Street Rod Front Disc Brakes

One of the major deviations from the typical US JZR build I have done is to NOT use the Chevette front brakes suggested by the JZR's US distributor.  I wanted something better  - in both looks and function.  In fact, the typical European builds do not use Chevette brakes.  So, obviously other braking systems can be adapted as well.  

My concept for the front brakes centers around the use of the front Moto Guzzi brake rotors that came on the donor motorcycle.  To do this my first step was to design wheel hubs that would allow these rotors to be used.  Unfortunately, I just did not find the Guzzi's front Brembo brake calipers to be easily adapted - I am not saying they can't be, I just decided I would be better served by use of another type of caliper.

After looking at various brake calipers, I decided on using a Wilwood, 175 series caliper.  Wilwood offers 2 styles in the 175 series, standard cast aluminum case and a polished billet aluminum case - I chose to use the billet style as seen below along with some dimensional information:

I purchased my calipers from Total Performance after talking to them about my application.  These calipers are used frequently on the front of street rods and do well, the only drawback being the need to replace the pads more often than normal, general service pads on a normal car.  They will most likely need to be changed every 10K miles, the pads are under $25.00 a set.   Below is the pad specifications:

The Wilwood, 175 series brake caliper in its basic configuration is NOT capable of fitting the Moto Guzzi brake rotor, a set of spacers are needed additionally.  The spacers used were obtained from Total Performance as well - part number 4560026 - pictured below.

One VERY important point to understand about this caliper is that it is a single cylinder, "floating" type caliper.  This means that the caliper has only one move brake pad - the one on the inside.  And, in order for the caliper to function properly the entire caliper must be allowed to side in and out on its mounting bolts!  So, this MUST be an aspect designed into the brake brackets!

The brake brackets I designed are very simple and straight forward.  They mount to the original brake bracket location on the Chevette/Fiero spindle and can be used on either the dropped or stock height spindles.  Also you will find a pre-made eMachineShop.com file of them  on this website - see the Getting Custom Parts Made Online article for more information.

The Picture above is of the finished brake brackets (note that each bracket is showing an opposite face and that is why they do not look alike in the picture). The forked end of the bracket holds the brake caliper and the other mounts to spindle.

A close-up view of the brake bracket fork shows the 2 bosses within which the brake caliper will "float" in and out as it grasps and releases the rotor.

Above is an even closer view of one of the guide bosses.  The holes in the bosses are 1/2 inch.  But, in addition, the inside of each hole has been sanded and then polished to allow for a slip-fit of the bronze bushing that will pass through them - more on those bushing later on in this article.  I used a dremel-moto tool to do the sanding and polishing.   And remember, slip-fit, NOT sloppy-fit!

The picture above show one of the Wilwood 175 Billet calipers assembled with the disc spacers I talked about before - I had the center space powder coated black just for looks.  You see that I have removed one of the caliper's bolts.  By the way, the bolts came with the calipers.  Note the washer and the bronze sleeve bushing; and, the way they are positioned on the bolt that is affixed in the caliper.  I obtained the bronze sleeve bushing from the local hardware store - these bushings are 1/2 inch outside diameter, 3/8 inch inside diameter, and have a small flange. 

Above is a view of a Wilwood caliper complete.  Take note of the way the bearings are positioned and the washers just under the bolt heads.  As I stated before the calipers are meant to "float"; they will move in and out of the brake bracket's bosses on the bronze sleeve bushing.  You also see in the picture above how the aluminum caliper spacers seem to hang over a bit.  You can leave them or trim them down flush - I chose to leave them, as this can be done anytime.

In the picture above a caliper is mounted on a brake bracket.  A close look shows the bronze sleeve bushings on which the caliper slides and how the washers just under the bolt heads retain the caliper from sliding out of the brackets.   The following is a down loadable MPEG video file that will demonstrate the movement of the caliper in the brake bracket - sorry its a bit out of focus, but I am just learning this feature on my digital camera.

To view this movie, please right click and select "Save Target As" and save it.  Again, sorry its a bit out of focus, but you will get an understand of how the caliper moves, if you haven't yet.   

