A different way to hook up 911 e-brakes, Another way to do the 911 parkbrake -merged threads Options

[craig downs]

and

[craig downs]

911 shoe on the left and a 944 on the right it the same shoe except the 944 has a notch for the spreaders instead of the pins for the 911. Also the 944 has a slot instead of a hole for the retainer spring that holds it to the backing plate.
The spreader on the left is out of a BMW which the cable pulls 90 degrees to the backing plate. The spreader on the right is from a 924/944 and the cable comes in at an angle to the backing plate.
The tangs on the back of the BMW spreader is so the loose pin that hooks the cable to the spreader doesn't fall out.

[smdubovsky]

Just about every porsche other than the 911/912 & 914 uses the same newer lever design and same brake shoes 930/964/993/996/986/997/924/944/928.

Hmmm, I have some E30 parts laying around somewhere taken off the racecars. I should compare. FWIW, the E30 has a bolt on support (part #3). If its the same width as the stop plate you have to weld on anyway it could kill 2 birds w/ one stone.

Craig downs is correct. The reason for the ears is to keep the pin from falling out when you pull on the cable.


http://www.realoem.com/bmw/showparts.do?mo...hg=34&fg=30

[andys]

Guys,

Keep up the good work. This thread is getting real interesting and informative.

Andys

[Richard Casto]

Just spent a few minutes looking at PET for 924, 944 and 928 (can't get the 924S PET to download right now)

* The pad spacer is part of the 911 rear suspension arm and not the backing plate. (already knew this)
* The 76-79 924, 82-85 944 and all years of the 928 have a backing plate but the pad spacer is part of the backing plate. Hard to tell, but plate looks thicker than 911 plate.
* The 88+ 944 did not have a backing plate (or pad spacer), but rather it is part of suspension arm.
* All 928 use the same spreader (993 352 073 00) which looks to be a 90 degree pull
* All 924/944 use the same spreader (951 352 090 00) which looks to be a side pull


My take away from this is ...

* The 911 backing plate it too thin to handle loads when the e-brake is engaged. (some people weld the spacer to 911 backing plate, some weld it to the 914 rear suspension arm)
* Backing plates for the 924 and 928 were made thicker so they can incorporate the pad spacer and can cary the braking load??
* Some later cars did away with the backing plate and incorporated it into the rear axle casting.
* Backing plates between models look to be significantly different. Not sure how much if any swapping can happen.
* Would the 924/944 spreader work better as it is a side pull and that might line up better with the stock 914 e-brake setup since if I remember correctly the rear 914 e-brake is a side pull and not a 90 degree pull? Could this mean no need for a bellcrank if you use the 924/944 spreader, but just a short custom cable to bridge between the spreader and the stock 914 cable?

[Richard Casto]

Craig,

Excellent job! It looks like you are well on the way of figuring this out!

I assume the next step in the photo below is to weld in a spacer for the pad and that same spacer might do the same job as the 924/944/928 backing plate and act as a brace for the spreader? After you run cables, it looks like you might have a working solution using the pull spreader!

Richard

[Richard Casto]

911 shoe on the left and a 944 on the right it the same shoe except the 944 has a notch for the spreaders instead of the pins for the 911. Also the 944 has a slot instead of a hole for the retainer spring that holds it to the backing plate.
The spreader on the left is out of a BMW which the cable pulls 90 degrees to the backing plate. The spreader on the right is from a 924/944 and the cable comes in at an angle to the backing plate.
The tangs on the back of the BMW spreader is so the loose pin that hooks the cable to the spreader doesn't fall out.

Questions and comments...

It looks like you are using a 911 backing plate. With the 944 shoe having a slot vs. a hole for the retainer spring does that mean you have to use the 911 shoe? If you are using the 911 shoe, are you grinding a notch for the spreader?

Also, you mention that the 90 degree spreader is from a BMW. If you look at the PET diagram for the 928, the BMW and 928 spreader look the same if not identical.

[ClayPerrine]

I have had sitting side by side in front of me a 944 backing plate and a 911 backing plate.

You have all seen the 911 backing plate.

the 944 backing plate is a cast aluminum part that incorporates both the shoe stop and the caliper mounting point, plus the bearing cap. The center of the cast aluminum part won't fit over the 914 trailing arm, it is too small. And he offset for the shoes and the caliper mount is completely wrong to work with the 914 trailing arm, even if it would fit. Plus, the caliper mount is on the back of the trailing arm on a 944, so to use it on a 914, the cable would have to come from the rear.

I like the idea of using 944 shoes and the spreader, but I will be much harder to do than the 911 setup. If someone made a custom backing plate with a cable pull from the front in parallel with the trailing arm it would be a slick item.


(DAMN... now I am thinking again!!!!)

BTW.. my park brake works fine. I drove it to work this morning.

[craig downs]

I'm totally aware of how the backing plate is on a 944 and I'm not using or trying to use it I'm using a 911 backing plate. I don't understand what difference which backing plate you use. When I was looking into this idea if it would work I checked the shoe size, position, and the gap between the shoes where the spreader goes to see if they were the same as the 911 and they were. The only difference in the shoes are the pins for the 911 spreaders and the holes for the retaining springs that holds them to the backing plate. The 911 has a hole and the 924/944 has a slot.
If you want to use the 911 shoes you have to remove the pins and grind a notch for the spreaders. If you want to use the 924/944 shoes all you have to do is to drill a hole where the slots are for the spring retainers.
The shoe anchor will have rear support for the spreaders and be welded to the trailing arms.
I know your a big fan of cables which is fine. Just looking at another alternative

[Wes V]

Craig;

On the prior page, jcd914 posted a photo showing in green lines where the spreader would bear on the backing plate.

The PET backing plate diagram I've seen has the spreader sitting on a raised area.

