# 1991 Pontiac Bonneville - losing tranny fluid and gaining oil

**URL:** <https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676>\
**Category:** Maintenance/Repairs\
**Tags:** pontiac, bonneville\
**Created:** [October 1, 2020, 3:38am UTC](https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676 "2020-10-01T03:38:42Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![snowback](https://avatars.discourse-cdn.com/v4/letter/s/ed8c4c/32.png) [@snowback](https://community.cartalk.com/u/snowback)\
**Post date:** [October 1, 2020, 3:38am UTC](https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676/1 "2020-10-01T03:38:42Z")

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im losing tranny fluid and gaining oil

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**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\
**Post date:** [October 1, 2020, 3:57am UTC](https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676/2 "2020-10-01T03:57:44Z")

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And if you keep driving that way you will need a new engine at the very least .

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**Author:** ![oldtimer-11](https://avatars.discourse-cdn.com/v4/letter/o/e79b87/32.png) [@oldtimer-11](https://community.cartalk.com/u/oldtimer-11)\
**Post date:** [October 3, 2020, 2:12am UTC](https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676/3 "2020-10-03T02:12:37Z")

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Sounds like a bad vacuum modulator and worn rings/

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**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [October 3, 2020, 2:23am UTC](https://community.cartalk.com/t/1991-pontiac-bonneville-losing-tranny-fluid-and-gaining-oil/170676/4 "2020-10-03T02:23:58Z")

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Remove the vacuum hose from the vacuum modulator.

If transmission fluid leaks out of this connection, transmission fluid is being sucked out of the transmission and into the engine.

Here’s how to replace the transmission vacuum modulator.

[![](https://global.discourse-cdn.com/cartalk/original/3X/6/7/6762ba40f46bb592da21b29b410e2c4e9dbddfe7.jpeg "Transmission modulator replacement (early GM 4T60-E models)") ](https://www.youtube.com/watch?v=ram2Ni0aUPM)

Tester