Solved: Brake pedal sinks when put in park (1 Viewer)

[Morgan Evans]

Hello mudders. I have very specific brake issue on my 62. I ran into the back of an F250 yesterday with my wife in the car. Fortunately it was fairly slow, 15mph roughly at impact, down from maybe 40mph. We are fine, but im embarrassed. I have an ARB bumper that destroyed the trucks rear bumper but only mashed my historic license plate. Best insurance I've ever purchased, big win for ARB I guess. I had plenty of time to stop and the rear brakes locked up but the fronts didn't. I stood on the pedal and it was shocking how bad they are. Enough back story, here's my situation.

I tore into the brakes today, put an old pair of calipers on, new master cylinder, truck has a new 4runner booster, blocked the rear brakes at master with a plug and tested with fronts only. Literally nothing changed the feel. I have a hard pedal and very weak performance.

While I was dicking around I noticed something funny, when I shift from drive into park or neutral I get another 1/2" of pedal drop! The pedal will be hard, almost like a failing booster, but then I shift into park and it feels like the brakes are working correctly! The pedal sinks into brakes like the calipers are really working. I took out a vacuum gauge and I'm reading 13" at idle. I live at 8,500' and 250k on the engine, that's all she's got.

Could my brake problem be low vacuum not activating the booster completely? When I shift into park the vacuum increases slightly while coming off a slight load (turning the automatic in my fj62) and I get full boost so the pedal sinks into the brakes a little more?
This is such a weird situation... thoughts?

 

[cruisermatt]

sounds like you got it figured out. 13' is really low for a 3FE. Should be like 20'. sounds like you have a vac leak

 

[Morgan Evans]

Checked for vacuum leaks heavily with starter fluid and propane, found nothing. Even unplugged a small port and it hardly dropped vacuum, barely noticeable. I imagine if it was a leak that significant I'd notice it more? I read vacuum decreases 1" per 1000' of altitude. That would put me right at 13" living at 8,500'. Car doesn't smoke at all, idles at 650ish, seems healthy.
Going to the junkyard to pull a vacuum canister and possibly an electric vacuum pump and switch to plumb in.

I can see how this accident may have happened. I was accelerating because traffic always pulls out faster than I can keep up, when it quickly stopped (you know how traffic does) I went from foot on gas to foot on brake rapidly, the vacuum had no time to recover from the loaded acceleration.

I'll report back after canister install.

 

[cps432]

sounds like you got it figured out. 13' is really low for a 3FE. Should be like 20'. sounds like you have a vac leak

When I lived in Denver I was pulling about 13-14’. That’s normal for that altitude. You’ve got a lot more air pushing down on you in Florida.

I’m wondering if there’s an issue with the “new” 4Runner booster. Is it brand new or is it remanufactured? How new is new? I run a 4Runner booster too and it works fantastic. I’m also using a new 1996 T100 master cylinder in the system. I would have to do some deeper research because I don’t recall, but I think the original 60/62 master cylinder has an insufficient diameter piston for the 4Runner booster. It’s been 5-6 years since I replaced all my brake components. Maybe that’s related to calipers? Hmmm..

 

[cruisermatt]

Yeah, I still don't buy it though. Plenty of 60/62 running around at that altitude and higher without brake complaints.

Vacuum pump would be a decent test to confirm booster function. Your engine could just be worn out. Compression #'s on it?

 

[cps432]

Yeah, I still don't buy it though. Plenty of 60/62 running around at that altitude and higher without brake complaints.

Vacuum pump would be a decent test to confirm booster function. Your engine could just be worn out. Compression #'s on it?

Yes, they function just fine at 13’. Mine did for years after I replaced the whole system.
Something else must be causing this.

 

[Morgan Evans]

Well the pump I picked up at the yard was shot, no way to test them in the yard unfortunately. So I'm waiting on one off ebay. I'll report once I get it. If increased vacuum pressure helps the brakes then I'm convinced that's the problem. If it isn't, but fixes it than that's ok too! Engine is at 240k, I'm sure it's not "healthy" but it doesn't smoke. Of course it has barely any power way up here anyway. No kinked lines, newer rubber lines on the corners. What about the lspv? Could that be reducing pressure? I moved it all the way up and all the way down with no noticeable change. My understanding is that will only affect the rear brakes anyway?

 

[Skreddy]

I commented on your post in the what did you do thread but just saw this one. Your 1” per 1000’ math is right.
Where are you taking your vacuum reading from? Direct from manifold or from a potentially ported vacuum source? Good way to check if it’s more vac off idle is just hit the brakes while revving it to 1000-1200 rpm and see if it stops better.

When you replaced booster/master, did you adjust the pushrod between the two for the correct height? Have you adjusted the pedal to booster pushrod for correct height (after the booster to master pushrod)? The vacuum booster assists braking function. Putting it in park and the pedal height decreases leads me to think the booster sees the brakes as partially engaged at rest, then the small increase in vacuum seen with the higher park idle makes the booster provide more assist.

 

[Morgan Evans]

I'm grabbing a new master and will follow all set up procedures and recheck! I did not notice change when revving so I think you are onto something....

Vacuum was checked at pcv port and booster port.

