Having problems with your 1996 Chevrolet Suburban ?

Auto transmission violently shifts after running at highway speeds

\015 1996 c1500 with 126xxx miles on it. Runs well around town but after highway running for about 20 min, the tranny begins to violently shift into second and third. Check engine light is on, but its always on. Any thoughts?\015 Posted / edited by AnonymousUser on : 26-02-2018

Answers :

You should have a P1870 error code stored, which is telling you the transmission is slipping. Reason for it is there's a bore inside the valve body that gets worn out; repair involves either replacing the valve body, or using a kit to **** the bore out to sleeve it. Either is acceptable and honestly the kit seems more like a long-term fix to me.

Any HONEST transmission shop will only charge you a few hundred bucks at most for this.

The problem isn't correcting because the transmission cools off; the code is cleared out when you're turning off the engine, and it takes a little while for it to set again. This is consistent with the behavior for the P1870 code. In a nutshell what is happening is the computer detects the transmission slipping a little due to loss of pressure from the internal leak, and boosts the line pressure in an event to save the transmission. This results in the harsh 1-2 shift. The other shifts are firmer too but they're softer by design than 1-2 so you don't notice it nearly as much, if at all.
Sounds like a possible accumulator spring problem. Many are externally accessible. don't know for sure on yours. Also check if you have a vacuum modulator on unit. that can do much the same thing ((small pot mounted on left side with vacuum hose attached)
Repair Help & Product Troubleshooting for 1996 Chevrolet Suburban

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