Limited slip differential for a 02C190P Roadtrek

[Floorman]

I'm in the process of getting a Eaton Detroit TrueTrac Limited slip differential (915A545) installed in my 02C190P Roadtrek. My rear end is a GM 14 bolt 10.5" 30 spline 4.10 differential (GT5), I think manufactured by AAM. The ID of the rear end has been verified by shape of the cover, by the bolted on Pinion housing and the rear wheel hubs indicating full floating axles. I am changing out at the same time the Onan KV spec F for the new QG 2.8HGLAA-8303A. I will be having the installation done by Hoopers Rear Ends in Sun Valley Ca. next week. My preps so far is to remove the old KV Onan and the undermount as it needs to be wire brushed and repainted. The RT brackets that the undermount attaches, to the rear cross member of the frame have also been removed for paint and the super rusted 3/8 bolts holding the undermount plates to the brackets. Those bolts were welded to the RT bracket, but are now cut off. Interestingly the bolts holding the bracket to the frame did not have a spot of rust. Maybe they are stainless steel. I am planning to use new grade 5 or even 8 bolts and nylox nuts to remount the undermount plates depending on what I can find here in Bishop Ca. Have a question at this point on the TrueTrac. Should I have them use the AAM master bearing kits for the differential and also the AAM master wheel bearing kits as long as they are changing things out. There's 70,000 miles on the RT and I'm thinking, correct me if I'm wrong, that even if the bearings are not worn new bearings, seals will be "best practice" kind of maintenance as access into the differential will be limited once the new generator is installed. I think Booster might even recommend the addition of a sway bar. The front end of the RT was completely renovated last year everything replaced that had a ball joint, the bearings, brakes, steering links so I'm thinking I need to end up with a rebuilt rear end. Hoopers is legendary in So Cal and I guess they'll might only replaced what's needed to not waste $$. To me the parts and additional labor is what you do when you have things apart. Add the accessibility limitations with a generator in the way, this should be a no brainer, which in my case is not far from wrong. Thanks

[booster]

Originally Posted by Floorman

I'm in the process of getting a Eaton Detroit TrueTrac Limited slip differential (915A545) installed in my 02C190P Roadtrek. My rear end is a GM 14 bolt 10.5" 30 spline 4.10 differential (GT5), I think manufactured by AAM. The ID of the rear end has been verified by shape of the cover, by the bolted on Pinion housing and the rear wheel hubs indicating full floating axles. I am changing out at the same time the Onan KV spec F for the new QG 2.8HGLAA-8303A. I will be having the installation done by Hoopers Rear Ends in Sun Valley Ca. next week. My preps so far is to remove the old KV Onan and the undermount as it needs to be wire brushed and repainted. The RT brackets that the undermount attaches, to the rear cross member of the frame have also been removed for paint and the super rusted 3/8 bolts holding the undermount plates to the brackets. Those bolts were welded to the RT bracket, but are now cut off. Interestingly the bolts holding the bracket to the frame did not have a spot of rust. Maybe they are stainless steel. I am planning to use new grade 5 or even 8 bolts and nylox nuts to remount the undermount plates depending on what I can find here in Bishop Ca. Have a question at this point on the TrueTrac. Should I have them use the AAM master bearing kits for the differential and also the AAM master wheel bearing kits as long as they are changing things out. There's 70,000 miles on the RT and I'm thinking, correct me if I'm wrong, that even if the bearings are not worn new bearings, seals will be "best practice" kind of maintenance as access into the differential will be limited once the new generator is installed. I think Booster might even recommend the addition of a sway bar. The front end of the RT was completely renovated last year everything replaced that had a ball joint, the bearings, brakes, steering links so I'm thinking I need to end up with a rebuilt rear end. Hoopers is legendary in So Cal and I guess they'll might only replaced what's needed to not waste $$. To me the parts and additional labor is what you do when you have things apart. Add the accessibility limitations with a generator in the way, this should be a no brainer, which in my case is not far from wrong. Thanks

I went through the whole question of whether or not to replace the bearings when I put the Dana full floater in our 07. By the time you buy the pinion, carrier and wheel bearings, you will probably have way more in them you paid for Truetrac. Ours had about 140K on the axle and the shop that I do the final setup (I was unable to get a good pattern myself) said the 10.5" axles will generally go to 300K without issue so I did not change them. We have had no issues to this point. I would ask your shop what they think.

The bolt in pinion housing is a really nice thing to have. Our Dana 70s has the conventional style which is more of a PITA to get setup right.

