rotors and hubs? I have found some new hubs at a slightly more reasonable price so I think I am going to buy the new hubs and have them drilled rather than taking a chance on using the old ones because I just don't know how good the bearings are.

Dave

Edited April 21, 2007 by davidjonh

[grobb284]

quote grobb284'

Would suggest drilling the hubs and rotors. Provides a factory style solution without "add-ons", and keeps the halfshafts and cambers bars longer. We can drill them for you if you wish.

Grobb, thanks for the information, who would I contact to drill the rotors and hubs? I have found some new hubs at a slightly more reasonable price so I think I am going to buy the new hubs and have them drilled rather than taking a chance on using the old ones because I just don't know how good the bearings are.

Dave

David:

Enjoyed speaking with you on the phone yesterday. I hope you found some of the answers to your questions useful.

Sent you an email today with more information on narrowing the Corvette independent rear suspension. Call again if you think it would be helpful.

Best regards.

[davidjonh]

[quote 'grobb284'

Enjoyed speaking with you on the phone yesterday. I hope you found some of the answers to your questions useful. Sent you an email today with more information on narrowing the Corvette independent rear suspension. Call again if you think it would be helpful.

I did find our discussion on the phone very helpful and I sent a reply to your email last night. I picked up the rear end and parts today after getting them cleaned. I am now at the point where I need to decide how I will get this rear end modified and into the Avanti frame. I like the idea of having one source for modifying the rear end and possibily making the necessary components for mounting the rear end into the Avanti frame.

Thanks, Dave

Edited April 28, 2007 by davidjonh