Marshmallow brakes

jrohland · 10-21-2009, 04:29 AM

I've been trying to get rid of the sponge brake problem. That is, pushing on the brake feels like stepping on marshmallows.

So far I've done a full pad and shoe job which was needed anyway. Fixed a rust seazed right side parking brake bell crank. (In case you don't know, the auto-adjusters activate when the parking brake is used. If you don't use your parking brake on the T100, your rear brakes will not auto-adjust.) Replaced the drums (rust). Flushed and bled the entire system.

I'm quite sure the mush problem is a worn master cylinder. The factory replacement is about $212. I found an aftermarket for $115. Any of you use an after market master cylinder? How does it work for you?

As a rule I don't like using after market for critical systems but that is a big savings.

jrohland

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desertcamper67 · 10-21-2009, 07:44 AM

How's your rubber brake hoses? They can be damaged inside and swell but not leak. Or maybe you haven't actually gotten all the air out of the system. Do you get good pressure out of each bleeder?

jrohland · 10-21-2009, 09:11 AM

Quote:

Originally Posted by desertcamper67

How's your rubber brake hoses? They can be damaged inside and swell but not leak. Or maybe you haven't actually gotten all the air out of the system. Do you get good pressure out of each bleeder?

I don't see any ballooning in the flex tubes. The brakes do not pump up so I have no reason to believe there is air in the system.

Having done the bleed job alone, I can't really tell about the pressure at the nipples. I don't have a brake pressure tester. Maybe I can borrow one. I would like to calibrate the load balancing valve.

jrohland

jrohland · 10-21-2009, 10:30 AM

I got a used MC from one of the Yotatech members for a good price. When I get it, I will try that. If it does not correct the problem I will keep going with other components.

jrohland

Gnarly4X · 10-21-2009, 12:22 PM

Quote:

Originally Posted by jrohland

I've been trying to get rid of the sponge brake problem. That is, pushing on the brake feels like stepping on marshmallows.

So far I've done a full pad and shoe job which was needed anyway. Fixed a rust seazed right side parking brake bell crank. (In case you don't know, the auto-adjusters activate when the parking brake is used. If you don't use your parking brake on the T100, your rear brakes will not auto-adjust.) Replaced the drums (rust). Flushed and bled the entire system.

I'm quite sure the mush problem is a worn master cylinder. The factory replacement is about $212. I found an aftermarket for $115. Any of you use an after market master cylinder? How does it work for you?

As a rule I don't like using after market for critical systems but that is a big savings.

jrohland

A bad master brake cylinder is easy to diagnose. If it leaking... it's bad. If you can push the brake pedal down and hold it and the pedal goes down, the fluid is seaping past the piston. A spongy pedal is typically not a master cylinder problem.

jrohland · 10-21-2009, 02:44 PM

Quote:

Originally Posted by Gnarly4X

A bad master brake cylinder is easy to diagnose. If it leaking... it's bad. If you can push the brake pedal down and hold it and the pedal goes down, the fluid is seaping past the piston. A spongy pedal is typically not a master cylinder problem.

Well I checked the brake troubleshooting table (see the image below).

While faulty MC is near the bottom of the list, it is there.

Actually, the MC is two MCs connected together. I believe the rear brake piston is not working.

At any rate we will know when I replace the MC. If the brake feel more solid, there was a problem. If not, that was not the problem.

jrohland

Gnarly4X · 10-21-2009, 02:50 PM

Quote:

Originally Posted by jrohland

Well I checked the brake troubleshooting table (see the image below).

While faulty MC is near the bottom of the list, it is there.

Actually, the MC is two MCs connected together. I believe the rear brake piston is not working.

At any rate we will know when I replace the MC. If the brake feel more solid, there was a problem. If not, that was not the problem.

jrohland

Yeah, it could be, but like I said, "typically", a spongy pedal is not the master cylinder. But with a dual cylinder and one being bad, it's definitey possible.

gNARLS.

BamZipPow · 10-21-2009, 08:49 PM

How good was the fluid flow when you were bleeding out the rear brakes? Did it come shooting out or did it sort dribble out?

Spongy = air in the system...

I had the same symptoms as you did on my 1993 T-100...I started by replacing my MC first as well. It ended up being that there was crud stuck in the LSPV and not allowing proper flow to my rear brakes. I found a simple test to see if the LSPV is doing it's job.

