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Progress on Ron's old J-H IT car  Rating:  Rating
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 Posted: 11-16-2008 03:12 am
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Jensenman
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I promised myself that I would get the suspension done before swapping in a new powerplant. I have the 13B rotary ready to go; I am saving that fun part for last. Gotta get the ugly dirty bits done first!

The stock J-H suspension has no provision for camber adjustment and that just won't do. The brake upgrades are pretty limited as well and J-H's also have a weird bump steer curve. So, I figured hit all three areas at the same time and add ride height adjustability as well.

Brake upgrade: Miata front knuckles and calipers, this opens a whole new world of possibilities.

Camber adjustability: add plates to the upper control arms to allow moving the upper ball joint in/out to set the camber.

Here's the front suspension about halfway done.



And here it is completed and ready to install. I used QA1 coilovers with 550 inch pound springs, Super Pro poly bushings and retapped the stock Miata outer tie rod ends for 1/2 - 20, they now thread straight onto the J-H inner tie rods. That mod is what took care of the bump steer, it leveled out the tie rod in relation to the lower control arm and moved the tie rod pivot out close to the wheel centerline. I also can now get up to 3 degrees of negative camber.



 

The rear axle got clobbered during the driveshaft failure; the pinion gear shaft is bent. :-0 I have to admit I have never seen that before. There's no aftermarket to speak of for the J-H axle, so I decided to upgrade to a RX7 piece. This one is from an '83 GSL, it has a 3.909 ratio, limited slip and rear disc brakes. It's also 57 3/16" long and the J-H is 54".



So I diassembled the rear axle, cut all of the non essential bracketry off and narrowed the housing. I still need to have the axles shortened and resplined and have the flanges drilled for the 4x100 mm Miata bolt pattern. Dutchman Motorsports has done this type stuff for me in the past. Here's the housing that's been narrowed:



I still have to build a jig to align everything before burning it all together.

Next project: reversing the RX7 clutch fork to allow use of the J-H 'pull' cable instead of the RX7 'push' slave cylinder. This means moving the release fork ball to the other side of the bellhousing. Should be fun!

Last edited on 11-23-2008 11:22 pm by Jensenman

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 Posted: 03-08-2009 08:25 pm
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roblanford
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Hey Jensenman, How is your project coming along? Would you recommend the front end mods for a street car? What year Miata knuckles did you use? Did it alter the track width on the front? Are you going to use the watts link on the rear? Thanks for any info.

Robert

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 Posted: 03-09-2009 01:43 pm
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Jensenman
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The front end mods will work on a street car but it's pretty extensive. I went the way I did because I want to be able to raise/lower and corner weight the car without using shims, etc.

The knuckles I used are from an early 1.6 Miata. The later 1.8 cars have larger diameter brakes and some 13 inch wheels won't clear the later calipers. The front track width remains the same.

I'm using a Panhard rod in the rear, mostly for simplicity. A Watts works fine but takes a lot more bracketry and if you want to change the roll center you have to move the whole thing. Its only real advantage is the axle does not move side to side as it goes up/down. If a Panhard is long enough, the axle's side to side movement is pretty minimal. My Panhard is 39" long which should keep the side to side at around 3/8" max.

The rear axle project is still ongoing; I wound up using an RX2 housing and axles (53" from wheel face to wheel face, the J-H is 54"), a 1st gen RX7 diff with clutch type limited slip and 4:87-1 gears and 1st gen RX7 rear calipers and rotors. It's just been time consuming gathering all the bits and pieces plus I had to make my own rear caliper adapter brackets so I could mount the calipers at the front of the axle rather than the rear (more room for the Panhard rod bracket). That's all pretty much done, final assembly will be done sometime in the next few weeks, then I have to fab the rear shock upper mounts.

Then the noisemaker goes in. :-D

 

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 Posted: 03-09-2009 03:12 pm
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roblanford
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Thanks for the information, J'man.

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 Posted: 04-29-2009 02:01 am
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Jensenman
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I started another thread in the 'Projects' section showing more recent progress.

http://www.jensenhealey.com/forums/view_topic.php?id=1248&forum_id=15

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