Yep. Doesn't make it any easier to come to a very slow crawl or complete stop on a steep slope. The 80 isn't the only vehicle where I have to do this. Low gearing, a torquey motor, an automatic and a steep decline will make brakes suffer.
mushy brakes only in 4-Lo? (1 Viewer)
- Thread starter riffman12
- Start date
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Replace all your soft lines. Old brake hoses often swell under pressure. Check the LSPV works and nice new fluid all round.
Check the hose to your brake booster for splits.
I'm running 35"s and a 25% low reduction box and I can stall the engine and hold on steep slopes with my brakes.
Check the hose to your brake booster for splits.
I'm running 35"s and a 25% low reduction box and I can stall the engine and hold on steep slopes with my brakes.
I agree with changing all the soft rubber lines, remember the newest of these trucks is now at least 20 years old, and most of these hoses have never being changed. When the rubber lines get old the reinforcing cords in these hoses break down allowing the hose to swell in size, thereby not allowing the brake system to maintain it's correct operating pressure. That swelling in size will cause your brake peddle to feel soft when you press on it.
Malleus
Far west of Siegen
I thought the FSM specified, in order, rear (R/L), LSBPV, front (R/L), but I could be mistaken.
I did the math once. The rubber lines would have to be super trashed before this would start to be noticeable. Not saying it's a bad idea to replace the lines, but most people shouldn't expect massively improved pedal feel
If you are going to replace the soft lines just go with a slee kit and replace all of them with braided. I had a soft line fail and its easier to replace on your schedule, not when you are ready to head out and there is brake fluid dripping on the driveway.
I agree with others that the 80 does a good job with compression braking, even with the automatic. I can creep down many hills in 4 low, 1st gear without even touching the brakes.
I agree with others that the 80 does a good job with compression braking, even with the automatic. I can creep down many hills in 4 low, 1st gear without even touching the brakes.
Malleus
Far west of Siegen
Can't argue with math, unless you're Einstein...
You may be right, I don't know.
I've done a couple now, and struggled to bleed the rear until it was bled at the LSPV.
I also found disconnecting the lever at the chassis end and tying it to mimic a fully loaded position helped bleed this quicker as you get full flow through the LSPV.
Malleus
Far west of Siegen
Opening that valve fully while bleeding is vital. I'm surprised this isn't in the FSM.
You're probably not used to the lower gearing in 4lo (ie the sensation that your truck is pushing through the brakes) compounded by the suggestions here of old fluid, brake maintenance etc.
- Thread starter
- #31
quick update: I flushed/bled about half a gallon of new brake fluid through the system and the brakes are night and day different. My girlfriend got a leg workout on the brake pedal as a bonus.
I haven't had a chance to try them out on the trail yet, but I can safely put myself through the windshield with 33's if I want to. Nice firm pedal feel as well, which I never had before. I can't imagine I'll have any issues in 4-Lo
I think the fluid was just really old and compressible, making everything mushy.
The process was not nearly as scary as a lot of members made it out to be. It was basically like every other car I have ever bled with the addition of the LSPV:
1) Turkey baster ~70% of the old fluid out of the master cylinder to save yourself some time. Top it up with fresh fluid. Throughout the process, always make sure the fluid is topped up so you don't draw in extra air.
2) bleed the Passenger rear until clear fluid comes out
3) bleed the driver rear until clear fluid comes out
4) bleed the LSPV until clear fluid comes out. Push down on the rod to "open" the interior valve of the LSPV before you open the bleed nipple. Thanks @Malleus for the tip.
5) bleed the passenger front until clear fluid comes out
6) bleed the drivers front until clear fluid comes out
7) make sure the brakes operate safely, then go and find a patch of dirt to lock up the ABS a few times. Or like me, you can find a parking lot with lots of pine needles where cops like to eat their lunch and laugh at you.
8) repeat the entire process minus the turkey basting. You should be good to go with nice firm brakes. If not, then you bled wrong or your MC is bad or you have a leak somewhere.
Hope this helps others out there. You do not have to live with mushy brakes!
I haven't had a chance to try them out on the trail yet, but I can safely put myself through the windshield with 33's if I want to. Nice firm pedal feel as well, which I never had before. I can't imagine I'll have any issues in 4-Lo
I think the fluid was just really old and compressible, making everything mushy.
