V8 Roadsters Cadillac Getrag Differential. INSTALLED.
 

I've had this in my car for about a month now and have just been lazy and busy to post.

V8R kit
CTS 3.23 w/LSD

I'll post more details as the thread progresses. Overall I love it.

https://lh4.googleusercontent.com/-p...0119151632.jpg

V8 Roadsters link.

Getrag Differential Conversion - V8 Roadsters

Supposedly there are a few of these kits out there, but I haven't seen anyone say anything so I figured I'd just start this thread so if anyone had any questions, they could ask here.

I also have a 3" Artech exhaust sitting on the floor waiting to be installed. Did it need to be modified to fit?

Which ratio did you get and how do you like it? I assume it's paired with the MSM 6-speed?

Subframe braces waiting to be installed in that pic?

Thanks,
--Ferdi

As all of Abe's kits are 1 offs (or at least they used to be), I can't tell you for certain you'll be ok. But the CTS diff is known for being smallish and as you can see from the pic, my ARTech setup was really nicely routed.

Yes, paired with the stock MSM 6 speed and 3.23 ratio.

Subframe braces are now back on the car and fit without issue as well.

wow, thats a super clean installation. What ratios are available for it?

As from the V8R website.

We utilize the Getrag in our road course and street cars. When sourcing the Getrag look for the 2006-2008. The later models have casting and seal updates. G80 series limited slip
GM part numbers:
3:23 - 25978162
3:42 - 25873500
3:73 - 25873497
3:90 - 25968531

I think the most common with the LSD are the 3.23 and 3.73

I'd kill to have a 3.23 R&P. Just not desperate enough to spend that much money to do so. 3.63 is "good nuff'"

Ok, so this comes with the axles too? As in buy the kit, buy a getrag diff, and bolt it all in and go?! If so I'm sold!

They way I rationalized it to myself was this.

I spent $500 on a 3.63 R&P, but sat on it for a while because I don't have a local gear shop around here that I trust enough to pull my diff, put it back in and hope it works correct.

Also figure around $1000 for the labor to swap out the gears.

So I sold it, and ran my 4.10 for another year or so which isn't that cool w/260-270whp.

Then I found out V8R was going to start making the kit which was about $1700 for everything you need; diff mount, PPF adapter, drive shaft and axles w/abs. All I had to do was find a diff and they go for around $300 pretty regularly in ebay.

So around $2000 to pretty much just bolt everything together and I sold my stock parts for $1000.

So total out of pocket was $1000 plus my time.

I actually have my car on the lift trying to install this kit now.

Did you notice that the CVs were different in length? Mine appear to be the same length from spline to spline.

V8R has not produced instructions for this kit yet (ugh) but according to the differential section in FM's V8 conversion the driver side should be 1/2" shorter than the passenger.

Regardless of which CV I use I am finding that the driver side upright does not want to bolt back in easily. The CV seems to be fully compressed with the bottom bolt holes still about 1/4" away from aligning. When I push a bit and get it bolted up the hub does not rotate freely and it's clear that the CV is binding. The passenger side dropped right in and is not having issues when the driver side parts are uninstalled.

Charlie,

I actually didn't even read that bit about the sides being different length until I was reading around after I already finished the install. So I never measure them.

I just put it together and didn't have the same issue as you.

Pretty awesome stuff. Saw this on m-s.com. Nice to have an option down the road.

Mine is going in Sunday. I got a newer diff that has the extra ribbing and had to do some grinding on the diff case to get the ppf to clear.

I too had to grind ribbing off of the diff case, and I found that the PPF needed some additional cutting outside of the template. My diff was out of a 2006 CTS.

Edit: Here's a video of the issue I am currently having with my kit. It's a bit dark, but you can hear the CV become fully compressed and see how far in the upright still needs to go. I took the upright off of my car and measured it and it seems to be in spec. I also put the upright back into the car without the CV and found that it fit fine.

OK, I'm not the only one then. I ran into the same issue myself having one of the newer diffs.

For those curious, the diff used for this swap was used in the 2004-2007 CTS. The early one 04/05 is considered weaker and came with not as good seals from the factory. The 06/07 diff had revised webbing to make it stronger and newer design seals.

The strength issue I don't believe applies to us as our cars are 2000lbs lighter but I'm not sure about the seals. I think if you're buying used either the seals have probably been replaced, or you can change them out yourself.

Also this diff was used on other cars like the STS, SRX and maybe others with varying years. The hardest part of this swap was figuring out exactly which diff I was looking for. I even accidentally originally ordered a FRONT LSD from an AWD STS. Luckily the eBay seller fixed their mistake and paid for shipping back.

Charlie,

I couldn't tell for sure from your video, but are you sure you've tightened the axle nut down all the way? If's it's not, I can see that causing extra length that might be causing the binding.

