Rick's Free Auto Repair Advice

Transmission slipping

Transmission slipping, won’t go forward, clunks, won’t shift

When a transmission starts slipping, clunking, not shifting, or won’t move, it doesn’t take a brain surgeon to know something is major league wrong with it. Owners who have ignored maintenance on their vehicles up to this point usually engage in “magical thinking” by thinking that a transmission fluid change will fix the problem. Dream on! All of the problems are caused by improper pressure inside the transmission that prevents clutches and bands from applying full force. Low pressure can be caused by seals that have hardened or cracked and no longer seal properly. Not changing your transmission fluid on time contributes to this accelerated aging and cracking. And low pressure can also be caused by a faulty shift solenoid. Finally, low pressure can be caused by a worn pump (you guessed it, not changing your fluid causes accelerated wear in the pump).

Rather than waste your money on a transmission fluid change (and it will be a waste of money at this point), get it to a transmission repair shop so they can do a diagnostic check first. Now, DIYers also run to the auto parts store and buy “miracle” transmission fix products. What are they? Well, they’re seal swellers. That’s right. Dump in the miracle and drive the vehicle. The chemical softens the seals and make them seal tighter. Do these products work? YUP—but only for a while.

If all you need is 6 more months of life out of the old beast, go ahead and dump in a can. Just don’t delude yourself into thinking that you’ve fixed the root problem. You haven’t. You’ve just put a short lived band-aid on it. On the other hand, if you plan to keep your vehicle for a long time, dumping in one of these seal sweller products can actually cost you far more money when you really do get around to the repair. Like I said, seal swellers help the seals work better. But they never seal 100% like new seals. So there’s always some pressure loss. And when there’s pressure loss, there’s slippage. Slippage causes excess heat, and excess heat causes transmission fluid breakdown, which in turn reduces it’s cooling and lubricating abilities. See where this is going? Yeah, when it finally fails, that single can of transmission fix will probably add $500 more to the cost of the rebuild due to additional damaged parts.

The best way to prevent transmission damage is to change your transmission fluid at regular intervals and make sure the shop uses ONLY the manufacturer’s recommended fluid.


© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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