In all disk brake installations, the shoes sit on raised sections. This is true on 911 backing plates and also on 924 backing plates.

Now the question I've got (and hopefully you have a 924 backing plate you can look at) is if the raised pad supporting the spreader is at the same elevation as the pads that the shoes rest against.

Wes V

[Wes V]

Craig;

Here is some more "food for thought" stuff.

If I was going to do it, this is the bracket that I'd weld to the housing.

(IMG:http://www.performanceforum.com/wesvann/914a/my-rear-brake/924bracket.jpg)

It would serve the function of having the bearing pads for the spreader and also the shoe stop.

It would be positioned where I'm holding the scale in the following photo;

(IMG:http://www.performanceforum.com/wesvann/914a/my-rear-brake/924.jpg)

If after fabricating and installing it looked too weak (at the top), it would be possible to add a stiffener on the car side that matched the radius.

Personally, I'd just go with the 924 spreader (straight pull), but if you used the BMW one, the opening for it could be smaller. (the opening wouldn't have to clear the "tangs" on the 924 spreader, just the arm it's self.

Wes (I've got to get a life) Vann

[ClayPerrine]

In the middle of the day today a stray thought about this subject crossed my mind, and in the process got stuck.


(IMG:style_emoticons/default/blink.gif) What does the stop block everyone adds to the trailing arm actually do? (IMG:style_emoticons/default/idea.gif)

When the brake is off, the shoes rest against it.

When the brake is on, the shoes are held outward by the spreaders, and they don't touch the stop block.


So why do we need it????????? (IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/confused24.gif)

[Eric_Shea]

When the brake is on, the shoes are held outward by the spreaders, and they don't touch the stop block.

Not sure if that's accurate. I believe they pivot off it.

Make a circle in front of yourself with your thumbs and forefingers. The spreader would be between your forefingers. Open the circle pivoting off your thumbs. The pivot offers stability for the shoes and prevents them from simply being ripped off by the wheel if engaged while moving.

Much needed. I believe the stop block is in the wrong position above. It should be below and the spreaders should be above.

[Eric_Shea]

Wait... rethinking. You're right.

The spreader creates the pivot.

[ClayPerrine]

When the brake is on, the shoes are held outward by the spreaders, and they don't touch the stop block.

Not sure if that's accurate. I believe they pivot off it.

Make a circle in front of yourself with your thumbs and forefingers. The spreader would be between your forefingers. Open the circle pivoting off your thumbs. The pivot offers stability for the shoes and prevents them from simply being ripped off by the wheel if engaged while moving.

Much needed. I believe the stop block is in the wrong position above. It should be below and the spreaders should be above.

I don't think the shoes pivot off the stop block. They would have to pivot off the star wheel adjuster. The stop block is on the end with the spreaders....

[ClayPerrine]

Wait... rethinking. You're right.

The spreader creates the pivot.

Ok.. then what does the added stop block do??????

(I call it a stop block because I don't know what else to call it.)

(IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/screwy.gif) (IMG:style_emoticons/default/confused24.gif)

[Richard Casto]

I think another way to say what Eric is saying is...

While you have the pins that keep the shoes attached to the backing plate, pretty much the shoes, spreader and adjuster pretty much float. If you didn't have what we are calling the "stop block" or "spacer", if you engaged the e-brake and tried to move the car, it would either rip the pins from the backing plate or break the pins as the shoes, spreader and adjuster rotated with the disk/drum and the backing plate remained stationary. You also wouldn't rotate much before your cable broke or yanked the spreader out from between the two shoes.

So while the spreader moves them apart, most likely one or the other shoe (depending upon which way the car wants to move) is in contact with the stop block. This is why in my opinion you should not weld the stop block to the thin walled 911 backing plate. And as you mention Clay the 944 backing plate it a heavier cast part and not a thin stamped part because it includes the stop block and can take the load.

The load at rest on the level is probably pretty small/next to nothing. But I think that the load is much higher if you tried to engage the e-brake while moving or if you are parked on a hill.

[Wes V]

I agree with what Richard is saying.

Think of the shoes, adjuster and spreader as an assembly that is free to float.

To play with numbers:

When you first pull on the parking brake, each shoe moves away from the block an equal 1/8". You then push the car forward, the assembly would rotate until one of the shoes came in contact with the block. Then you push the car rearward, the assembly would rotate in the other direction and the other shoe would come in contact with the block.

Using those numbers, if you rocked the car back and forth, the spreader would move 1/4".

If you yank on the parking brake while the car is in motion, one of the shoes is going to hammer into the block!!! All of the rotational force gets transfered through that small contact surface on ONE shoe!!!!!

Wes

[smdubovsky]

If you yank on the parking brake while the car is in motion, one of the shoes is going to hammer into the block!!!
Wes

Richard & Wes are right. You can see the rub marks on the block on a 911 where this happens. The block on the early steel trailing arms is ~1/4" thick. IIRC, The aluminum ones are even thicker. I have both at the house and can measure tonight. This is one place you want to use something beefy.

[PRS914-6]

Guys, you have to have a firm stop and the shoes have to float. When you apply the parking brake when moving the entire shoe assembly rotates . Picture the rotating drum, the shoes go out and when contact is made the spinning drum tries to rotate the entire shoe assembly. That's why the bottom is not anchored. It's called self energizing and uses the rotation of the drum to help with the braking action. It's supposed to rotate against the stop and why the flimsy sheetmetal backing plate can not be used to stop the rotating force. That method is an accident waiting to happen. You ever wonder why car brake shoes have more material on one side than the other? It's the self energizing effect that shoves the shoe harder against the drum and the driven shoe gets more material to compensate.

If you anchored top and bottom it wouldn't work worth a crap.