losing brakes going over bumps at speed

I did some brake work on my truck after I did a light bilstein leveling lift. New calipers, pads, braided brake lines. Bled the fronts and BPV with a pressure bleeder a bunch of times. Haven't been able to get the rear bleeders loose to bleed them as theyre seized and haven't had time to deal with the ramifications of them breaking off.

The pedal feels firm and the brakes feel great but going over bumps on the highway or on streets at speed and braking abruptly at the same time results in an almost complete loss of brakes for a couple seconds. it feels like the ABS kicks in but weakly, which doesnt help the situation. They usually catch after a while. it's somewhat terrifying.

Done a bunch of googling and searching on the forums but getting mixed messages. Some are pointing at ABS issues. But sometimes the brakes go out in those moments and the ABS doesnt seem to kick in at all. Anyone run in to this kind of thing?

 

Sounds dangerous. I’d park it until you can work the rear bleeders.

 

Yeah I’m inclined to... I should have noted the brake work was done on the front.

 

Pull the abs fuses (x2) temporary and see if it goes away.

If it does then you know it's abs related.

If it doesn't stuck then back in and keep bleeding.

 

Will do thanks!

 

Google “brake pedal freeplay”. Don’t know a ton about it but sound like it could be your issue. If your pushrod is engaging the master cylinder prematurely then you could be blockin off the master cylinder reservoir ports. Learned it from Mustie the other day while elbow deep in a bag of potato chips

 

Curious, braided lines up front only or did you do the rear one as well?

 

Did you pull the rear drums off and check the rear brakes? If the bleeders are seized that's telling me that you might have a corrosion issue and could have problems inside the drums. I would inspect them to either eliminate them or confirm there is an issue.

 

Only did the front lines.

My mechanic just prior had checked the rear brakes and said they were in reasonable shape. the truck has trailered a lot of boats into salt water which is why I think the bleeders are seized up. But it’s certainly possibly there’s something going on in there.

I also did the bpv extension bracket for the helper springs I put in the back. I’m wondering if that also created some of the problem.

I’ve basically created a mess of variables...

 

you may need to bleed the ABS as well as the lines

 

If they're stuck, new rear wheel cylinders are pretty cheap and not hard to replace.

 

My bet is that there is air in the back brakes and when you hit a bump the push rod goes up and sends more brake bias to the rear. The air in the back brakes then causes the feeling or sensation of losing brakes.
To test this, remove the extension from the rear axle and either bolt the push rod back on or leave it loose.

 

What @Scuba says is along the lines if what I'm thinking.

 

Have you tried using Kroil? I would soak those bleeder valves in kroil several times, over the course of a week or two. Kroil works a lot better than PB Blast. Try that before you break them off.

 

I had the same thing happen on my old 2000 tundra. Sometimes bumps or choppy road would lead to ABS kicking on for a few seconds. I never figured it out but I thought I remembered reading about an ABS issue. Are you sure the ABS isn't kicking in? The ABS is kicking on because your truck is thinking the wheels are trying to lock up and pulsing the brakes on and off real quick. I think something is happening to trick the ABS to think the wheels are locking up.

 

i have soaked the bleeders in kroil repeatedly. i was considering trying one of those "brake free" tools but im not sure it'd fit in there.

i did see some folks saying they thought it was ABS on other threads. definitely could be. it does trigger abs, but sometimes it just goes out completely for a second (which is a long time when youre trying to stop quick) before the abs starts pulsing.

if its not air in the brake lines (which i havent proven but plan to address) im wondering what portion of this equation of a slight lift in front and rear, BPV relocation bracket, larger tires would be messing with the ABS situation.

fully realizing im a novice compared to a lot of folks here, so apologies if any of my questions / thought processes here are dumb...

 

Try pulling your abs fuse.

 

When you say you have a complete loss of brakes do you mean that you lose pedal pressure or that the pedal stays firm but you don't feel the vehicle slowing?

In rereading your original post I see that you don't mention anything about the rotors. If you put new pads without replacing or turning your rotors that could be your problem if your pedal is staying firm. The pads didn't bed well and are not gripping the rotors proper. I have seen it happen and if your brakes were working fine before the work I always look at the parts that were replaced as a possible cause.

 

Ah yes I left that out! New OEM pads and rotors, reman calipers, braided lines.

pedal stays firm, the brakes just go out briefly (very weird feeling) then go into abs mode.

 

Grasping at straws. The brake work you did shouldn't have changed your brake function. Your problem appears to be related to fluid flow and the only thing you did that could affect that is install the braided lines. Are you positive the hose ID is the same as factory? There are no manufacturing defects inside the hose? I've had replacement parts that I'd swear could not be the source of my problems, be the problem. If it was me I would put the factory hoses back on just to make sure I wasn't going in circles. Anyway, that's all I have as suggestions.

 

Might be time to heat up those bleeder valves..

 

Wheel cylinders are inexpensive. At this point I would just replace them and that would also let you put your own eyes on the condition of the rear brakes.

 

Maybe the ABS sensors are hit and miss. I would think about removing the sensors and cleaning them up. Also I don’t think I would go any further until I get those rear brakes addressed.

 

also going to look into cleaning the sensors and potentially doing new cylinders. kinda terrified of taking those rear brakes apart, but probably smart.

 

hadn't considered this as a potential. i did cross check them before putting on, but could certainly be something wrong with them.

so. many. variables. ugh.

 

Start with the simplest thing. Occam's Razor.
You've got to bleed those rear brakes and LSPV. How difficult is it to replace the bleeder valves? Anyone know?

 

Difficulty will be based on condition.
The bleeder valve is just a threaded plug. I could go replace all 4 of mine in 5 mins. But if they’re rusted solid you’ll be better off replacing the wheel cylinder as previously mentioned.

 

Update: Bled the rears (I’d been soaking them for weeks and they came off easy finally) and removed the BPV extension.

There was air in the right rear for sure and the bpv valve was basically always closed.

I have an AAL and new struts in the back and was told to put the extension in, but it’s not enough to warrant the extension I guess (credit that to old leafs maybe?). Also afterwards put a new cap thing on the back and it’s given it some weight back there which may help.

So far so good! Will be monitoring and report back. Really appreciative of everyone’s help in here!