What is wrong with my Mark II Grande?

Dear Paul,
I own a Mark II Model 2000 (Grande).
Over the last six months, it has developed a number of problems which I feel have not been addressed well.
It all started with the “check engine” light not going off, to which, my mechanic aised to change the plugs and eventually the sensor. After checking all these apparently with a computer, months later the car acceleration started going up and down without stepping the accelerator pedal. He said some adjustments needed to be made, which, he eventually controlled (not so sure what he did).
Months later, when I went out of town, I started feeling like the car would jerk (like being shaken by wind) whenever the speed exceeded 90kmh. My mechanic said that the propeller shaft had a problem and part of it had to be replaced, which, he did but the problem still persists.
I am now fed up with this mechanic. What could be the problem and where can it be addressed from.
AK

AK, I think your mechanic’s initial response and fault diagnosis to the engine symptoms was correct hence the parts replacement which fixed the engine problem. In my opinion, the more recent car fault is not engine related as your mechanic seems to have figured out. The fault symptom described by yourself as jerking when you drive at 90 KPH+ is most likely due to a damaged component in the wheel hub suspension or final drive systems which are by a change of wheel rotational speed. The areas to check range from: damaged wheels (rims), wheel hub assemblies, front suspension or lateral arm bushes which are directly connected to or affect wheel rotation. The trouble spot can only be identified by road testing to observe the symptom before dismantling the components. I would progress the inspection and search curve to final drive components
(drive shafts and propellor shafts) only after ruling out faulty wheels (rims), wheel hubs and suspension parts which usually cause wobble or what you call ‘’jerking’’ when they are damaged.

I have a situation with my Corolla S 2005 model. I have an issue with my reverse gear. When I put the car on reverse, it sometimes goes on smoothly as in normal or the car will jerk as if the car is on hand brake. Please aise me on what to do because my mechanic has tried to service the gear box but the issue persists. Bitrus.

Hello Bitrus,
The jerking experience when you engage the reverse gear on the automatic transmission may be the result of a faulty pressure regulator or sticking reverse gear solenoid switch in the electro hydraulic unit or valve body of your gearbox. This situation causes excessively high fluid line pressure which results in violent gear engagement. The valve body or electro hydraulic control unit works as a logistical hub which releases transmission fluid to a particular set of gear clutch packs for the forward or reverse gears in response to an electronic signal from the gearbox computer when you select a gear.

Delay to renew or service your automatic transmission fluid (ATF) especially when it becomes brown, dirty or smells burnt will damage the solenoid switches in the gearbox valve body. At this point, flushing or changing the gearbox ATF may not reverse the damage which may have spread to the gear clutch packs. The first step towards resolving this situation should be finding a good transmission diagnostic and repair mechanic.
A computer diagnosis will be useful to establish whether the failure of the valve body is caused by electrical circuit or hydraulic- mechanical factors. The valve body may be dismantled to test the suspect gear solenoid (electric ATF fluid valve switch). In case it’s just the solenoid valve that can be replaced with a good one. Depending on the extent of damage your repair technician will choose the range of parts to replace.

During tests, it is also important to rule out gearbox mounting (suspension) failure which can cause some level of jerking during gear engagement. Gearbox mountings can be damaged due to the violent jerking of the gearbox when you engage the reverse gear.

SOURCE: Daily Monitor

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