With the caliper and bracket assemblies finished, it is time to turn our attention to the spindles; or, more specifically the spindles' mounting ears where the brake brakes are affixed.

A comparison of the ear area on both spindles showed the driver's side spindle to be thick than the passenger's side. This may be an issue in properly aligning the calipers.  So, a few thousandths of an inch was removed. as shown in the picture below:

Unfortunately, the only way to accurately surface the inner face of the spindle's bracket ear area is to have it milled.  I have a mill, you may have to have this done by a machine shop.  I then feathered and blended the machined surface with the rest of the spindle's inner face as seen below:

The feathering shown above was done with a simple electric hand grinder.  It isn't a necessity, but it will improve the finished look of the spindle.  With this correction made, its time to mount the wheel hubs, rotors, and calipers.

Above are a few photos of the driver's side assembly completed.  At this stage you need to check to ensure the brake caliper has the proper clearance and does not rub the brake rotor.  And, as seen below, there can be some dimensional differences between each assembly that will need to be compensated.

The picture above is a comparison of the different alignments of the calipers and the brake brackets - with both assemblies setting on the same surface, look at how the brake bracket on the left is higher - this is due to differences in the cast spindles.  Set the assemblies on a flat and level surface (like a table top) as shown; this allows the caliper's inner face to hang down to its closest point of travel (float) to the rotor's face.  the distance between the caliper's inner face and the rotor's face should be around 1/8th to 3/3232nd of an inch.

The picture above shows each completed assembly side by side of each other.  Note how the distance between the rotor's top surface and the calipers inner surface is about the same for both - 1/8 to 3/32 of an inch.

So, how did I compensate for the differences mentioned above to achieve the proper 1/8 to 3/32 distance?  Look at the caliper bolt on the assembly to the right and note the extra washer just under the bolt head - that was all that was needed.  You may wonder why do the calipers need to be at a reasonably same distance from the rotor?  Well, as to allow the calipers to make contact with the rotors at about the same time.  If their distances were a great deal different then the caliper with the smallest amount of travel would engage first and thus constantly pull the vehicle in that direction during braking.

Above is a top view of a completed brake assembly.  You can see how the caliper sets in relation to the brake rotor.  Note the rotor is not in contact the caliper's brake pads on either of its faces - about a 1/8 to 3/32 of an inch clearance on both sides.  Depending on the play in the brake pedal later, I may tighten the clearances up on the outside.

Here is a view of the outside face of the finished driver's side assembly.  I like the look of these brakes!  Oh, the silver you see on the Moto Guzzi brake rotor is actually a ceramic coating like is used on exhaust parts and good to over 1500 degrees.  So, it should hold up well, even better than conventional powder coating.  But, one other aspect is that brake dust does not stick to and is easily removed from it.

Also, note how I have had the splinned wheel adapter powder coated silver - remember to NOT coat the splines or threads!  Finally, please note that while not in view above, the wheel hubs have also received a silver powder coat treatment as well. 

Below is a short movie of me spinning the rotor on a finished assembly - mounted to the JZR.  I thought it might be of interest.

To view this movie, please right click and select "Save Target As" and save it.  Again, sorry its a bit out of focus, but you will see the rotor free spin.   

I have walked you through the fitment of a Wilwood 175 series brake calipers to the JZR.  Its important to understand that there are most likely other systems that can be used as well - you don't have to settle for or use the Chevette calipers and rotors.  Another positive point to this brake configuration is a reduction of sprung weight from the Chevette setup as well - always a plus to improving a vehicle's handling characteristics.

Some of you might wonder about the stopping power of these small Wilwood calipers as compared to the Chevette's?  Well, first off its not just the calipers; remember the increased diameter of the Guzzi rotors over that of the Chevette.  The larger diameter rotor disc allows the caliper to use more mechanical leverage in its applied stopping power.  Also, the thinner, and lighter Guzzi disc rotor has less inertia to overcome as compared to that of the Chevette rotor - again improving stopping power. 

Finally, if you still doubt the abilities of the Wilwood 175 calipers, remember that these units are used on the front of street rods usually weighing twice as much; and, usually having 4 or more times as much horsepower slinging them down the highway!

 

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