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Old 05-03-2021, 09:25 PM   #1
dagnabbitt
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Jumps in Reverse

I just took my 70 swb out of hibernation. Power steering fluid and oil were down and battery is on its last legs. What concerns me though is when I put it in reverse it jumps a few inches backwards even with the brake on. Does not do that when moving forward. Hoping my rear diff isn't shot, looking for a diagnosis and advice. Thx in advance!
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Old 05-03-2021, 09:29 PM   #2
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Re: Jumps in Reverse

A stuck or dragging brake? Automatic or manual transmission? If auto did you check the fluid?

Last edited by body bolt; 05-03-2021 at 09:35 PM.
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Old 05-03-2021, 10:24 PM   #3
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Re: Jumps in Reverse

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A stuck or dragging brake? Automatic or manual transmission? If auto did you check the fluid?
It'd an automatic, don't think it is a brake issue. Will check the fluid level, thank you.
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Old 05-03-2021, 11:36 PM   #4
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Re: Jumps in Reverse

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Does it kill the engine if you put the brake on in reverse? My '39 Ford Coupe did that and it was a vacuum leak in the line to the modulator. 350/TH350. Check all of your vacuum hoses....

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Old 05-04-2021, 08:04 AM   #5
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Re: Jumps in Reverse

If it hits hard in reverse, maybe the idle is too high??
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Old 05-04-2021, 12:04 PM   #6
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Re: Jumps in Reverse

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Does it kill the engine if you put the brake on in reverse? My '39 Ford Coupe did that and it was a vacuum leak in the line to the modulator. 350/TH350. Check all of your vacuum hoses....

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No, it doesn't want to stall, it just flies backward
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Old 05-04-2021, 12:04 PM   #7
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Re: Jumps in Reverse

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If it hits hard in reverse, maybe the idle is too high??
I was thinking that, but wouldn't it do the same moving forward?
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Old 05-04-2021, 12:32 PM   #8
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Re: Jumps in Reverse

Maybe a bad motor mount ?? .....
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Old 05-04-2021, 12:40 PM   #9
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Re: Jumps in Reverse

My guess is brakes . Reverse is a very low gear as opposed to forward gears . So it can overpower the brakes if they aren't working properly.
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Old 05-04-2021, 01:00 PM   #10
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Re: Jumps in Reverse

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No, it doesn't want to stall, it just flies backward

I would still check all the vacuum lines and the modulator.

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Old 05-04-2021, 03:42 PM   #11
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Re: Jumps in Reverse

Sometimes the slack in the differential spider gears can cause slack in the differential.
Looks like excessive backlash in the gears but it's not. It can jump when the slack it taken up.
A lot of good suggestions on things to check on. This Board is a wonderful resource.
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Old 05-04-2021, 03:56 PM   #12
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Re: Jumps in Reverse

.

I'm thinking brakes. Imagine if the hardware in the rear needs adjustment or is just worn out. Add a little slack in the gears the rear may not have much rear brake force applied when you place it in R. With the R being lower geared and nothing stopping the rear axles it could pull the truck back a bit.

Try putting your parking/hand/foot brake on as hard as you can before shifting to R.

-klb
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Old 05-04-2021, 05:31 PM   #13
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Re: Jumps in Reverse

Thanks for all the suggestions, I will be checking my vacuum hoses and modulator, but the brake question is a good one too, it has 4 old drums on it and it might be as simple as that. Thanks again everyone I appreciate it.
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