Converting rear drums from 9mm to 10mm (1 Viewer)

Joined
May 26, 2007
Messages
590
Location
Baton Rouge, LA
I'm about to start a disc brake conversion on my '70 FJ40. I just purchased the knuckles for a FJ60 from a fellow mudder and have a mini truck booster and a master cylinder from a 4Runner.

Since my truck currently has the original single circuit brake setup I'm obviously going to have to build a whole new set of brake lines. I'm ready for that. The last detail I have to work out is tying the new (10mm) brake lines into my existing drums, which are plumbed for the original 9mm lines.

What parts do I need to replace on my rear drums to convert them to 10mm? Can I just swap out the cylinders from a later truck?

For the record: yes, I did a search before posting this question!
 
Joined
Aug 11, 2004
Messages
457
Location
Burlington, VT.
 
 
 
I took one of my 9mm fitting to the local parts store and bought a few 10 mm adapters. So the 9mm fit into the wheel and the new brake line with the 10mm fitting threads right in. Easy and cheap fix.

Good luck
Albee
 
Joined
Jan 2, 2009
Messages
205
Location
Gillsville, Ga.
Sweet...
My son and are doing almost the same thing. In fact, we re-arranged the basement garage just last night to do the work.

I'd like to see the single to dual circuit done.... and follow along if you plan on posting what you do. ??

In FAQ's... (faq has been very helpful to me btw)
https://forum.ih8mud.com/40-55-series-tech/117559-69-older-9mm-brake-line-adaptors-faq.html

And this via search.
https://forum.ih8mud.com/40-55-series-tech/154402-best-place-buy-brake-parts.html

Also been watching this thread.
https://forum.ih8mud.com/40-55-series-tech/269434-72-fj-55-buildup.html

Guppie's build has been helpful too...

Good luck with it!
 
Joined
May 26, 2007
Messages
590
Location
Baton Rouge, LA
I took one of my 9mm fitting to the local parts store and bought a few 10 mm adapters. So the 9mm fit into the wheel and the new brake line with the 10mm fitting threads right in. Easy and cheap fix.

Good luck
Albee
Thanks for info. I'm really fired up that something is actually going to be easy and cheap-- so far everything else I've done has been complicated and expensive!!!!
 
Joined
May 26, 2007
Messages
590
Location
Baton Rouge, LA
Thanks for all of the great advice. Would there be any problems if I used the adapter between the flex line and the original tee fitting on the rear axle, and kept the 9mm lines from the tee to the wheel cylinders? Or will the fact that the rear brake lines are smaller than the lines upstream from the tee present some problem with the hydraulics?
 

liko

SILVER Star
Joined
Jul 28, 2006
Messages
199
Location
Hilo, Hawaii
 
 
i think the brake lines are actually the same diameter, just the fittings are diffrent, so should be no problem, but if someone knows otherwise, they will chime in.....
 
Joined
Feb 24, 2004
Messages
1,628
Location
Monroe, WA
 
 
 
If you're not going to change the rear brakes at all, there is no reason to even touch or convert anything behind the engine bay.

When I did my single- to double-circuit conversion, I disconnected the brake line that runs to the rear axle at the RF shock mount. I left that line basically intact and bent it to run straight up the firewall. I cut the end off the hardline, slid on a 3/16" flare nut and flared a new end on it so that it would connect directly to the proportioning valve.

I built a new hardline to connect the rear circuit of the new master cylinder to the proportioning valve right across the top of the firewall.

For the front circuit, everything is already in place. You just need to either plug the empty port on the junction block by the shock mount, or disconnect the other two lines from it, and join them. I found a plug, but I don't recall where it came from.
 
Joined
May 26, 2007
Messages
590
Location
Baton Rouge, LA
i think the brake lines are actually the same diameter, just the fittings are diffrent, so should be no problem, but if someone knows otherwise, they will chime in.....
Man, that piece of information makes my life a whole lot easier!!!

If you're not going to change the rear brakes at all, there is no reason to even touch or convert anything behind the engine bay.

When I did my single- to double-circuit conversion, I disconnected the brake line that runs to the rear axle at the RF shock mount. I left that line basically intact and bent it to run straight up the firewall. I cut the end off the hardline, slid on a 3/16" flare nut and flared a new end on it so that it would connect directly to the proportioning valve.

I built a new hardline to connect the rear circuit of the new master cylinder to the proportioning valve right across the top of the firewall.

For the front circuit, everything is already in place. You just need to either plug the empty port on the junction block by the shock mount, or disconnect the other two lines from it, and join them. I found a plug, but I don't recall where it came from.
Okay, based upon liko's bit of information I had already decided to simply keep the rear lines from the firewall back. But I'm still curious about whether keeping the front lines is the right play.

On an early 40 (mine at least) the flex line attaches to a frame mount right above the axle. But it seems like this is the point of maximum movement of the axle relative to the frame, which means that the flex lines are going to get worked here more than any other location.

I'm planning on making new front lines anyway, so what is the "best" layout/routing? Or should I just get long enough flex lines and not worry about it?
 

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