Shudder when braking

[Emory]

Don't know if this has been discussed, so please bare with me. Vehicle: 2008 ST AWD, 4.6. When I come down to a near stop and begin to brake to make a turn (such as in my driveway), I get a "shudder" from the frontend. It presents itself as coming from the brakes. It does not usually do this when stopping straight such as at a light or stop sign, but mostly when making a slow braking turn. And that seems to be more prevalent turning left (but that could be just me). Any ideas on this? If this was rotors, wouldn't it do that no matter what? Could it be the calipers?

 

[Evox]

Have you inspected the brakes? Are the caliper pins moving freely?

 

[MVanover]

I believe it's your differential. I had a similar thing in my 2008 4.6L. Only when starting turning left when very slow. Apparently the limited slip needs an additive. I also upped the weight of gear lube. I think only the rear differential has limited slip. I still had it a little bit and it felt like it was the front. So I added the additive to the front. I'm not sure if it did anything, but the chatter stopped. Maybe I wasn't patient enough. I got the gear lube and additive from the Ford dealership.

 

[Emory]

Thank you MVannover. Yes, it sounds like you had the same issue. So it's not the brakes? Mechanic couldn't find anything wrong with them either. Do you remember what the additive was called? Did you drain both the rear and front and refill and additive? Chatter is an appropriate word for what I'm feeling. Oddly, it's not as much present as it is at other times. Strange.

 

[Emory]

By the way, I have the typical rear diff pinion whine. Did you have that as well? And did it go away with the new lube and additive?

 

[MVanover]

The gear lube is Motorcraft 75W-140 Synthetic Rear Axle Lubricant. The additive is Motorcraft Additive Friction Modifier in a 4 oz. bottle. The rear diff has a drain, so that is easy. The fill port is hard to reach, so you have to be creative. Ford will try to sell you 3 or 4 quarts of gear lube. They have that wrong in their system. I don't think it will hold 2 quarts. You can get the friction modifier at Walmart for about $10. I don't remember what I paid at the Ford dealer, but the Motorcraft gear lube is listed for $29.01 on Amazon. That synthetic Royal Purple gear lube might work just as well. You can get that for about $20 at Walmart. Yes, the chatter went away with the new lube and additive. It did take awhile though.