As to the carrier bearings needing to be replaced anyway, that could be a maybe. The Truetrac that I put in my Roadmaster wagon 10 bolt gm axle used larger carrier bearings than stock, so I did have to replace them. I was doing a total rebuild anyway so it really didn't matter much as the company I got the Truetrac and the rebuild kit from just substituted the right bearings for it. Your shop should either know offhand about that or they can call Eaton and find out.

There will probably be a discussion about what differential oil to use in the Truetrac as they are specifically stated to not using any oil with limited slip additive in it. There are very few oils these days that don't have limited slip in them so that may be an issue. They also say to not use synthetics because of possible friction differences causing an issue. Perhaps your shop would have a source for mineral based oil without limited slip additive. I did a lot of calling about using synthetic oil, though, as that would be my preference and nearly all the oil companies for the good synthetics like Motul and Redline said that there no additive differential oils were used in lots and lots of Truetracs and Thorson (same helical gear setup) of the years without any issues. I like the Motul oil and have it in the Roadtrk also.

I finally just got some industrial gear oil in 80 weight to do the initial run in of the gears (I had a new gearset to change ratios) and a couple hundred easy miles and then I changed it out for Motul with no additive and It has run very well and extremely quiet.
Two things that I did to the Roadtrek and the Buick is to add a drain hole to the differential, is it doesn't have one, and to also add drain and fill holes to axle hubs so you can drain them also at oil changes. These two changes make oil changes easy, especially if you have the generator in the way of getting cover off the diffy to get the oil out. Drain it out of drain hole and refill through the hubs so they are full and it is also much easier to do if the cover is blocked by the generator. I used 1/8" NPT pipe plugs both places as there are no bosses to have enough thread engagement with larger plugs in the castings.

I would, and am, strongly recommending the rear sway bar for it. It is the perfect time to do it besides as you are replacing the generator with a different model. This will allow you to mount the generator a bit further to the rear to clear a swaybar. I am not sure on a 2002 but the later Chevies have a Hellwig 1.375" bar available that is well done.

The bolt in pinion housing is a really nice thing to have. Our Dana 70s has the conventional style which is more of a PITA to get setup right.

[Floorman]

Originally Posted by booster

I went through the whole question of whether or not to replace the bearings when I put the Dana full floater in our 07. By the time you buy the pinion, carrier and wheel bearings, you will probably have way more in them you paid for Truetrac. Ours had about 140K on the axle and the shop that I do the final setup (I was unable to get a good pattern myself) said the 10.5" axles will generally go to 300K without issue so I did not change them. We have had no issues to this point. I would ask your shop what they think.

The bolt in pinion housing is a really nice thing to have. Our Dana 70s has the conventional style which is more of a PITA to get setup right.

As to the carrier bearings needing to be replaced anyway, that could be a maybe. The Truetrac that I put in my Roadmaster wagon 10 bolt gm axle used larger carrier bearings than stock, so I did have to replace them. I was doing a total rebuild anyway so it really didn't matter much as the company I got the Truetrac and the rebuild kit from just substituted the right bearings for it. Your shop should either know offhand about that or they can call Eaton and find out.

There will probably be a discussion about what differential oil to use in the Truetrac as they are specifically stated to not using any oil with limited slip additive in it. There are very few oils these days that don't have limited slip in them so that may be an issue. They also say to not use synthetics because of possible friction differences causing an issue. Perhaps your shop would have a source for mineral based oil without limited slip additive. I did a lot of calling about using synthetic oil, though, as that would be my preference and nearly all the oil companies for the good synthetics like Motul and Redline said that there no additive differential oils were used in lots and lots of Truetracs and Thorson (same helical gear setup) of the years without any issues. I like the Motul oil and have it in the Roadtrk also.

I finally just got some industrial gear oil in 80 weight to do the initial run in of the gears (I had a new gearset to change ratios) and a couple hundred easy miles and then I changed it out for Motul with no additive and It has run very well and extremely quiet.
Two things that I did to the Roadtrek and the Buick is to add a drain hole to the differential, is it doesn't have one, and to also add drain and fill holes to axle hubs so you can drain them also at oil changes. These two changes make oil changes easy, especially if you have the generator in the way of getting cover off the diffy to get the oil out. Drain it out of drain hole and refill through the hubs so they are full and it is also much easier to do if the cover is blocked by the generator. I used 1/8" NPT pipe plugs both places as there are no bosses to have enough thread engagement with larger plugs in the castings.

