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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Feb 2016 Posts: 1,989 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,989 | I have been chasing an "off idle hesitation" on the '57 LCF. I figured after I finished the new exhaust it would improve, I also cleaned the carb and put a new kit in it, dialed in the ignition dwell and timing. Still some hesitation after all of that so I connected my vacuum gauge and fine-tuned the idle mixture, a little better but not great. Then I disconnected and plugged the vacuum line that feeds the brake booster and 2 speed differential and had a big improvement in idle vacuum. I then isolated the 2-speed shift circuit, not much change in vacuum. I thought dangit!, that HydroVac rebuild is not very old, but I never checked the leather oil in the last couple years. Added oil to the site plug and now have great idle vacuum and great throttle response! I'm old but can still learn something new.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: Aug 2010 Posts: 601 'Bolter | | 'Bolter Joined: Aug 2010 Posts: 601 | My Hydrovac was new in the '90s, so I don't know if it still has the leather seals that require oil. Also not 100 percent sure where I'd put it, or what type of oil. Would something like power steering fluid work? I also have suspension fork oil from 5 to 15w to hand.
It does work just fine, although I do notice an intermittent lean/rough idle condition. I haven't really chased that down tho.
Last edited by Tronman; 03/04/2024 2:18 AM.
1965 C60 school bus | 1967 GMC 6500 school bus
| | | | | Joined: Feb 2016 Posts: 1,989 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,989 | My HydroVac is a Bendix brand, the site plug/oil fill port is on the end of the large vacuum can, the plug is quite low on the end as it is a deterrent to overfilling. I use motorcycle fork oil, the original specs called for shock absorber oil, I figure the fork oil is about as close to shock oil as I can get. I rebuilt my HydroVac, the kit was complete with a leather vacuum seal, I would expect yours to be the same.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: Sep 2011 Posts: 1,455 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,455 | Great lesson that an engine problem isn't always an engine problem!
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Feb 2016 Posts: 1,989 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,989 |
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | I think any 10 weight oil like sewing machine or 3 in 1 oil will work to keep the leather soft.
Mike B | | |
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