I cleaned the splines out of my hubs really good with a wire brush and WD40, and then put a lot of antiseize in there during the reinstall of the half shafts and it was still super hard. I took the 1/2" impact to them and they took a lot of torque to get them to pull through the hubs all the way.

Shane,

Thanks for the reply. I tightened the axle nuts with my 3/4" ratchet and socket with the wheels on the ground. I may need to get the nuts tighter, but I did tighten them until they stopped. The hub is new on the driver side and the CV seemed to slip in smoothly.

I put the car back together making sure to use the (slightly) shorter CV on the driver side. I took a couple more pics, one with the car in the air and one with the weight on the wheels. I apologize as I am not the best photographer.

Looking at your picture, it appears that your driver side CV is a bit more pushed in than the passenger side, but it seems mine is pushed in even more so. See the bellows of the CV boot and how compressed they are on mine? I'm not positive but I think the CV is adding resistance to the drivetrain.

When you spin one of your rear wheels, what happens? Spinning one wheel on mine causes the other wheel to spin too (same direction) as well as the driveshaft. I'm conflicted as to whether the resistance in the drivetrain is from the clutch based LSD or if it's being caused by the CV.

Edit: Talked to Steve at V8R and he walked me through a few checks and the CV play is within spec. Will update with my experiences on Sunday once I get the car back together.

I'll take some pics today. I need to do a little more clearancing on the PPF and I'm thinking about making an extra brace for the front of the diff. My pinion still deflects up and down more than I'd like. I'd like to see others experience when more of these get into people's cars.

When I spin one of my wheels, the other wheels spins the same way as does the drive shaft. This is what I believe to be normal behavior for a clutch type LSD and it is what Corvettes have done since the 60s.

Any update? I took these on saturday.

Something else I thought of... Are you sure the axles are all the way into the diff?

What direction did you have the gap on the circlip when you installed the new axles? The gap is supposed to be UP.

https://www.miataturbo.net/attachmen...ine=1425338433
https://www.miataturbo.net/attachmen...ine=1425338433

You added a washer between the ppf and the v8r mount? I could barely get the mount between the ppf rails. Don't think I could get a washer in there. Did you clearance to make it fit?

I opened up the end of the PPF to allow just a little more space to slide it in. I didn't like how the adapter fits into the PPF. It's too small to sit flush and too big to actually slide into the hole. With the washer, at least it has a flat surface between the two instead of rolling around in the hole.

EDIT: I don't think it really matters. Mine still moved around a lot and I ended up making this.

https://lh3.googleusercontent.com/-s...0228151559.jpg

Wow I love that front brace/mount. Want to make another one for me?

Charlie. What's the status on your axles? Did you see my comment about how to install them properly with the circlip gap facing up when you push the axles into the diff?

And I don't know if I'll be making any of those for anyone else. Took me like at least 4 hours. I do have the template for it though.

Shane,

Well definitely don't get rid of the templates, you made a very nice piece there.

My axles are in and have similar gap to yours. I didn't see your circlip comment until after I had installed them but I am fairly certain they are all the way in. I drove the car around my neighborhood yesterday. Seems okay, few little issues.

-Some clunking around back there when starting off (which I believe is from the PPF needing a bit more trimming or possibly the diff needing that front bracing as you have added)
-knocking noise on hard left turns (sounds like maybe exhaust needing some adjustmenting, will address this week)
-Good bit of added NVH from the swap, did you have this experience? Specifically on power. I listened to videos of CTS-V diff whine and I'm not quite convinced that's what it is.

Glad you got it driving around. Trust me. Once you trim the PPF more, things will still clunk. Even after you get that taken care of, the lash in the gears is probably going to clunk too. I hear it all now thanks to that front brace.

Also about gear whine. It sounds like there is a large variance in how much people hear. I didn't hardly hear any until said brace. I used to just hear it from 40-60. Now that sounds about the same, but I can also hear it a little as speed increases. Plus now from like 20-100+ there is a very high pitch but quietish sound that seems like it's being transmitted through my roll bar. I am going to try and get a little urethane between the brace and the factory ladder bar bracing.

That's really disappointing to hear about the clunking, was hoping to have this be a pretty invisible mod as this is still a street car. I wonder if getting a new diff from GM is worth considering. Considering the weight difference from a CTS I would assume the differential will have a much longer lifespan.

I was also looking at how they mount the front of the diff on the V8 cars. It appears they weld a tab on the subframe to bolt into the front bushing. I wonder if something like this could be done here.

Yeah. That's exactly what they do with the V8 kits. And I'm kind of doing the same thing as the bracket I made. I was talking to someone who actually has the V8 kit with the 3.42 ratio and he says his is pretty noise in regard to gear whine.

