[arnoldcp]

I think I have isolated the knocking noise I experience occasionally on hard bumps down to the subframe. Now I am looking for a DIY on their replacement.

I might simply be missing it but I didn't see one when I searched. My real question is, do you need to drop the entire subframe to replace the mounts or can you basically let it hang on the car and just replace one mount at a time.

Its probably easier off the car but I am not looking forward to the removal of the entire subframe.

Thanks in advance.

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[Iowegian]

What year Passat? What engine type? What trans type? Do you mean motor mounts or trans mounts or both? There really isn't a 'subframe mount' that I can think of. If you are planning to replace the motor mounts it is easiest to drop the sub-frame to do so. You will need new bolts to attach the sub-frame since they are one-use bolts. They are about $3 each at your local dealer or on-line. You can try to keep the sub-frame alignment through the process but you might want to plan on a wheel alignment afterwards also. I replaced the motor mounts on my 1.8t tiptronic without removing the sub-frame but it required an engine hoist and was a very tight fit on one side. If I had to do it again, I just drop the sub-frame.

 

[PZ]

Have you checked the subframe bolts? I have not seen a bad set of subframe bushings yet on a Passat, but there is always a 1st.

They need to be pressed in and out, so it would not be easy to do on the car.

 

[ylwagon]

If the issue is motor mounts, I've changed them on our B5 Passat 1.8T and a B5 Audi A4 2.8 without disturbing the subframe's alignment. In both cases the cars were on jack-stands, with the engine supported by by a floor jack with a plank of wood to spread the load: the engine is lifted until the mounts are loose. The sway bar needs to be released at the two bushing clamps I believe, then one side at a time, unbolt the aluminum mount bracket so the old mount can be swapped for the new one. Then bolt the bracket back, ideally using new bolts, or old bolts with Loctite if unconcerned like me. The engine should be idled with the mount nuts loose to allow natural alignment before final tightening.

 

[arnoldcp]

Yeah, sorry, should have provided that info but I figured since the subframes were all the same it was probably a moot point.

1998, 1.8t, FWD, manual

I have done the motor mounts I found those to be pretty quick and simple other than a stripped sway bar stud.

I guess I am talking about the subframe bushings, not mounts. The subframe mounts to the car through these bushings...

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[arnoldcp]

I will double check the subframe bolts. I personally have never loosened them but the car has been aligned a couple times.

This knock only occurs at medium speed when driving over something like a change in pavement height. Or one of those steel plates they put over holes. I have double checked all the suspension arms, and attempted to rock the wheel backwards or forwards with it raised above the ground. I can't apply any force hard enough or fast enough to get the knock to occur.

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[PZ]

Check the 4 main bolts at 90ft/lbs and the smaller motor mount bracket ones at 60ft/lbs. The 4 13mm at the back of the subframe plates also need to be tight but they don't take much torque. If the bolts are loose, replace the mains one at a time using the proper torque.

 

[Iowegian]

I guess I am talking about the subframe bushings, not mounts. The subframe mounts to the car through these bushings...

Gotcha. My bad on misunderstanding, sounds like you have a good handle on this. If it turns out the bushings are bad I'd just replace the whole sub-frame. If you could find a car at pick-n-pull where someone has already snagged the engine or trans the sub-frame may be just lying on the ground waiting for you

Aside from the alignment issues and the torque specs involved, it isn't that big of a job to remove the sub-frame. At least here in CO. I imagine every job under the car is a bit tougher in PA with the rust issues you'll encounter.

And to your original point, you can probably interpolate how to remove the sub-frame from this writeup: Control arm replacement and steering knuckle removal -B5 Passat and Audi | VW TDI forum, Audi, Porsche, and Chevy Cruze diesel forum

 

[rhauff]

I had a similar knock. Turned out to be the brake pads on passenger side. To verify just put very light pressure on the brakes as you go across an offending bump or pavement crack. The knock should disappear. I ended up putting sheetmetal shims around the edges of the pads to take up slack.

 

[ATWPASSAT1.8T]

Probably unlikely that the subframe bushings are bad. I've replaced mine while the subframe was out (engine rebuild & transmission swap), but in all honesty it was not necessary, as the original were fine. They were 14 years old and had more than 200,000 miles. I would say it's nearly impossible, if not impossible, to replace the bushings without pulling the subframe out.