After towing my 2002 Pontiac Grand Am GT front wheels up on a tow dolly (according to the manual this is ok to do, and a call to Pontiac confirmed it), I had no brakes until I pumped them. The brake fluid reservoir is full. Pontiac could give me no reason why this would happen. Does anyone have any ideas? The brakes work fine otherwise. We intend to tow the car behind our RV, so should I just accept that I should pump the brakes before backing the car off the dolly? Does anyone have any ideas about this or maybe someone has experienced a similar problem.
Master brake cylinder replacement sounds like the first guess.
+1
Your brake master cylinder needs to be replaced, and the fact that it only became apparent after that tow is merely a coincidence.
Chalk this up to coincidence and nothing more.
A loose wheel bearing on the Pontiac would allow the wobbling rotor to push the pads back into the caliper while the vehicle was being towed…This would cause an unexpected low brake pedal, but there should have been SOME pedal and the rear brakes should have worked…The brake warning light should have come on too…If there was NO brakes and the pedal just went to the floor, yes indeed, replace the master cylinder…
Thank you for your input. Sounds like we’d better have the master cylinder checked. Good information.
Daisy
If the brakes are firm and function well after pumping them back up then I would not be inclined to assume a master cylinder issue. I might be inclined to bleed them. I’d also wonder how old the brake fluid is. Although I can’t say exactly why anything like that would cause this. Caddyman’s suggestion could be plausible.
Brake fluid level is low!
So far, Caddyman’s explanation is the only plausible one I see. I don’t think you need a new master cylinder or the need to bleed the brakes. I’m not actually sure that you even need new wheel bearings, but it wouldn’t hurt to check.
When you are driving the car, you are using the brakes frequently, that is keeping them tight. When you are towing, you are not using the brakes at all so if the pads back off from small variations in the rotors path, in other words, flexing due to cornering etc, there is nothing to keep them tight.
I think you are just going to have to pump the brakes before backing off the dolly.
I am assuming that you have disc brakes on the rear and that you released the parking brake before towing.
Did you have the circuits o the car energized at all? This vehicle comess with ABS and Traction Control, both of which use the wheel speed sensors and the ABS modulator. The modulator “pulsates” the brakes by interfering with the hydraulics via solenoid operated valves. If you were towing and the circuits were on att any time, the system would have believed basedon a comparison of the front wheels speeds and the rear wheel speeds that the front wheels were sliding and constantly hammered away with the abs system. That could have caused those valves to stick and pumping could have freed them.
My theory is, granted, “out there”. but I have to suspect that the ABS system and/or the trac control system was somehow involved.
I like Caddyman’s theory too.
MB
If the brake pedal was not applied while the car was being towed, how would the ABS be activated?
If the car was not in “drive”, would traction control be activated?
You may be correct, but at this point you have me confused.
Excellent points.
I’m stumped.
That makes two of us!
I’m going to suggest that there might be air in the system. Don’t ask me why it manifest the problem only after towing.
When i first read the post I wrung my brain out trying to figure out how air might have gotten into the system from towing. I’m open to the thoughts of others, but I’ll be doggoned if I could figure out a possible passage.
The only thing I could come up with on “air” is old brake fluid with plenty of water in it. The towing heats up the rear wheels - boils the fluid - gives it gas. But unless the rear brakes were sticking there shouldn’t have been nearly enough heat.
Here’s one more theory. To the OP: was the car turned off when you first pushed the brakes? If so, there was probably some vacuum reserve in the booster to pull down the brake pedal. That would be gone after a few applications and the brakes would suddenly feel very firm. Someone could mistake that for having an initial soft pedal.
I suggest air only because it’s an easy first step to bleed the system while we can’t say for sure what caused it while towing. And it certainly is old enough to have enough moisture content which lowers the boiling point, and introducing fresh fluid may firm up the pedal. It is definitely a good maintenance practice whether it works or not…besides, if nothing else is obvious and the towing were not involved but with those symptoms, it would be the cheapest and easiest thing to do before investing anymore money.