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951 Brake Conversion... *pulls hair out*

 
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Thu Dec 04, 2003 4:08 am    Post subject: 951 Brake Conversion... *pulls hair out* Reply with quote

Ok, guys. I'm about to throw in the towel.

Someone posted recently that the front is difficult while the rear is a snap. So far, it's only succeeded in making my temper snap.

The front is largely a bolt-on affair. I used the entire strut with hub and calipers. I have no idea which year, but the rotors are NOT like the 944 type. It had a little hub like the rears. I have yet to figure how to get the speedo to work though... But that's least of my worries....

The rears are driving me crazy! I believe the parts I got are from a '86 as the arms are not the longer type. The part numbers end with 513 and 514. Am I supposed to use my old rotors? The new ones have a much deeper e-brake hub. Then I tried to swap the stud hub, but the splines are different. Then I thought I was brave and hoisted up the car to swap the control arms and then the driveshaft is now too short and the springplate won't fit.

Do the 951s have a different springplate or is the springplate different for snailshell cars? And to swap out the springplate, it looks like I gotta drop the entire rear torsion beam? True? I'm really tired and dirty... Someone save me...

Sprint.
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81turbo  



Joined: 03 Nov 2002
Posts: 1065
Location: Oakland, CA

PostPosted: Thu Dec 04, 2003 4:11 am    Post subject: Reply with quote

Late 944s and 924s have different spring plates. You cannot use the alloy trailing arms on the 931 unless you replace the spring plates. I went through this a while back and decided to just keep the steel arms.
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Thu Dec 04, 2003 4:57 am    Post subject: Reply with quote

81turbo wrote:
Late 944s and 924s have different spring plates. You cannot use the alloy trailing arms on the 931 unless you replace the spring plates. I went through this a while back and decided to just keep the steel arms.


I don't mind keeping the steel arms! But how do the rotors fit? The 951 rotor has a 'deeper' handbrake hub.

Sprint.
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81turbo  



Joined: 03 Nov 2002
Posts: 1065
Location: Oakland, CA

PostPosted: Thu Dec 04, 2003 5:25 am    Post subject: Reply with quote

They won't. Why did you think that they would? I have never heard of the 951 brakes fitting a 931 w/o problems. They will work on a 924s because of the rear trailing arms and brake line routing. Have you looked into re-routing your brake lines? The valving is different on the 951 and later 944/924S. If you do not re-rout the lines the brakes will not function properly on the 931. This is why no one does this conversion.
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Thu Dec 04, 2003 6:16 am    Post subject: OMIGAWD... Reply with quote

81turbo wrote:
They won't. Why did you think that they would? I have never heard of the 951 brakes fitting a 931 w/o problems. They will work on a 924s because of the rear trailing arms and brake line routing. Have you looked into re-routing your brake lines? The valving is different on the 951 and later 944/924S. If you do not re-rout the lines the brakes will not function properly on the 931. This is why no one does this conversion.


Gosh... I'm in real trouble now.... Searched for that thread and it looks like I really misread it. The dude has a 924S.

Sprint.
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gohim  



Joined: 02 Nov 2002
Posts: 4459
Location: Rialto, CA

PostPosted: Thu Dec 04, 2003 7:04 am    Post subject: Reply with quote

At the time that the tread was posted about the 951 brake conversion, I posted several messages asking about further details on the guy's conversion, and how he intended to solve what I thought were going to be major problems.

If I remember correctly, after bragging about how easy the conversion had gone so far, I asked the guy to post again when he was finished and had tested the car for correct brake balance, as I questioned his plan to not install the rear brake proportioning valve that is plumbed into the 951 that is not included in 924, 924S, and 944 brake systems.

The tread died with the original author replying with any final result to his conversion. So I guess the question would be, was the conversion ever completed, if not, why was it abandoned, and how well did it work (if at all)?
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Thu Dec 04, 2003 7:24 am    Post subject: Reply with quote

The only way I see getting the rears on is to get-

Alloy trailing arms.
Matching spring plates (means pulling the old ones off and screwing with the torsion bars).
Later shocks.
Later, longer axles.
Hubs from an '86 951 or 924S (or '86 944 too?) - the 944/951 hubs will require the longer wheel studs to be removed and replaced with shorter ones.
Re-route the brake lines to a TT split off the MC.
Install an adjustable proportioning valve.
Find a way to setup the proper proportioning?
I think the later handbrake cable is different too.

With all this $$ it should bolt up with no problems.