But I definitely wouldn't take my word as final as far as the clunking and whining goes. This is all still pretty new here.

After you get some more time on it, let me know how much the shifter moves around when you load and unload the motor.

How many miles were on the diff you got Shane?

Supposedly 20k. But looks like it has less.

I don't see how you get a grand for labor to swap the gears. Even with bay area labor rates, doing mine at the "rear end speciality" shop only ran $300 (pull the diff at home, take it to the shop with the gears, have them put them in and set the lash/etc).

There are a bunch of good reasons to use the V8R CTS diff, but I don't think cost compared to a Mazda 3.636 is really one of them.

--Ian

You're right. After reading around some more, $1000 sounds way too expensive. I just have little faith in the gear shops around our area, which was one of the main factors of why I never even tried to in stall the 3.63s I had.

If you have good vendors in your area like Puttymod, then that may be worth it as you won't be worried about having to pull the diff multiple times for the diff shop to get their shit right.

It appears V8roadsters has some work to do as far as a good mounting solution for this differential. Making your own custom front brace after already purchasing this solution shouldn't even be an option.

Here is another look at the getrag kit.

minute 3:00-7:30 ish.

Nice vid.

I'm exploring utilizing the weld-in mounting tabs with the ppf setup.

While the car drives well now, I agree with Shane that there's too much motion of both pinion and shifter (thus trans) during hard driving, especially with abrupt weight/force changes.

Hey Charlie! I was wondering when you were going to chime back in with some progress information. I too looked at the idea of trying to use the weld in front pinion brackets with the PPF. But it really doesn't look like there is an easy way to do it. There's not much room and as I remember it, the PPF is completely in the way. Which led me to my design.

Also my passenger side axle seal started leaking a bit more so I replaced with with a new GM one. I can't believe how easy it is. With a lift, I took the wheel off, unbolted the top bolt of the hub, loosened the lower, pulled off the ABS line, popped the axle out, replaced the seal and had it back together in probably 30-45 min.

It's funny, my passenger side axle seal is leaking too. I have one waiting to go in, glad to hear it's an easy process.

Are you happy with how your mounting solution has turned out?

Looking at that diff compared to the one I got, now I know why I had clearance issues. Case is way different.

How is your kit coming along? Did the front pinion mount work out ok?

Haven't had much time to work on the car. Just got the engine set back in. Planning to install the rearend Sunday.

My main advice is, if you don't have a lift and tranny jack, try to remove as much material from the diff case and the PPF as possible the first time. That way you're not having to pull the assembly in and out of the car multiple times.

Not having a template, I had to do this.

Well, ran into a bit of a problem. The PPF was very close to our custom fuel cell. Apparently the getrag set up moves the rear of the PPF over a little and now there's interference and it won't go in place. What doesn't make sense is that if the rear of the PPF is over further, I don't know how the mounting holes for the tranny could still line up. Moving the rear over would cause the front set of holes and rear set of holes to no longer be parallel to each other.

I see your fuel cell, but I can't quite make out where it's at and where the PPF is.

If the getrag kit moves the back of the PPF over, then there must be enough slop/room in the front for it to not be a problem. I unbolted the front a few days ago and left the back bolted in, and then was able to put the front bolts back in with out much issue when I was done.

Yeah, that's an old pic and the whole rear subframe is out. I was only showing how low the cell is mounted so when I said the ppf hits it, people aren't scratching their heads trying to figure out where my fuel cell is. I'm gonna leave the mount bracket in place and pull the diff and get the ppf on it and try to get it up there. If that doesn't work, which it doesn't look like it will, we will need to make a new fuel cell.

Wouldn't go. Time to build another fuel cell. :facepalm:

Blahh. Sorry about that. If it's any condolence, you're going to absolutely love the gears. I think about it almost every time I drive the car. I'd say first is still a little short, but 2-5 is amazing.

Doing all of this to only use 2nd gear. ;)

Some are more crazy dedicated than others :)

Thread bump. To any of you that had issues with this, have they been resolved? If so how? Have you guys been in contact with v8r in regards to the issues and have they communicated any interest in implementing a fix in their current kits? Almost a year since the last post here which Is plenty of time to make fixes to the kit.

I guess not much to report on from my end.

Disclaimer: I got a super early kit (they didn't even have instructions yet) and I don't know if they are offering different parts yet. Also, everybody's car may have individual circumstances that could be different.

You should call them yourselves if you have any questions. And, as much as it may sound like I'm griping, V8Roadsters customer service is probably one of the best experiences with a company I've ever had.

Now that said; it's a great kit to get you most of the way there, but depending on your level of acceptance, you may spend some extra time making it work better.

I gave them my opinion with pictures to them of the issues I was having and they politely said I either had some pieces wrong or needed stiffer bushings. Whether or not anyone else provided them with feedback since then, I do not know.