Chock the front wheels.
Release the parking brake (if applied).
Jack up the rear by the differential.
Put the trans in neutral.
Spin one of the wheels by hand.
Stomp on the pedal.
If the wheels do not stop...it's most likely the LSPV/bleeder valve needs a good clean out.

I whacked the heck out of the LSPV with a 2x4 and then bled it out. The time before...nothing came out. After the "persuasion" with the 2x4, fluid came shooting out along with a ton of air bubbles. Moving to the rear brakes...got more air and lots of fluid flow. Pedal was gitting firmer. Back to the LSPV fer a little more air bubbles and strong fluid flow! Pedal was really firm now. Bled the fronts and system was darn near perfect! That's my story...

Jason4X4 · 10-21-2009, 09:50 PM

make sure your rear shoes are adjusted properly, if not, i've seen them cause funny pedals.

hotshoe · 10-23-2009, 07:24 AM

Check rear shoes and the crappy LSPV- Most likely that's it- Same problem on my T

jrohland · 10-23-2009, 09:38 AM

The shoes are new and adjusted properly. The LSPV is a possible problem. When I bled it I had to take the nozzle out and drill the rust our of the bleed holes. It bled OK after I cleared the nozzle but it could be gummed up inside the valve.

Like I said I am getting a good master for cheap so I will start with that. If it does not fix it the LSPV is next on the list.

Thanks for the help,
jrohland

DIHOWARD · 10-23-2009, 10:44 AM

We like these, we like these ALOT!

SS hoses made by Stop-Tech.

10-21-2009, 10:30 AM	#4 (permalink)
jrohland Registered User Join Date: Aug 2009 Location: Northern Virginia, USA Posts: 108	Try that I got a used MC from one of the Yotatech members for a good price. When I get it, I will try that. If it does not correct the problem I will keep going with other components. jrohland

10-23-2009, 07:24 AM	#10 (permalink)
hotshoe Registered User Join Date: Sep 2004 Location: At my anvil or under a horse in Southeast PA Posts: 179	Check rear shoes and the crappy LSPV- Most likely that's it- Same problem on my T __________________ 00 Tundra Stonewell Body Ready for shoeing 97 T100 Under the Knife! I am the Toe Cutter! Have you seen the Night Rider?

10-23-2009, 09:38 AM	#11 (permalink)
jrohland Registered User Join Date: Aug 2009 Location: Northern Virginia, USA Posts: 108	Tight shoes The shoes are new and adjusted properly. The LSPV is a possible problem. When I bled it I had to take the nozzle out and drill the rust our of the bleed holes. It bled OK after I cleared the nozzle but it could be gummed up inside the valve. Like I said I am getting a good master for cheap so I will start with that. If it does not fix it the LSPV is next on the list. Thanks for the help, jrohland

10-23-2009, 10:44 AM	#12 (permalink)
DIHOWARD Contributing Member Join Date: Mar 2006 Location: WAUCONDA, IL Posts: 291	We like these, we like these ALOT! SS hoses made by Stop-Tech. __________________ 2003 4RUNNER LTD V6 FUSION LIFT/COOPER ATR/CAI/MAGNAFLOW/IPF LIGHTS

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10-21-2009, 08:49 PM	#8 (permalink)
BamZipPow Registered User Join Date: Feb 2007 Posts: 129	How good was the fluid flow when you were bleeding out the rear brakes? Did it come shooting out or did it sort dribble out? Spongy = air in the system... I had the same symptoms as you did on my 1993 T-100...I started by replacing my MC first as well. It ended up being that there was crud stuck in the LSPV and not allowing proper flow to my rear brakes. I found a simple test to see if the LSPV is doing it's job. Chock the front wheels. Release the parking brake (if applied). Jack up the rear by the differential. Put the trans in neutral. Spin one of the wheels by hand. Stomp on the pedal. If the wheels do not stop...it's most likely the LSPV/bleeder valve needs a good clean out. I whacked the heck out of the LSPV with a 2x4 and then bled it out. The time before...nothing came out. After the "persuasion" with the 2x4, fluid came shooting out along with a ton of air bubbles. Moving to the rear brakes...got more air and lots of fluid flow. Pedal was gitting firmer. Back to the LSPV fer a little more air bubbles and strong fluid flow! Pedal was really firm now. Bled the fronts and system was darn near perfect! That's my story...

10-21-2009, 09:50 PM	#9 (permalink)
Jason4X4 Registered User Join Date: Jun 2006 Location: Chandler, AZ Posts: 92	make sure your rear shoes are adjusted properly, if not, i've seen them cause funny pedals.