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79 F250 460 w/ C6 - Problem when shifting into reverse

Hi all - I have a 79 F250 2wd Supercab with a 460 and C6. This weekend I encountered an issue that is new to the truck. When I shifted the truck into reverse to back out of my driveway, the RPMs increased by 1500-2000 above normal idle speed. Thankfully, my foot was on the brake, otherwise I'd have been in the rosebushes across the street! To give an idea of the engine speed, it was enough to power-brake the rear wheels. I immediately threw it back into park and the idle went right back to normal. I repeated this a couple of times to make sure it wasn't a one-time fluke, but nope, every time I put it in reverse, it wanted to make a run for the hills. Next, I rapidily shifted from park to drive without any issues. Once in drive, I was able to shift from D to N and back to D to 2 to 1 with no change in RPM (idle speed). Then shifted from N to R and same thing - high revs. At this point I shut things down to consider what the problem may be.

It appears to be strictly a reverse issue. I haven't had a chance to do any troubleshooting yet, so I thought I would reach out to the community for thoughts on the issue. My initial thought is it's an issue with the linkage, so I'll probably start there. I don't know a lot about transmissions but can't imagine that being the problem. The only other thing that came to mind was a vacuum problem, but again, I don't have a lot of experience there either.

Any thoughts, tips, ideas will be appreciated. Thanks!


Staff member
Definitely check the linkage, specifically the rod that goes from the carb to the kickdown on the transmission. That is the only direct connection between throttle and transmission. I doubt the vacuum has anything to do with it as it only controls shift points. If it were to fail, you can actually draw transmission fluid into the intake.

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