Diagnosis for an automatic gearbox with hiccups

Hello Paul, what causes jerking of an automatic vehicle after engaging the gear lever at D (Drive)? Previously, this problem would occur when R (Reverse) was engaged. The mechanic had advised that I change the gearbox after which the problem was shifted from R to D position of the gear lever. One even suggested that there could be a problem with the vehicle computer. It is all guesswork. What is the solution? Maingi.

Such defects and their causes vary quite starkly from make-to-make. However, the most likely problem is a blocked filter in the gearbox sump. The first solution is to drain the ATF (automatic transmission fluid) oil, remove the sump, clean the filter, and put fresh ATF. None of that will upset your bank manager.

If that does not solve the problem, the unlikely but possible problem would be the “clutches” (there are a dozen or more in automatic gearboxes) which are automatically engaged and disengaged by oil pressure. The hydraulic pipes to one or more clutches may be clogged. The longer a dysfunctional filter is allowed to continue, the more likely that problem will be. Remedy for that is a more elaborate gearbox overhaul.

Actually, “changing” the gearbox should be a last resort. If the replacement is brand new, it will be a very expensive way to remedy a possibly minor fault. If the replacement is old salvage, its condition is probably unknown. What has it been doing, why is it not still in the vehicle it came from? Unless the unit has been overhauled so thoroughly that the seller will give you a full written guarantee (not common practice here) you would be buying a discard and gambling good money on really bad odds.