944 NA Rear Brakes

[raygreenwood]

Just from looking at that picture ...though I cannot see the bearing cover behind it......that looks identical to all the 411/ 412's I have seen. Though the type 4 stub flange in that picture does not look like a type 3 flange...it is bolting up to a type 3 drum (the type 4 uses teh same part # rear drum.....so it should bolt up to most anything that is designated for type 3.
So if a rotor is designed to bolt up to a type 3 stub axle...then it should bolt on. What Ido not know...is if the aftermarket type 3 rear disc kits are using a stub that has adifferent offset from the stock type 3 stub.....in order to get the rotor to be parralell at the right height for teh caliper. If they are not using a stub that has an offset different than stock....then any aftermarket type 3 kit could bolt right up.

Also...if the new stub has positive offset...meaning it moves teh flange surface outward (wider than stock)....then it could be as simple as bolting on a shim plate between the stock type 4 stub flange, and teh new rotor. Ray

[Wally]

Another option is to use a 924T bearing/adpater plate, which was kindly lended to me by a friend for fitting purposes:
This is the front side, so when you are looking towards the wheel:



Althought I originally thought it was the same from a 924 turbo as a 944-1, it surely is different in two ways:
- its made from (cast) iron istead of alu like the 944 part;
- the bearing plate is separately from the adapter plate (where the caliper is bolt-on to.

Here's the back side, so where it sits against the trailing arm:



As you may have noticed, I have used a 964 rear caliper, which has the same bolt spacing as the sliding steel 944 or 924T rear caliper.
This ones are very nice: alu and a 44mm cup. They do however use a 24mm disk (against 20mm of the original 924T and 944 rear disks) and if there is a suitable porsche disk for it, I dunno. It was displayed just for illustration.

The steel part does give some extra options for different mounting difficulties I may encounter when I'll try to mount this on the rer of my 412. That's why I wanted you to show this 'odd', but more flexible part as well.

I think we are getting somewhere...

Greetings,
Walter

[Bill K.]

Awesome! That should work. The 944NA alum backing plate is too thick and the ebrake rubs on the inside of the T4 hub flange. An insert could be done like the one in the picture from an earlier post to move the ebrake inboard while using the T4 bearing retainer, but a steel version would be much stiffer and easier.

The 944NA ebrake is 35 mm (1.375") thick from backing plate to lever pivot. I expect the 924T steel backing plate is the same as the T4 (5.5mm or .21"). The distance between the T4 trailing arm face (backing plate surface) and T4 inner hub flange surface is about 1.85" (47mm), so there is room - 1.585" stackup with 1.85" room.

A hub spacer will be needed to push the disk outboard so the e-brake pad lines up with the drum (about 1" on the 944 NA disk). Sounds like the stock part...

Sounds like plug and play
Nice find Wally!!!

[Wally]

I expect the 924T steel backing plate is the same as the T4 (5.5mm or .21").

Nice find Wally!!!

Thanks Bill; your extra info on fitting the 944NA alu adapter plate makes me more confident as well
However, 924 Turbo parts are not an easy swap-meet find I suspect, so if this is really practible, I dunno.

BTW, you are close on the above measurement guess: the 924T steel backing plate as shown is actually 5,0 mm

[func412]

I'm curious, what is the bolt pattern between those two holes in rear caliper mounting.

[Wally]

94mm IIRC

[Bill K.]

Wally - does 924T ebrake fit? what is thickness from inboard mount surface of backing plate to ebrake face of backing plate? It uses the 944 ebrakes, so that would add another 1.1". We have 1.8" with the stock hub, so I hope 924T is less than 0.7" (18mm) from face to face.

[Wally]

I don't know yet, as I will first tackle the front spring/shock thing.
I an measure on the part I pictured, but don't understand towards what you want the measurement taken
I have no drum (ebrake) parts with it, so if thats mandatory for your measurements, than sorry...
(dismantling my rear 944 brakes on the squareback to measure with those parts, is a bit ..uehh.. )

[Bill K.]

No worries, just measure the 924T backing plate/ebrake thickness please.
Measure from "back" surface shown in your picture #2 where it mounts to the trailing arm to the "front" surface in your picture #1 where the side of the ebrake shoe rests against the backing plate. I have ebrakes (add 35mm).

I'm interested in the 924T distance from where my ruler zero is above on the 944NA assembly to the back mounting surface of the backing plate.

The ebrake needs to fit in the 45mm gap between the trailing arm and the hub shown below.


Good luck with the front springs.

Bill

[Wally]

Hi Bill,

Thanks

Those pictures are very good and informative!

So, with that info: The distance you wanted to know is 18mm.
Please let us know what that means

Tnx,
Walter

[Bill K.]

So, to clarify, the 924T backing plate is 5mm thick at the trailing arm mount surface and then steps up 13mm to the ebrake surface for a total mounting thickness (offset) of 18mm. We stack 35mm for 944 ebrake thickness (ebrake surface of backing plate to outboard side of ebrake lever) on top and we have a total offset of 53 mm. I got a measurement of 45mm between the T4 trailing arm and inside of the hub, so we may have 8mm interferance between ebrake and T4 hub flange. I'll double check the 45mm dimension tonite.

Therefore, I think our measurements mean the 924T ebrake assembly has the same effective offset as the 944NA. If so, the 924T ebrake will rub the T4 hub also.

[Wally]

Hmm, well the fact that the same sort of dimensions apply to both the steel 924T and 944 backing plate, would seem logical, as the alu 944 part is very probably just a cast from the earlier steel 924T part...
Bummer nontheless..

So, either one has to give a little
Wonder what made the 944 hub so different that that one fits easily. Yeah, I know its made to work with the 944 parts in the fist play, but still, it would give some more room for thought as what/how to modify...

Tnx so far. Now I may have to dismantle and try for myself
Walter

[Bill K.]

Now I may have to dismantle and try for myself

I agree. Our "virtual" measurement needs to be challenged. I'll try to come up with a local 924T backing plate to try as well.

The 944 backing plate modification would push the ebrake inboard to clear the T4 hub flange. The thickness of the backing plate at the control arm will remain 5 mm so the T4 bearing retainer is used. Seem like a hybrid could work. T4 backing plate modified to fit inside the 944 ebrake shoes (keep center hole, bearing retainer holes, and diameter intersecting the corners of the bearing retainer). 944 backing plate modified by making square through hole for clearance over the T4 trailing arm - now have ebrake and caliper mounts, but no trailing arm mount. Bolt modified T4 backing plate to modified 944 ebrake/caliper mount using appropriate spacer behind (inside) T4 backing plate. I'll illustrate later...

[raygreenwood]

This is getting interesting. Though 924 and 944 parts can be hard to come by here....I know where there is a bit of a supply. Nice work! Ray

[Bill K.]

Some creative grinding got the 944 NA ebrake skinny enough to seat the T4 hub without rubbing. Backwards ebrake shoe springs for clearance.


I'm not sure the skinny ebrake pivot arm is going to hold up...


The inboard surface of the T4 hub will need to be spot faced to accomodate studs.


What is the minimum thickness for planting studs in the T4 hub? Can the inboard face be spot faced for studs so the heads are flush?

Maybe there is hope in the 944 conversion...