Straight Axle Problem

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J

JTinAZ

Joined
Jul 12, 2004
Threads
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148
Two weeks ago, I called Alma Imports in Mesa and found out it had a straight axle from a 1984 4Runner for a disc brake conversion on an FJ40. Went today to get it, but it was gone. I called around and have not been able to find another one, except from Toyota Salvage for $400. Alma Imports was selling theirs for $250. Anyone have any suggestions where I can find another one? A friend and I were planning to do the coversion in two weeks. He is coming out from Michigan, and I already requested the tie off. By the way, I just sent in my application to join the club. Thanks.
 
Rush--Thanks for trying to help out. Turned out I found an axle today. Spent $300, but I am kind of short on time. It's kind of rusty, because the truck is from Wisconsin. I might buy a sand blasting cabinet because everything has a crust of rust. I will be starting the job on Sunday, 1-22 if anyone is interested in checking it out. I am asking anyone to pitch in on the work, so please don't be afraid to show up. It would be nice to see someone who had done this to their truck just to get some tips. If anybody is interested in just watching, that would be cool also. I live in Mesa near McKellips and Country Club. I am finally trying to get this truck running. It has been sitting for almost a year now, because it didn't pass emissions. I will work on that stuff in February, but the front axle leaks so much grease into the drums, I need to get it fixed to make it safe to drive. Might as well do a disc brake conversion since I need to tear into the axle anyway. Anyway, thanks again.
 
disk swap

RUSH55 said:
You're swapping the whole axle or just the hubs, Birfs and brakes? Just cause its leaking grease or oil doesn't mean you have to swap the whole unit.
Click to expand...

I am planning on the same swap, I but I decided to put it off as my drums work fine. Besides the birf on out, you need the master cyl and proportioning valve from a 40 w/ disks, or get it all from the mini. I'd like to know how it all turns out.
 
I am just doing hubs, birfields and brakes. From the websites detailing this procedure, I didn't see a need for a different master cylinder and proportioning valve. But if that's the case, I guess I will need to go out and get those. I will look into this in more detail. Thanks guys. I will let you know how this turns out.
 
You need the proportioning valve only if you have disks in both front and rear. If you are just doing the front conversion to disk, the only thing you need to make sure to eliminate the residual pressure valve for the front (it sits in the master cylinder where the brake line attaches, take it out). Disk calipers don't work with residual pressure. Once you convert the rear to disks, the brake power of the rear calipers has to be less than the front, and that's why a proportioning valve is installed in the rear brake line. Just did the rear disk conversion two weeks ago. :D
 
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I think you're all insane! Drums have short commings agreed but all and all I wouldn't go through much trouble at all to do the swap, just don't see it being worth the time... I honestly sorta like drums, and I surely don't like disks so much more I'd pay to change to them...
 
Thank you for your opinion, I just hope I won't be in the way on any of your braking paths. So, are you implying the whole auto industry, by switching to disks is only doing so to promote crashes and sell more cars?
 
For me the swap is worth it just for the maintenance issue, the early double wheel cylinder drum brakes are a pain to adjust and maintain. Not to mention much better stopping power with disks.
 
collecting parts for the disk swap

DSRTRDR said:
You need the proportioning valve only if you have disks in both front and rear. If you are just doing the front conversion to disk, the only thing you need to make sure to eliminate the residual pressure valve for the front (it sits in the master cylinder where the brake line attaches, take it out). Disk calipers don't work with residual pressure. Once you convert the rear to disks, the brake power of the rear calipers has to be less than the front, and that's why a proportioning valve is installed in the rear brake line. Just did the rear disk conversion two weeks ago. :D
Click to expand...

Hi Claudia,
I am collecting parts for the swap and thought I needed a proportioning valve for two main reasons. Disks require much greater pressure than drums, given the lower surface area present to apply the friction. So all else being equal the valve must shunt more pressure to the disk axle than the drum axle.

Second, equal pressure should not be applied to both axles. Even if the disk brakes were designed in such a way (e.g. size or mechanical advantage) that results in equal friction w/ the drum axle, you still need a valve because the front axle does more stoppping than the rear as the front axle loads up and vehicle rear lifts up during stopping. This second condition will only exacerbate the former problem. I supposed these were the reasons every vehicle I have owned w/ disk/drum setup had proportioning valve installed at the factory. That’s why I thought to just grab one off a disk brake 40 and have the factory-like setup.

