1958 Imperial Brake Conversion with Change-Over to 15" Wheels
Posted 2019-07-28 12:02 AM (#585313)
Subject: 1958 Imperial Brake Conversion with Change-Over to 15" Wheels

New User

Posts: 1

OK, Gang - this is a re-focused look on an older subject. I really need to some good, specific thoughts from experienced Imperial fans like you.

I have a 1958 Imperial Crown convertible… and I want to implement two improvements that may be connected: convert from nylon bias-ply tires to radials – and – upgrade from the grossly under-powered, small drum brakes on the 1958 model to disc brakes.

Before we sidetrack into the bias-ply vs. radials debate, please know that I'm NOT one of those who denies that nylon bias-ply tires deliver certain advantages in older cars with suspensions designed with high-ratio (80%-85%) bias-ply tires in mind. These cars actually conceived the tires as being part of the suspension system. And a quality nylon bias-ply tire added a cushion effect to those designs. But nylon bias-ply tires do have serious tracking and skipping issues… and if those drive you crazy (as they do to me), there is a radial option that is less problematic than installing modern radials (which do present problems when useed on some cars from the 1950s and 1960s).

The key if you decide to switch from nylon bias-ply tires to radials to get better tracking and cornering is (a) getting modern rims that flex less and can take the added stress that radials impart on the wheels, and (b) finding radials with higher profiles that can provide some of that cushion effect from old-design bias-ply tires (such as bias-ply style radials from American Classics). NOTE: you can likely use old rims that flex more, but be cautioned that your valuable, ancient hubcaps might fly off and be lost to you, LOL.

Imperials between 1957 and mid-1959 came with 14” wheels – a mistake in retrospect, IMHO. This resulted in drum brakes that were woefully too small for this ginormous car. In addition, it is now quite hard to find 14” radial tires… none have adequate overall diameter (the closest is 2” closer to the ground than the original 950-14 tires)… and that would result in a risky low ground clearance. So, if you want to convert to radials, the best option is to get 15” rims and use the 820-15 bias-look radials from American Classics (Coker or Lucas) – which are darn close to identical height and width dimensions as the car’s original 950-14 tires.


So now, the big question is: how best to upgrade to disc brakes on this car.

Jay Leno has a 1958 Imperial convertible, and on one of his “Jay Leno’s Garage” videos on YouTube, he spends 15 minutes bragging about the conversion to 15” wheels and disc brakes he had done for him by Wilwood.

So I called them.

They essentially begged off, saying that the work for Leno was a one-off and not worth their while to do for anyone else, as converting the 1958 to discs was not a simple matter of a conversion kit, but required a number of changes and perhaps even some fabrication. So… a dead end there.

That brought me to this great blog, where several of you exchanged ideas on how to best do such an upgrade, and what would be required. Some of you seemed intent on keeping the 14” wheels… but, respectfully, I think that makes it harder. I think the best first step is to bite the bullet and accept that – if you want to improve the brakes on a 1957-1959 Imperial – you're best off accepting the concept of changing from 14” to 15” tires, to make room for the better brakes.

Once you've crossed that Rubicon – then it all comes down to specifics: what do I need to do, what parts will I need to do it, and how can it be done… AND THAT’S WHERE I NEED LOTS OF SPECIFICS FROM ALL OF YOU.

Here's what I've been told so far:

1. “Get a master cylinder that will fit under the brake booster.” I'm not entirely sure what that means, LOL.

2. Replace your Imperial front spindles with spindles from a 1957 or 1958 New Yorker, which has a hub with a 4.5x5 bolt pattern (vs. the 5.5x5 bolt pattern for all Imperials). This one I think I understand.

3. Replace your Imperial rear axle with later 1960s C-body rear axle, with a 4.5x5 bolt pattern.

4. Get a set of modern 15x6 or 15x7 rims with a 4.5x5 bolt pattern designed for radial tires.

NOTE: Converting to spindles and axle with the 4.5x5 bolt pattern allows the use of more common Chrysler disc conversions, like those from Scarebird and AAJ.

5. Bite the bullet and buy four 15” Imperial hubcaps from 1955/56 or 1960-1966. I'm partial to the 1956 caps myself.


As you can see, I am a novice in a steep learning curve on this. So any corrections, greater detail, clarity, and guidance is both welcome and greatly appreciated.

Thanks much to one and all,

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Posted 2019-07-30 1:29 PM (#585391 - in reply to #585313)
Subject: Re: 1958 Imperial Brake Conversion with Change-Over to 15" Wheels

Expert 5K+

Posts: 6932
Location: Victoria, BC, on Vancouver Island, Canada
Hi Josh,
Welcome to the forum, not sure why no one else has chimed in yet... but there are lots of differing opinions on the disk brake conversions as you can imagine. I've done 2 conversions over the years, first on a 1962 Chrysler 300 and the current on my 1960 Chrysler Saratoga. These are a full kit supplied by AAJ Brakes in Portland, Oregon. http://aajbrakes.com/

He specializes in Mopar brakes for Forward Look. They will fit with both 14" wheels and 15" wheels. Roger the owner is quite helpful. Having said all this, the rotors he uses might be a little small for a 5000 lb Imperial. I'm not sure what others on this site may have used for Imperials but hopefully someone will get on here with some other advice.
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Posted 2019-07-30 2:04 PM (#585392 - in reply to #585391)
Subject: Re: 1958 Imperial Brake Conversion with Change-Over to 15" Wheels

Expert 5K+

Posts: 6932
Location: Victoria, BC, on Vancouver Island, Canada
Here is another supplier making complete conversion kits https://www.hobbycar.com/Disc-brake-conversion-kits.html
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Posted 2019-08-05 10:57 PM (#585676 - in reply to #585313)
Subject: Re: 1958 Imperial Brake Conversion with Change-Over to 15" Wheels

Extreme Veteran

Posts: 302
AAJ or something similar for the front. Its an easy conversion that uses ford half ton truck rotors that were in production for something like 20 or so years. Consider a loaded truck stopped with these so it will be fine for your imperial. The master cylinder is tricky since the hemi engine is so wide. Someone here used a modern type aluminum slim body master cylinder and remote type reservoir to make this work. How stock do you want to keep the brake setup in the engine compartment?

There is a bracket, master, and booster setup that will work with the hemi engine. I purchased one of these for my project. It essentially raises up the master https://www.ebay.com/itm/Mopar-8-Dual-Power-Brake-booster-1-1-8-bore...

Now the rears require some work on your end if there is no kit available yet. There are different approaches but this is what I did. It retains the 5x5.5 bolt pattern and uses the same ford rotors except the rear is 4x4 not 2wd. You keep the rest of it stock. I made some errors when I did mine (first time experiment)but can tell you what to avoid. Its really mostly straight forward. http://www.forwardlook.net/forums/forums/thread-view.asp?tid=65789&...

The other thing to consider is the calipers. You can opt for the parking brake type rear calipers or the non parking brake type. I changed to a modern A518 (46RH) from a 1995 ram truck transmission so adding the parking brake was needed on the rear calipers. Feel free to contact me with any questions.
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