 

[Miloslavich]

I get about 16'' to 14'' of Vac up at 6500 feet altitude in Colorado. About as perfect as i could get it..

I'm guessing you may have had a booster fail, and or vac leaks as well

 

[Morgan Evans]

Thank you all for your feedback and advice. This forum puts all others to shame. Few things to report.

I replaced the master with a brand new 4runner unit, 4runner calipers are back on, all lines were blown out with compressed air, at first i had no change....SO i went further.

1: I bypassed the LSPV with a bubble flare union and a brake bender at the LSPV location. I connected the front brake lines directly with another union at the passenger side firewall, removing that T union. This seems to have provided the largest improvement. I actually now feel like the brakes are working pretty well. This took a little time.

2: The first line (closest to the firewall) feeds the rear brakes, but the port closest to the firewall on the 4runner master is the first to activate. Maybe the original master is backwards in this way? Possibly due to the LSPV that is how Toyota set up the brake system? Regardless, without the valve I see no reason the rear brakes should come one first. I swap the lines at the master so the first to activate now goes to the front brakes. This also seems to have made a huge improvement.

3: I adjusted the push-rod length on the booster to the master, I didn't notice anything different but it is possible that made some improvement.

I have been working on getting the brakes bled and the pedal is going pretty far right now, but based on previous brake bleeding experience, this just takes time so I will keep hammering away at it. My vacuum pump and brake booster specific vac canister is coming this week. I will probably add the canister regardless, and see how things are.

To sum up for those not looking to read the whole thing! 1) Bypass LSPV, this is connected into the front brakes per the T union on the passenger fender well. I think this was actually my main culprit 2) Swap the lines at the master so the first to activate is the front brakes.

I'll add another update when the brakes are fully bled and my vac canister is installed.

 

[cruisermatt]

have you verified your booster actually works? Drive it, disconnect the booster and plug the hose, see if there is difference.

 

[Morgan Evans]

have you verified your booster actually works? Drive it, disconnect the booster and plug the hose, see if there is difference.

Good call, I will do that when I can get back to fiddling with it.

 

[Miloslavich]

cant hurt to check your Vac, see if you have any leaks.

 

[Morgan Evans]

Checked vacuum per post #3. Just an unapologetic member of the unskilled public here who prefers to work on his own vehicle vs. spending money taking it to a shop

 

[Morgan Evans]

Well here we go, final report. Fixed!!

I still get that funny pedal sink when I shift into neutral or park, but the cruiser stops well now. Maybe something someone would be interested in seeing if their rig does the same?

1: Removed the LSPV, believe this was the culprit overall. 60's don't have them? and I think it's a pretty janky design anyway compared to a regular prop valve. I'll add a standard valve later if It needs it.

2: Adjusted the rear brakes, this took up some slack in the pedal.

3: I switched the lines at the master so the first to activate is the front brakes. This is contrary to something I read about cars with rear drums and front disc's, they want the drums to activate first. This might be due to a traditional prop valve being present on most other vehicles. Either way, I tried it both ways and it seems to stop better with the lines swapped.

4: I added a vac canister to help the booster. More for insurance with low vacuum coming off acceleration and having to get on the brakes quickly. Booster pushrod was adjusted, and booster is operating correctly.

Hope this thread helps someone who is having brake problems on a 62. I'd definitely check the LSPV first since it is integral to front and rear brake function. Thanks for the input and help. Happy driving.

 

[duncanrm]

Well here we go, final report. Fixed!!

3: I switched the lines at the master so the first to activate is the front brakes. This is contrary to something I read about cars with rear drums and front disc's, they want the drums to activate first. This might be due to a traditional prop valve being present on most other vehicles. Either way, I tried it both ways and it seems to stop better with the lines swapped.

Crikey.. thats a brave move. It seems a very murky area - the physics and design involved. I'd be super careful in your first wet weather - please do report back if its trouble free though.

 

[Morgan Evans]

Crikey.. thats a brave move. It seems a very murky area - the physics and design involved. I'd be super careful in your first wet weather - please do report back if its trouble free though.

Good call. I think I'll order up a traditional prop valve and get it installed.

 

[Spike Strip]

60s have a LSPV, it's under the Master cyl.

Here's a replacement for FJ62s

Load Sensing Proportioning Valve LSPV for Land Cruiser FJ62

Load sensing proportioning valve (LSPV). Prevents rear brake lock-up. Fits: '88 to '90 U.S. spec Toyota Land Cruiser FJ62 8/'80 to 8/'87 non-US FJ60, HJ60, FJ62 Corresponds to OEM part # 47910-60060.

www.cityracerllc.com

 

[Morgan Evans]

What are your thoughts

60s have a LSPV, it's under the Master cyl.

Here's a replacement for FJ62s

Load Sensing Proportioning Valve LSPV for Land Cruiser FJ62

Load sensing proportioning valve (LSPV). Prevents rear brake lock-up. Fits: '88 to '90 U.S. spec Toyota Land Cruiser FJ62 8/'80 to 8/'87 non-US FJ60, HJ60, FJ62 Corresponds to OEM part # 47910-60060.

www.cityracerllc.com

What are your thoughts on the lspv vs. the traditional valve found on a 60?