3FE brakes diagnostics (1 Viewer)

[rghouse]

Need some tips on troubleshooting sub-par braking performance.
1992 3FE 215k, 3310.50 on steel wheels.
Brand new front drilled slotted rotors/pads 250 miles ago.

No change in braking performance after front redone. Stopping distance sub-par and pedal feels soft, needs good amount of pressure to really stop quickly 45mph and faster. Is this normal? Since tire/wheel upgrade braking has bugged me often and seems inadequate. Backing up yesterday to park with an empty trailer, on an incline, and had to stomp down hard on pedal to get it stop rolling, like when you bleed brakes, traveled extra 2” ish inches. No pulling, no nose dives. Smooth stopping but distance could be way better I think. Don’t know when rears were serviced/replaced last.

-Bad Brake booster symptoms I hear is the the opposite: hard pedal.
-no leaks
-seem to remember guys were putting on a beefier master cylinder but can’t find anything on that
-my mechanics did front job and inspected lines, not sure if they bled at LSPV

Maybe this is normal and since she is not my DD anymore I’m not used to the 1990s performance ?

 

[SaturnAscends]

There could still be air in the system. It's a PITA to bleed the brakes on these.

 

[Marco Lau]

air in the system...slotted and drilled rotors does not increase stopping power, and they are prone to crack, and i would avoid them. I can lock up my all 4 wheels and i am on 37s. Plenty of stopping power for the 3FE. Also check your rear brake bias proportioning valves if lifed. That made the most difference for me.

 

[leonard_nemoy]

Either overhaul the rear brakes and bleed again or upgrade the rear to disc brakes.

 

[jonheld]

I've said this a bunch of times.
Brakes are a system, not just a bunch of parts. Your system is now 30 years old and items will need to be replaced as basic maintenance.
Rear drums can work very well if maintained and serviced regularly, but folks love to complain about them because they don't maintain them. They require periodic maintenance, more so than with disk brakes. It helps to have all 4 corners stopping the truck.
Regular usage of the handbrake will keep the shoes in alignment if the adjusters are working properly.
Front calipers can be rebuilt using OEM parts, or replaced if needed.
I would replace all rubber brake lines, regardless of who "inspected" them. They're 30 years old and don't owe you anything.
These trucks are not difficult to bleed. I gravity bleed both my 91 and 97 without issue. Not really sure why folks have problems bleeding brakes. You don't have ABS to concern yourself with.
The emissions/vacuum system can have a profound effect on brakes. Make sure it's working properly and all vacuum lines are in good repair.
Brake fluid should be water clear. The darker the color, the more contaminated it is.

 

[rghouse]

Already up on the lift. Mechanic suspected rears right away. No friction at all when spinning by hand. Shoes looked brand new, save for a little wear on the underside. Basically I just had front brakes. Once we get it back together we’ll see how it works and go to the next (if need be) bleeding and or pressure valve adjustment.

 

[rghouse]

Rear Brake adjustment did not help. Vacuum tested the brake booster and had no residual suction with the car turned off. Took out the vacuum tester gun and brake booster has noticeable slow pressure drop when charged up. There is also discoloration where the master cylinder bolts up. I was really hoping that wasn’t the problem but

 

[jonheld]

Why are you pulling axles to do brakes?

 

[rghouse]

I was waiting for that. I have had a lunchbox locker sitting around for a couple years waiting to go in. With drums off I decided to have the mechanic throw it in there. I have to sneak in upgrades some times

 

[rghouse]

brake booster on order, dont ask me what brand it is lol.

Question, is it mandatory to replace master cylinder? another $180 in parts. Assuming all gaskets are replaced at BB. Parts seem so robust and i'm just curious what parts in the MC could experience degradation. Are there smaller seals in there at the lines or is it all metal? I know this is a drop in the preverbal bucket but, at the same time, if it aint broke don't fix it.

 

[SaturnAscends]

brake booster on order, dont ask me what brand it is lol.

Question, is it mandatory to replace master cylinder? another $180 in parts. Assuming all gaskets are replaced at BB. Parts seem so robust and i'm just curious what parts in the MC could experience degradation. Are there smaller seals in there at the lines or is it all metal? I know this is a drop in the preverbal bucket but, at the same time, if it aint broke don't fix it.

I’m about to replace my booster, and I plan on leaving the MC alone unless it gives me trouble later. Others will say you should replace it, but it’s up to you at the end of the day.

 

[White Stripe]

Well what comes to mind for me is how old is the lspv? If it's old replace it. How old is the master cylinder? If it's original replace it. Rock auto has decent deals on denso and aisin parts. Also check the website from @Racer65 he has good stuff. I would replace the wheel cylinders too. Calipers usually last a very long time so I would leave those unless they are leaking fluid. Replace rubber hoses as well as mentioned earlier. Replacing the booster is mandatory as well as your doing.

 

[rghouse]

update: Booster replaced (Seiken) and all 5 locations bled again. Brakes got better but not right. Fluid very dark. Have new LSPV on hand but not sure that is my next step here in diagnosis.

Next idea is replacing lines unless advised otherwise before parts get here.

 

[SaturnAscends]

update: Booster replaced (Seiken) and all 5 locations bled again. Brakes got better but not right. Fluid very dark. Have new LSPV on hand but not sure that is my next step here in diagnosis.

Next idea is replacing lines unless advised otherwise before parts get here.

Did you end up replacing the MC? That could be affecting the brake feel. I'm not sure replacing lines and hoses would help with the feel, I think that's more of a PM thing to avoid a catastrophic failure.

Vacuum lines are a good idea to replace also as was advised above.

 

[toy_tek]

Also check your rear brake bias proportioning valves if lifed. That made the most difference for me.

@ OP - This - did you adjust your LPSV after the lift?

I had to install a 2" spacer between the LPSV arm & the axle mount to regain rear braking after lift install. If you didn't account for the lift... then there's a good chance your rear brakes are not contributing much, if anything, as your LPSV is basically closed and not allowing brake pressure to the rear.

 

[rghouse]

no master cylinder replacement yet. I only see two vacuum lines on brakes, one supplying suction to BB and one going into engine and both are intact (one just replaced because Seiken located port at 2 O'clock). I will inspect other lines.

@toy_tek Interesting, so the LSPV is confused because of height of rear-end? I Have not adjusted. You mean the spacer goes in this part on the axle:

 

[toy_tek]

@toy_tek Interesting, so the LSPV is confused because of height of rear-end? I Have not adjusted. You mean the spacer goes in this part on the axle:

Yes essentially. Check my post here with a pic of the spacer I made

here's a thread with some 80 info.

LSPV Adjustment after 4" Lift

All- I have been looking over every forum I can find regarding adjustments of the LSPV after a 4" lift. I am unable to find a photo of what the finished product looks like. All of the Mud threads about it no long have the pictures working. Currently mine is going under the upper arm and...

forum.ih8mud.com

 

[jonheld]

Fluid very dark.

Brake fluid should be water clear. The darker it is, the more contaminated it is.

 

[rghouse]

Will flush system more, thanks Jon. Bleeding was just like Dad taught me btw, no special power bleed required. maybe that is an ABS thing? My 6 year old did a great job! I couldnt believe how far the front seat actually slides forward . maybe that is for more room in the back lol

This shows how LSPV works. looks like there is not enough pressure. Will likely get it on the lift and adjust at mechanics shop to make sure I have good ratio of pressure going front and rear.