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Discussion Starter · #1 · (Edited)
Just curious if anybody has experience with Vacuum pumps going out. I just bought a 92 4x4 W350 5spd and notice the brake pedal feels alot different than the 93 that I had.

The first step on the brake pedal felt as it should but than continued to the floor. I figured it was the master cylinder and replaced it. It felt better but it still goes farther down than my 93 did. The prior owner told me the truck just has brakes all the way around.

I pulled the rear drums and the right rear was metal to metal. Oil seal had failed and the emergency brake cable was seized. Left side was dry but needed shoes.

Replaced everything and turned drums. The first push on the brake pedal it feels fine but, a second push and the pedal feels harder to push. As if it’s not recovering vacuum fast enough between taking my foot off the pedal. And when I am backing up it’s worse.

I don’t hear the brake booster leaking air anywhere so I am curious as to what kinda characteristics a failing Vacuum pump makes when they start to go out. I’m not ruling out the booster, I’m just trying to figure out which way to go first.

Edit: Forgot to mention vacuum pump is attached to the engine and ps pump is attached to it.
 

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Hook a vac gage up and see what the kind of reading it is giving. Then let us know.
 

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Discussion Starter · #3 ·
Checked vacuum pump tonight.

First test, tested vacuum at booster check valve with accessories still installed. At idle, it measures 5psi and goes up to about 10 psi when idle increases, and stepping on the break pedal it bounces between 12 to 15psi.

Second test, unhooked accessories capped ports and numbers were the same.

Third test, unhooked the hose from the check valve and tested vacuum directly from the pump. Started the engine and it shot directly up to 20psi at idle.

My guess, going by the numbers is that the booster is leaking internally somewhere. Any thoughts??
 

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I think your guess is right on the money.

Our boosters are known for vac seals going bad.
 

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Vacuum booster replacement for non intercooled

The power steering went bad on my 92 W250 and When I tried replacing it, I couldn't get the vacuum pump off the PS easily and ended up mangling the housing and cam bearing.

Now I need a vacuum pump but can't seem to locate one for a non intercooled truck. Anybody have any resources?
 

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You can use a later model vac/PS setup.
 

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The vac pump is different. I am not sure on the PS eather. As a complete assy. The later model pump will bolt on and work.
 

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92 d350 xcab flatbed 5spd. 04 2500 QCSB 4x4 built auto. All over 500k mi
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p/s pumps ARE different from nonIC to IC.

UPdate to the 91.5+ is a near bolt in. You need to trim some of theh bottom of the throttle support bracket, and add an oil supply line for the vacuum pump (I had mine made at a CaseIH tractor dealer in the hydraulic dept).

Dan
 

· I bleed Diesel
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how hard is it to rebuild the vacume pump.? i am putting on a new powersteering pump and thinking about rebuilding it.
 
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