compatible brake booster?

[mad4hws]

Hi everyone,
So, doing a little work on the Minion Missle the past few weekends. It started with noticing that one of the reservoirs on the master brake cylinder was bone dry. Filled it up and bled the lines and still almost no response from the brakes. I had a new master cylinder and decided to put it in. I also bought new Motive power brake bleeder and completely replaced all of the brake fluid with fresh.

Even after doing this, there is very little response from the brakes. At this point, the only thing I haven't replaced has been the booster. Does anyone have a recommendation on a replacement? Not sure if that is the culprit, but might as well put a new one on.

thanks.
Don.

[RiverPatrol]

Could you explain what you mean by 'no response from the brakes?' Are the wheel cylinders not responding? Pedal feels mushy or sinks to the floor? Barely wants to stop?

[Esteban]

RiverPatrol questions will help with the troubleshooting of the problems your facing. In situations like this I like to tackle one issue at a time, so not to compound unsolved problems.

Don, there's ways to check if the booster is working. I will try to rule out that first, before jumping into replacing it. I was looking at pictures of your engine bay, and it's difficult to see from there what brake booster could be a good replacement. The booster you have is a good adaptation done by the previous owner, but if they kept the original master cylinder, chances are that the booster might have come from an 80s model Patrol, like the G61 (no other Nissan/Datsun model in Colombia from what I know) so nothing that can serve you here for searching a spare.

If the booster is working ok, you'll notice a substantial difference when you try to brake with the engine off, and with the engine on. Let's say that you're on an incline in neutral, and then do a braking test. First with the engine off. Pump the brake pedal a couple of times to deplete the remnant vacuum that might be present in the booster (if it's good) then let it roll on the incline and brake. While you're still braking, start the engine and notice whether the braking improves or not.

I found this guide on the internet that will probably help you:

https://axleaddict.com/auto-repair/Bad- ... ster-Check

[mad4hws]

Could you explain what you mean by 'no response from the brakes?' Are the wheel cylinders not responding? Pedal feels mushy or sinks to the floor? Barely wants to stop?

Hi RiverPatrol and Estaban. Thanks for the replies and thanks for trying to read my cryptic post.

The brakes worked well a few months ago. Then life got in the way and I got busy with other things (i know, I know). I found time one day to fire it up and run it around the culdesac. Good thing I didn't go very far because the brakes were 90% gone. There was enough there to stop me, but just barely. When I checked the master cylinder, I found that one of the reservoirs was bone dry. The other was fine. I topped off the fluid and bled the system (Manual pumping of the brakes). That didn't do anything. Brake pedal still very very spongy. It didn't drop to the floor, but it didn't take much effort to push it all the way down.

#1 Daughter and I decided to replace the master cylinder. Seemed like a good thing to do at the time as I had one from Australia sitting in the box waiting for such an opportunity. We removed the old one and put in the new one. We bled the brakes the same way and ended up with the same result. After thinking about it over the weekend, I figured that we were bleeding the brakes incorrectly and there was still air in the lines. I purchased a Motive Products power bleeder and 64 ounces of Dot3 Brake Fluid. Saturday, we hooked it up and replaced all of the fluid in all of the lines. Some of it was really nasty - no telling how long it was there. Probably 50 years. Anyway, I thought that was it, but even after having done that, there was no change in the result. Brake pedal still has very little resistance.

I jacked up the rear axle to see what it behaved like in-gear. The brake pedal did work at stopping the rear axle. I haven't done the same to the front yet. In addition to replaced master cylinder, I have rear wheel cylinders and brake pads. I haven't done the same for the front. I suspect that the front doesn't work at all. Could all of the cylinders be frozen? Seems somewhat unlikely as the last time i had driven it (maybe 3 months ago) they worked fine, but maybe? Hard to tell I guess without pulling off the wheels and evaluating further.

Any ideas out there as I contemplate next steps? I do need to rebuild the booster at some point, so if someone has ideas on that, please let me know.

Thanks all.

[Esteban]

I think you need to open the front axle brakes and check the 4 wheel cylinders. I don't think the booster could be at fault here, since even with a failed booster you will be able to brake, although with a lot more effort. I suspect that one or both of the wheels will be soaked with brake fluid inside. Some people recommend relining the shoes in that case. I had a leak a few months ago that I left unattended for two months (didn't move the car). One side had the shoes soaked in fluid, and since they were in good condition still, I put them is water with detergent for a couple of days, and then cleaned again with hot water and let dry for a couple of days. After correcting the leaking cylinders, the cleaned shoes worked just right. (disclaimer to follow )

In situations like this I don't like to tackle two issues at once, and rather go one by one, starting with the simplest one.

Post some photos of your progress.

[RiverPatrol]

When you bled the brakes with the power booster what sequence did you use? Which wheel didi you start with and end with?

You've definitely got a leak if one of the reservoirs was empty. Go with Esteban's suggestion.

[mad4hws]

Hi guys,
So after some deliberation, I decided to crate up the spare axles that I pulled from the chassis last year and send them to L60Boerne's guy down in TX. I tried to find a local guy, but no one was interested or gave me any confidence. After speaking with Rafael, he's the right guy to work on these and the shipping costs are worth it. it didn't make sense for me to overhaul the brakes on the front axle when the rest of the axle was suspect. Until we get these back, the patrol will be relegated to driving around in the culdesac at really low speeds. I'll update my thread as the project gets underway.