Rear ride height question

[ICPete]

I'm about to replace my rear suspension leveling valve, which has been leaking for a while now.

I've got the new part and since I'm rebuilding the wooden bed (that's a subject for another topic!), now is the time to access the leveling valve.

Of course before I remove the old one I will measure the current ride height. However I would also like to have some assurance that when I set the new valve back to that same height, that it is correct.

Here is the table from the Volvo manual:

 

 

I know I have a Meritor RT40-14 axle, but how do I find out which size, i.e., 10.47 vs 11.81 (266mm vs 300mm)?

And what do RRH200 and RRH160 refer to? I have searched online but cannot find any indication what this stuff means.

I know my axle spacing is 1320mm, but even with that the choice of ride height varies from 7.13" to 8.86", depending on the other variables shown.

Here are my axle specs on the door jamb label:

 

 

I saw in a thread from about 13 months ago someone said to set it to 7.75"; I guess that's a good average??

 

Pete

[porky69]

10.47" or 11.81" is the height of your frame rails(just the c-shaped steel), just measure the height of your frame rails. Will either be just shy of 10.5" or just over 11.75", my guess would be 10.5" unless your truck is a fairly heavy spec chassis.

 

The RRH200 or RRH160 is in reference to which suspension you have and can be identified by:(copied from the page 7 of http://www.hhrvresource.com/VolvoDocs/60-79/PV776-TSP178199.pdf )

 

Group 72 Volvo Optimized Air Suspension Specifications Suspension Applications Note: There are two vehicle suspension ride height versions. The RRH-180 and RRH-200 have a stamped sheet metal torque rod bracket (on the axle) and a different torque rod. The vehicles with this version are equipped with a Meritor axle. The other version is the RRH-160, this suspension has a cast iron torque rod bracket and is available on all Dana/Eaton axles as well as Meritor. The difference between the two versions is that the bumpstop has changed and this has impacted the total suspension travel that is available.

 

Make sure to set your suspension to the recommended height as improper setting can impact your pinion angles and can cause vibration issues in your driveline, some of which you may not feel but over time they will do damage.

[ICPete]

Thanks Porky! Funny thing-- I only looked in the Group 72 service document that applied to 1999+ vehicles, which didn't have that last paragraph that you quoted. The document you linked to is the 2002+ version of the Group 72 pages, and they apparently added that paragraph since so many of us were left confused by the earlier version of the document!! I need to learn to read EVERYTHING in my service manuals, and not necessarily just the sections that apply to my model year!

 

The frame rail height is a good thing to know. I had thought it might have something to do with crown gear diameter, like you see all the time on GM LD trucks, which come with different diameter gears in the differential. Frame height makes more sense!

 

So I measured my frame rail height and it is definitely 300mm, or 11.81". I measured it in several locations; there is no doubt about it. However my torque rod brackets are definitely cast iron, extremely heavy things. There is no way they are stamped sheet metal.

So that says I have the RRH-160 rear ride height version. The chart for ride height doesn't provide for the option of both 300mm frame rails and RRH-160 torque arm brackets.

 

Applying a little calculation, I see that the ride height difference between RRH200 & 10.47" vs RRH200 & 11.81" happens to be 0.67", which also happens to be exactly half the difference between the two corresponding rail heights. So the taller the rail, the less the ride height, which is of course measured to the bottom of the frame rail. That tells me they are keeping the distance from the CENTER of the frame rail to the center of the axle constant, between the two rail versions. If we apply that logic to the RRH160 dimensions, we would subtract 0.67" from the listed 7.13" ride height for RRH160 & 10.47" rail. That produces 6.46" for the theoretical ride height dimension for RRH160 & 11.81" rail. Sounds logical, no?

 

Unfortunately I'm measuring something between 7.5" and 8.0" for my current suspension ride height dimension. That's an average between the two axles, as right now the truck is not on perfectly level ground. I have to move it to a level paved area in order to take a more accurate reading.

 

Maybe the Volvo dealer can shed some light on the discrepancy?

 

Pete

[ICPete]

10.47" or 11.81" is the height of your frame rails(just the c-shaped steel), just measure the height of your frame rails. ...

 

 

 

Porky,

OK now I see on the chart where that column is labelled "Frame Height mm (in.)". Geez, I never even noticed that in all the time I was staring at that table. Duh. It's heck getting old... Maybe I better ask my wife to read the service manual for me from now on...

Pete

[ICPete]

After carefully reading the manual's instructions on checking the axle pinion angles and intermediate driveshaft angle, it's clear to me that these angles are at least as important as the simple ride height number.

So I think I'm going to get a digital inclinometer (I'm seeing cheap ones under $50 on Amazon) and go through the angle measurements and calculations, before I touch the old leveling valve. That should help me understand whether the ride height, as it is currently, is too high or too low, if either.

That could help determine whether I should be aiming for 6.46", as calculated for my RRH-160 torque arm brackets and 300mm frame rail height.

Pete

[heavyduty]

Where are the ride hight measurement taken. Very interesting stuff

[ICPete]

HD: the measurement is taken from the center of the axle (theoretical axis of rotation -- some people use the parting line or seam in the axle housing casting) to the bottom face of the frame rail. In practice, the manual describes measuring from the ground to the axle hub center hole, then subtracting that number from the distance between the ground and the underside of the frame rail. Doing it that way may be simpler, but it requires a decently smooth and flat ground surface (like a concrete shop floor).

 

So the higher the number, the higher your truck off the ground.

 

Pete

[heavyduty]

Thanks pete

[adept99]

Hey Pete;

 

Keep in mind that you're setting to truck level, not earth level. So no matter what means you use, you need to establish a lubber line, i.e. a line that will represent a zero angle line as it relates to the truck and from which you can set the drive angle.

 

The plastic inclinometers sold a big box hardware stores will work pretty well for a one time thing if you're careful. And they're cheap.

 

A 3 piece machinist's square will work also. More accurate but harder to use unless you have 3 hands or mag mounts.

 

And finally, with no protractor at all, a little trigonometry and a few bits of fishing line will get you very, very close.

 

Good Luck

Paul

[WeBeFulltimers]

(1) Find a good level place to park.

(2) With tractor sitting at normal level measure from bottom of frame rail to the ground.

(3) Replace old valve with new valve.

(4) Adjust new valve until same height in (2) is achieved and make sure all fasteners are tight.

 

As a retired trucker I did this several times and it worked for me. Why make it so complicated?

[Ronbo]

I just replaced my valve. Old setting was incorrect. I measured from seam on front of axle to bottom of frame. Kenworth calls for 9 1/2 inches

[Scrap]

Not to be nitpicky, but KW is 9" from center of axle shaft to bottom of rails. T2 & AG200 is a little higher but I don't remember exactly what it is or why. Not that it matters much though as ride height isn't as critical on an 8 bag anyways.

[Ronbo]

T2000 and it is 9 1/2 but I agree, I don't think it is that critical over 1/2 to 1 in when it will be flexing going down the road.