LocostUSA.com

Hey guys. Again, I've searched but couldn't find a definative answer on this one.

With my current plan, my half shafts will end up about 5 degrees up towards the outside @ my target ride height (5"). So obviously, it will be higher angle in bump. I will have to measure this.

Does this sounds excessive? My half shafts are from a 2nd gen RX7, and from what I understand, are CV's outboard and tripods inboard.

Any help is appreciated. Thanks.

_________________
-Emile
Scratch building an IRS, RX-7 based book chassis @ myBuild Log

*Make way for the luckEseven!

Yes, cvs are locked to the axle and are outboard. Tripods allow the plunging action by sliding in the cups.

Generally, the axle should be straight out under load (i.e. traction, full power= full compression of the rear suspension). Pinion angles are setup in a similar way, so that under load, the driveshaft angles go to zero as the pinion lifts, trying to climb the ring gear.

The two issues with tripods are bottoming under compression and deflection of the mounts (i.e. axles are a little too long) and axle-to-cup contact during full droop. Between the lobes of the cup are raised areas. Clearance should be verified with the shocks full extended.

You could alter the length of the control arms and diff height so that very little plunging action takes place, similar to placement of the rack to minimize bumpsteer.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

All the joints you're talking of are cv joints, whether inboard or outboard. There's quite a few different kinds of joints though.

5 degree's is fine. Most half shafts are able to take up to 20. Of coarse the more angle they have, the faster they are supposed to wear out.

My intent is to show that tripods are always inboard, not to indicate that tripods are not constant velocity. Instead of tripods, some vehicles have splined receiver tubes with outboard-type cvs on both ends.

The outboard joints have much greater range of motion than tripods do. When the axle is anything other than straight, the balls skid instead of roll. This is why irs joints last so much longer than fwd joints.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

The original poster asked how much angle is "too much." The answer depends upon both load and mechanical limits. That is, for maximum load you want them straight. When not at max load, you just have to make really sure nothing binds. Due to the compound angles that can be tough to ensure. I found that physical inspection was the only way to really know. I mention this in my book.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Man we are going to need to start calling KB58, "Dr. Phil"


If you read my book.

Listened to my tapes.

Watched my vids.


haha Just playing Kurt I will be ordering your book shortly

_________________
http://kenbuilt79.blogspot.com/

Yeah, yeah. FWIW, I made my driveshafts too long the first time, and though I caught it during fit-up, it was still a painful expensive lesson.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Don't get me wrong. Your one of the reasons that i'm taking on this project I have followed your build for years! Your providing a great service to the hobby I have a great respect for your skills and your finish product.

Keep up the great work.

_________________
http://kenbuilt79.blogspot.com/

Dr. Kurt,
It is a simple procedure to ensure adequate clearance. I show the procedure step-by-step in the book I'm writing however, I would be happy to share that info here.

I have the impression you don't want me to purchase your book while I write my own, and thats fine. I will not. I'm writing because I want to, not to impress or get rich. I'm not allowed to write about my career so I write about my hobbies. What is your motivation?

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Heh my wife asked me if i plan on making a book chassis with all of my books since i have actually done nothing but read and go look at parts so far. So keep on writing about it, all of you. More mistakes can be caught and corrected early on for those of us still walking the path.

You will probably find the books hard to weld and not too durable.

I decided today that I would be better off cutting the boots off to see for sure the travel I was getting, instead of just guessing. It turns out I learned a few things by doing so:

1- 2nd gen RX-7's have CV's both inboard and outboard
2- There is a decent amount of travel... about 1.5"

So with that much travel, originally meant for a street car with a lot of suspension travel, my little car should be just fine.

_________________
-Emile
Scratch building an IRS, RX-7 based book chassis @ myBuild Log

*Make way for the luckEseven!

I have not taken rx7 or miata axles apart so this info is general.

No need to cut. Remove the boot clamps by first loosening the crimped area of the strap with diagonal cutters, then unhook the end of the strap.

New boots may be necessary if the oem boots are old and hard, making it difficult to slide the boots out of the boot retaining groove on the axle. If they won't budge, a hack saw applied diagonally across the small end of the boot with little pressure works well. Just don't scratch the axle if you can help it. A little scratch is not the end of the world. You would have a very difficult time trying to cut the axle with a hacksaw anyway.

