Building a 904

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Hanns Mueller-Rech
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Re: Building a 904

#31 Post by Hanns Mueller-Rech »

looking forward to the further „height adaption“ of the seat, but with my 6‘5“ still there will be not enough space, no? would love to test seat your version…

br
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Martin Benade
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Re: Building a 904

#32 Post by Martin Benade »

I was just going to ask if you had to make suspension parts. Looks like I’ll find out.
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Bill Sargent
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Re: Building a 904

#33 Post by Bill Sargent »

In my last post I said suspension would be next, but I just returned from a week in the UK to work with Barrie Martin on fitting me in the car. So I will post about that first.

The driver’s seat in a 904 is fixed and part of the bonded fiberglass body structure. The position of the pedals and steering column are adjustable, but the “tall” setting is only good for someone about 5 ft 10 inches. I am 6 ft 2 inches so something has to be done.

This is what the unmodified driver’s seat area looks like.
Stock driver’s seat
Stock driver’s seat
The limit to lowering the seat is the belly pan/floor which is about 1 inch below the seat bottom. Moving the seat back is limited by a chassis cross member about 3 inches to the rear of the lower seat back. Our solution was to cut out the seat bottom and back and move it as far back as possible and also recline it a little more to gain headroom.
Driver’s seat removed view from inside
Driver’s seat removed view from inside
Drivers seat removed rear view
Drivers seat removed rear view
Drivers seat moved back 3 inches
Drivers seat moved back 3 inches
Driver’s seat side view
Driver’s seat side view
These changes gave me plenty of legroom and about 1 inch of headroom without a helmet.
Legroom looks good
Legroom looks good
About 1 inch headroom
About 1 inch headroom
However with a helmet on it rubbed the roof so we will add about a 1 inch Gurney bubble on the driver’s side.

Before I arrived in the UK most of the roll cage had been installed, with the exception of the harness bar and the main hoop diagonal. After we completed the mock up of the changes to the driver’s seat we took the car back to Robinson Race Cars for them to complete the cage. They were then able to tailor the harness bar and diagonal to hug the modified driver’s seat. The resulting cage is FIA certified for circuit and rally use.
Main roll cage hoop, harness bar & diagonal
Main roll cage hoop, harness bar & diagonal
Door and dash bars
Door and dash bars
After the car returned from the roll cage shop we made some measurements to see if a 911 motor could be fitted with the “tall guy” seat mod. The answer is a provisional yes - if the main hoop diagonal is omitted and the harness bar may need an upward bend to clear the 911 motor fan shroud. I am using a 4 cam motor so this is not an issue for me but we were checking as a buyer in line behind me is 6 ft 4 inches and plans to use a 911 motor.

The next steps on my car are to complete binding the body to the chassis, reglass the driver’s seat and install the movable panels. In parallel Barrie will have the suspension parts, gas tank and oil tank fabricated.

I am 7.5 years into this build and it is great to finally see progress. Still a ways off from delivery, but we are getting there.

Thanks for following along.
Regards,

Bill Sargent
#151489 59A Cab - Faux Cam
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904 clone in the works

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Adam Wright
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Re: Building a 904

#34 Post by Adam Wright »

When I first got my body I thought something was wrong, the fit was too tight, or so I thought. I'm 5'9" so figured I wouldn't feel squeezed. Then I went in sat in my friends, 904-0014 and nope, they are just that small. Glad you could make it work at your height!
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Hanns Mueller-Rech
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Re: Building a 904

#35 Post by Hanns Mueller-Rech »

love this adaption ...luckily I am not that tall when I do sit....…:)

br

haul

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Bill Sargent
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Building a 904

#36 Post by Bill Sargent »

I had earlier promised to describe the suspension. I will attempt to do so here, but others with more knowledge please chime in. This post will cover the front suspension.

The 904 uses dual A arms up front with a suspension upright that was carried over to the 906. I believe the 904 front suspension uprights were cast Crome molly steel while the 906 front uprights were forged titanium. A period photo of the front suspension is shown below
Front suspension
Front suspension
Barrie Martin for may years modified early 911 front struts to make his front suspension uprights. A photo is shown below.
Modified early 911 front uprights
Modified early 911 front uprights
By 2016 the early 911 parts were getting expensive and hard to find. Barrie had a factory drawing of the front suspension upright so I put it in CAD for him. He then had T shaped forged chrome molly billets made to CNC machine the front uprights from. Photos below show the process for the front upright manufacture.

