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The Transmission On My 1979 Chevy Coachmen Motor Home Will Not Shift

by Dennis
(Hazleton, PA, USA)

I only have reverse and low 1st gear, what could the problem be and what trouble shooting can I do? It has a 350 engine tranny model MX1 option # NA1 standard emissions engine class 113.

ANSWER: Greetings Dennis thanks for submitting your question on our Ask An RV Question Page.

I will tell you up front that there are not a lot of things that a do-it-yourselfer can do to repair a transmission. Unless you have been trained to rebuild a transmission, it is not something you want to tackle. There are a couple things you can do to see if we can diagnose the problem of your transmission not shifting. Please follow the steps below.

1. Look under your RV for signs of any transmission fluid leakage. Even a little leakage of transmission fluid is neither normal nor acceptable. If you find a leak it will have to be repaired.

2. Check the transmission fluid. Your RV should be on level ground, engine warmed up and still running with the transmission in park (and emergency brake on). Locate the transmission fluid dipstick and check the level of fluid as well as look at the fluid on the dipstick.

If the fluid is clean looking, but low you will need to top it off. Low fluid levels in the transmission can cause the fluid to get aerated which can damage a transmission. Overfilling the transmission fluid can also cause the fluid to become aerated.

When adding fluid to the transmission the engine should still be running etc. Put the fluid in slowly and check the level often. On your transmission the difference between the Add mark and the Full mark is only 1/2 quart of transmission fluid. You do not want to overfill the transmission.

If the fluid is dark brown in color the transmission fluid needs to be changed immediately. When getting the transmission fluid changed make sure that the fluid in the converter and tranny oil cooler are also drained and flushed (this is not always done, but it should be).

Just a note here because this transmission is in a motorhome it is considered to be a heavy duty use, so the transmission fluid should be changed every 25,000 miles.

If the transmission fluid is a dark brown color with dark brown specs in it and has a varnish smell to it then in all likelihood the transmission has damage and needs to be rebuilt.

If the transmission fluid is milky pink in color it means that the tranny cooler is leaky into the radiator and the radiator fluid is going into the transmission damaging the transmission.

If you are frequently getting low on transmission fluid and there are no leaks but you notice a whitish smoke coming out of your RVs exhaust system it means that the Vacuum Modulator is bad and it is allowing the transmission fluid to go into the engine.

3. With the engine running, listen for any vacuum leaks on your engine. If you hear a sucking or air sound from any of the engines vacuum lines you need to repair them. Because a vacuum leak can cause a problem with the transmission shifting properly. If you did find a vacuum leak and repaired it and the transmission fluid was OK you might try driving the RV to see if it shifts. If not I am afraid that you are going to have to have your motor home towed to a repair facility that works on transmissions.

I hope the above information helps.

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Happy RVing

RVing Al

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