1985 Series 3 restomod with s5 13BT on LPG, R&P steering

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gt_james
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by gt_james » Tue Apr 11, 2017 12:18 pm

When I was researching it didn't look like T2 brakes fit under 14" wheels, although you can probably use NA FC brakes. All UK FCs were 5 lug I believe.

I don't think Id ever have anything to do with ACBRON again if I can help it. Even if the quality of his work is very good, his lead times are too long for me.

I would like to try Aran's barina/corsa rack method one day, although instead of welding tabs to the existing cross member, I would like to fabricate a tubular cross member for the rack

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KYPREO
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by KYPREO » Tue Apr 11, 2017 1:21 pm

I don't what specs your FCs were, but all of ours (turbo and NA) had the 276mm rotors and 4 piston calipers. This will require 15 inch wheels minimum (depending on the wheel). 14 inch not a chance

I am going with the FD brakes. Calipers have the same pad size and piston diameter, they are just nicer looking and a bit more compact, which will make them easier to fit with my particular wheels. Rotors are 294mm diameter. These require 16 inch minimum to fit (depending on the wheel).

The single piston calipers that came on the NA FCs in the US were actually identical to s3 brakes. This is what makes the hubs great - you can use alloy hubs with 4x114.3 pattern and keep series 3 size brakes that will fit the stock 14" wheels. It would probably still require some custom caliper brackets so that you can use the s3 brakes on the FC strut bodies. I haven't thought too hard about it though. I would've gone this option had I stuck with 14" wheels.

A bit of interesting trivia. All RX-7 brake pads from 1984 to 2002 are the same, front and rear, even though the caliper and rotor configuration evolved throughout.

That tubular crossmember idea looks great too. Shouldn't be too hard to fabricate really if you know someone who can weld (or do it yourself). Arran documented the other aspects of the conversion pretty well. A lot of it involves simply bolting together off the shelf components. The hard bits are steering rack mounts and fabricating a bracket for the steering column.

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gt_james
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by gt_james » Tue Apr 11, 2017 1:43 pm

How Did I only just find out that all RX7 Brake pads front and rear are the same from S3 up to S8? is that definitely true? if so that makes lots more brake pads available :D

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KYPREO
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by KYPREO » Tue Apr 11, 2017 2:15 pm

gt_james wrote:How Did I only just find out that all RX7 Brake pads front and rear are the same from S3 up to S8? is that definitely true? if so that makes lots more brake pads available :D
I wanted to be sure so I went back and checked.I got confused and misspoke. :oops: The front pads differ in mounting configuration, but surface area is similar and the front disc thickness is the same - this is where I got confused.

The rear calipers are all the same basic design with same piston size - only minor differences like where the handbrake cable hooks up etc. Rotors are all the same thickness, they just got larger diameter with each generation. Even the series 8 RZ/Type RS/Spirit R which had the massive 314mm cross-drilled rotors still had the same basic rear caliper specs as the series 3 RX-7.

Depending on the manufacturer, the rear brake pad has a different part number but the shape looks the same and they are all listed as 107x39mm by 13mm thick. Most manufacturers don't even list s3 RX-7 so it's hard to say definitively. The ones that do, show the same dimensions. So I am fairly certain they are interchangeable (but can't say I have personally done it).

Apologies for going all guns blazing and getting your hopes up.

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gt_james
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by gt_james » Tue Apr 11, 2017 2:32 pm

No worries, Easy mistake. So to confirm fronts are different between S3/4 to S5-8?

And Rears are interchangeable from S3-8

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KYPREO
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by KYPREO » Wed Apr 12, 2017 12:19 am

gt_james wrote:No worries, Easy mistake. So to confirm fronts are different between S3/4 to S5-8?

And Rears are interchangeable from S3-8
Front: series 3 is the same as series 4/5 NA with the single piston calipers and 4 stud wheels (only came out in the US as far as I know). See eg http://www.hawkperformance.com/performa ... 152e540-38

Series 4/5 turbo with the 4 piston calipers and 5 stud wheels are the same as s6-8.