The first step after getting the front upright in CAD was to 3D print the parts and check that they were correct.
3D printed plastic front upright and steering arm.
3D printed plastic front upright and steering arm.
After this was done Barrie had the T shaped forged chrome molly billets made.
Forged billets
Forged billets
The spindle was first created using a lathe
Spindle machining
Spindle machining
The body of the upright was then machined on a 5 axis machine
Upright body machining
Upright body machining
The steering arms were made in a similar manner. A coupe of sets of the final product are shown below.
Completed uprights
Completed uprights
I mentioned earlier that the 906 used forged titanium front suspension uprights. A photo of one is shown below.
Forged Ti front upright
Forged Ti front upright
Original style ball joints and the suspension bushings (Flan Blocs) are still available.

The photo below shows complete front and rear suspension parts. Note that the larger curved front A arms are the later 906 style to allow use of wheels wider than the 5” ones used on the 904.
904 suspension parts
904 suspension parts
Thanks for following along. The next post will cover the rear suspension.
Regards,

Bill Sargent
#151489 59A Cab - Faux Cam
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#460603 67 912
904 clone in the works

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Joris Koning
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Re: Building a 904

#37 Post by Joris Koning »

Very impressive Bill. Thanks for sharing. I have some
Original dated Koni 904 shocks if you need any measurements etc. Not sure what shock options are these days
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Bill Sargent
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Re: Building a 904

#38 Post by Bill Sargent »

Hi Joris - If you have time, some photos would be interesting, Post them to this thread if possible. Koni still supplied a double adjustable shock that we will use for my build.
Last edited by Bill Sargent on Sun Nov 13, 2022 8:59 am, edited 1 time in total.
Regards,

Bill Sargent
#151489 59A Cab - Faux Cam
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#460603 67 912
904 clone in the works

Hanns Mueller-Rech
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Re: Building a 904

#39 Post by Hanns Mueller-Rech »

Bill,

perfect and impressive work, love the modern 5 axis to work on billets…all is possible nowadays…

br
haul

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Bill Sargent
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Building a 904

#40 Post by Bill Sargent »

I went to the LA Lit meet last weekend and, besides having a great time, pre ordered all the soft oil line fittings for the 904 oil system from Peter Hofmann of Classic Parts in Germany. He then brought them with him.

The majority of the 356 carrera soft oil lines use M22 fittings with the exception of the suction line from the oil tank to motor which is M26. The 904 upsizes everything so most fittings are M26 and the suction line fittings are M30. The 904 thermostat also differs from the 356 carrera one.

The 904, 906 and 917 all use the same 3 port thermostat that has M26 port threads. A similar thermostat was used on the 69 - 72 911S but the port threads were M22.

The 904 and 356 carrera use the same oil filter top cover but the cup and filter for the 904 are about 30mm taller. The same taller filter cup was used on the 911R.

Since the taller 904 type filter cups are very hard to find I plan to make a few using CNC machining. The originals were die cast aluminum do after a CNC machined one is tumbled it will look close to original. Send me an email if you want one and I will let those interested know pricing after I complete the CAD design.

Below is a diagram of the 904 oil system from the factory parts manual.
Oil system diagram
Oil system diagram
All but a couple of the fittings are shown in the photo below. The filter cup shown is a stock 356 carrera one borrowed from Jacques for the filter adapter project described in a separate thread.
Oil system parts
Oil system parts
We went to San Diego to fly home from the lit meet on Monday as prices out of LA Sunday were astronomical. We went to Tijuana Sunday evening for street tacos - they were fantastic! We took the trolley to the border, walked across and got a taxi to/from the taco place. Then walked back across to the US. The wait to drive into the US was 4+ hours! Here is the cook at the taco place.
Taco cook
Taco cook
And here is the car line to get into the US - 30+ lanes!
Border crossing line
Border crossing line
Regards,

Bill Sargent
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#159176 64C Cab
#460603 67 912
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Harlan Halsey
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Re: Building a 904

#41 Post by Harlan Halsey »

As I recall, the story was that Piech had a new suspension design for the all new 906. But Ferry Porsche pointed to a batch of left over 904 front suspensions and dictated, "use those."

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Bill Sargent
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Re: Building a 904

#42 Post by Bill Sargent »

Harlan - you are correct. The 904 and 906 use the same suspension components. Porsche had made suspension parts for a second run of 100 904s, but decided not to make them. Thus they had a lot is suspension parts.
Regards,

Bill Sargent
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Joris Koning
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Re: Building a 904

#43 Post by Joris Koning »

Harlan Halsey wrote: Thu Mar 02, 2023 6:27 am As I recall, the story was that Piech had a new suspension design for the all new 906. But Ferry Porsche pointed to a batch of left over 904 front suspensions and dictated, "use those."
Cool, learn something new every day
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Jacques Lefriant
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Re: Building a 904

#44 Post by Jacques Lefriant »

Hi Bill
did only the 906 and Werks 904 use needle bearings instead of Fanblocks?
j
 

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Bil Brown
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Re: Building a 904

#45 Post by Bil Brown »

I have a couple of original 904 alloy/steel wheels.....if anyone is looking.
Bill Brown

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