924Board.org

[owenexile]

Is there a diffrence between these models in the 5lug?

1987 924s and 1982 931

Which one would be the easiest to swap to a 924 1982 N/A?

Thanks
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924 1982 N/A
For some reason theres always a earth problem somewhere with this car...

[!tom]

I am hardly the authority, but I believe the answer is yes.

The cars based on the 924 come with the X split, so both bores in the master cylinder are the same, and the bias is completely controlled through the relative sizing of the disk calipers.

The cars based on the 944 come with the TT split, so the master cylinder is a stepped bore. Bias is controlled by both the relative sizing of calipers and the relative sizing of the two bores in the master cylinder.

Using the 924 based solution should not require re-plumbing your brake lines or replacing your master cylinder and booster (although different master cylinder sizes and boosters were available).

Using the 944 based solution (which is where the 924S comes from) would require all the work from the 924 solution plus re-plumbing brake lines, replacing the master cylinder, and replacing the brake booster.

I'd suggest the 931 based solution would be an easier swap.

I am not familiar with the other possible complications that relate to aluminum suspension components, etc., these may or may not be relevant to the 924S solution.
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78 924 NA
5-lug

[gohim]

The 5-bolt brakes from a 931 would be easier to a 82 924 than the 5-bolt brakes from a 87 924S because the 924S has alloy rear trailing arms, and different length cv axles.

While most of the parts are compatible, as time went on, Porsche tweeked the parts in the brake system, upgrading them. The brake systems of newer cars have more alloy/lighter parts than the older/earlier cars, and it will be easier to finder newers cars with brakes in better condition, than it will be to find earlier/older cars with brakes in good condition.

A 931 uses the same steel trailing arms, and cv axles as a 82 924, making the conversion simpler.

The front conversion for a 1982 924, you would use the same parts, whether you take them from the 931 or 924S. You would use the steering knuckles, spashplates, rotors, brake calipers, and flex hoses.

Note that the 924S has better splashplates alloy vs steel (on the 931). You can take install the alloy splashplates from a newer car's brakes on an earlier car's brakes.

And most used rotors are not worth using, because the rotor only have 1.5-2.0mm of wear thickness when new. Most used rotors are worn out. Look at the outside and inside edges. Check both sides of the rotors. If there is a wear lip forming that's a fingernail thick, or thicker, then the rotor is wornout.

On 85/2 and newer 944s and 924S, the cars have alloy rear trailing arms, with the additional track width created by the spacers Porsche added to the rear wheels built into the trailing arms. The cv axles, trailing arms, wheel hubs are different as a result. To use these parts any of these parts from a 924S or alloy trailing arm 944, you would need to change all of these parts.

Somewhere between the 84 model year, and the 85/2 944 when Porsche changed over to alloy rear trailing arms, the stamped steel metal, and cast iron rear splashplate/ disc brake caliper mount, and separate bearing cap components that were used since the introduction of the 5-bolt four wheel disc brake and the 931 were replaced with a stamped alloy splashplate, and a single cast alloy partto replace the other two parts.

On a 924 or 931 with rear disc brakes, the parking brake assembly mounts on a stamped steel backing plate. The caliper mounting plate is a cast iron piece welded to the steel backing plate. The outer bearing cover is a cast iron piece that fits over the top, and four bolts go through the outer bearing cover, and the backing plate to secure the parts to the axle carrier.

On the updated 944 rear brakes with steel rear trailing arms, the backing plate is a stamped alloy piece bolted to a cast alloy combination piece that functions as the outer bearing cover and caliper mounting bracket. This single piece is much lighter (and stiffer) that the original sheet steel and cast iron parts, without the rust problem that the earlier parts suffered from.

So, the easiest conversion between the two choices you offered would be a 931. But the best conversion would be a 85/1 944 with steel rear trailing arms, and the improved parts that bolt directly to a steel trailing arm 924.

The stepped diameter master cylinder vs straight straight diameter master cylinder really is not an issue. Use a 1980 924 master cylinder for 79 and earlier 924 that came with the smaller diameter master cylinder (with the brake switch on the master cylinder), or the existing master cylinder if you have a 1980 or newer 924, as long as it's in good condition. 924, 931, early 928 (79 928 used the same master cylinder as the 924 Sebring Edition with four wheel disc brakes), and early 944 with five bolt four wheel disc brakes all used the same brake calipers. If there was a problem with brake performance, Porsche would have changed the master cylinder to a stepped version much earlier than they did.

You do not need to change from diagonal braking to straight brake plumbing to use either master cylinder either. Porsche went back and forth with the straight master cylinder and the stepped master cylinder, diagonal and straight brake plumbing. Just use parts that are in good condition. I converted to four wheel disc brakes using parts from a 85/1 944 back in 1998 (for my 1981 924), and have never had any issues.