Ok, so a couple months ago I had the issue where I just lost brakes.. All the way to the floor, was able to pump them and get a little ... replaced the master cylinder and alls been good till today.

I was going about 40 when the car started to feel like It was really out of balance, could feel the shake in the whole car. Then is got worse, felt just like I had a front flat on top of the shaking. Pulled over and actually checked the tires... Was running late to work and was close so figured I would just get it the last couple blocks there and deal with it later. Pulled back out and no brakes! all the way to the floor again. Was able to pump them and get just enough to stop the car but just.

Car sat in parking lot 8 hours

After work go to get car and get it home.

Suddenly, brakes feel Tight, hard peddle, but like it had no power brakes. You really have to push on them to stop. Shake, gone. Drove it home an hour and ran fine, get home will not shut off. had to use the shut off lever....

First I was thinking bad or sticking caliper, but now I'm leaning toward vacuum pump failure. Plus why the sudden flat tire like shake? (sticking caliper?) that went away? Just odd... I wish when things broke they just broke so it was obvious.

Oh, this is on the 85 300 TDT.

A vacuum leak in a gas engine could make the engine shake (lean), but shouldn't affect a diesel much, except that the EGR is vacuum operated. If originally a CA 85 car, it also has a turbo air valve in the EGR controls.

Often when a booster goes, the tear in the rubber diaphragm self-seals as you brake, making the brakes come on suddenly stronger, sometimes throwing you into the windshield. However, you could be losing vacuum from many things (bad pump, leaking trunk or gas-door lock). I would plumb a temporary vacuum gage to different suspect points and monitor it as you drive.

... odd, for sure.
pedal to floor, could be low fluid, or a stuck caliper, causing the fluid to boil...
no shut off, sure sounds like VP to me...
shaking COULD have been caliper, but I guess a failing vacuum pump might cause engine shake enough to feel strange...
I agree, troubleshooting would be simpler if a red flag popped up and said !here I am... fix this!

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I had everything from the cab back disconnected vac wise. So only things could be engine and trans. going out to see if I can "see" anything" but looks like I'll be parking her for a while till I figure this out.

Looks like vac pump... I disconnected everything from the main vac line and hooked up the Mighty vac, I get almost no reading (maybe 6) I can just feel a little vac there but just. The mighty vac starts reading at 5 so it does not really even register. I think I should have around 14? I thought I had it when I found a broken tee... but alas that was not it. Checked all the lines etc and car will still not shut down on it's own and still no power brakes. Now the tough call, order a new Vac pump, or steal the one from my new engine for now.

If you have to press really hard to stop......like using 2 feet.....but still have good pedal resistance, then you most probably have NO vacuum assist. Key not turning off engine confirms loss of vacuum. I'd disconnect the main vacuum hose from the vacuum pump, start the car, and feel for vacuum at the top of the vacuum pump. If you don't feel any, then remove the vacuum pump and check to see if the bearings are still all there. If so, then replace or rebuild the vacuum pump.

__________________
daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

Yup, that was exactly my next step but I had to leave for work. Hopefully weather is good tomorrow.

I thought I read you say originally that you had almost 30" Hg vacuum directly from the pump. Was that someone else's post or did you edit your first post? I know I am getting old. I still don't see how loss of vacuum could make the whole car shake (or the engine).

Maybe a failed check valve?

Perhaps you can remove that and check for any stronger vac.

__________________
83 SD

84 CD

Ok, so tested the cars pump today. Almost 30 pounds of vacuum at the pump. Same at other end of the main vac line if removed from booster. So pump seems fine.

Oddly, I can't seem to get any readings from any of the secondary lines.

I guess next step is to pull the vac diagram and go though it with a fine tooth comb.

Still, with that kind of vac, the booster should have been working... Wonder if it's whats bad.

Wait! I may have found the answer in another thread.... http://www.peachparts.com/shopforum/diesel-discussion/318994-w123-brake-booster-failure.html

Broken check valve... Will check that tomorrow, but the symptoms are exactly the same.

I caught your reply after finding the other thread lol.

I think the shacking is possibly unrelated... unless this caused my pass front brake to lock up just enough to feel like I had a flat? Odd that it went away and then the brakes failed.

I'm leaning toward the check valve in the vac pump currently, just need to take a look.

Well, it does not seem to be the check valve. I removed it today and it worked just like it should. Does not even look all that old to begin with. So more trouble shooting. Cars been down for over 2 months now.