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rear spring and shock

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rear spring and shock

Post by MC247 on Wed Jul 05, 2017 12:43 pm

Morning,

Been away for a few weeks, so now getting back to the car project. We picked up our rebuilt 302 from my Speedy Racing Engines yesterday, looks awesome in black and red, now to go shopping for performance parts!

We're also working on completing the rear suspension so we can get wheels on etc etc.

Question: We've gone with the 4 link hook up in the rear on a ford 8.8 rear end, I've been looking at coil and spring options, but not sure what height I should go with as we don't have wheels and weight on the car. What have others used?

I'm thinking of a medium spring - 110lbs range with a QA1 double adjustable shock 13" compressed, 20.5" extended?

Cheers in advance,

Mark

MC247

Posts : 64
Join date : 2016-10-11
Age : 49
Location : Ontario

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Re: rear spring and shock

Post by rawshealey on Wed Jul 05, 2017 5:39 pm

i have the same set-up and went with the air bag for the same reason. not sure how light the rear is and its adjustable. I am not done with my build so dont have info on how it works

rawshealey

Posts : 27
Join date : 2016-02-12

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Rear Suspension

Post by DrJ on Thu Jul 06, 2017 8:38 am

Measured unsprung weight Drivers side on mine was 152.25 lbs; Passengers side at 148.50 lbs. Sprung weight was 487.75 drivers; 420.50 passengers. I removed the separate OEM spring (spring rate undetermined) and shock, fabricated and welded in attachment points for coil-overs. Used Vi-King units (double adjustable) with 12" 110 lb/ft spring rate.
You want to use a spring in the rear that has a higher natural frequency than the front spring. Doing that minimizes pitching which is an undesirable ride characteristic.
I converted the front as well on mine to compliment the rear. When purchased my MX had the ride characteristics of a Mac Truck. Substantially better ride now. The short wheel base is another ride issue with our cars but there is nothing to be done about that.

DrJ

Posts : 139
Join date : 2014-06-19

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Re: rear spring and shock

Post by Tony T on Fri Aug 18, 2017 7:15 pm

I am working on my rear suspension. It is a Ford 9 inch rear end. Rear end is a little wider than it should, therefore the tires that I have in the rear stick out a wee bit too much. Tire size is 255-60-R15. This axle came off a 79 Lincoln Versaille. It came with disc brakes. I need a smaller tire size and I hope this solves the problem. Thinking of replacing Mustang coil spring to "coil overs". Need advice.

Tony T

Posts : 5
Join date : 2017-08-18

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Rear Suspension

Post by DrJ on Sat Aug 19, 2017 6:55 am

Will try, what questions specifically?

DrJ

Posts : 139
Join date : 2014-06-19

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Re: rear spring and shock

Post by Tony T on Sat Aug 26, 2017 7:36 pm

What I need, before I can go any further is the exact part numbers QA 1 coil overs. I think if I can adjust the height up or down, I'd be good to go. I don't want to guess as I depend on a shop to do the work. I assume there are members who have gone through this or want to. Anyway, I could listen to anyone who knows from their experience. I talked to QA1 techs and they want more info as this is more or less a custom setup. Thanking you in advance. Sorry I was so late in responding. Tony McFarland, WI 608/ 838-1106.

Tony T

Posts : 5
Join date : 2017-08-18

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Rear Suspension

Post by DrJ on Sun Aug 27, 2017 10:11 am

I went with Vi-king coil overs because they have a working relation with Gayle Bridges who has access to springs the rate of which met my specifications. He is also super knowledgeable and helpful (read that as patient...I was new to suspension engineering when I started this project). Anyway I believe Vi-king was started by former QA1 guys. I liked the fact that their units are adjustable in both bump and rebound. Being coilovers they all permit ride height adjust-ability. Give them a look/call and if any of that works for you I can give you the part specifications and numbers. Just got back with mine from a 1,200 mile tour of the Adirondack mountains, the subject of a piece I will write up and post. Spoiler Alert...she came back on four wheels and not a flat bed!

DrJ

Posts : 139
Join date : 2014-06-19

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Re: rear spring and shock

Post by Tony T on Mon Aug 28, 2017 8:33 pm

Thank you D. J. I talked to the tech guy at Fabquest today and got a little more info. He gave me some basic specks, depending on the measurements, I'm going to give him. Thanks again, I'll let you know.

Tony T

Posts : 5
Join date : 2017-08-18

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Re: rear spring and shock

Post by MC247 on Wed Aug 30, 2017 12:17 pm

So I'm stuck with the rear suspension. Called jegs and they asked if its a stock rear shock and spring sizing form the 89 mustang with the two eyelet pickup or i need something else and to measure the size? I literately have the frame on axle stands, so not sure what to measure, do I go with a single adjustable stocker star - compressed height at 13.5" and extend to 21" then a coil spring of some size......ideas?

