Vacuum Reservoir? Good Idea?

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sanramonrover
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Isuzu vehicle(s): 1991 KB (AKA TFS) 4X4 with 4JB1 Diesel

Vacuum Reservoir? Good Idea?

Postby sanramonrover » Sat Oct 07, 2017 7:22 pm

I have a 4JB1 diesel in a pickup. This motor is fitted with an exhaust brake, operated by vacuum. The vacuum comes from the pump on the rear of the alternator. Via a TEE the same pump supplies vacuum to the brake booster.

On long gradual downhill runs the vacuum brake works fantastically. However sometimes extra braking is needed, so I step on the brake. After about 15 seconds the system runs out of vacuum and neither the exhaust brake, nor the brake booster work. Turn the exhaust brake off, and in a few seconds there is sufficient vacuum to operate the brake booster.

So, would installing a reservoir tank in the line from the vacuum pump solve this? I realize it would mean that it would take longer to build up a vacuum, but that might just mean idling for a few seconds longer before starting to drive.
1991 KB 4X4
1988 VW Westfalia
1975 Triumph Spitfire

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Paul
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Re: Vacuum Reservoir? Good Idea?

Postby Paul » Sun Oct 08, 2017 11:23 pm

I think a reserve reservoir would help. But, I don't think you should be having this problem. I am thinking you have a vacuum leak in one or both of the brake systems. Neither system should continue to consume vacuum, after the brake is applied.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

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sanramonrover
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Posts: 128
Joined: Fri Oct 11, 2013 11:58 am
Location: Canada & Costa Rica
Isuzu vehicle(s): 1991 KB (AKA TFS) 4X4 with 4JB1 Diesel

Re: Vacuum Reservoir? Good Idea?

Postby sanramonrover » Mon Oct 09, 2017 7:18 am

Thank you Paul. I too had wondered about a leak. Recently had the alternator regulator replaced - which meant the mechanic dismantled the whole unit. Perhaps not re-assembled correctly. Haven't had time to evaluate his work yet.

I have also wondered what the vacuum actuator for the exhaust brake actually is. Is it a piston or flexible diaphragm? Haven't had it apart yet.

Does anyone else have a vacuum actuated exhaust brake on their 4JB1?
1991 KB 4X4
1988 VW Westfalia
1975 Triumph Spitfire