I would, and am, strongly recommending the rear sway bar for it. It is the perfect time to do it besides as you are replacing the generator with a different model. This will allow you to mount the generator a bit further to the rear to clear a swaybar. I am not sure on a 2002 but the later Chevies have a Hellwig 1.375" bar available that is well done.

The bolt in pinion housing is a really nice thing to have. Our Dana 70s has the conventional style which is more of a PITA to get setup right.

Thanks again Booster for your valued comments. Been looking this morning into each of the issues you have addressed. In the installation instructions of the TrueTrac there is general information and there are notes to specific model numbers. The 915A545 Truetrac does not have any specific model notes. It takes the OEM carrier bearings and I did call Eaton to double check and ask more questions. They are the real deal when it comes to tech support. There is a AAM master bearing kit for about $200 so that's affordable with the future limited access issue in mind but the Rep also thought that the shop would know best. We had a small discussion about gear oil. The instructions mentioned 80-90 weight GL5 non synthetic gear oil. The Tech mentioned the Lucas brand. I did ask about the limited slip additive in the Lucas product . He said good question and that there was a very limited amount in the oil and it was not a problem for the TrueTrac. He did say to absolutely avoid the synthetic gear oils. A drain is a good idea. I'll have to check out what's available over the counter as I have limited skill sets. The sway bar ........ There is 24 inches between the diff cover and the propane tank. Both the new and old generators are 16 1/2" leaving 7 1/2 inches of total clearance. Before removing the old Onan, I had measured 2 1/4" of clearance between the Onan and the diff cover and about 5" between the Onan and the propane tank. The Hellwig 7635 sway bar fits from '97 to 2020 3500 Express and has shallow bell shaped curve paralleling the rear axles. There is a Youtube by Steven R of moving the generator back 3" and another he did of the installation of the 7635 Hellwig on his 04C190P Roadtrek where he says 4 inches of clearance is necessary. Long story short I think moving the generator 4 inches back so that it's 7 inches from the differential limits access into the generator. I did find a Roadmaster sway bar, but I think that it's also a problem for clearance. I have already installed a super spring add on to the top of the leaf spring pack that has provided some relief to the rear of the RT suspension. I have a good 3/4 inch between the leaf pack and the overload leaf from this added spring. Going to take a pass on the sway bar in favor of generator clearance. Thanks again Booster. Totally appreciate the help and advice.

[carlN]

you know you can TAKE a breath when making long post by hitting the return button.

it give some space so normal people can read the novel.

the locker in the rear will be almost like having 4 wheel drive.. I saw some vans power through a sandy area heading to the BLM land at Dalton Wells near Moab.. both tires throwing roster tail going through..

Originally Posted by Floorman

I'm in the process of getting a Eaton Detroit TrueTrac Limited slip differential (915A545) installed in my 02C190P Roadtrek. My rear end is a GM 14 bolt 10.5" 30 spline 4.10 differential (GT5), I think manufactured by AAM. The ID of the rear end has been verified by shape of the cover, by the bolted on Pinion housing and the rear wheel hubs indicating full floating axles. I am changing out at the same time the Onan KV spec F for the new QG 2.8HGLAA-8303A. I will be having the installation done by Hoopers Rear Ends in Sun Valley Ca. next week. My preps so far is to remove the old KV Onan and the undermount as it needs to be wire brushed and repainted. The RT brackets that the undermount attaches, to the rear cross member of the frame have also been removed for paint and the super rusted 3/8 bolts holding the undermount plates to the brackets. Those bolts were welded to the RT bracket, but are now cut off. Interestingly the bolts holding the bracket to the frame did not have a spot of rust. Maybe they are stainless steel. I am planning to use new grade 5 or even 8 bolts and nylox nuts to remount the undermount plates depending on what I can find here in Bishop Ca. Have a question at this point on the TrueTrac. Should I have them use the AAM master bearing kits for the differential and also the AAM master wheel bearing kits as long as they are changing things out. There's 70,000 miles on the RT and I'm thinking, correct me if I'm wrong, that even if the bearings are not worn new bearings, seals will be "best practice" kind of maintenance as access into the differential will be limited once the new generator is installed. I think Booster might even recommend the addition of a sway bar. The front end of the RT was completely renovated last year everything replaced that had a ball joint, the bearings, brakes, steering links so I'm thinking I need to end up with a rebuilt rear end. Hoopers is legendary in So Cal and I guess they'll might only replaced what's needed to not waste $$. To me the parts and additional labor is what you do when you have things apart. Add the accessibility limitations with a generator in the way, this should be a no brainer, which in my case is not far from wrong. Thanks

