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FYI, these are the part numbers for the Grand Prix GXP's RPO code FE4 front lower control arms: #25853339 and #25853338. The Buick dealership my GXP is at right now says they think they can get one of the #25853338 from another dealership somewhere in the US, despite it being discontinued. Why one is discontinued and the other isn't, I don't know. I'm surprised both aren't discontinued due to the age of these cars...
Just because I like to be informative for people searching for info and sharing my research and experience just so it isn't a waste of time for only my benefit...
My old ~2009 parts manual says that the part numbers for the "sport" front lower control arms (that GXPs theoretically used) were part numbers 10327401 and 10327402. I'm not 100% sure if these were previous part numbers for what I listed above or what the deal is. When I googled the numbers the dealership texted me (above), GMpartsgiant said they were for FE4, so that was good enough for me. #25853339 and #25853338 are definitely for a GXP.
In my car's case, my front bushings are both torn, which is why my GXP feels unstable at pretty much all times right now (on any imperfect road... so all of them here...) and seems to shift a bit when making turns. If your GXP no longer feels like it corners on rails like it previously did... you could have torn front lower control arm bushings too. Why replace the entire lower control arm instead of the bushings? Short answer: because the front LCA comes with new bushings and lower ball joint already installed as part of it. And in my case, I'm not DIYing this repair myself because I don't have the tools for doing bushings and I don't have all the tools for removing everything to replace the front lower control arms either. If one 16 year old bushing is torn on both due to age, I bet the rear bushing and lower ball joint are pretty worn out too.
This isn't the case with all cars, but with a GXP, it's not that much more expensive to replace the entire control arm (if you're paying for labor) than to replace both bushings and the lower ball joint (which honestly, I'm not 100% sure it is even replaceable on the OEM LCAs). The dealership mine is at told me it would only be $126 extra to replace the LCAs, totaling $799 for parts and labor, instead of $673 for parts and labor replacing both bushings on each LCA. You're supposed to get an alignment after replacing the bushings (or the LCAs), and I luckily got the Buick dealership to put it in writing and agree that I can just drive it down the road and get a free alignment from Firestone, instead of pay them $152 to do it. Why do I get free alignments from Firestone? Because their ~$160-$180 Lifetime Alignments package lasts the entire time you own your vehicle, so I've been benefiting from that for the last 13 years.
Why not just have Firestone do the bushings or LCAs? Frankly, I could, but at this point, I don't necessarily trust that they'll be able to get the right parts (or use high enough quality aftermarket parts--they told me they don't use Mevotech parts unfortunately and this location told me I could not supply them the parts--some do allow that on rare occasions though). They'd probably end up ordering parts for a regular Grand Prix, since that's all that is plentiful online. I did get a quote for them doing the work, and it was going to be $241 per LCA and $290 for labor, so a total of $772. Or, if they just did the bushings, it'd be 2(59.99+26.99) for bushings and $348 for the labor, so a total of $521.96. So... in the case of replacing the LCAs... it's actually only $27 more expensive to go with the dealership... and the dealership provided me a loaner car for free so... pretty easy decision for me.
One thing that you'll find on RockAuto and other places is that most front LCAs available have an extra tab with a hole in it for mounting a sway bar. Well, the GXP swar bar (which is a 20mm one, as far as I know) mounts to the struts, not the LCAs like other Grand Prixs as well as the other LS4 cars too (as far as I know). If you get LCAs with that tab, you'll have to cut it off (and paint over the bare metal), or it'll interfere and hit other suspension components when you hit a big bump in the rode. The most popular (and probably best) aftermarket front LCAs are the Mevotech CTXMS20329 and CTXMS200328 (which are around $95 each), but they have those tabs and the stud on the ball joint will also need to have around 1/8" cut off the tip of it to not interfere. Mevotech's TTX products are typically major improvements over OEM parts, and I love their front hubs I installed on my GXP, so if I was doing this myself, I'd be getting those just to be confident I wasn't buying (1) something low grade intended for a base model GP and (2) something that's surely as good or better than the GXP ones. However, those are painted an unusual brown/khaki color, so if you cut off that tab and you're a perfectionist, you're probably going to be repainting the entire LCA and not just spraying a bit of random colored spray paint over the cut you made. There are other options, but most do have that tab, but at least most other options are just painted black. Again, it's hard to tell which (if any) of them are intended to be used on a GXP instead of a base model GP... if that matters to you.
Bushings are pretty cheap, so most of y'all with the tools would probably just replace those. To my knowledge, these are the part numbers for the GXP bushings:
10412124 for the front bushing (I'm 100% sure this is for FE4)
10260991 for the rear bushing (not sure if the GXP had a different one than other GPs...)
88955451 for the lower ball joint (not 100% sure if this is for the GXP or not... not even 100% sure this is a serviceable part on the OEM LCAs)
Thanks for posting! I’m glad to see it’s not completely dead over here. I bought myself the $500 zzp sport bushings a few years back I thought it had a much cleaner look but I can’t say if it added rails. Probably better then stock. Yeah if the bushings are gone you have to do something.
Glad you got it fixed keep the ls4s on the streets!
be nice to the tranny and you should be good right.
