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Converting to a manual trans just got a little easier
As you may know, doing the conversion to a manual trans for your automatic-equipped 928 requires mounting the clutch master cylinder to the firewall, and that requires having a mount for it.
Up till now, this is commonly done by acquiring a clutch master mount from a manual-equipped donor car, and riveting it in place on the project car. Recently, however, we discovered that these firewall bits were starting to come into short supply. My response was to see if I could have some of them made.
Here it is, below. Was able to get it done at a reasonable cost, too, so the price isn't too bad, $66. Made from steel, and powder-coated for rust resistance. https://928motorsports.com/parts/mas...nder-mount.php
More good news: the relative scarcity of these firewall mounts from donor cars made me a little worried about whether my customers and I were going to be able to find used 928 clutch pedal assemblies. Called Mark at 928 International and he said I had no need to worry - they've got plenty of pedals.
very good idea Carl , sure for the Corvette box swap on a auto... as i think there are almost as many oem parts like that to cut out as there are manual Porsche 928 gearboxes ?
But even then , at $66 i wouldn't even bother cutting one out !
Neat. I was fortunate when doing my swap in that I got the whole corner of the firewall so I was able to cut out enough metal to use the brake booster mounting holes to line up everything in my car. Is there a way to get this lined up without doing something like that still?
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
I was fortunate when doing my swap in that I got the whole corner of the firewall so I was able to cut out enough metal to use the brake booster mounting holes to line up everything in my car. Is there a way to get this lined up without doing something like that still?
Sounds like you did what we did, Matt. Made a template from a donor firewall that we use to show us where to mount it.
When we install them, we line them up with the thru-wall for the power brake booster and hold it in place with a vice-grip so we can mark where to put the hole. This is why we put a square bend in the top - so you can clamp it to the steering column support in the same way, without the need for a template.
These pics are using the stock mount, not our mount, but the location and idea is the same. These pics show our process when we do it here. Careful cutting of the sound deadening material with a box cutter allows us to put it back and seal it nicely.
Engine side, brake booster removed. Sound deadening cut away. Template shows us where to put it. Holes (3) are cut in and connected. View from the engine side. The clutch mount is riveted to the firewall. A sealant is applied between the two to make it watertight. Clutch master in from the driver's side. Clutch master from the inside. Sound deadening put back on and sealed. It's interesting that the sound deadening floor covering even on automatics has the bump in it for the master cylinder mount.
Sounds like you did what we did, Matt. Made a template from a donor firewall that we use to show us where to mount it.
When we install them, we line them up with the thru-wall for the power brake booster and hold it in place with a vice-grip so we can mark where to put the hole. This is why we put a square bend in the top - so you can clamp it to the steering column support in the same way, without the need for a template.
These pics are using the stock mount, not our mount, but the location and idea is the same. These pics show our process when we do it here. Careful cutting of the sound deadening material with a box cutter allows us to put it back and seal it nicely.
Engine side, brake booster removed. Sound deadening cut away. Template shows us where to put it. Holes (3) are cut in and connected. View from the engine side. The clutch mount is riveted to the firewall. A sealant is applied between the two to make it watertight. Clutch master in from the driver's side. Clutch master from the inside. Sound deadening put back on and sealed. It's interesting that the sound deadening floor covering even on automatics has the bump in it for the master cylinder mount.
Yep, that's just what I did, expect I didn't do nearly as neat of a job cutting it out as you did. Your auto to manual swap guide was a great reference for me while doing my swap this summer, so thanks for that.
Maybe it doesn't matter as much if it's not exactly perfectly lined up, but maybe a template could be drawn up that lines up with both the brake booster holes and the rivet holes around the perimeter of the new pieces (I'm assuming they're in the same spot from piece to piece with the new ones, unlike the spot welds that get drilled out on the factory ones). Even if it's something that can just be printed out on paper and attached to a thin piece of cardboard, I bet it would be helpful to those who don't have a template from a firewall to go by.
Forgive my awful paint skills, but maybe somethings like this:
I was able to transfer the cutout for the hole (which I cut out using an air nibble to avoid removing the brake booster) and transfered the locations of 3 or 4 spot welds that I had drilled through to make sure I got it lined up just right.
PS: strongly recommend that you use a broach, not a regular hole saw, when placing the holes. Broaches do a much better job in metal. Brands go by Roto-broach, RotoCut, Haugen, others. I've used most and they are good. Well worth the investment especially if you have ever had the Home-Depot level hole saws screw up a project.
Maybe it doesn't matter as much if it's not exactly perfectly lined up,
It doesn't. The pedal assembly and the linkage have a fair amount of forgiveness in them, so if you are off a little this way or that, its not a big deal.
One thing I don't "get", in your pictures: Why use the spacers that normally go between the two layers of the firewall on the bolts to secure the master into the car?
Porsche made the original clutch master cylinder mount, in the manual cars, with both inner and outer layers of metal, in order to "spread" the load out into twice the surface area (only in this area.) Both the 924 and the 944, with their relatively "light" clutches suffered from the clutch slave (just a cable in the 924) severely cracking the entire firewall area....which is an incredibly difficult thing to repair....the cars that have this problem are essentially junk.
You've apparently decided that this is not necessary and the single wall is adequate for use in the heavier pressure 928 application?
In that picture, the longer bolts with the spacers were supplied as OEM, and we used them. I also wondered why we should, but the customer wanted pure Porsche parts installed, so he got them.
Know of the 944 firewall cracks on the early base models - did not know that extended further back to the 924. Have never seen a 928 with a crack in the firewall around the clutch master cylinder.
Have never seen a 928 with a crack in the firewall around the clutch master cylinder.
Nor have I.
My question is directed entirely at that fact.
Simple logic tells me that Porsche added a second piece of metal, only at firewall where the clutch master cylinder bolts into, in order to "deal" with the increased pressure on the firewall, from the stiffer 928 clutch.
I can't think of any other reason why they would go to the cost/trouble to add a second piece of metal into this specific area.
Can you?
01-02-2020, 10:21 AM
Converting to a manual trans just got a little easier