-nick
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Thu Dec 04, 2003 2:53 pm    Post subject: Reply with quote

gohim wrote:

The tread died with the original author replying with any final result to his conversion. So I guess the question would be, was the conversion ever completed, if not, why was it abandoned, and how well did it work (if at all)?


Well, I'm not about to die off! Keep this thread in your favorites!

So far, I've fitted the fronts with no trouble. How do I identify the '86 vs. later fronts? The car is still on the hoist so I can't vouch for alignment. I hope the front control arms are the same so no alignment is out from factory spec (I understand I need to realign, I just hope to get back factory spec without further monkeying around).

The rears I've fitted the alloy diagonal arms and the spring plate don't line up in terms of holes. But they are in the same plane. I believe when fitted, the car will have same track, meaning you don't need to get new wheels and tires but you need to get the whole she-bang worth of parts....

The halfshafts are too short. I'm wondering if I can machine spacers rather than get 951 ones.

Well, I'm post more as it comes along. Will take some pics today.

Sprint.
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Thu Dec 04, 2003 2:57 pm    Post subject: Reply with quote

-nick wrote:
The only way I see getting the rears on is to get-

Alloy trailing arms.
Matching spring plates (means pulling the old ones off and screwing with the torsion bars).
Later shocks.
Later, longer axles.
Hubs from an '86 951 or 924S (or '86 944 too?) - the 944/951 hubs will require the longer wheel studs to be removed and replaced with shorter ones.
Re-route the brake lines to a TT split off the MC.
Install an adjustable proportioning valve.
Find a way to setup the proper proportioning?
I think the later handbrake cable is different too.

With all this $$ it should bolt up with no problems.

-nick


Any idea if the 951 springplates will fit with no problems? I'm far away in Singapore. Would hate if if I were to buy them, have them shipped just to know they don't fit....

And with the snailshell, it looks I have to lower the entire suspension to swap the plates, ya? Well, time to get larger torsion bars then. Anyone knows a good company?

And about the drive shafts. I'm about 4.5" short on each side. You reckon I can get away with spacers? I'm thinking of machining and attaching them to either the stud axle or tranny end. Any thoughts?

Thanks for any info.

Sprint.
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gohim  



Joined: 02 Nov 2002
Posts: 4459
Location: Rialto, CA

PostPosted: Fri Dec 05, 2003 5:37 am    Post subject: Reply with quote

The shock mounting bolts for the alloy trailing arms is larger, so you will have to either ream out the hole in the chassis where the shocks bolt on (hope you have enough metal and the bracket hole does not break out from metal failure down the road), or you can have a shoulder washer/bushing machined that can be inserted into the shock bushing to take the diameter down to the existing bolt size.

You should also switch to the larger diameter master cylinder and vacuum brake booster from the 951 to make sure that you have enough fluid capacity, and lower the brake pedal effort.
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Fri Dec 05, 2003 1:39 pm    Post subject: Reply with quote

81turbo wrote:
Have you looked into re-routing your brake lines? The valving is different on the 951 and later 944/924S. If you do not re-rout the lines the brakes will not function properly on the 931. This is why no one does this conversion.


The brake lines... Are you talking about the front/rear split of the 951 vs. the X-diagonal of the 931?

Thanks.

Sprint.
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SprintStar  



Joined: 26 Aug 2003
Posts: 150

PostPosted: Fri Dec 05, 2003 1:41 pm    Post subject: Reply with quote

gohim wrote:
The shock mounting bolts for the alloy trailing arms is larger, so you will have to either ream out the hole in the chassis where the shocks bolt on (hope you have enough metal and the bracket hole does not break out from metal failure down the road), or you can have a shoulder washer/bushing machined that can be inserted into the shock bushing to take the diameter down to the existing bolt size.

You should also switch to the larger diameter master cylinder and vacuum brake booster from the 951 to make sure that you have enough fluid capacity, and lower the brake pedal effort.


Good idea on the shock bushing and I'll look into the brake master pump too. Thanks!

Sprint.
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Joes924Racer  



Joined: 03 Nov 2002
Posts: 11960
Location: Oregon, Denver Colorado native!

