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Rx7 Steering rack swap... into a volvo

Posted by Eric Ewert 
Eric Ewert
Eric Ewert
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Rx7 Steering rack swap... into a volvo
November 06, 2015 09:32AM
...Specifically stuffing a FC rx7 rack into a volvo 240

I have had this idea in my head for a while for a few reasons. I know that the xr4 rack swap has been done successfully but despite having one I rather not go this route simply because of the lack of availability if I do manage to kill one. No a rx7 rack isn't exactly common but they still way more common than a merkur rack will ever be.

That aside they are closer dimensionally from what I read. Also by the looks of it the mounting system is very similar to stock volvo rack, it might work out that minimal modification is needed to bolt it in.

here are some specs I found.

Rx7

Rack & Pinion Type Power Steering
Rack Length 47.5
Total Turns Lock To Lock 2.75
Steering Input Shaft Type Splined, Grooved
Inlet Size 12mm X 1.25
Inlet Attachment Type O-Ring
Outlet Size 16mm X 1.5
Outlet Attachment Type O-Ring
Tie Rod Ends Included Inner

Volvo 240

Rack & Pinion Type Power Steering
Rack Length 46.75
Total Turns Lock To Lock 3.5
Steering Input Shaft Type Splined, Whistle Notch
Inlet Size 14mm X 1.5
Inlet Attachment Type Banjo
Outlet Size 16mm X 1.5
Outlet Attachment Type Banjo
Tie Rod Ends Included Inner

XR4
Rack & Pinion Type Power Steering
Rack Length 49.88
Total Turns Lock To Lock 2.75
Steering Input Shaft Type Splined
Inlet Size 10mm X 1.5
Inlet Attachment Type Manifold
Outlet Size 12mm x 1.5
Outlet Attachment Type Manifold
Tie Rod Ends Included Inner

So what I need is...

RX7 inner and outer tie rod thread/ pitch
Volvo 240 inner and outer tie rod thread/ pitch

If any of the threads are the same between the two it could end up being fairly straight forward. So if anyone knows either please share!
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Robert Culbertson
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Re: Rx7 Steering rack swap... into a volvo
November 06, 2015 09:56AM
I've looked into all sorts of racks to stuff into a ovlov to make it steer a bit quicker. The main problem is that the outer tie-rod is a loooooong ways from the centerline of the strut/lower ball-joint. So the Volvo rack is already a "quick" rack in terms of mm of rack travel per turn of the steering wheel (xratty is better, but those racks are not exactly common).
If you can move the tie-rod end closer the the knuckle, you would be miles ahead (same fab work as mounting a different rack, at least in my eyes)

Why not just mount up a steering quickener? There's a nice little spot where the stock Volvo steering damper thing is under the brake MC. The quickener will fit in there with room for the steering u-joints..... just a thought
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john vanlandingham
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Re: Rx7 Steering rack swap... into a volvo
November 06, 2015 10:11AM
Are RX-7 racks "common" enough to be considered "common"?
Seems everything old and rear drive is getting less common.


The thread on inner and outer tie rod assembly is same on Volov ZF and Xratty.

Eric you say you are worried "what if something happens"..

Have you made any efforts to find a spare Xratty rack?
Any?
Called Matt to get Pat Hoodgendycks number?

If you haven't done any effort to find a spare, seems like expending effort to try and adapt some completely different thing is maybe premature..maybe..

Now Culbertson we would expect to waste lots of time searching for all kindsa racks, that's what he does, he has to, he is convinced he has the ONE true answer to everything.. in advance, before the problem even enters his consciousness. He even says he likes to find involved, tricky solutions to simple problems..time and effort mean nothing to him.

But you....I am confuse.



John Vanlandingham
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Robert Culbertson
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Re: Rx7 Steering rack swap... into a volvo
November 06, 2015 10:29AM
Quote
john vanlandingham

Now Culbertson we would expect to waste lots of time searching for all kindsa racks, that's what he does, he has to, he is convinced he has the ONE true answer to everything.. in advance, before the problem even enters his consciousness. He even says he likes to find involved, tricky solutions to simple problems..time and effort mean nothing to him.

But you....I am confuse.

Ha. The RX7 rack is something way beyond what I would do. I can't think of the last time I've seen an rx7, or an xratty, in the junk yard.

I don't always search for the tricky and involved solution. It's actually the opposite. Sometimes the simple solution has one KEY element that it needs to work, and that is the tricky part (geometry, design, materials... It's what I do for a living).

I actually like very simple and elegant solutions. Grafting in a xratty rack is pretty straight forward, except they're a little hard to come by. The steering quickened is $150 with the adapters, and it'll basically drop in. You also get to keep your Volvo rack, which you can order through any autoparts store, or pull one from a junker.
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Eric Ewert
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 03:39PM
I considered the quickener but dumped the idea because I was concerned about it causing play in the steering. That being said it may be worth a revisit.

John no I haven't bothered to look into a spare. I know you have mentioned your xr4 friend may have one. But Im not going to be getting one until I am decided on what route to go.

Also you said volvo and xr4 tie rods have same thread... what is that thread size/ pitch for inner and outer?

Robert your idea on moving the outer tie rod is an interesting idea, but correct me if Im wrong but aren't the volvo knuckles cast iron? In other words isn't welding to them a bit of a no-no?

