New FJ owner with brake problem (1 Viewer)

[Boiler Guy]

First post, first FJ40, This unit was built in 76, sometime during its life it was rewired with a painless fuse box, of course all the labels are faded away. I believe at a later date a Mercedies OM617 5 cylinder turbo diesel was installed.

I took delivery in December and have been working on small repairs , lighting/ electrical, door handles, general inspection, oil change ect. Now that the weather is warming up I plan to get more serious. On the brake problem, one of the front calipers was stuck so both replaced with new pads, disk were OK. Also replaced master cylinder. I have not had the rear wheels off yet so thats unknown. The brakes are week, I first suspected a vacuum problem, found vacuum low around 5 inches, this was converted from millibars as thats what the gage from Amazon displays. I removed vacuum pump from Diesel, cleaned and inspect and it was in nice shape, after more investigation I learned the outlet check valve fails causing low vacuum, I installed aftermarket check valve and vacuum jumped to 20 inches. I expected my problem was solved, NOT I have never worked with a vacuum brake booster, not sure if that is part of the issue or maybe the proportioning valve. I will add no apparent leaks. looking for direction.

another issue I have is leaking transfer case, front output shaft is loose, rear is leaking oil and I expect a few dried-out gaskets, I intend to remove and rebuild t case, is it reasonable to remove t case and leave trans in place, helpful hints here appreciated also.

 

[TheBussman]

can you be more specific on the brakes being weak?
the pedal is low?
the pedal is soft?
the pedal is hard?
removing the drums is a great place to start, see if the wheel cyls are leaking, what the shoes are like.
did the brakes feel ANY different after you fixed the vacuum issue? should have felt much easier to brake going from 5 to 20 inches.

 

[Boiler Guy]

can you be more specific on the brakes being weak?
the pedal is low?
the pedal is soft?
the pedal is hard?
removing the drums is a great place to start, see if the wheel cyls are leaking, what the shoes are like.
did the brakes feel ANY different after you fixed the vacuum issue? should have felt much easier to brake going from 5 to 20 inches.

The peddle does not appear to bottom out but I have to stand on it to get mild braking action, even if the rear axle drums are all froze up, I know the front should work, I think today the drums come off for inspection as I have at least 1 broken wheel stud to replace.

 

[Pighead]

If you really have to stand on the brake pedal to get any braking I might suspect the booster first. 20" of manifold vacuum should be plenty for it, have you checked to see if you are getting 20" at the booster? when you replaced the Master Cylinder did you adjust the pushrod between the booster and MC?
Do you have the one-piece Toyota transfer case? You can certainly remove it from the transmission to rebuild it.

 

[pb4ugo]

Make sure the brake booster holds vacuum. Check the rear drums and adjust them. The rear brakes don't self adjust, so they need to be adjusted periodically. Rear brake adjustment effects pedal height.

 

[TheBussman]

yea check the booster or check for a clogged check valve on the booster.

did the brakes feel ANY different after you fixed the vacuum issue? should have felt much easier to brake going from 5 to 20 inches.

 

[60 40]

So...

" I believe at a later date a Mercedies OM617 5 cylinder turbo diesel was installed."

That's not a very common engine swap but guessing very reliable, good MPG and inexpensive and easy to source replacement parts?


If you want to remove the transmission and transfer case together as a unit, remove driveshafts, speedo cable, reverse light wire and then support with tranny jack or remove seats and tranny cover and use engine hoist and chain in the cab. Remove bolts to bell housing then either slide transmission and transfer case back and lower from below with tranny jack or use the engine hoist to back out and lower to the floor or dolly.

 

[65swb45]

As it was explained to me 30 years ago, on a diesel conversion it is necessary to install an intermediate vacuum reservoir to hold vacuum between the engine and the brake booster. A diesel will not naturally produce any vacuum of its own. Chances are that you have a vacuum pump on the engine; the pump will not produce enough vacuum in real time to properly operate the booster.

This does not eliminate the possibility that your booster is bad

 

[45Dougal]

Yea you should have a vacuum reservoir under the passenger side floor, but of it was originally petrol then you won't have that. I found one for mine from an Isuzu trooper - you'll struggle to find an original one.

Your master cylinder has two pressure switches on it which should be connected but aren't.
These tell you which circuit is short of pressure when you press the pedal and should illuminate a warning light.
I suggest that you connect a continuity meter to each of these in turn, and press the pedal to see which circuit is causing you problems - possibly both.
The switch should connect circuit to ground when there is no pressure, and be open circuit when you press the pedal.

 

[mrboatman]

You can also use one of these 009428081 Electric Vacuum Pump Power Brake Booster Auxiliary Assembly For GM | eBay - https://www.ebay.com/itm/145200743370 if you don’t want to mess with a canister.

 

[45Dougal]

You can also use one of these 009428081 Electric Vacuum Pump Power Brake Booster Auxiliary Assembly For GM | eBay - https://www.ebay.com/itm/145200743370 if you don’t want to mess with a canister.

That looks identical to mine, but it still needs a reservoir.
If you want to go down this route then let me know and I'll share a few tips, but it sounds like your mechanical pump is working fine.

 

[TheBussman]

the Mercedes 300d that the engine came out of does not have a vacuum reservoir (for the braking system) and those cars stop fine. I'm pretty sure the advantage of the vacuum reservoir is that if you make frequent hard brake pedal presses at low engine RPM you'll never run out of vacuum. it would not be a bad idea to add one after the OP fixes the brake problem.

 

[45Dougal]

the Mercedes 300d that the engine came out of does not have a vacuum reservoir (for the braking system) and those cars stop fine. I'm pretty sure the advantage of the vacuum reservoir is that if you make frequent hard brake pedal presses at low engine RPM you'll never run out of vacuum. it would not be a bad idea to add one after the OP fixes the brake problem.

That's exactly what it does; if I hit the brakes, then my tank vacuum drops, and the pump powers on for about 10 seconds to recharge it - the 40 had a fairly big Booster tbf.

Are you certain about the Merc? There's a big one in the back for the locks etc, but i thought there was also one in the wing for the brakes? (I'm not a Merc guy at all btw).
They seem pretty common in modern diesels now across the board

 

[Boiler Guy]

yea check the booster or check for a clogged check valve on the booster.

did the brakes feel ANY different after you fixed the vacuum issue? should have felt much easier to brake going from 5 to 20 inches.

no difference

 

[Boiler Guy]

Update, removed rear brake drums to find only 1 wheel cylinder on each side moved, ordered 4 new, drums and shoes looked good.
I did verify check valve at brake booster is working and that was good. I have a small tank I can plumb in for an experimental vacuum reservoir , I am thinking a new Brake booster is in my future.

On the transfer case subject, I did remove it, kind of tight getting it off the trans output shaft and clearing crossmember, the seal was loose on the shaft, not so sure I will be able to reinstall without damaging seal, TBD. Dismantling TC that apparently had water in it at one time was a joy, bearings stuck to shaft. Overall gears looked good, bearings were beyond shot.

Thanks for the input.

 

[TheBussman]

no difference

yea your on the right track. a smoke machine test would reveal any leaks in the booster, pretty sure its bad if changing your vacuum supply makes no difference.