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Limited Slip advice, scrapping idea of RX7 rear end

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My only reservation about the RX7 rear end is the lack of choices of gear ratios. They are more limited than the stock sprite units. Since you have a 5 speed, it may not matter to you.
 
bugedd said:
So if I were to use a pedal box with 3 masters, where could I find one that is more affordable than the Speedwell unit? I'm torn with the options. I want limited slip, which will cost about a grand to put in the stock housing. Or I can spend the money on a pedal box with independent masters, use the RX7, and get LSD and disc. Which seems that will cost a grand.
I'm trying not to go down the slippery slope of endless modifications. I rebuilt a ribcase, put that in, wasn't happy with it and did the Datsun conversion. I'm not in the financial position to do things twice like I did there, so I need to make sure I do it right the first time.
Click to expand...

You can buy everything to do this for for under $500, the master cylinders are $80-90 each, the pedal assembly with balance bar about $200-250. I done three of these conversions, bascily you cut a little larger opening in the footbox top to drop the pedal thru, then built a sub structure to go on top of the footbox that levels the master cylinder and make a cover to cover holes. If you can work with metal and weld, not a terribly bad job. Here's a race car I did this to.

busterenginebay.jpg
 
That is one slick engine bay! I wish I had fabrication skills, but I am a nuts-and-bolts kinda guy. If it doesn't bolt up, I can't do it.
Fortunately Dan Gesick, a master fabricator/welder I know, is into doing the rear end mods for me for next to nothing. I don't think I can talk him into that project though.
 
This is what I did with my original pedal box and 2 series 74 Tilton 3/4" master cylinders. I think I paid about $70 for each MC kit and the modification was nothing more that sheet metal welded to each side.
HTH, Rut
 

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So... did anyone address the question about if you could use rx-7 calipers on the back with nothing more than a proportioning valve and a single brake master cylinder?
 
Like I said earlier, I managed to find a later model pedal box that someone had already modified by welding on an additional tab to the left side of the pedal box and making some modifications to the pedal arms. More fabrication work than I would want to do myself.

Tilton and others make a overhung pedal assembly that isnt terribly priced but it isnt a bolt in solution as you would have to come up with some method of mounting it.
$(KGrHqN,!okFCf+yY9FsBQ4CwB)OIg~~60_12.JPG
https://www.ebay.com/itm/Tilton-Ove...Parts_Accessories&hash=item4d08449795&vxp=mtr
 
BillW103 said:
Speedwell has one for a Spridget
Click to expand...

Bob Hubbard, long time Spridget racer used to make something similar to Speedwell, what I don't like about them is they still tilt the matser cylinders, what I built on the above race car levels the master cylinders.
 
Trevor Jessie said:
So... did anyone address the question about if you could use rx-7 calipers on the back with nothing more than a proportioning valve and a single brake master cylinder?
Click to expand...

Working from theory here, not experience, but I don't think a proportioning valve gives a linear pressure difference the way two masters and a balance bar does. The valve can prevent rear wheel lock when matched to the current traction, but it will not fix an unbalanced setup.

I suspect the RX-7 rear disk would be too much to run at the same pressure as the front, but you'd have to know the disk, pad, and piston size to be sure.
 
Rut,
Did you have to do anything with the pushrods on this set-up or did you use the originals? I was thinking of doing exactly what you did to simplify my system and get 'standard' parts.
I was originally excited to see the new 3/4" MC by TRW, then heard they aren't all that great. Then there are the usual issues with pushrod length, proper pistons....etc...etc..on the original MCs is enough to make me look at the Tiltons..and be DONE.

Thanks D
Rut said:
This is what I did with my original pedal box and 2 series 74 Tilton 3/4" master cylinders. I think I paid about $70 for each MC kit and the modification was nothing more that sheet metal welded to each side.
HTH, Rut
Click to expand...
 
64rocksprite said:
Then there are the usual issues with pushrod length, proper pistons....etc...etc..on the original MCs is enough to make me look at the Tiltons..and be DONE.

Thanks D
Click to expand...

Devin,

In case you weren't aware, I worked out all those details years ago using original Lockheed MC's. Your original MC will come back to you better than new, brass sleeved, (eliminates corrosion issues) and with 2 new, precision correct alloy pistons, completely assembled with new seal kits, gaskets and button head screws. New cad plated, correct length pushrods are also available separately.

More info here:

https://gerardsgarage.com/Garage/Tech/DbrakeUg.htm

LockheedPushrods2.jpg
 
The Tilton 74 series come complete with the pushrod and they screw in like the originals. The internal spring on the MC is strong enough that you won't need an external spring either. I measured the distance with the pushrod screwed half way into the yoke on the pedal and used that for my mounting mark. Next time I would take a spare pedal box (bugeye) and cut it out enough to drop the MCs a little lower in the rear to level them out. My pedal box is not very professional looking and I did it the quick, easy way.
Rut
 
Thanks Rut and Gerard.
Gerard - I was aware of your services..very nice bit of engineering. It is (rightfully so) a bit more than two new Tiltons..I guess it will come down to how concerned I am on originality. Building a new pedal box is just metal and welding..which I've gotten pretty decent at. I'll PM you for more detail on my situation.
 
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