[Floorman]

Update. I have had the True Trac installed this past week at Hoopers Rear End in Sun Valley Ca. They were hesitant to do the work as lift points on the RT are questionable issues. Being a previous customer, the 250 mile commute and having the correct True Trac made the job finally acceptable to them but they did have to do the job with the RT on ramps rather than lifting. They had the master bearing kit replacing all the bearings and seals including the pinion. There was excessive wear on the bearing and seals they thought, due to old probably original gear oil. Along with the replaced universals on the drive shaft, I like to think I had a smoother ride back to Bishop. Have not had any chirping around corners and its tested ok on dirt roads. This was a worthwhile and necessary upgrade and recommend Hoopers highly.

[booster]

Originally Posted by Floorman

Update. I have had the True Trac installed this past week at Hoopers Rear End in Sun Valley Ca. They were hesitant to do the work as lift points on the RT are questionable issues. Being a previous customer, the 250 mile commute and having the correct True Trac made the job finally acceptable to them but they did have to do the job with the RT on ramps rather than lifting. They had the master bearing kit replacing all the bearings and seals including the pinion. There was excessive wear on the bearing and seals they thought, due to old probably original gear oil. Along with the replaced universals on the drive shaft, I like to think I had a smoother ride back to Bishop. Have not had any chirping around corners and its tested ok on dirt roads. This was a worthwhile and necessary upgrade and recommend Hoopers highly.

Good to hear on the chirping, apparently the extra weight can overpower the preload in it. Did you do the standard test of putting on wheel on the gravel shoulder and the other on pavement to see how quick it locks up?

[Floorman]

Originally Posted by booster

Good to hear on the chirping, apparently the extra weight can overpower the preload in it. Did you do the standard test of putting on wheel on the gravel shoulder and the other on pavement to see how quick it locks up?

Haven't done the paved /dirt test yet, however, have a dirt transition from the street to the driveway that has a bump. It is slightly uphill backing in and the single drive tire used to spin. Think I felt the driver side wheel kick in. Am not certain what is meant by chirping. Looked it up on google and they gave the definition of it being sign of a worn bearing going bad. In an old Chevy PU in the past with the GM limited slip, I had the tire skipping around a corner that Hoopers fixed. Cornering with the new Truetrac is perfect. I'll do the paved /dirt test as soon as I get the New HGLAA generator completely installed. Waiting on a few items for the 12vdc connection. The previous owner had the old KV serviced 3 years ago and I'm guessing it was them that spliced a new section of SAE30R14-T2 line to the old line. I reused the 1/4 barbed fitting to connect the new Gen. The inside diameter of the fitting is less than 1/4 and the old fitting at first split the end of the old hose. I could not deal with dropping the gas tank at this time to replace the old hose but will replace it if I ever have to do a fuel pump or if there are issues with the new Gen being starved for fuel. The new splice is easily accessible in the driver side rear wheel well as it's strapped tied to the gas filler pipe. It's a good location for either an inline filter or a shutoff valve. The Installation Instructions on the new HGLAA Gen are meant for techs and not DIY. The connection accessories had no installation instructions at all, however Cummins has a great tech support available at 1-800-CUMMINS. I've shared installation notes on another post . Thanks again for all the advice and comments.

[booster]

Originally Posted by Floorman

Haven't done the paved /dirt test yet, however, have a dirt transition from the street to the driveway that has a bump. It is slightly uphill backing in and the single drive tire used to spin. Think I felt the driver side wheel kick in. Am not certain what is meant by chirping. Looked it up on google and they gave the definition of it being sign of a worn bearing going bad. In an old Chevy PU in the past with the GM limited slip, I had the tire skipping around a corner that Hoopers fixed. Cornering with the new Truetrac is perfect. I'll do the paved /dirt test as soon as I get the New HGLAA generator completely installed. Waiting on a few items for the 12vdc connection. The previous owner had the old KV serviced 3 years ago and I'm guessing it was them that spliced a new section of SAE30R14-T2 line to the old line. I reused the 1/4 barbed fitting to connect the new Gen. The inside diameter of the fitting is less than 1/4 and the old fitting at first split the end of the old hose. I could not deal with dropping the gas tank at this time to replace the old hose but will replace it if I ever have to do a fuel pump or if there are issues with the new Gen being starved for fuel. The new splice is easily accessible in the driver side rear wheel well as it's strapped tied to the gas filler pipe. It's a good location for either an inline filter or a shutoff valve. The Installation Instructions on the new HGLAA Gen are meant for techs and not DIY. The connection accessories had no installation instructions at all, however Cummins has a great tech support available at 1-800-CUMMINS. I've shared installation notes on another post . Thanks again for all the advice and comments.