Please let me know if I don't need the valve. It very well may be the case the mini-truck swap just happens to work well w/o the valve given this particular case (load distribution, wheelbase, calipers etc.)

thanks
:cool:
 
What would happen if you install a proportioning valve even if it's not required?
 
mike_az said:
Hi Claudia,
I am collecting parts for the swap and thought I needed a proportioning valve for two main reasons. Disks require much greater pressure than drums, given the lower surface area present to apply the friction. So all else being equal the valve must shunt more pressure to the disk axle than the drum axle.

Second, equal pressure should not be applied to both axles. Even if the disk brakes were designed in such a way (e.g. size or mechanical advantage) that results in equal friction w/ the drum axle, you still need a valve because the front axle does more stoppping than the rear as the front axle loads up and vehicle rear lifts up during stopping. This second condition will only exacerbate the former problem. I supposed these were the reasons every vehicle I have owned w/ disk/drum setup had proportioning valve installed at the factory. That’s why I thought to just grab one off a disk brake 40 and have the factory-like setup.

Please let me know if I don't need the valve. It very well may be the case the mini-truck swap just happens to work well w/o the valve given this particular case (load distribution, wheelbase, calipers etc.)

thanks
:cool:
Click to expand...

Here's the deal, having converted my '40 to 4-wheel disk:

1. Drum brakes have a residual pressure valve (in order to prevent the springs in the drum to pull the shoes too far from the drum) - not to be confused with a proportioning valve. Disk brakes (in most cases) won't need the residual pressure valve, actually, you'll wear the pads quickly by having them too close to the rotor. But there are many combinations out there, some vehicles combine residual/prop (e.g. 1/2-ton Chevy), others have them separate (e.g. load-sensitive prop valves on higher-rated pickup trucks, etc.)
2. If you convert the front to disk, the residual pressure valve in the front brake circuit at the master cylinder needs to go. It's behind the big fitting that holds the brake line.
3. If you convert the rear, ditto. The residual pressure valve needs to go, rear circuit at the master (I hope you have a dual circuit master for safety reasons; if not, I'd sure get one).
4. The brake system needs to be calibrated so that the front brakes lock before the rear brakes do. In a disk-front-drums-rear setup, the front will lock before the rear without any prop valve, due to the superior stopping power of disk brakes.
5. Once you convert the rear brakes to disk as well, it was our experience that the rear will lock up way before the front brakes do - this was with a dual circuit master and no modification other than taking the residual pressure valves out of both circuits.
6. To correct this - i.e. to make the front lock before the rear does - we needed a proportioning valve that decreases fluid delivery to the rear and therefore brake power to the rear. We used a Wilwood valve, installed at the Master in the rear circuit outlet with a series of fittings (to go from NPT via -AN to Toyota metric inverted flare). I believe you can get a similar valve a bit cheaper from Summit Racing, and you don't need the -AN etc. fittings if you know how to make a double flare for a brake line; the Wilwood valve is for standard 3/16" brake line inverted flare, and it needs to mate up with the Toyota metric 10mm x 1.0 inverted flare threads.
7. The rear does not need more flow, and it doesn't need equal flow, it needs less.
8. We dialed in the setting on the prop valve simply by going on a dirt road and check which axle locks up first when braking from about 10mph, then adjusting the valve until we were satisfied with the setting. Without the valve (or in our case with the valve fully open), the rear axle would lock up on dry pavement. Drums were not even close to that kind of stopping power, it's not even funny. In addition, disks don't fade - if you've ever driven a trail like Hell's Revenge in Moab, you'll know what I mean by fade.

If you need more info or part numbers for the fittings, feel free to PM. If you want to see the prop valve setup, you may have to ask Tools for a picture....:grinpimp: :grinpimp:
 
Claudia--Thank you for your excellent input on this matter. As far as sonoranfun goes ... to each his or her own. I prefer disk brakes. After I get the front axle finished, it's off to the emissions issues. Then possibly the rear brakes. This truck was not safe to drive with grease all over the inside of the right front drum.
 
Also, any recommendations on what grease to use on knuckles, bearings, and hubs? Thanks.
 
Ok here's what I plan on doing sometime (got side tracked with these old FJ25s). Over the years I picked up a mini axle and a 76-78 axle, plus the master cylinders with the booster from the 76-80 model FJ40s. These master cylinders do have prop valves on the brake line right after leaving the master cylinder. If you check SOR web site and look at brake lines you will see it shows a prop valve for 76-80 models part #60 (disk brakes and dual wheel cylinders). I plan on keeping the rear brakes stock so this setup should work for me. Just my .02


John
 
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