Replacement straps are a completely different design, requiring a special (but cheap) tool to apply tension. Then the excess strap is folded back and a sliding loop retains it, similar to metal straps in legal folders. The best thing about the new straps is one size fits all with trimming of the excess. The old design was very specific on the size boot that could be clamped.

Work on the inner/tripod end first. Slide the boot toward the center of the axle. On the tripod end, a thick snap ring keeps the tripod from sliding toward the center of the axle. Spread this ring and slide it toward the center of the axle an inch. The tripod will now slide toward the center of the axle, exposing the soft, round wire retaining ring on the end of the axle. Remove the ring and the tripod, thick snap, and boot will come off.

Slide the outer boot off the inner end. Carefully inspect the axle where it meets the cv. If there is a snap ring, compress it to remove the cv. If there is no snap ring, then it is the hidden type. The hidden type is another soft round wire ring that is strong enough to hold the axle to the cv but soft enough to break without damage to the cv or axle during tear down. When the cv and axle are assembled, the soft ring compresses in the axle groove, then is allowed to expand out of it when the axle is seated in the cv.

There is a special, expensive tool made by several big name professional tool mfgs which is a flat-faced chisel with an offset handle, designed to allow hammering the center section of the cv off of the axle, which is clamped in a vice. The cv center is extremely hard and is not damaged by this procedure.

My method uses a piece of plumbing pipe, one inch longer than the axle from the exposed end to the base of the cv. The pipe id is slightly larger than the axle. The pipe od does not contact anything but the cv center. With one hand on the cv (to catch it when the axle separates if it completely comes out of the cv), the pipe is brought down in a stabbing motion on to a block of wood.

The snap ring may compress back into it's groove and not require replacement. The cv should still be taken apart to for cleaning. Keep the 6 balls in there original positions as tolerances vary from ball to ball.

Okay, we now have a bare axle. Remove the soft wire hidden ring from the cv end or snap ring from the cv itself if so equipped. reinstall the tripod. Leave the boots off for now.

Install the cv's fully into the wheel hubs. I make a tool from 3"x .250"x 24" steel plate. I make a cardboard pattern of two lugs that incorporates the profile of the hub-centric ring. I transfer the lug holes and curvature of the hub ring to the end of the steel. This tool allows much easier cv torquing without someone holding the brakes or applying that force to the gears in the transmission. I install the plate so it presses toward the hub whether I am tightneing or loosening. The lugs are torqued.

Now for the simple part. Remove the spring from the shock but keep the bump stop installed on the shaft. Align the rear suspension. Fully compress the shock. Slide the axle out of the outer cv, toward the diff. Since the outer ring/snap is removed, the actual clearance can be felt and measured if you chose to. Extra clearance is necessary because under load, bushings will deflect and the clearance will not be the same.

Lower the hub as far as the shock will allow. Can you move the tripod radially in it's cup? Does the axle contact the raised areas between the lobes of the cup? If so, the angle is too steep. The diff should be lowered or the shock travel limited by using longer bump stops or raising the upper shock mounts.

What if the axles are too long or short (i.e. altered wheelbase)? Using a friction cutter like a die grinder, cut one of the axles in half. If the axle is too long, cut some length from it. Using a piece of angle iron and two, worm gear hose clamps, clamp the axle ends loosely into the angle. Adjust the length of the axle for both extremes. I order my custom axles from Moser Engineering for around $150 each. Write a letter with contact info, material desired, and the over all length required. Send the cut axle and letter. They should call you with their quote. The more grooves you have, the more it costs. Boot retaining grooves in the axle are not necessary.


You may need to go to the dealer for the soft rings. They used to be included in the replacement boot kits for the outers.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

People buy books, read them, form their own opinions, feel said books are lacking, and write there own. Why would you not buy a book before writing your own? I bought and read over 20 design books before writing mine, and I assume you've done the same. All of my references are listed in the back of my book, and I have no problem seeing my book listed as reference in other books.

I guess I don't understand the question, "What's is your motivation?" I, too, discribe how to check for clearences, and it still bit me. There's nothing wrong with how I describe it, but it's the nut behnd the wheel that can be the problem. I found the secret is to use a cut shaft, moving the suspension through it's full range, and measuring how the gap varies. Measure the shortest gap, and you have absolute assurance of the needed length (not counting drivetrain motion, though).

I can't tell if you're trying to turn this into something it's not.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/