Ah yes, lots of different definitions for what I called chirping. In the clutch type limited slips it is often referred to as "chatter" and is a stick/slip issue they get rid of by adding some limited slip additive to the oil. Others may call it bounce or wheel dragging, maybe wheel hop.



Basically it is all the same sound, but probably with different causes. A true locker diffy is an extreme example especially if it is a fully locked (welded commonly one) as you drag the inside tire around the corner because it needs fewer revolutions than the outside tire. You see that commonly on semi trucks leaving a dotted skip mark around corners.


I think with the Truetrac in the Buick it is just because it locks the wheels at much lower a load than a typical clutch type limited slip would. If I turn the corner with light power no noise, but if I put the power on it in the corner it gives the familiar "irk, irk, irk" sound of the tire slightly spinning" to even out the revolutions side to side. Different tire brands and styles will sound quite a bit differently, though. Cars set up for drag racing with clutch types will do the same thing, even with additive because it is a not a stick/slip as such with the diffy, it is in the tire traction. On a clutch type you can tighten them up to any preload you want with a flat clutch style by adding shims to the clutch pack, and on a cone type you change the springs or space them. You can go from loose enough for silent cornering to so tight it is almost a locker and shakes the whole car because of the tire spinning to make up the revolutions needed. If you have a fully locked you can actually break the axle if you have enough power and traction, or cause other damage.


I expect the Buick Truetrac will loosen up over time as all limited slips do. The current chirps are so minor they leave no mark on the road unless I really get on the power so that it fully locks up.


When I did the one tire in gravel and one on asphalt with the Buick, I could hear a very short burst of gravel spin sound and then it slightly chirped the other tire as it locked up very quickly. The gravel showed only a tiny bit of spin mark.


The physics of it all dictates that when turn a corner either the diffy or the tire slipping has to happen to make up the different distance the inside tire has to travel compared to the outer one. You need to balance that slippage location by having the right amount of preload of force through the diffy allowed by the limited slip feature, be it clutch or helical gears like the Truetrac.

[Floorman]

Originally Posted by booster

Ah yes, lots of different definitions for what I called chirping. In the clutch type limited slips it is often referred to as "chatter" and is a stick/slip issue they get rid of by adding some limited slip additive to the oil. Others may call it bounce or wheel dragging, maybe wheel hop.



Basically it is all the same sound, but probably with different causes. A true locker diffy is an extreme example especially if it is a fully locked (welded commonly one) as you drag the inside tire around the corner because it needs fewer revolutions than the outside tire. You see that commonly on semi trucks leaving a dotted skip mark around corners.


I think with the Truetrac in the Buick it is just because it locks the wheels at much lower a load than a typical clutch type limited slip would. If I turn the corner with light power no noise, but if I put the power on it in the corner it gives the familiar "irk, irk, irk" sound of the tire slightly spinning" to even out the revolutions side to side. Different tire brands and styles will sound quite a bit differently, though. Cars set up for drag racing with clutch types will do the same thing, even with additive because it is a not a stick/slip as such with the diffy, it is in the tire traction. On a clutch type you can tighten them up to any preload you want with a flat clutch style by adding shims to the clutch pack, and on a cone type you change the springs or space them. You can go from loose enough for silent cornering to so tight it is almost a locker and shakes the whole car because of the tire spinning to make up the revolutions needed. If you have a fully locked you can actually break the axle if you have enough power and traction, or cause other damage.


I expect the Buick Truetrac will loosen up over time as all limited slips do. The current chirps are so minor they leave no mark on the road unless I really get on the power so that it fully locks up.


When I did the one tire in gravel and one on asphalt with the Buick, I could hear a very short burst of gravel spin sound and then it slightly chirped the other tire as it locked up very quickly. The gravel showed only a tiny bit of spin mark.


The physics of it all dictates that when turn a corner either the diffy or the tire slipping has to happen to make up the different distance the inside tire has to travel compared to the outer one. You need to balance that slippage location by having the right amount of preload of force through the diffy allowed by the limited slip feature, be it clutch or helical gears like the Truetrac.

Thank you for the explanation and definition. I was aware of the wheel hop as it had happened to me previously but appreciate greatly the more definitive explanation. You have a good Thanksgiving and holiday season and good corners in the Buick