I was seeing a ton of flex from the pinion of the diff even after I replaced the OM GM bushing with a poly bushing. When you loaded or unloaded the tranny hard in gear, it looked like the shifter was rowing a boat. And I was missing 1st to 2nd gear 50% of the time when shifting fast. In my opinion there is just too much leverage on that 1 front pinion bushing no matter how stiff a bushing(even a solid metal bushing). It needs to be securely mounted like the welded tab they use for the V8 cars that get rid of the PPF, or a bracket like I made. If you saw this in person, you would understand what I mean.

The bracket I made completely fixed the issue and I can't remember the last time I missed 2nd gear. It's better than the OEM setup. I think what causes people to miss 1-2 is the slop of everything moving from the engine mounts, down through the PPF to the diff mounts. The bracket I made adds a 3rd mounting point. So I have polly diff bushings, the bracket connecting the pinion to the ladder bar, and original motor mounts.

I opted for the aluminum drive shaft when they had the special when the kit first came out. It ended up being really out of balance, and V8Roadsters was great in helping me send it back in exchange for a regular steel one. It was only 2lbs heaver and didn't have any balance issue. 8Roadsters does not make these, they are from another company.

The bushings that came for the diff mount bracket are thin at the top which moves the whole diff futher up and causes the top of the PPF to hit the rear sub frame. I bent the top of the PPF down a little and glued on a hard rubber sheet to it which is basically sandwiched between it and the subframe. I showed this to them and they said I must have had something wrong. And even if it were further spaced down, the PPF would just hit it anyways under load when it flexed.

The Getrar diff kinda has a lot of slop in it and makes a little noise under certain conditions like slow speeds/parking lots when fuel overrun kicks in and CL idle kicks the fuel back in. Other than that, you never notice the slop. It also whines around 50mph, but that's the only time it does.

You'll need to re calibrate the speedo pulse width somehow, but I haven't gotten around to it yet. 60 indicated is around 72mph and 70 indicated is ~85 with 15x8s.

That's most of all I can think of right now. I've got probably between 5-10k miles on it so far. The gearing is absolutely wonderful for a street car with at least 250whp. I've even got my boost down to 12psi right now, so maybe 200whp and yeah it's doesn't pull through the gears as fast, but it's still great. 1st to 2nd is a little big. Under full throttle, mine drops from 7400 to 4800.

Anyways, sorry for the essay. Curious to see what the other members who have the kit have to report.

Zero issues with my kit, don't use the PPF though (v8). Did have to add 2 feet of hose to the breather cap to keep the diff from puking, there is a TSB out on that from cadillac. Cars with less power may not have an issue, the exocet is pretty retarded at 404hp/1650lbs

Build thread? I don't want to scroll through FB shit.

FB would be quicker.

V8 Exocet #134, Manhattan KS | MEV OWNERS GROUP - A top kitcar forum for kit car builders

Quoted and prop'd. :likecat:

Does anyone have details on the template provided by V8R? Getting them to actually ship me all of the pieces has been like pulling teeth and they have not responded to my requests for the template.

https://cimg0.ibsrv.net/gimg/www.mia...a90cf0e9b4.jpg

Is this the same "template" everyone else was given?

Are you really required to cut away the captive nut mounts? Has anyone had success using this kit or has everyone been required to build their own solution?

Bump / just checking in - I just 'finished' the swap in my MSM. I really like the gear ratio change, but there is A LOT of clunking. My differential had 98k on it, so it could be partly that, but I'm not sure yet - need to do some diagnostic work. I'm also going to get underneath and verify my axles are fully seated - they went in and clicked but I'm not sure...

My preemptive slop solution:

Attachment 180887

Axles (EDIT: I confirmed with V8R that there should be 0.25-0.375" exposed, so this appears to be correct - leaving pictures for additional reference):

Attachment 180888

​​​​​​​Attachment 180889

I am experiencing the same exact problems.... the mount pushes the PPF against the rear subframe, the driveshaft also can contact the PPF and the fill plug hits the exhaust.

I completely forgot they supply a template until after I cut it on my own. I never went back to look for a template, but that doesn't look like what I cut though?

I had to twist an arm and a leg to get them to actually send me a template.

It appers as if you cut away one of the mounting points for the PPF.

I actually wasn't supplied a bolt for that, and the stock bolts are way too long, so I assumed just the back hole was necessary. I see now that the adapter is threaded, and I still have 3/4 of a hole, so I can throw another bolt in there. With the front bracing I made though the diff is pretty secure.

Here's a video of the noise I'm getting. My conclusion right now is that it is just noise within the diff itself (the noise occurs whenever I take up slack in the diff - aka, engage the clutch).

It looks like the driveshaft is binding the way it is skipping.