"71 FJ40 won't run with vacuum line from Carb connected to Brake Booster. Disconnected and plugged the line and she runs good. Vacuum gauge check at the '71 brake booster, drops rapidly. I Pulled brake booster from my '89 FJ62, should I install it on the '71?? Anyone know how to check a brake booster? Do I really need one on the FJ40?? Thanks.
Brake Booster Vacuum?
- Thread starter Derf62
- Start date
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If you're getting a huge vacuum leak when you connect that line, it could only be a bad booster or a big hole in the hose. Assuming you plugged the line at the booster end, you've got a bad booster. You've already done the test.
A failed booster will make it difficult, but not impossible, to apply the brakes. I don't think it would be safe to run with a failed booster for any length of time.
I can't help you on fitting a different booster to your 71. Maybe someone else can.
A failed booster will make it difficult, but not impossible, to apply the brakes. I don't think it would be safe to run with a failed booster for any length of time.
I can't help you on fitting a different booster to your 71. Maybe someone else can.
The booster off the FJ62 will bolt up. But, the length of the brake pedal push rod under the dash may be a different length. I used a booster out of a mini truck (don't remember the year) and had to add a 3/4" spacer between the firewall and booster to compensate for the mini's longer push rod. Sometimes these spacers can be found already on the vehicles the booster comes off of. I got a piece of 3/4" thick aluminum and made my spacer.
The master cylinder to booster push rod length may need to be adjusted also. Put a very tiny bit of grease (smaller than the match head in a book of matches) on the end of the rod that goes into the MC cup. Very carefully attach the MC to the booster and then carefully remove it. The bit of grease on the end of the push rod needs to show that it just barely touched inside the MC. There needs to be a space of only a few thousandths of an inch between the cup in the MC and the push rod.
One other thing to know, the 40 series booster has a check valve built into where the vacuum line connects. I'm not sure about the 62 series, but the mini truck check valve was in the vacuum line itself, not in the booster connection. The check valve is a must have for proper booster operation.
Don
The master cylinder to booster push rod length may need to be adjusted also. Put a very tiny bit of grease (smaller than the match head in a book of matches) on the end of the rod that goes into the MC cup. Very carefully attach the MC to the booster and then carefully remove it. The bit of grease on the end of the push rod needs to show that it just barely touched inside the MC. There needs to be a space of only a few thousandths of an inch between the cup in the MC and the push rod.
One other thing to know, the 40 series booster has a check valve built into where the vacuum line connects. I'm not sure about the 62 series, but the mini truck check valve was in the vacuum line itself, not in the booster connection. The check valve is a must have for proper booster operation.
Don
- Thread starter
- #4
Booster
Thanks for the info guys. The control cylinder (brake pedal side) of the boosters are not centered between the mounting bolts. The '71 has the short side down while the '89 has the short side up. I removed the master cylinder from the '89 booster, and had to rotate it 180 deg. (upside down from its original position from the FJ'62). I did cut 3/4 inch off the threaded adjusting end and added a washer between the firewall and booster (never thought of just using a wider shim or washers for a spacer like handcannon did). I will use the master cylinder from the '89 to avoid any differences between the '71 Master cylinder piston and the '89 booster piston rod.
Any way to check if the check valve need replacing?
Thanks for the info guys. The control cylinder (brake pedal side) of the boosters are not centered between the mounting bolts. The '71 has the short side down while the '89 has the short side up. I removed the master cylinder from the '89 booster, and had to rotate it 180 deg. (upside down from its original position from the FJ'62). I did cut 3/4 inch off the threaded adjusting end and added a washer between the firewall and booster (never thought of just using a wider shim or washers for a spacer like handcannon did). I will use the master cylinder from the '89 to avoid any differences between the '71 Master cylinder piston and the '89 booster piston rod.
Any way to check if the check valve need replacing?
It's been several years since I did my booster swap and completely forgot about having to rotate and set the booster upside down on my 40 as compared to how it was mounted in the mini. Orientation doesn't make any difference in the working operation of the booster.
To test the check valve with the booster in the 40, after having the motor running and vacuum in the booster and then shutting down the motor you should have at least two pumps of the brake pedal before losing the boosted feel.
Alternatively, putting a vacuum gauge in the vacuum line between the booster and the check valve should show residual vacuum after motor shutdown, as long as you don't touch the brake pedal. I'm not sure just how long it should hold though since I've never tried this.
Don
To test the check valve with the booster in the 40, after having the motor running and vacuum in the booster and then shutting down the motor you should have at least two pumps of the brake pedal before losing the boosted feel.
Alternatively, putting a vacuum gauge in the vacuum line between the booster and the check valve should show residual vacuum after motor shutdown, as long as you don't touch the brake pedal. I'm not sure just how long it should hold though since I've never tried this.
Don