Vibration after Intrax install

[PCGUY112887]

I just had my Intrax springs put on, along with new KYB struts and HD mounts. I had him cut the bumper so the car doesn't bottom out on it, and everything seems to be great, tight steering and front end it's great. My left side lower ball joint was bad too, so both were replaced.

One issue however, now when accelerate from a stop, from around 7-20mph and usually I'm around 2100-2500 RPM's I get a vibration from the front of the car, I feel it through the wheels and the petal and everywhere. I know my alignment is fairly off but I don't see how it could cause a feeling like this.

Ideas?

[IsaacHayes]

I don't know how your car is built, if it's like the 97+ GP's lowering can give you vibrations IIRC. From when I used to read clubgp.com

[gpse3400]

When you drop the car you change the natural sitting point of the axle. They work best parallel to roadway. Further if you drop the car then your alignment is going to be off. Your car should be toed out now. If you get it realigned then you should be ok. If the vibration is still there then its most likely the axls and I dont know how you can fix that other than putting the car back up.

[PCGUY112887]

Well hopefully an alignment will fix this since if lowering caused vibrations like this for everyone, no one would ever do it!

Your right about the toe however...

[IsaacHayes]

I think the 97 GP guys would put spacers on the subframe to raise the motor back up so the axles are aligned again.

[PCGUY112887]

Sadly, the alignment has not helped the vibration. It's odd, if I accelerate faster then it doesn't do it, but when I do a slow acceleration up to say about 2200 rpm's then it vibrates till just 20mph.

Ugh!

[IsaacHayes]

Did you look on clubgp.com for info about raising the motor? Or is your car different than the 97 in that regards?

[PCGUY112887]

Well I found it... but I have never heard any of the gen 1 GP guys talk about vibrations after lowering??

http://www.clubgp.com/newforum/tm.asp?m=3683662&p=&mpage=1&tmode=1&smode=1&key=lowering+vibration&language=single

One thing I wonder about is the fact that I know my motor mount is shorter than usual because I bought a NAPA solid mount, which turns out is/was incorrectly made and is like 1/2" to 3/4" shorter than the stock mount.

[torq455]

maybe you have an axle binding a little?

[PCGUY112887]

Well I have the alignment now, makes the ride much nicer (I could tell how towed in they were from the way it drove) but it didn't help my vibration.

Here is how it goes. If I take off from a stop, around 1800-2300 RPM's accelerating I can feel this vibration in the entire front of the car, through the petal, steering wheel, everything. It's not TOO violent but I can very much feel it. If I am in a turn while accelerating, it doesn't do it, but as soon as my wheels are straight again I can feel it.

This doesn't happen past about 20mph, and I never feel vibration at any other time aside from taking off from stoplights and such. If I just accelerate faster to about 2600 RPM's before I hit 20 then I don't really feel it as much either. It's definitely a low acceleration vibration at low speeds.

Here is what I have found out so far. Some of the newer GP guys have been putting spacers under their trans/engine mounts to make their axles align, see here.

http://www.clubgp.com/newforum/tm.asp?m=3683662&p=&mpage=1&tmode=1&smode=1&key=lowering+vibration&language=single

With other w-body cars, there have also been people who have made offset dogbone bushings that are supposed to take care of this vibration.

http://www.zzperformance.com/grand_prix/products1.php?id=130&catid=138

However I already have a nice set of poly dogbone mounts from Intense Racing, and I really don't want to try to add spacers to my mounts since 1 of the bolts on my engine mount will probably never work right again if I take it out, it got misthreaded and it's in there good now but if I take it out I would probably have to have those threads in my block repaired to put a bolt back in there.

I have seen mentions of shortened dogbone mounts, so I found them here.

http://www.wbodystore.com/grandprix/shortened-dogbones-reduces-vibration-on-lowered-cars-p-177.html

This is the cheapest option, I am willing to try it but I am afraid they may make my headers hit my firewall, since they would have to pull the engine forward and my engine can't come too much more froward without my headers hitting on the firewall.

[PCGUY112887]

Well I got the shortened dogbone mounts, I didn't know how much shorter they were but now that I have them I see that they are far too short for me to be able to install. My headers hit the firewall a bit when I give it gas in reverse anyways, the headers also rub on the fire blanket on the firewall... there is no way I can get enough clearance to install these things, or offset mounts that would torque my engine forward.

Any other ideas? I know custom axles was a solution, but where could I get that done? How would I know how the axles would need to be changed?

[IsaacHayes]

I don't think custom axles will help, since the axle isn't centered/aligned right to begin with...

[PCGUY112887]

I'm really wondering if it could be my motor mount that is causing it...

Reason - Awebb and most other lowered earlier w-body cars never complain about vibration. If it was typical, you would hear a lot more about it, and there would be a "standard fix" already, such as the pogo mod on newer GP's.

Mine should be no different, but I noticed how those tranny/motor mount spacers worked, and it got me thinking. My current motor mount is a solid mount sold by NAPA. Apparently this same part # came in 2 versions, 1 a perfectly manufactured version, and the other a "lesser quality" mount that was like 3/4" shorter than what it should have been. I didn't know of this at the time, and just installed the motor mount as usual. It was almost the same height as my blown hydraulic mount that came out, but I didn't think anything of it (not really thinking about the fact that the blown mount was of course going to be shorter).

There was a big post on ClubGP somewhere, since they use the same motor mounts and people used solid ones of the same #.

So I am really wondering, maybe that extra lowering on the engine was never noticed before, but now it's causing vibrations since I'm lowered.