Rear: correct. Interchangeable s3-8. They're also the same as some Mazda 3 and Mazda 6 models. See eg: http://www.hawkperformance.com/performa ... /hb158z515

One of the sources of confusion is that in the US and Japan there were 2 specification levels for wheels in brakes in 84-85 models: (1) small brakes and 13" 4x110 wheels like the 81-83 models; and (2) large brakes and 14" 4x114.3 wheels. UK and Australia only got version 2. So when you look up brake parts etc, you get a lot of info for the US lower spec models.

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KYPREO
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by KYPREO » Sun Apr 23, 2017 10:02 am

Some more progress. Modifications to the FC subframe are complete. Unlike the write-ups of the FC conversion you'll see on the internet which essentially bolt on the subframe, mine looks like this:
JPEG_20170423_165222_601695652.jpg
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Basically, extra metal has been added to the front chassis attachment points with new bolt holes drilled. This allows the subframe to be bolted to the factory 1st gen crossmember mounting point, but 20mm further back to restore the factory axle centre line. The angle of the mounting face is altered also to allow the rear of the subframe to sit slightly lower (explained further below):
JPEG_20170423_165243_1062794803.jpg
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The rear of the crossmember then has 2 new mounts added. These attach to the factory steering box and idler arm pointing points but also tilts the back of the subframe sown slightly. This way, ride height, engine and transmission sit as per factory;
JPEG_20170423_165302_1335500665.jpg
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Now to mate the 1st gen and 2nd gen steering column together. This will apparently be a bit fiddly, but it will retain factory steering wheel position and retain collapsability for safety and engineering compliance.

Then we'll dummy up everything and assuming it all sits right, bits will then go off to the powdercoater.

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ian65
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by ian65 » Sun Apr 23, 2017 1:23 pm

this is awesome.... if it solves most of the alignment issues right from the start it will be a great mod... the only reason i haven't done mine is that no-one seems to have definitely solved the issues the fc subframe swap throws up. This is very cleverly thought out though.
Can you explain a bit more about the front mounting point... I can't quite picture it. I get that the subframe mounts 20mm back to centre the wheel but how have you used the FB front mounting point? Redrilled the front holes on the FC Subframe?

Regarding the steering column, it's worth considering trying to get a column from a PAS car from the USA... they make it a doddle to mount up plus they have the factory shear pins still in place... you can see one here...

http://www.rx7fb.com/viewtopic.php?f=8&t=275

.

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KYPREO
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by KYPREO » Sun Apr 23, 2017 2:01 pm

ian65 wrote: Can you explain a bit more about the front mounting point... I can't quite picture it. I get that the subframe mounts 20mm back to centre the wheel but how have you used the FB front mounting point? Redrilled the front holes on the FC Subframe?
No problem. the subframe isn't actually long enough. So, a new section is welded on to the subframe to effectively extend the mounting face further forward:
JPEG_20170423_225231_1911480012.jpg
JPEG_20170423_225231_1911480012.jpg (44.65 KiB) Viewed 1599 times
This newly added section was then shaped and a new hole drilled to end up like the end product i posted earlier.
Regarding the steering column, it's worth considering trying to get a column from a PAS car from the USA... they make it a doddle to mount up plus they have the factory shear pins still in place... you can see one here...

http://www.rx7fb.com/viewtopic.php?f=8&t=275

.
I was not aware of this! Thanks very mich and great to know. It may not work out cheaper in the end for me but it would certainly help others. And you can still use LHD so finding a GSLSE one is actually doable. The Jap ones are very hard to find.

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ian65
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Re: 1985 Series 3 restomod with s5 13BT on LPG, R&P steering

Post by ian65 » Sun Apr 23, 2017 2:07 pm

thanks, got it now th: The FB has a pair of studs on each chassis rail to mount the crossmember... do you use all 4 studs?

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