I (like many have before me) am replacing my '74 Pinto 6.75" rear end with an 8" rear end (I believe out of a '76 Mustang II). I have been pricing parts to do a complete brake replacement (upgraded stock) around the entire car. When looking at the rear brake components for both the '74 Pinto and '76 Mustang II, I found that they both use the same drums and wheel cylinders. "Cool", I thought, "stock replacements there too."
Then I saw something weird. Despite using the same drum and wheel cylinder, they use different shoes.
My question, are the shoes supposed to be interchangable as well as the other parts or is there something I'm not seeing yet? If they are supposed to interchange, what is the difference between the two?
Please let me know. I don't want to by new brake shoes until I'm sure which ones to get.
Check the WIDTHS of both the drums and the shoes, as well as the length of the shoes, and the frictional material that was originally specified. (Some cars from that era were not originally designed to use semi metallic frictional materials.)
In. re. overall size of the frictional material:
Sometimes a narrower width set of shoes or a shorter length and/or width friction materials on the same overall size shoes is used with the same DIAMETER drum (or even the identical drum) on a lighter car. (If memory serves, the Mustang ll was generally heavier than the Pintos year by year, and had a higher percentage of it's weight carried on the front wheels, but I could be mistaken.)
In any event:
Even when the front to rear wheel cylinder or caliper piston size to wheel cylinder size ratio is maintained, and the OEM sized master cylinder and proportioning valve are used, if a larger than original effective braking frictional surface (larger # of square inches total) of the rear shoes is used without ALSO increasing the effective front braking frictional material surface, the brake balance from front to rear of the same vehicle may be noticibly upset, by giving a greater percentage of stopping power to the rear brakes than was originally designed in. Under those conditions, the net results being a rear wheel lockup that is happening sooner, and with less pedal pressure.
The lighter the car, the more noticible a difference such as this may produce,-especially during hard/fast stops, as weight transfer during this type of braking unloads the rear of the vehicle considerably.
I know that you can bolt your 6.75 backing plates right on your 8 inch and use your original drums and such.
So, if I'm reading this correctly, I should get the brake shoes meant for the Pinto due to them being meant for the lighter car. That the Mustang II brake shoes could be too much and cause excessive braking on the rear axle.
If that is wrong please let me know.
The brake shoes are the same size for both applications but different part numbers.
My guess would be that the only difference would be the mounting hardware holes might be in different places. I do not think you will have too much brakes on rear.
Only way to know for sure:
Go to your favorite parts store.
Have them pull both sets of shoes, from a GOOD brand, not the cheapos, and make sure that the 2 different sets are the same model line/warranty, etc., and from the same supplier.
Compare the 2, noting any differences.
I vote we ALL go to autozone at the same time same day, and get them to do this. I wonder if anyone at autozone would notice that 1800 people asked for the same parts at the same time? :surprised:
Were you looking up the part #'s for the 6.75 pinto brakes vs. the 8 musty 2 brakes? Try looking at the 8" pinto listing and see if the part #'s are diff?
Now im curious too, This could be fun, the parts people already get a funny look when they see me coming.
The brake shoes are the same whether it's 4-cyl, V6, or V8 (Mstg II). The break point is between 1974 and 1975. '74 uses #391 shoes, while '75 and later uses #474 shoes. This holds true for both Pinto and Mstg II, regardless of engine or rearend type. They are also the same size - 9"x1 3/4". The #474 shoes are also listed for the Fox Mstg up to '93. I would go with the later shoes as there is much wider application for them so they should be easier to get. I also checked the hardware for both the '74 and the '75 & later applications and could find no differences in the part numbers for the different pieces. Maybe the 474s could be substituted for the 391s?!? If anyone finds out more info, let us know!!
I ordered the 474's as they matched the rear end. I will try to see the differences (if there are any) when I swap rear ends hopefully within the next month or so.