MC247

Posts : 64
Join date : 2016-10-11
Age : 49
Location : Ontario

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Rear Suspension

Post by DrJ on Wed Aug 30, 2017 12:50 pm

When I dissembled my 4-link coil spring rear this is what I found:
OEM Springs: .50" od wire with slight taper down to 5/16" on the last two coils
Overall length out of the car was (D) 13" (P) 12.5", due to age probably
OD of spring: 4.75"
ID of spring: 3.75"

Sprung weight rear: (D) 487.75 lbs (P) 420.50 lbs, that with a (Ford 8" posi)

OEM Shocks: Brand and numbers missing
Out of car and measured eye to eye
Extension: 16"
Compressed: 12.5"

Now with all that said it is generally accepted that the OEM specifications for the MX was stiff and harsh, mine certainly was. Converting to coilovers generates the flexibility to adjust the ride height, the shocks stiffness in one or both functions depending on which one you go with and it opens the door to selecting softer springs more commensurate to the cars actual sprung weight. It also allows you to establish the proper natural frequency for the springs, the car itself and one another (front vs rear). By doing this you can engineer out a lot of the OEM's shortcomings. One should accept that there are going to be limitations on how well a car with a short wheel base and a live axle is going to drive. It will never be a Miata, but it does not have to shake the fillings out of your teeth either. Mine no longer does.

DrJ

Posts : 139
Join date : 2014-06-19

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Re: rear spring and shock

Post by MC247 on Wed Aug 30, 2017 12:53 pm

fantastic DrJ! that really helps us out over here.

MC247

Posts : 64
Join date : 2016-10-11
Age : 49
Location : Ontario

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Re: rear spring and shock

Post by Tony T on Wed Aug 30, 2017 11:28 pm

This is what I needed. Thanks for all your help. Tony

Tony T

Posts : 5
Join date : 2017-08-18

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Re: rear spring and shock

Post by Tony T on Tue Sep 05, 2017 5:07 pm

I have a few more questions
1. Regarding mounting of new coilover. Is it mounted where the existing coil spring is now?
2. Does the replacement coilover assembly be mounted where the existing shock Is?

Thanks a lot TONY

P.S. Do any members live in the Madison, Wisconsin area?

Tony T

Posts : 5
Join date : 2017-08-18

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Rear Suspension

Post by DrJ on Wed Sep 06, 2017 9:01 am

The OEM rear spring is nested between the trailing arm and a perch mounted to the frame rail. That real estate could be modified to accept a coil over. I chose to abandon that location and fabricate/weld in mounting points just aft of the axle using 3/16" channel. I did that to create a structure where the mounting bolt is in double shear at both ends. That may have been overkill but I am pretty sure that it is not going anywhere. I have pictures which I could try to email to you, having a little tech trouble with my laptop lately. PM me with your email address and I will try to get you what I have if interested. There are other way's to do it. If you are OK with the sprung corner weights I gave you being similar to yours, you could divide them by the spring rate of the springs you intend to use. That would give you the static compression. ex: an average rear corner sprung weight of 450 lbs and a 110 lbs/inch spring that has an unloaded length of 12" ends up being compressed down to 8" in the car under that load. The shock should be adjusted so as to allow 60% of it's travel be available for "bump", 40% for rebound. The adjustable lower spring saddle will allow you to tune that in once installed. So with all that in mind you mock up the rear so that the rear tire is where you want it relative to the fender well, you make sure that there is acceptable clearance between the top of the axle and the rubber bump stop on the frame rail at rest (because the bump stop is what will limit your travel in bump, not the shock as that could damage it). You determine the length of your coil-over, shock eye to shock eye, in its statically compressed length and you mark where the mounting bolt holes on your brackets need to be positioned for welding. That should get you close and adjusting the spring should get you home.

DrJ

Posts : 139
Join date : 2014-06-19

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Re: rear spring and shock

Post by MC247 on Wed Sep 06, 2017 10:20 am

So we have our QA1 spring and QA1 shock (which can be adjustable) but we decided that we would mount the spring into the upper and lower rear control arm, and mount the shock using upper and lower eyelets from the rear of the axle up into the frame mount. This will require us rotating the lower shock pick up so its angled slightly to mate up with the frame. If that makes any sense! LOL.....I have attached an image showing what I'm thinking. What is missing from the image is the attachment point the upper part of the spring sits in. Its a bracket with a 4" diameter circular cupe which the spring is supposed to sit inside.

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[You must be registered and logged in to see this image.]

MC247

Posts : 64
Join date : 2016-10-11
Age : 49
Location : Ontario

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Re: rear spring and shock

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