'90 964 C2 brake upgrade to 993 system - some detail issues

[Undutched]

Hi all,

I am working on upgrading my old 964 brake system to the 993 system to run larger brakes, so I want to switch over the master cylinder and brake booster from 964 to 993. Now I do have an issue, because it isn't all as easy as it may seem. I have most of the parts required, but need to know which parts I actually need to change over:

The main issue I'm having is the diameter of the lines and the connection to the wiring harness.

1. Second pic: Do I only need the lines 1 + 2 to connect connecting the master cylinder to the ABS Block? They are different size from 964
2. First pic: Do I need to change the whole ABS block? Then it doesnt fit the wiring harness of the 964, what would be the solution?
3. Are the lines the same diameter going to the back of the car?

[Bill Verburg]

Originally Posted by Undutched

Hi all,

I am working on upgrading my old 964 brake system to the 993 system to run larger brakes, so I want to switch over the master cylinder and brake booster from 964 to 993. Now I do have an issue, because it isn't all as easy as it may seem. I have most of the parts required, but need to know which parts I actually need to change over:

The main issue I'm having is the diameter of the lines and the connection to the wiring harness.

1. Second pic: Do I only need the lines 1 + 2 to connect connecting the master cylinder to the ABS Block? They are different size from 964
2. First pic: Do I need to change the whole ABS block? Then it doesnt fit the wiring harness of the 964, what would be the solution?
3. Are the lines the same diameter going to the back of the car?

The main issue is the connections of the brake lines to the m/c , all the other lines can be reused except the one from the hard ines to the front calipers, use a 964t line for that

wrt the lines that connect to the m/c; 964 is 10mm 993 is 12mm

solution use an adaptor

one way to do it is to have some custom lines made 'Classic Tube' can do that
or use an adaptor 'Fedhill' can supply these
or use a BMW brake line 34-32-6-752-405




no need to touch the ABS

in back use the stock rotors w/ 993 rear calipers and gut the p/v

front rotors will depend on the wheel carriers and the caliper adaptors that are used.

[Undutched]

Bill. Thanks very much!
Ordered the bmw lines. Easiest for 20€ each.

About the 964t line? You mean the one to the passenger side or both?

[Bill Verburg]

Originally Posted by Undutched

Bill. Thanks very much!
Ordered the bmw lines. Easiest for 20€ each.

About the 964t line? You mean the one to the passenger side or both?

Other than the m/c connections the only lines that might need changing are the flex lines from the hard chassis lines to the calipers, the ends on these depend on the caliper so if using '95 993 caliper use flex lines for a '95 993, in front 964t & 964RS flex lines should be the same as the 993 versions, I think that the 993 might be cheaper though.

[Undutched]

thanks pretty much to your posts and input I am able to get further on my 964 build. The info on the BMW brake lines, the info on the p/v, etc. helped incredibly!

I am looking to get the 993TT brakes as I'D like to have 2 piece discs? Is there a con for this as opposed to the 964T calipers and discs?

Just a quick point. I bought a 993 brake booster setup (the whole thing).
There 2 things.

1. The aluminum front part (connecting the pedal) is longer on the 993 (about 1cm) and you can't switch it over form the 964, because it doesnt fit on it. I don't see it mentioned anywhere in your posts, but may be useful.
2. You can't switch it over from the 964, because it doesnt seem to fit on top (larger diameter)

I made some pics.

[Bill Verburg]

Originally Posted by Undutched

thanks pretty much to your posts and input I am able to get further on my 964 build. The info on the BMW brake lines, the info on the p/v, etc. helped incredibly!

I am looking to get the 993TT brakes as I'D like to have 2 piece discs? Is there a con for this as opposed to the 964T calipers and discs?

Just a quick point. I bought a 993 brake booster setup (the whole thing).
There 2 things.

1. The aluminum front part (connecting the pedal) is longer on the 993 (about 1cm) and you can't switch it over form the 964, because it doesnt fit on it. I don't see it mentioned anywhere in your posts, but may be useful.
2. You can't switch it over from the 964, because it doesnt seem to fit on top (larger diameter)

I made some pics.

You need to ust both 993 pedestal and booster and associated 993 parts
993.355.910.00 master cylinder
993.355.023.10 Vacuum canister
993.355.301.00 gasket
993.355.163.03 MC support

[Undutched]

Great ok, then it is just a tight fit.

For the front I'D like to use the 993TT discs (2 piece) with big reds, as I need stock parts for TÜV.
BTW: I havent found any Info on JP Dansk Big Reds. Any ideas?


for the rear calipers, to use the noted 993 N/A (34/30 pistons 299x24mm discs), 964T (34/30 299x28mm discs) or the 993TT/RS/C4S rear ones (28/28-TT , 36/30-RS, 30/28-C4S with 322x28mm)

I am asking, because you usually recommend the 993N/A setup, but yourself use the 993TT or RS setup in rear for your own car.

I can find the Turbo or C4S calipers used online, but not the RS ones, btw.

[Bill Verburg]

Originally Posted by Undutched

Great ok, then it is just a tight fit.

For the front I'D like to use the 993TT discs (2 piece) with big reds, as I need stock parts for TÜV.
BTW: I havent found any Info on JP Dansk Big Reds. Any ideas?


for the rear calipers, to use the noted 993 N/A (34/30 pistons 299x24mm discs), 964T (34/30 299x28mm discs) or the 993TT/RS/C4S rear ones (28/28-TT , 36/30-RS, 30/28-C4S with 322x28mm)

I am asking, because you usually recommend the 993N/A setup, but yourself use the 993TT or RS setup in rear for your own car.

