Vertical Link Separation : 4 link rear axle

Question for you wise ones out there:

Any recommended vertical separation of the top and bottom link attach points above and below the axle for a 4 link rear axle? I have set this at 7" total (3.5" above and below the axle's centerline), but am considering reducing it to 6" for various clearance reasons. Paper calculations with safety factors shows I still have lots of link strength to spare at 6". Any good precedents or thoughts out there?

Thanks,
Mark B.

I think you nailed it as far as reasoning Mark.

Wider is stronger...if you go too narrow you need stronger brackets, thicker and/or larger diameter tubes, and stronger heim joints.

On the other hand, if you go too wide then ground clearance can suffer as can the protrusion inside the cabin area.

I ended up making a template to plasma-cut some brackets for my various Opels with Toyota axle upgrades. I have two holes top and two holes on the bottom, giving me three optional spacings and multiple heights to choose from for geometry changes. I have 6.75", 7.5", and 8.25" spacings available to me. But I'm also putting some power behind these things...my road racing Manta should see about 350 whp with turbo, and will be running slicks. Don't know how that correlates to gravel forces seen in rallying however.

Bob

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Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/

Cool Bob; glad it looks like we are in the ballpark. FYI the calcs done here were:
- with 150 ft lbs engine torque with a 2.96 1st gear and 4.56 rear gear = about 2000 lb ft of total axle torque if it hooks up (not typical on gravel to put that torque down at a launch with no slip but it could happen on the rifth surface)
- static torque on the axle from the rear weight acting off centerline of the axle = 325 ft lbs
- combined torque at about 50% power, and landing from a jump onto a bad rock with about 6-7 g impact load worked out to an axle torque of about 3000 ft-lbs
- with 6" link separation that works to about 6000 lbs transient load spread between the links --> about 1500 lbs per link --> about 3000 lbs with safety factor (or more if I figured the link torque wrong by 2:1)

Rods end being used here have >10000 lbs radial load and tubing min strngth at threads is >15000 lbs. So I think the big issues become: ripping out the link anchors or the brackets welded to the axle (or actually breaking the shocks or wheels or something on the landing!)

I doubt we would ever exceed 200 hp if we ever reach that, so we are pretty safe compared with what you are doing. I have seen 90 HP per driven wheel on gravel as rule of thumb here or somewhere fro traction limits (though really it's torque).

Thanks for the input!
Mark B.

Mark, here uner Ford Motorsport manual scans" is the MkII Escort manual.
Drawings, specs, patterns, lengths etc for the axle, and juicy templates for the reverse swing pedal box, etc.
Foggy ol memory says they did 5" c-c on the ears.

And as with a lot of stuff, seems copying them is a good starting point

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Thanks John, another good data point and appreciated. FYI, I calculate things so I can have some solid data to build a knowledge base. The real life working examples help to guide and validate the caclulations so that evenutally one gets a feel for the rigth inputs to use in the calcs to make them really useful. I'll check out the scans!

Regards,
Mark B.

starion887 Wrote:
-------------------------------------------------------
> Thanks John, another good data point and
> appreciated. FYI, I calculate things so I can have
> some solid data to build a knowledge base. The
> real life working examples help to guide and
> validate the caclulations so that evenutally one
> gets a feel for the rigth inputs to use in the
> calcs to make them really useful. I'll check out
> the scans!
>
> Regards,
> Mark B.


Just to make it easier:http://www.rallyanarchy.com slash EscortRallyPrep slash Suspension%20Rear.pdf

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Mark:

I've got the 4link measurements for the Kadett C/Chevette HSR if you want them.

Wilson

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"Talk about drugs. Driving a car like that, going that fast, it’s like all the drugs at once." - Tommy Byrne

"Now, Pinky, if by any chance you are captured during this mission, remember you are Gunther Heindriksen from Appenzell. You moved to Grindelwald to drive the cog train to Murren. Can you repeat that?" - The Brain

went with 6" on center, feel like i should have done 5.5
if done again, would likley size it based on pumkin size.

slight ovalizing due to thin ear material, >.08" (dum dee dum)

ears were taking rocks at the ground ends. though, i definitely bent links before seeing ears deform.

"rock spray" put a deflector or cover on the lowers. nuts get rounded.
let the rod end body take the abuse rather than the ears.
set the width to the high misalignment type end. not to something arbitrary like say, 1in.

if you do circle track catalog links, an O2 sensor socket can be used to tighten the inboard jam nut by sliding over the link. (brilliant!)

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"I put the hurt on dirt" - adam crane
http://CraneRallyCrew.com
corolla gt-s "Patches"
Op: S.S.

Yes please Wilson.

Hey Adam, Thanks.

Ears here are 3/16" each (.187" so less issues here, and closed in the back to stengthen them. They will be spread 2" apart and heavy spacers made to center them; the side space allows variations in lateral alignment. Links are 1" OD, 5/8" ID (heavy duty!), to be drilled out to 11/16" ID to be tapped.

Lower link lateral separation is 36" and upper will be 18". The uppers need to clear both the upder body subframes and leave a space for the exhaust on one side.

Thanks again!
Mark B.

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"Talk about drugs. Driving a car like that, going that fast, it’s like all the drugs at once." - Tommy Byrne

"Now, Pinky, if by any chance you are captured during this mission, remember you are Gunther Heindriksen from Appenzell. You moved to Grindelwald to drive the cog train to Murren. Can you repeat that?" - The Brain

Many thanks, Wilson.