PostPosted: Fri Dec 05, 2003 1:52 pm    Post subject: Reply with quote

Sprint haven a little trouble I dont know where you are located ,
though I know of a couple people who can help with parts
and not charge you your soul for. Give Mike a shout up in
Bellingham Washington. Ive bought stuff from him.
http://www.924board.org/profile.php?mode=viewprofile&u=915
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Sat Dec 06, 2003 2:34 am    Post subject: Reply with quote

I haven't, nor have I heard of anyone doing this swap, so don't take any of this as the gospel-

The alloy control arm spring plates are all the same, as far as I know. In fact, all cars with the alloy arms have identical parts *except for the hubs*. Later 944's with the alloy arms used hubs that pushed the wheels out further- that's when the 944 offset was changed from the early 23mm to the later 52mm.

I made a mistake earlier- the '86 951 hubs use the same length studs as the 924S.

Brake lines- yes. The 944 brake MC had one outlet for the FR brake, one for the FL brake, and one for both the rear brakes (*I'm not positive which outlet goes to which, but this is the idea- same goes for below too). The front outlets run off a 23mm bore and the rear outlets run off a 19mm bore.

On the 924's the brake MC has one outlet for FL, one for RR, and one for both the FR and RL. The MC bore is 23mm all the way through.

Using the 924 MC won't give you the decreased bias you need in the rear. Some folks don't seem to have any trouble with this on the ordinary 4-bolt to 5-bolt brake swap. 951's had an additional proportioning valve inline on the rear brake line. Brake bias has a lot of variables and what might work on a stock 951 might not be the best on a 931. This is something you would need to tune, and to do this you need to separate the FR and RL brake lines.

I think the brake booster was the same size from ~'79 on up? I don't think you would need to worry about this.

You will need to do something about the shocks. The alloy control arm uses a larger diameter lower shock bolt. You could either use early shocks and rebush the lower ends with the correct size metal sleeve. Or you can use later shocks and add a cylindrical spacer to make up the difference between the shock bolt and the bushing on the top mount.

Don't forget the parking brake. I hope you got the shoes & hardware with your alloy control arms? I believe you'll need the later cable too.

924's with the later suspension mount setup (mid '78+) require dropping the rear suspension to replace the spring plates. You just have to drop things down low enough so you can pull the plates off past the body. Having a snailshell adds extra fun since the tranny mounts to the suspension you need to drop. You're going to need to disconnect the tranny from the torque tube to drop the suspension. Feel like doing a clutch while it's all apart?

I wouldn't add spacers to the driveshafts. But I suppose you might be able to get away with it. They will need to be perfectly balanced pieces of aluminum of pretty precise measurements. I would think getting later axles would be easier and less worrysome. You should be able to find them relatively cheaply from someone breaking a later car. Of course, shipping is obviously a tad expense for you!

If you're going to replace the torsion bars then just find some stock 25.5mm bars from an M030 944. I saw a set on ebay a little while ago that went pretty cheap. These will really stiffen things up compared to your stock 23.5mm bars. Of course, then you'll need stiffer front springs to match the rates...

This is one hell of a project you've undertaken. I hope it works out, I'd sure like to hear about it!

-nick
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mrobbo612  



Joined: 07 Nov 2002
Posts: 8

PostPosted: Sun Dec 07, 2003 9:40 am    Post subject: Reply with quote

i have done this same conversion and encountered the same problems you speak of. the problem you have at the rear is that you have late turbo rear arms and brakes. the disc fitted to these are 100 mm high with a 299 diameter and is 24mm thick at friction area[height refers to the dimension if you lay the disc flat on the ground and measure up to the wheel mounting face]. if you can obtain early turbo rotors from an early 944 turbo they are only 71 mm high [as per standard single piston aliper disc]with the same diameter and friction area thickness and will fit your current steel control arms/handbrake and driveshaft combination. you will however require the small spacers that fit between the caliper mounts and the arm[approx 6mm thick and used on alloy rear control arms for 944 turbos] and may require spacers betwwen the hub and the wheel to clear the caliper[i have 16" fuch alloys and required 10mm spacer between huband wheel please note i had previously removed standard 21mm spacer so the fuch wheels would fit under the bodywork]. the caliper spacings for standard single piston caliper and turbo rear calipers are the same and the brake pipe requires only a minor bend to fit also. i have used the standard master cylinder and rerouted the lines to have a front rear split [line modification done under o/s floor] and have had no problems with the balance. later m/c combinations used a stepped m/c with smaller bore area suppling the rear brakes. if you reduce the m/c bore you actually increase the force applied to the caliper pistons and increase the pedal travel.by using standard bore 931m/c you are actually reducing pedal travel and pressure/force to rear calipers thereby reducing the tendancy to lock rears and also reducing the need for a proportioning valve.
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