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Discussion Starter #1
Hi,
I am new to the forum. I recently bought a 1972 Mustang convertible with a 351c, 2 barrel, and an automatic transmission. The car has been 90 pecent restord. The transmission, I am told was a rebuild transmission. When in reverse it rumbles and slips if i give it gas while backing up. It has been rebuilt about 5 or 7 years ago and the car may have been sitting around for a few years. Could the filter and fluid just need to be changed or could there be more going on. It appears to be fine in all of the forward gears.

Thanks
 

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Changing the fluid and filter couldnt hurt. Make sure you have
type F fluid in your trans. All Ford transmissions built before 1977 need this to work properly. The chatter you talk about is a classic sign of having dex/mercron in it.
I'm just curious how well it works in forward gears? Reverse is a combo of low/reverse clutch pack and the direct clutch pack which is 3rd gear. Check to make sure you have compression braking in low range. To check this just pull out onto a side street with no traffic and select 1 st range on the gear selector. Accellerate to about 15-20 and then let off the gas. You should hear and feel the car decellerating. If it chatters and/or slips I'd say first try the cheap route which is flushing the trans fluid and changing to
Type F.

Here is the textbook definition of why you need Type F or not. I got this from my intro to automatic transmissions book from tech school.

".....The various chemicals added to ATF ensure its durability and overall performance. Zinc, phosphorus, and sulfur are commonly added to reduce friction [friction modifiers]. Detergent additives are added to ATF to help keep the transmission parts clean. Dispersants that keep contaminants suspended in the fluid so they can be trapped by the filter are also added.

Because some chemicals used in the composition of transmission fluid may adversely react with the fibers or synthetic materials used in the seals of the transmission, the compatibility can result in external and internal transmission fluid leaks due to deterioration, swelling and/or shrinking of the seals."

"To reduce ware and friction inside a transmission the most commonly used transmission fluids are mixed with friction modifiers. Fluid types A, CJ, H, Dextron, and Mercon have friction modifiers [reduce friction] added to the ATF. Transmission fluids with these additives allow for the use of lower clutch and band application pressures, which, in turn, provide for a very smooth feeling shift. Transmission fluids without a friction modifier, such as type F and G tend to have a firmer shift because higher clutch and band application pressures are required to avoid excessive slippage during gear changes.

If an ATF without friction modifiers [type F] is used in a transmission designed for friction modified fluid [Dextron III] the service life of the transmission is not normally affected. However, firmer shifting will result and the driver might not welcome this change in shifting quality. Transmission durability is effected by using friction modified fluid in a transmission designed for nonmodified fluids. This incorrect use of fluid will cause slippage, primarily when the vehicle is working under a load. Any amount of slippage can cause the clutches and bands to ware prematurely. Also, because of the high heat generated by the slippage, the fluid may overhead and lose some of it's lubrication and cooling qualities, which could cause the entire transmission to fail." Hope this helps.
 

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Discussion Starter #3
Thanks for the reply. I will try this and get back to you. The car appears to be fine in forward, but I do question third gear. It doesn't feel like it shifts into third.
 

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:kooky: Welcome to AFM. :yup:
 
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