I will say it again on the availability... no the rx7 isn't what I would consider common but it is miles ahead of the xr4 for availability. Around here they do show up in pick n pull from time to time. I have never seen an xr4 and only one scorpio.
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tdrrally
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 03:43PM
is the volvo front steer or rear?



I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!
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Eric Ewert
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 03:50PM
I assume this means rack at the front or rear of the cross member. Its at the front.
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Pete
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 04:39PM
C4 Corvettes are also front steer, and they are around 2 turns lock to lock real world.

I have a real world RX-7 rack, the "fast" power rack (there were two flavors), and it's not 2.75. It's a little over 3 turns. It's actually slower than the power recirculating-ball unit I took out.



Pete Remner
Cleveland, Ohio

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1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 11/08/2015 04:41PM by Pete.
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tdrrally
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 05:25PM
fox mustangs racks are front steering as are pinto and very easy to get for not much money
The 87-93 5.0 rack is 2.25 turns lock to lock.
autozone lists them for $75 plus a $20 core
http://www.autozone.com/suspension-steering-tire-and-wheel/rack-pinion/duralast-rack-pinion/ford/mustang-cobra/1993/8-cylinders-d-5-0l-sfi-ohv-ho/261058_0_6207_2368/

http://www.maximummotorsports.com/tech_steering_rack.aspx



I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!
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Eric Ewert
Eric Ewert
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 07:33PM
All interesting ideas but without actually knowing the steering ratio, or better the travel per turn its all questionable if there is an improvement to be had.

I can have 2.5 turns lock to lock with the volvo... just need to reduce the travel. It could be 400:1 ratio with 2.5 turns lock to lock.

If memory is correct volvo is 17.2:1 and 55mm of travel per turn.
Xr4 is 64mm of travel per turn. No idea what ratio but point is it is significantly faster.
FC rx7 has a 15.2:1 ratio.

What im confused by is if the steering ratio is influenced by the steering geometry or if it is solely based on the speed of the rack itself.
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tdrrally
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 07:46PM
if i recall moving the outer tie rod closer to the centre line of the spindle makes it quicker (some) but will increase steering effort (less leverage)



I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!
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Robert Culbertson
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 08:47PM
The "fast" mustang racks are slower than the XR rack. Flaming river lists total rack travel as well as the number of turns lock-to-lock.

The play can be adjusted out very easily on the quickeners. You just change the mesh on the gears.

The Volvo knuckles/spindles/uprights are cast STEEL, not iron.
Dorifto kids shorten and weld them all the time (it's really common on Nissan 240s). The downside is that it changes the steering geometry (but I don't know what the effect is).
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alkun
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 08:47PM
I usually try to keep an open mind but this is a silly waste of time. I have the quickener in my volvo and it works perfectly. I think monkeying around with steering racks is a bad idea; if any of the mounting brackets, cobbled together tie rods or steering shaft has a problem you could get seriously fucked. Racks from 240 are plentiful, practically free and work just fine with a quickener, why make your life more difficult?



There. I said it.
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tdrrally
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 09:19PM
Quote
Robert Culbertson
The "fast" mustang racks are slower than the XR rack. Flaming river lists total rack travel as well as the number of turns lock-to-lock.

The play can be adjusted out very easily on the quickeners. You just change the mesh on the gears.

The Volvo knuckles/spindles/uprights are cast STEEL, not iron.
Dorifto kids shorten and weld them all the time (it's really common on Nissan 240s). The downside is that it changes the steering geometry (but I don't know what the effect is).

we did all the time on stock builds and the odd BMW too. it did require bump steering the to get things back in order.

there is a charm in running oe as delivered from the factory, low fuss low muss and go



I would rather drive a slow car fast as a fast car slow!
first rule of cars: get what makes you happy, your the one paying for it!
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john vanlandingham
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Re: Rx7 Steering rack swap... into a volvo
November 08, 2015 09:21PM
Quote
Pete
C4 Corvettes are also front steer, and they are around 2 turns lock to lock real world.

I have a real world RX-7 rack, the "fast" power rack (there were two flavors), and it's not 2.75. It's a little over 3 turns. It's actually slower than the power recirculating-ball unit I took out.

Be interesting to know:

rack travel in mm per turn XR is 64mm, Volvo is 55mm
Tie rod end taper and nut size
outer tie rod thread Both Xratty and Volvo are M14 x 2
Inner tie rod thread and male or female.. Both XRatty and Volvo ZF racks are male M12 x 1.25

The actual diameter of the tie rod...

The nice thing with the Xratty rack is it is good enough at 2.65 turns, and with the tir rod stuff being same, between various Volovs and Xratties and Scorpios you have a variety of tie rod lengths and can use the Volvo tie rod end so the taper is correct so that requires no fucking with.
Jap tapers are invariably different and usually much smaller.

Now Eric and Culbertson both say they can't find more Xratty racks....Neither has bothered to ask the one person here who is the supposed Xratty and volvo 240 evil genius and who daily for years ? 20+? years talked to people all over USA, Canada and beyond..
Kinda ironic when on the South side of Calgary is a helpful friendly guy that the other good guy in the Calgary area Matt got 2 nice cars that I set him up with for only $800.
Have you called Pat, Eric.

Culbertson we expect to not call because he know better and can figure out everything himself

--but he strikes out...
Wonder how many are needed?

This is not a thing anybody needs to worry about at the level of development all the country's 240 guys are at---which means they have time to liesurely find a couple of racs and get them freshened up..Planning = happiness.

Oh well.



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
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