If the speed limiter did not work that does not always have something to do with the car.
On some tracks the speed limiter in the pit lane is not available.
If at the BMW M1 mod the speed limiter does not work, in the hdc file under the entry [ENGINE], the value will be set to 1 for the speed limiter.
The whole thing should look like this:
RevLimitAvailable = 1
Speed Limiter = 1 // Whether a pitlane speed limiter is available
Normal = PROCARENGINE
RestrictorPlate = PROCARENGINE
I hope this helps you.