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'68 Coronet 500 Rebuild

D Jay Hopkins

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Location
Antioch, CA
I have owned my 68 Coronet 500 since 1978. The car has not been on the road since 1985. I recently retired and ready to rebuild the car for the last time. A couple of Suspension questions:
1) The front and rear suspension have not been touched. I want to be able to participate in an agility course. I viewed the QA1 K member and control arm replacement video. I was sold on the fact that I needed the RMS Altercation suspension but Members advised that I can save some money by strategically replacing stock components to achieve a comparable result.
2)The car has power steering but I would like a manual steering box. I don't like the hoses and the pump would foam. Maybe a manual rack with a larger steering wheel would provide more header clearance and not compromise the steering effort ?
3) The stock K member doesn't have a sway bar and I believe it is essential for proper handling. Do I need larger Torsion Bars or will the stock do? Can I lower the front stance with the Torsion Bar adjustment or do I need dropped spindles?
4) I would like disc brakes front and back. Can anyone suggest a reliable conversion kit for all 4 corners?
5) QA1 has showcased a link rear end system. I have the 8 3/4 banjo and wondering if anyone out there can provide a review? Is there a more economical solution? I have been welding / fabricating for 40+ years so I am not afraid of metal manipulation. I have never touched the rear end beyond brake replacement. The differential is 2:91 so that will have to be replaced. I know that the bearings and seals probably need to be replaced. Is there a checklist for items that I need to check and replace? Any comments are appreciated - Jay
 
HI. It sounds like you have a fun project in your future. One additional item that will play into this is your selection of tires (and probably wheels). Sticky tires are going to be the most important part of making your car handle better. Other items will need to be addressed, but without good tires you will not get very good performance in cornering. When I updated my tires, I couldn't find anything in 15" that were considered very good for handling. Because of this, I wound up going to 18" wheels with Michelin Pilot Sport 4s tires, P245/40R-18 on the front and P285/35R-18 on the back. These fit nicely in the wheel wells of my 69 Coronet, which should be very similar to your 68, and are muck stickier than my previous BF Goodrich Radial TAs. Here are my thoughts on your questions:

1) I have no experience with the Alterkation, but Rick Ehrenberg (of Mopar Action) is a big fan up upgrading the stock suspension. Things you should probably look at are:
1.1) Replace all the bushings, front and back, they will most likely be pretty tired after 50 years. You can go with stock rubber replacements or polyurethane ones. The polyurethane are stiffer but require lubrication. I used rubber for a couple of places, the front of the strut rods as there is quite a bit of movement required at this point and the lower control arm bushings because the polyurethane ones don't provide locating for the control arm in the fore and aft axis.
1.2) Replace all the ball joints and tie rod ends.
1.3) Replace the upper control arms. The stock ones don't allow enough negative camber and positive caster to be set in the front end alignment to take advantage of new radial tires. The stock upper control arms were designed for use with bias ply tires which could not use modern radial settings.

2) I replaced my stock power steering box with a Borgeson unit (kit purchased through Bergman Auto Craft), so I can't speak to converting to manual.

3) You will definitely want anti-roll (sway) bars, front and back. My car did not come with anti-roll bars, so I added them to both ends. I used the Firm Feel kits. The front was very easy to install as it mimics the mounting of the stock unit. The rear one was reasonably easy to install but required some reshaping of the fuel and brake lines where the bar mounted to the rear subframe. These are important as they are used to control the amount of roll your car gets during turns. You may wish to go with larger torsion bars to stiffen the front end, but you may not. The only real reason to use larger torsion bars is so that you don't hit your bump stops when hitting a bump during cornering (which will be the worst case). Hitting the bump stops will definitely upset your handling at that point. If you lower the car by adjusting the torsion bar adjusters, you reduce the clearance between the control arm and the bump stop. This is definitely a place you want to make sure your torsion bars are stiff enough to prevent that happening. I have seen a recommendation of starting with a torsion bar wheel rate of about 10% of the front end of the car's weight. On my car, I went with Firm Feel 1" diameter bars with a wheel rate of 175 lb/in. These are certainly not too soft, and I may switch to a softer bar in the future (more testing is required). The low profile tires also increase the suspension stiffness a surprising amount. If you are trying to reduce the body roll in your car, this is better addressed with larger anti-roll bars than stiffer springs.

4) I installed front disks from Dr Diff, which went very well. I still use the stock (but rebuilt) rear drums, but Dr Diff has a kit for that as well. If you go with larger wheels, which I expect you will want in order to fit better tires, you will have a lot more selection of larger disk brake kits.

5) I am still using my stock rear end (8.25") and suspension, so I have no thoughts on this.

I would suggest picking up a couple of books for this project:

"Mopar B-Body Performance Upgrades" by Andy Finkbeiner
"How to Make Your Car Handle" by Fred Puhn

Both of these are very good. I would also suggest looking for articles on these topics by Rick Ehrenberg as he is very knowledgeable about these cars. Cheers!
 
You, like many are being sucked into advertising hype... Rack, four link, coil overs..... Do you want to re-engineer the car to have all the coolest bling stuff... Or do you want to massage and tweak whats there to actually preform.... Realize that back in the day Mopars out handled most other cars... You have a good platform to start from, why toss it?

Generally I go with all new OE parts with offset bushings, big sway bars, premium shocks & a performance alignment but if your serious about autocross type competition after having a ride in their demo Challenger I'm a big fan of Hotchkis, I don't see a need to look any further.... Well actually I say that based on the performance of the car, I haven't studied the rule book to see if Hotchkis deviates from stock enough to move you into a higher class.... Thats something you need to research...

https://www.summitracing.com/parts/hss-80110/make/dodge/model/coronet/year/1968

https://www.summitracing.com/parts/hss-79020013/make/dodge/model/coronet/year/1968
 
Can't thank you enough 1 Wild R/T. I viewed the Hotchkiss website and saw the attached package. It is an affordable option and a great place to start (in addition to the OEM component replacement). I am going to move soon on a purchase and will keep you posted - Jay
 
If you have a welder, some scrap metal and some hole saws[ I used Blair Rota Broaches] you can do quite a bit of improvements on your stock k-frame. Just takes some time. I added in 120+ welds to mine, over the factory 30 or so, plus added reinforcements around the lower control arm tube and the strut rod mount. Good time to add a skid plate but thats not free unless you do your own. The big washers I used around the control arm mount were sourced from Fastenal.

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If you have a welder, some scrap metal and some hole saws[ I used Blair Rota Broaches] you can do quite a bit of improvements on your stock k-frame. Just takes some time. I added in 120+ welds to mine, over the factory 30 or so, plus added reinforcements around the lower control arm tube and the strut rod mount. Good time to add a skid plate but thats not free unless you do your own. The big washers I used around the control arm mount were sourced from Fastenal.

View attachment 1072295 View attachment 1072296 View attachment 1072297 View attachment 1072298 View attachment 1072299 View attachment 1072300

Definitely a worthwhile low cost upgrade.... Just a little time & effort... Firm Feel offers a gusset package if you want a shortcut...
 
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