Steering, Suspension, & Brakes

I am designing my rear suspension but I am having trouble with what size coil-over shocks to get (10,12,14). I have been searching the internet and forums but nobody really says what size shocks they used for there application or how to determine what length is needed. My car is a chrome bumber car and I have 245/45/r17 tires that are going to be installed and would like to try and keep the ride hieght the same. One problem to mention is that I already have the old suspension off the car and it was sagging so bad I really couldnt get an acurate measurement of ride hieght. So I am trying to figure out coil over size with the car jacked up and how to located the rear end with it slid underneath the car on jacks. Any Help or suggestions? Thanks in advanced



Edited 2 time(s). Last edit at 07/08/2012 07:00PM by 63BlueMGB.

Depends where your mounting points are. Measure the distance between them w/the car @ ride hight. Then pick a shock length that'll put the shock at about the middle between it's fully extended and fully compressed lengths.

NB, You haven't metioned what "brand". QA-1 cannot be used to limit jounce or rebound. Many rear STA set-ups run more rebound travel than jounce. Longer coil-overs offer more reserve capacity and usually cost the same. "Bags" not an option ? Good Luck, roverman.

Cost is a factor. I am open to any brand not looking to due "bags", I am really looking for a coil-over that will improve drivabilty and spirited driving.

EBay has some for good prices.

I got my used Carreras off of Ebay, I just need to step up in spring rate next, the length IIRC is 14"

I've done my own four link coil over rear suspension on my MGB GT V8. The coil overs are mounted on inverted lower damper mounts, modified to give me double shear bolt fixing, and at the top on brackets I've made to bolt as high up as I can to the original lever arm mounts. I've ended up using 120/85 AVO rose jointed shock absorbers with 8" long 1.9" diameter 200 lb/in Faullner springs. They are perhaps a little short at 12" as I had 140/95 on before and I got a bit more droop, but the 14" shockers had a compressed length of 9.5" which meant that I ran on to the internal bump stops at a sensible ride height. The 8.5" compressed length of the new ones seems fine.

My suggestion, which is what I didn't do, is to make a pair of dummy dampers around about 10" long and use those in your mock up. Once you've got a bit closer to the final version then work out the bump and droop that you want and buy the right length damper units.

Good luck

Your upper links go back to the shackle mounts? I've never seen a design like that before. I really like how you used stock mounting points. How does it ride/work?

Hi Jim,

Thanks for your kind comments. When I was designing this I had a few things in mind: firstly I wanted to use the original mounting points, partly because that is where the suspension loads are intended to go into the bodyshell, and partly because I didn't want to cut and weld the shell in case the whole thing was a failure! Secondly, I wanted a low roll centre to try and balance the front and rear roll moments and thirdly I wanted to minimise the lateral movement of the axle during articulation as I wanted to run 7x15 wheels under standard arches.

The result is what you see: a sort of hybrid between the longitidinal Watts linkage that was on the AlfaSud and the Rover P6, and the Satchell link that is widely used, but usually on the upper links. The roll centre is now below the diff unit and is perfectly central and the long links to the shackle mounts control and minimise rear steer in roll.

I've only had the car on the road for three weeks, including a 1100 mile trip to Le Mans Classic as its first journey over 10 miles! It works really well; supple, lots of grip even without an LSD; and very predictable. My friend on the Le Mans trip in a TVR Griffith struggled to keep up in the tight roundabouts! Another of my friends who is an ex-Ford and Weslake development engineer was impressed when he drove it on the French country roads.

I've still got some setting up to do; the axle toes out very slightly due to the welding, which is fine for me, but I think it would be better to toe in by half a degree. I'm planning on taking it on a track soon and that might show up the need for stiffer springs, but the 200 lb/in ones were a good guess, and the dampers are set half way in their range of adjustment.

Regards
John

Thanks for the info John!

Very, very cool - Welcome to BritishV8, John!

Are you familiar with our "How It Was Done" article series? I'd like to feature your MGB V8 in one of them.

Hi Curtis,

Thanks, I'm glad that you like it. I've browsed the "How it was done" series at length to get inspiration, so I ought really to put something back! It's a bit of a 'Marmite' car, some love it and other hate it, but I like it and it's nice when others do too.

Like all projects it will never be finished, but I'll get some pictures and words together and put something on the site.

Cheers, John

John,

I like your design as well, seems simple but efficent. I love to see a how to article as well! I think those articles really show what this site is about others helping others by sharing there knowledge. If you have any other pictures, I would love to see them. A picture is worth a thousand words! Thanks for the information and suggestion on how to measure my suspension. any info I can get good or bad is beter than what I have now. If there is anyone holding out on info please share!

thanks again!

Hi, here are a couple more. I'm putting some words together but it might take a little while!


This is in the early stages of development; I changed the brackets to the rear spring hangers as these are a bit flimsy, and I cut down the brackets on the axle to make more room for the bump stops. as you can see from the photos above. Also, these dampers are too long and I replaced them with 120/85 rose jointed ones.

This is one of the brackets to the front spring mounts. There are two locations for the Satchell links to change the roll centre and two holes into the spring mount. One is the original and the second is one that I had to drill. I'm not sure that I'd do it this way if I did it again, but it works well.

John,

Very nice design! Clean and straight forward. I, too, am looking forward to your build article. Have you had any bind issues with your U-joints? It looks as if the axle would rotate as moves through its travel range.

Cheers,
NCtim

John, I was thinking the same thing, Watts linkage design allows rotation. So is pinion angle 0 at road height to equalize movement? Most u joints allow max 7 degrees. Long control arms would lessen degree of movement. You might have to grind clearance on u joint. Is the DOM tubing of control arms thicker to prevent bending?

Hi Jim,

Yes, there is some rotation of the axle but it is small, and well within the range of the U joints. Over the full axle articulation the change in angle is less than 2 degrees.

The control arms are what is known as 'two force members' so there is no bending in them. Obviously that only works with spherical bearings and a conventional rubber bush would transmit some bending moment. The arms are actually cold drawn seamless tube with tig welded slugs to take the 5/8 UNF left and right hand threaded joints, so they are plenty strong and stiff enough!