Another rear disc conversion question..... (1 Viewer)

[SMG]

Ok, so this has probably been asked before or maybe this would be a good question in the FJ80 section.

I am currently in the middle of a rear disc conversion on my 76 FJ40. Do I still need to run a proportioning valve if I am using a early 90’s FJ80 master cylinder?

One would think that because the FJ80’s came with disc on all for corners, that maybe it’s all ready built into the master cylinder.

Can someone please chime in that’s running this combo?

Thanks!!

Test fit.

 

[tstepp920]

Not to derail your thread but what kit are you using and what are you doing about a parking brake?

 

[tstepp920]

Tell me about the Rancho bump stops.

 

[TheOneKnownAsMe]

Not to derail your thread but what kit are you using and what are you doing about a parking brake?

Parking brake on the rear axle started on 8/80 and later models, right? So he should be fine on the parking brake assuming it's still located on the tcase.

 

[SMG]

Not to derail your thread but what kit are you using and what are you doing about a parking brake?

Actually, I water jetted my own bracket.

1980’s front Monte Carlo Calipers,

1993 front Chevy K1500 disc non- heavy duty. (had to bore out the center. It sucked!!!).

 

[SMG]

Tell me about the Rancho bump stops.

They’re red and made of some kind of poly material.

Ha ha! Just joking!

No really, I have no idea. Probably just a generic bump stop. I had to reposition them because of my SOA.

 

[SMG]

Parking brake on the rear axle started on 8/80 and later models, right? So he should be fine on the parking brake assuming it's still located on the tcase.

Yep, parking brake is on the back side of the transfer case.

 

[pjohnson]

I'm running a similar rear disk setup with an FJ80 non-abs master and no proportioning valve. It works well, hard to lock up the rear.

 

[SMG]

Ok, this is good to know. Thanks for your feedback.

 

[Bluegrass40]

Ok, this is good to know. Thanks for your feedback.

I have a similar setup as well on a ‘78. I ran a proportioning valve because based on my research. If I open the valve up all they way, the rears would lock up very easily.

 

[Bluegrass40]

Actually, I water jetted my own bracket.

1980’s front Monte Carlo Calipers,

1993 front Chevy K1500 disc non- heavy duty. (had to bore out the center. It sucked!!!).

View attachment 1713592

View attachment 1713593

Did you design the bracket yourself? Just curious. I did my own because I found that some of the files floating around were not very accurate.

 

[SMG]

I have a similar setup as well on a ‘78. I ran a proportioning valve because based on my research. If I open the valve up all they way, the rears would lock up very easily.

Are you running a early 90’s FJ80 master?

Thanks

 

[Bluegrass40]

Ok, this is good to know. Thanks for your feedback.

It was a non abs 80 master. Don’t remember the year. It may be in one of my threads. Been a while. I’ll try to look it up when I have more time.

 

[steffan]

A lot depends on what calipers your using and the weight bias/ transfer of the rig once it’s done. I going with the same set up so it’s nice to know that it’s a good balance right out of the box

 

[1911]

I need to buy an early FJ80 master. Converted my rears to disc years ago, and even with a proportioning valve (and my stock '79-80 master cylinder) the rear still locks up too easily.

 

[FJ40Jim]

I am currently in the middle of a rear disc conversion on my 76 FJ40. Do I still need to run a proportioning valve if I am using a early 90’s FJ80 master cylinder?
One would think that because the FJ80’s came with disc on all for corners, that maybe it’s all ready built into the master cylinder.

No, having proportioning built into the MC is extremely rare.

A prop valve will be needed because of the small front brakes and ginormous rear brakes.
The imbalance can be mitigated by upgrading to the bigger 4runner front calipers & pads with an aggressive semi-met pad, and using the cheapest ceramic pad in the rear.

 

[FJ40Jim]

I need to buy an early FJ80 master. Converted my rears to disc years ago, and even with a proportioning valve (and my stock '79-80 master cylinder) the rear still locks up too easily.

Changing from the stock 7/8" MC to a 1" MC is gonna increase pedal effort by 30%, but has no effect on bias. The MCs are all 50/50 bias.
Try increasing front brake effectiveness with bigger caliper & sticky pads.

 

[1911]

Changing from the stock 7/8" MC to a 1" MC is gonna increase pedal effort by 30%, but has no effect on bias. The MCs are all 50/50 bias.
Try increasing front brake effectiveness with bigger caliper & sticky pads.

OK thanks for that Jim. The front calipers are the Toyota ones that came on the truck from the factory; I imagine there must be much better ones out by now (that will hopefully still fit inside the stock 15" wheels?).

 

[SMG]

Ok, this make total sense.

Thanks guys for the input.

Wilwood 10mm Proportional valve on order.

 

[lone gunman]

I went with that same master cylinder on my 76 and used the tsm manufacturing rear disc kit but upgraded to 4runner calipers in the front and do not use a proportioning valve. no issues braking at high speed and it has worked fine for about 10 years now. and the 4runner calipers fit fine with my 15-inch wheels.