I can find the Turbo or C4S calipers used online, but not the RS ones, btw.

To use 993 rotors you also need to use 993 wheel carriers, There are 2 versions normal and RS(there are several aftermarket equivalents of the RS version)

in back you have to use either 964 or 968 rear rotors all are 24x299 993 rear caliper is prefered for bias

you can't use 964t or any 993 rear rotor unless you are willing to give up the parking brake, If you are willing to delete the parking brake then 993tt rotor 28x322 and 993RS calipers 30/36 are the way to go

[drola]

I did this and used the bmw brake lines. They are a bit long but you can bend them to fit. As long as your 993 mc has the mounting bracket then you should be good to go. There is also a reducer you can use but it’s easier to just use the bmw lines

[stanglife]

Originally Posted by Bill Verburg

The main issue is the connections of the brake lines to the m/c , all the other lines can be reused except the one from the hard ines to the front calipers, use a 964t line for that

wrt the lines that connect to the m/c; 964 is 10mm 993 is 12mm

or use an adaptor 'Fedhill' can supply these

Originally Posted by drola

I did this and used the bmw brake lines. They are a bit long but you can bend them to fit. As long as your 993 mc has the mounting bracket then you should be good to go. There is also a reducer you can use but it’s easier to just use the bmw lines

Bump on this one. Seems an adaptor could be an easy move here? Anyone have an exact link? I've found a couple 10-12mm ones but I'm not up on all the different flares and such.

ANy of these?
https://www2.cip1.com/c31-611-017-1210/?srsltid=AfmBOoqzNvzybLTfqpQjd7i4TrUpo4gbmF1xzOUiO R08RAAELJhr1p8u
https://www.amazon.com/12mm-male-10mm-female-adapter/dp/B07KY4419P

[Bill Verburg]

Porsche uses bubble flare

the adapters appear to be another way to go.

[stanglife]

Ordering this:
https://www.agscompany.com/products/f-m10-x-1-m-m12-x-1-brass-adapter?srsltid=AfmBOoo_qaHjDMvuLd0ql244G8snBPknPe _zckWNmT3UKyRikHB4b_jP

Also have the bmw lines if this doesn't work out - but I like the OE packaging of the stock lines. The angle at which they enter the 993 master is more like a 45 vs 90 so the end will need to be bent slightly.

[stanglife]

I don’t have a lot of hydraulic experience so this is a little confusing to me.

Does it matter that the orifice in one of the MC ports in the 993 unit is significantly smaller? What does that mean? More initial bite and/or bias to the larger opening.




The dirty one is the 964

Also - obtained the adapters above and they show promise but again - a difference in orifice size, the adapter is slightly smaller. Should I enlarge to more closely match the one in the MC?

[Bill Verburg]

Originally Posted by stanglife

I don’t have a lot of hydraulic experience so this is a little confusing to me.

Does it matter that the orifice in one of the MC ports in the 993 unit is significantly smaller? What does that mean? More initial bite and/or bias to the larger opening.




The dirty one is the 964

Also - obtained the adapters above and they show promise but again - a difference in orifice size, the adapter is slightly smaller. Should I enlarge to more closely match the one in the MC?

It really shouldn't matter

[konrad911]

I’m finally trying to sort that 964 M/C and servo out for everyone. Maybe make an aftermarket „kit” available, rather than swapping to 993 C2 pieces. The plan I have is to have 25.4 M/C available to both 993 C2 and 964 C2.

[konrad911]

Side by side 25.4mm M/C and 993 C2 23.8mm M/C.

I will make an adapter / bracket that will substitute the missing mount point at the end of the M/C.

Not sure if it’s needed at all, but safety first.

[Cobalt]

Do you need to go to the 25,4mm M/C? The increase to the 23.8 from the 20.64 is a significant upgrade. I increased the M/C on my 964 with electro-hydraulic unit to the 25.4mm unit but I am pushing out a conservative 500 hp and can go considerably higher. My C2 has the 23.8 and is more than adequate.

What kind of bracket can you make to secure the unit? It is critical if the vacuum canister is to be secured.

[Bill Verburg]

Originally Posted by Cobalt

Do you need to go to the 25,4mm M/C? The increase to the 23.8 from the 20.64 is a significant upgrade. I increased the M/C on my 964 with electro-hydraulic unit to the 25.4mm unit but I am pushing out a conservative 500 hp and can go considerably higher. My C2 has the 23.8 and is more than adequate.

What kind of bracket can you make to secure the unit? It is critical if the vacuum canister is to be secured.

It's desirable from an ultimate performance perspective, but not necessary.

some where in the low to mid 40s is too high, there's no hard limit the brakes just get mushier and don't respond precisely.

993RS brakes w/ 23.8 that most of us common folks use has a pedal ratio of 38.331

stock base 993 is 37.342

stock RS w/ 25.4 is 33.654

I love a ratio ~30, particularly if boost is applied, the lower the ratio the better on the edge control is

I've wondered about that extra brace, the 993 is the only car that I've ever seen that uses anything like that, I suppose that there must be a reason though.

[konrad911]

There is more coming in the new year around 964 C2/C4 brakes from me.

Personally I’ve driven the 23.8 and 25.4 M/C and I love the need to push it a bit harder. Obviously not with the stock calipers.

My pick is 36/44 fronts and 30/34 rear end.

PS. All the best to You guys in 2026!

[Cobalt]

Thanks Bill

Konrad,

I like it. I was wondering how it would secure the canister but clearly you thought that through.

Will you have that CNC'd, cast or printed? So many options these days we didn't have not long ago. .