FJ80 MC swap problems

[BadlyBent]

I recently installed an FJ80 MC in my 71 FJ40 (4 wheel discs) when the stock MC failed. After some challenges with bench bleeding the MC I thought I had it nailed.

After an initial test drive, noted lots of drag. There is virtually no pedal play. I raised the front and rear up and noted major drag on all 4 wheels (hard to hand turn). Drove a bit more and as the brakes warmed, so did the drag - major league - actually nearly locks up only to "loosen" as the brakes cool.

I removed the MC and adjusted the piston from the booster to see if backing it off a bit would make a difference - no luck.

I did retrofit the old MC to see if I could figure out what was going on - seems the cup is deeper in the original MC, but I'm not sure that's the issue.

 

[Poser]

If when you put the master cylinder up to the brake booster, you can feel that rod pushing into the master cylinder piston, at all, this will cause drag.


Back the nuts off that retain the master to the booster and move the master away from the booster and see if you can rotate your tires.


Can you please post up some pictures of your master cylinder and brake booster?

 

[mr_manny]

Adjusting your Booster/Actuation rod:

Unbolt the MC, allowing access to the Booster-Rod.
Push the Booster-Rod into the Booster (towards the fire wall), now pull it out about a 1/4 inch.

Place your MC flush w/the booster.
I don't think It's necessary to install, as long as it is tightly placed against the booster. Now remove the MC so you have access to the BR.

Using your fingers, carefully push the BR back into the Booster.
If It does NOT move, it needs to be Adjusted.
I would say 1/8 clearance would be enough, but YMMV.

Your Brake Pedal also has an adjustment.
I believe the Toyota manual indicates 1/2" clearance (before it engages the brakes).

manny

 

[BadlyBent]

Adjusting your Booster/Actuation rod:

Unbolt the MC, allowing access to the Booster-Rod.
Push the Booster-Rod into the Booster (towards the fire wall), now pull it out about a 1/4 inch.

Place your MC flush w/the booster.
I don't think It's necessary to install, as long as it is tightly placed against the booster. Now remove the MC so you have access to the BR.

Using your fingers, carefully push the BR back into the Booster.
If It does NOT move, it needs to be Adjusted.
I would say 1/8 clearance would be enough, but YMMV.

Your Brake Pedal also has an adjustment.
I believe the Toyota manual indicates 1/2" clearance (before it engages the brakes).

manny

Manny,

Thanks for the advice. I adjusted the booster rod all the way down prior to getting this response (screwed the acorn nut down so no threads showing). Still no play. I will try the technique described above; though, I'm not sure where I'll get any extra play since I've adjusted the thing to its minimum length.

I also adjusted the brake pedal using the adjuster - still tight. I get 1/2" max play before I engage.

Mark

 

[BadlyBent]

If when you put the master cylinder up to the brake booster, you can feel that rod pushing into the master cylinder piston, at all, this will cause drag.


Back the nuts off that retain the master to the booster and move the master away from the booster and see if you can rotate your tires.


Can you please post up some pictures of your master cylinder and brake booster?

Steve,

Thanks for the advice. I greatly appreciate the response. Will do the above today and try to get some photos up. Will also try Manny's advice and let you know.

Mark

 

[BadlyBent]

Steve,

I tried this after a warmup (got the brakes warm and increased the drag). Backing the MC off 1/4 inch definitely decreased the drag. Tried tightening up again - increased drag. Tried this with the rig running to engage the booster - same results. See reply to Manny (tried this maneuver as well). So my booster rod is too long for the new MC?

Photos attached (sorry for the quality of the photo of the booster rod):

 

[BadlyBent]

Manny,

I tried your maneuver. After pulling the MC off (following advancing the booster rod by 1/4") - there is no play (unable to push rod any toward the firewall). So my booster rod is too long. Before I start cutting and grinding, I need to make sure that's the right move, though suspect it is in light of response to the maneuver Steve suggested.

Mark

 

[carslutt]

i had the same issue when i did basicly the same swap on a jeep, i installed a full size dodge truck master, i endedup cuting the rod in to 1/3's and welding teh 2 end pieces together bascily so it could still be adjusted slightly. worked fine.

 

[TOMSRYD]

I had the same issue and ground the rod down to get the proper freeplay...Working great for at least 3 years now...Just grind a little bit and trial fit until it's right....It doesn't take much

TOMMY

 

[bsevans]

I wonder what is different between a '71 and '78 LC MC. I did the same swap on my '78 and it was a bolt on with no adjustments.

 

[BadlyBent]

Thanks for the replies. I had also read that this was a bolt-on conversion with relatively little hassle - thus my reluctance to remove metal. At this point however, seems that's the problem. I'll do some judicious grinding and let you know how it goes. Honestly, I'm glad to see how well the rig CAN stop with a new MC and disc brakes!

 

[Poser]

Just be mindful of the smooth exterior of the actuation link, as there is a seal that rides on that surface and if you damage that rod, it will not seal properly and cause your booster to not function properly.

 

[BadlyBent]

I measured the depth of the cup from the booster and noted about 3/8 difference between the original and FJ80 MCs. Made me feel better.

I ground 3/8 off the booster rod (thanks for the warning on keeping the shaft pristine). Worked great. I now have brakes when I want them - not continuously! Pedal depresses about 1/2" before engaging the brakes and I have good emergency stopping (rears lock up before fronts but I haven't gotten around to thinking about a proportioning valve yet).

Thanks for all the help - until the next project...

 

[green40]

Does it make a difference which year 80 MC you use?
I'll be adding rear disc's this winter and would like to change the MC
while I'm at it.

Thanks

 

[JJS]

Did 80's come standard with rear discs, meaning no need for an external proportioning valve?

 

[cruiserbrett]

most 80's did have discs. unless you run exactly the caliper combination for the 80, you may need a proportioning valve. You can use it to avoid the early rear lockup, which is not really safe, or ideal. A squealing locked up tire does not afford as much braking effort as a tire still rotating... maximizing your rear brake effort will make a very noticable difference in braking efficiency, even though they may only give about 20% of the total braking effort.

 

[1973Guppie]

I had to space the fj80 MC away from a the minitruck booster with some spacers in order to get it to work. On the fj40 master the pushrod would come out easily, my fj40 booster was shot, so I got a mtruck booster, the pushrod on the mtruck booster would not come out of the booster and I didn't want to force it as the rebuilt unit was expensive. The spacing solution worked well for me.

Noah

 

[Poser]

The fact that the 80 series had disc brakes and used that master cylinder does not really apply to a 40 series considering that an 80 series master cylinder would be set up for a disc brake system for a six-thousand-pound vehicle with a braking system designed for that, opposed to, a truck that is not configured the same.