The process was not nearly as scary as a lot of members made it out to be. It was basically like every other car I have ever bled with the addition of the LSPV:
1) Turkey baster ~70% of the old fluid out of the master cylinder to save yourself some time. Top it up with fresh fluid. Throughout the process, always make sure the fluid is topped up so you don't draw in extra air.
2) bleed the Passenger rear until clear fluid comes out
3) bleed the driver rear until clear fluid comes out
4) bleed the LSPV until clear fluid comes out. Push down on the rod to "open" the interior valve of the LSPV before you open the bleed nipple. Thanks @Malleus for the tip.
5) bleed the passenger front until clear fluid comes out
6) bleed the drivers front until clear fluid comes out
7) make sure the brakes operate safely, then go and find a patch of dirt to lock up the ABS a few times. Or like me, you can find a parking lot with lots of pine needles where cops like to eat their lunch and laugh at you.
8) repeat the entire process minus the turkey basting. You should be good to go with nice firm brakes. If not, then you bled wrong or your MC is bad or you have a leak somewhere.
Hope this helps others out there. You do not have to live with mushy brakes!
- Thread starter
- #32
ok now I'm totally confused. Up until this weekend my brakes have been great - better than ever before. This was after flushing half a gallon of fluid through the system.
This weekend I went back to the Slick Rock trail where I started getting the mushy brake symptoms in 4-Lo. We did a lot of slow driving on the trail, crawling over rocks etc.
By the end of it, my pedal didn't go completely to the floor, but my brakes were useless. I couldn't even lock up the tires on gravel no matter how hard I tried.
I even tried putting it back in 4-Hi to see if it was related to the ABS being disabled and the brakes were still soft.
We stopped for about 30 mins while we aired up our tires, then after that my brakes were back to perfect. Firm pedal, plenty of stopping power and no fade all the way down the steep mountain roads.
I'm not sure where to go next with this. I found one thread where one guy said he had similar issues and he fixed it by replacing his brake booster...but that doesn't make sense to me. If the booster is failing I feel like I should be getting a rock hard pedal.
My master cylinder was replaced by the PO with an Aisin unit about 30k miles ago. No signs of leaks. I also have no air coming out of the bleed nipples.
Do I just keep flushing more fluid through the system in hopes that disabling the ABS in 4-Lo pushed some old stuff back into the system that I need to bleed out?
Could this be swelling brake hoses?
Thanks again for your help. This is driving me nuts!
This weekend I went back to the Slick Rock trail where I started getting the mushy brake symptoms in 4-Lo. We did a lot of slow driving on the trail, crawling over rocks etc.
By the end of it, my pedal didn't go completely to the floor, but my brakes were useless. I couldn't even lock up the tires on gravel no matter how hard I tried.
I even tried putting it back in 4-Hi to see if it was related to the ABS being disabled and the brakes were still soft.
We stopped for about 30 mins while we aired up our tires, then after that my brakes were back to perfect. Firm pedal, plenty of stopping power and no fade all the way down the steep mountain roads.
I'm not sure where to go next with this. I found one thread where one guy said he had similar issues and he fixed it by replacing his brake booster...but that doesn't make sense to me. If the booster is failing I feel like I should be getting a rock hard pedal.
My master cylinder was replaced by the PO with an Aisin unit about 30k miles ago. No signs of leaks. I also have no air coming out of the bleed nipples.
Do I just keep flushing more fluid through the system in hopes that disabling the ABS in 4-Lo pushed some old stuff back into the system that I need to bleed out?
Could this be swelling brake hoses?
Thanks again for your help. This is driving me nuts!
- Thread starter
- #33
Another update:
Over the weekend I went and did a lot of ABS stops on some gravel, also putted around in 4-Lo to simulate trail conditions.
Then went back to bleed, and I have super yucky old fluid coming out again.
I guess there must have still been a lot of old fluid hiding in the system after the first flush.
More bleeding to come this week. Yay!
Over the weekend I went and did a lot of ABS stops on some gravel, also putted around in 4-Lo to simulate trail conditions.
Then went back to bleed, and I have super yucky old fluid coming out again.
I guess there must have still been a lot of old fluid hiding in the system after the first flush.
More bleeding to come this week. Yay!
