jheis

A friend offered me a set of '97 993 C4 front calipers (and rotors) at a very good price.

So, the question is: will a pair of 993 front calipers bolt up to a S4?

PNs are 993.351.422.20 and 992.351.421.20

James

jheis

Nobody?

Jon B.

I highly doubt you will feel a performance difference swapping the calipers. The calipers on the S4 are VERY capable. If your S4 isn't performing in the braking department a good service and more aggressive pads will be eye opening.

Mark Anderson

You might check the piston sizes. I think they are smaller than S4

jheis

Jon: The reason I am considering the 993 calipers is that I have 86.5 calipers on my '82 and one caliper is wearing one pad about twice as fast as the other, so I'm in need of a rebuild and the seals on the early calipers are not available without replacing the pistons as well. I can probably get the 993 calipers for what it would cost to rebuild the 86.5 calipers - plus the calipers are 10 years newer.

Mark: The 86.5 calipers I have have 42/36mm pistons - the 993 calipers are 44/36mm - so, a small, but significant difference.

James

pcar928fan

86.5 calipers ARE S4 calipers. I agree with Mark, I think an S4 caliper is better than a 993 caliper. 42 vs. 44 is a significant difference? I doubt that seriously.

My S4 brakes harder than ANY of my other 928's (including all 3 GTS's) and I have no idea why, but you hit the brakes in my S4 and I bet it would pop the contact lenses right out of your eyes! That car is AMAZING! I do have the 911 Turbo bias bar installed so I am putting much more braking effort to the rear brakes than is stock... YMMV

Keep us posted if you do the swap...

Hilton

'86.5 (86 in RoW) have 36/42 pistons up front, 28/30 in rear.

S4 have 36/44 pistons up front, 28/30 in rear.

993 Carrera and Carrera S have 36/44 front and 34/30 rear
(993 RS has 36/30 rear calipers)

(taken from Tech Bulletin 8907 for 928 values, and 993 workshop manual for 993 ones)

jheis

Then why did Porsche think it was worthwhile making the change on the later S4s?

I agree, there is nothing wrong with S4 calipers. The problem is that I have the early (86.5) non-rebuildable (at least economically) calipers on my '82 - which are in need of a rebuild. I've been offered the '97 993 calipers cheap and they're shiny (almost) new! I'm just trying to figure out if I can make them work.

As far as I've been able to determine, the '97 993 caliper is the same as the '89 and later S4 caliper - except they are the "smooth body" Brembos (no raised lettering).

It appears that I will have to swap the cross-over pipe and bleed screw positions end-to-end since the 993 calipers are, I believe, mounted on the forward side of the rotor and the 928 calipers are mounted at the rear side. Other than that it looks like the calipers should bolt right on.

Anyone tried this - or know if it's doable?

James

jej3

I think it might be time to ask your friend if you can bolt them up and see if they work.

Just my $.02

Gary Knox

993 REAR calipers will bolt right onto a 928 (at least 86.5+), and they have larger piston diameters. Total increase in piston area is nearly 25%. No change in appearance or fit, just better rear brakes.

Gary--

hacker-pschorr

When was the last time you:

A. Were unable to lock up the brakes
B. Were unable to stop due to brake fade

If your anser is never.....it's a waste of time.
If your answer is something else and you were on the street, time to overhaul the brakes.

Porsche might have "upgraded" the calipers simply because Brembo changed the design and that is what they were given.
Never always assumed every change Porsche made was in response to a lack of performance or some inadequate design.

"Better" brakes in the rear from a 911 doesn't always mean "better" in a 928. Last time I checked there is a slight weight transfer difference between the two cars.

77tony

James, Check in with RL Handles: Jim Mayzurk and Chuck Schreiber. IIRC, they both have done the 993 brake mod. T

jheis

Thanks Tony.

I did a "test fitting" the other day. The 993 calipers bolt right up to the S4 hubs - no problem.


As expected I will, however, have to switch the cross-over pipes and bleed screws end-to-end. Which means it will have to wait until I can get my hands on a decent quality (meaning Snap On or equivalent) 10mm flare nut wrench so I don't bogger up the flare nuts on the cross-over pipes. I know from past experience that you do not want to have to replace the cross-over pipes. When I bought my "S4" set-up two of the calipers arrived with smashed cross-over pipes due to poor packaging by the seller. As I recall, replacement cross-over pipes were about $65 ea for 4 inches of tubing - 10 years ago....

James

Hilton

I replaced the crossover pipes on my 89's front calipers with new. I got them through Roger and they were in that ballpark.

The issue with removing them isn't rounding the fitting trying to undo it - its the years of grime bonding the fittings to the tube. When you start to turn the fitting, it just twists the end off the tube Something I don't think a better flare wrench will help with.

jheis

Took a while as I wanted to wait until I had a decent quality 10mm flare nut wrench before I tackled the conversion. Finally got my SK 10mm flare nut wrench and did the swap.

The calipers I bought looked "brand new," but heeding Hilton's comments, I hit them with PB Blaster a number of times while I was waiting for my wrench. No problem removing the cross-over pipes with a quality wrench.

After changing the cross-over pipes and the bleeder screws end-to-end, the 993 calipers bolt right up - no issues.

By the way, the Harbor Fright flare nut wrenches are absolute dreck - save your money.

James