Well, forums are a little dead, but I prefer this one since I'm a 4th gen f-body person, and plus, I don't like investing time in posting on Grand Prix forums, because I've already been burned twice by two that I was a member of that unfortunately went offline. I figure that LS1tech has a lower likelihood of disappearing due to hosting bills not getting paid.
I've owned my GXP since Jan 2009, and I still love it. It's difficult to find GXP-specific parts for it, mostly due to it being difficult to actually find documentation about what the GXP-specific part numbers are. What might be an aftermarket upgrade for a V6 Grand Prix could be a downgrade for a GXP, so I always try to keep that in mind. There's plenty of weight up front, so front suspension components wear out fairly quickly if you aren't the type who drives the car like it's a Toyota Avalon. The transmission isn't bad if you don't overheat it and drive exclusively in manual mode like I do. It's a terrible car for people to do burn outs and thrash, and that's how a lot of them have met their fate. Mine's still in great shape and won Pontiac Southern Nationals' best 2000 and newer car last year.
A lot of people go the junkyard route for parts, but with these cars not being THAT old yet, I think that's a waste of time personally, because I'd rather get another 10+ years out of NOS parts while they still exist.
The brand new NOS GXP front lower control arms brought it back to feeling a lot like it did 10 years ago. The car feels like it is on rails again. Previously, it almost felt like it was loose and flexing on uneven roads, and now it's tight. Replacing the entire LCAs instead of just replacing the bushings still seems like it was a great idea to me.
Interesting info: I went to Firestone for the alignment, and only the toe-in was off. Considering I didn't do the work (replacing the LCAs) and have no experience doing alignments, I can't say why that is, but I found it interesting that replacing the LCAs only affected the toe-in. I'm sure one of you guys probably know why that might be.
Just did both my LCA today for the second time since I bought the car over ten years ago. What a difference! Used the mevotech off rock auto. No tab if you get the one for the special suspension fe4. Yes keep this forum alive there is soooo much info on this site!
Thank you for the details, I've been considering replacing the lower control arms for my GXP recently hoping to get a more solid overall feel. Next will be the front suspension (any suggestions would be great!)
I also wanted to say thank you for all the effort you put into your guide for installing a trans cooler and the website you made. I used your guide to install the 30Ktrucool on my GXP, I don't think I would have felt sure enough to do it myself with your guide, and it's been great since. I used a bypass with mine since I live in Ohio so the set up was a little different but it turns out that there is a great little spot in the front plastic moldings to let it sit and get a lot of air to keep it cool but still protected from rocks/rain/etc. Really appreciate that there's still love for these cars almost 15 years later
Man, that's good to hear! I'm glad you found my guide useful! I haven't gotten a lot of feedback, and have only gotten one $5 donation via it, so I kind of felt like maybe I wasted my time making it because possibly nobody was even looking at it. Here's a link if anybody seeing this needs it. https://sites.google.com/view/grand-...grand-prix-gxp
I also have a good guide to the speed sensors and hub replacement on there.
I wish I had advice for suspension. The front Bilsteins (or the rear ones... can't remember which) are discontinued, and I don't know what is a suitable replacement. I have a terribly hard time shopping for parts and it's difficult on Rock Auto to discern what is for a GXP vs. a V6 Grand Prix. Without being able to compare compression rates or strength or SOMETHING, I don't know how to know what is similar to the Bilsteins.
I'm relatively satisfied with the new front LCAs. It's much more stable and like its on rails now, but the ride quality isn't that much better, and only feels very good when I have my wife with me (in the front passenger seat). My struts are probably getting a bit worn out since I have 84k on the car now. I'm not really sure when people usually replace them.
For suspension... I like the factory GXP front sway bar setup. It is unique compared to non GXP GPs, only problem is that a replacement bar long dried up AND no one company is making a suitable aftermarket solution what so ever for the front(rear upgrades exist). Shame about the front sway bar. If the front brakes then the only choice would be to find the "POLICE grade" front sway bar from GM PERFORMANCE via ACDELCO, and then use MOOG bushings.
A MOOG STEERING REBUILD KIT like this... https://www.moog-suspension-parts.co...packagedeal092 wouldn't be the craziest purchase especially if the front suspension is being overhauled. This kit would upgrade the individual tie rod ends to grease fittings which is a nice extra touch.
Overall though, GXP suspension upgrading ideally involves these four companies... MOOG, BMR, BCRACING, and ADDCO... however if not ideal you would look at parts from ZZP to change the front LCA design and/or bracing the struts... OR perhaps ACDELCO to upgrade the rear sway bar. If you want to delete the rear parking brake setup due to rear dust shields deteriorating then you might also consider this at the same time as the parking brake delete... https://www.milzymotorsports.com/mms...body-vehicles/
Fortunately there are lots of suspension upgrades for the Wbody.
Just did both my LCA today for the second time since I bought the car over ten years ago. What a difference! Used the mevotech off rock auto. No tab if you get the one for the special suspension fe4. Yes keep this forum alive there is soooo much info on this site!
thank you so much for your detailed post! Are these the ones you bought? I see the TTX you are talking about but I think the shop might be pissed if I buy those and then tell them they have to mod them (the shop I use lets me bring parts) I'm skeptical of a $40 piece honestly but this is the only one without the tab.
05-18-2022, 10:50 AM
Grand Prix GXP front lower control arm info 
