How to know if subframe mounts are needed?

[rwmastel]

How can one tell if subframe mounts are needed?  Is there a measurement that can be taken between subframe and body?  Is there a test that can be performed?   Asking for a friend: https://www.sl113.org/forums/index.php?topic=37806.0

[Vander]

You measure from the ground, to the bottom edge on the center of the fender. I got 25 11/16" or about 652mm if I converted correctly.

[Jordan]

You measure from the ground, to the bottom edge on the center of the fender. I got 25 11/16" or about 652mm if I converted correctly.

Is that all four corners?

[Sens]

Thanks for opening this tread Todd!

I measure 27,5 inch (approx 70 cm) for the front wheels.

But I have to say that I replaced my 4 shock absorbers some time ago, which made the car a little "higher".

I added 2 pictures of the mounts. Difficult to see, but should they be replaced?
I think so... the rubber on the last picture is about 3m thick.

Or is that correct?

[Vander]

Is that all four corners?

That was the front measurement.

I will add my measurements were with new subframe mounts, new motor mounts, new trans mount, new Bilstein shocks, and 195/75/14 tire.

[Kevkeller]

I don’t believe the shocks should change the height. They are just dampeners.  I believe there’s rubber pads on the springs that can adjust the height of the body above the ground.

[Sens]

If I use the pictures of Bpossel, you can see the difference between sub frame mounts:
new, older and mine (very old).

I think that could be the way to determine if they have to be replaced or not.

Halvor

[rwmastel]

I would think there is no one "correct" height of the wheel well lip from the ground.  We have too many variables:
- rubber spring pad thickness
- height of springs (incorrect replacements, heavy duty springs, etc.)
- tire dimensions that people select
- tire pressure at the time of measurement
- the sub-frame mount condition

How can we all agree that one measurement can be correct and we should all strive to achieve it?

Looking at the three pictures of the mounts in the previous post, I would think we need to measure the mount itself to determine if it is failed or good.  Maybe put a jack stand under the sub-frame cross member to keep the weight of the body on the sub-frame, remove front tires, and measure something like this distance shown in pic?  According to these two pics, one mount is old and collapsed and one is new and in proper position.  I wonder if these pics were taken with the sub-frame supported?

[stickandrudderman]

Measuring the height of the wheel arches is not a viable method for determining sub frame mounts condition.
There are various observation that can be made as seen in the above photos, or if you have the car on a lift with the wheels hanging you can see if the mount has separated.
Personally I always look at the gap between the steel sump edge and the sub-frame as this reduces, sometimes to the pointy of contact, as the bushes fail.

[rwmastel]

... look at the gap between the steel sump edge and the sub-frame as this reduces, sometimes to the point of contact, as the bushes fail.

"steel sump edge"?  I'm not familiar with that term in this context.  Can you elaborate?

[Mike Hughes]

The British terms for some vehicle features can be a little confusing for many of us on this side of the pond.  The term for oil pan is sump, the hood is the bonnet, the soft top is the hood, the trunk is the boot, the windshield is a windscreen and the rear window is a backlight, turn signal lamps are often called indicators or winkers, the side of the car closest to the edge of a two-lane road is the kerb side or near side and the side of the car closest to the middle of the road is called the off side. 

I've owned British cars for over 60 years and still get confused!

[rwmastel]

Personally I always look at the gap between the steel sump edge and the sub-frame as this reduces, sometimes to the pointy of contact, as the bushes fail.

The British terms for some vehicle features can be a little confusing for many of us on this side of the pond.  The term for oil pan is sump, ...

Noted.  Now, what else am I missing?  How do failed sub-frame mounts change the relationship between oil pan and sub-frame?  Wouldn't that be motor mounts?

[stickandrudderman]

Noted.  Now, what else am I missing?  How do failed sub-frame mounts change the relationship between oil pan and sub-frame?  Wouldn't that be motor mounts?

You're absolutely right! I must have been having a senior moment, sorry.

[rwmastel]

Is the answer that there is no definitive measurement to determine a failed sub-frame mount?

Is the answer to perform a test?  Jack up one side of the car using the body, and then examine the stressed subframe mount for physical damage and separation?

[Harry]

My advice would be that if now is a "convenient" time to replace the mounts considering ongoing other suspension work, do so.  These cars are long in the tooth and replacing the mount has to be an improvement.  Rubber has a working life.

Harry

[Pinder]

I agree with Harry.

One thing to note, before I changed my subframe mounts the Snorkel on my airfilter to throttle body did not line up well. After body mount replacement it was a a nice alignment. 

Here is my post from when I did this job.

https://www.sl113.org/forums/index.php?topic=36429.msg266418#msg266418

[rwmastel]

Harry - Well, I was thinking that it would be nice to have a specific measurement or test procedure so people could know for a fact if the replacement is needed.  Maybe "if you think it might be needed, then consider it needed."?

Pinder - That's a nice side affect that I never thought of.  All the body-to-drive train relationships will change.  I wonder how it affects throttle linkage?  Do the hard fuel lines connect directly to the main filter housing in the engine bay?  There are probably a number of things like this to consider.

[Pinder]

The hard fuel lines to the fuel filter switch to fuel hoses which has flex in it to compensate for the change of the engine height in relation to the body.

[Pinder]

The Linkage connection, I did not consider and its a good point.

[Harry]

It's a desirable point to be able to confirm with a measurement but my experience in measuring rubber mounts has been that it is always difficult to do with any certainty.  And often I'll talk myself out of changing something based on those measurements then second guess myself until I go back and replace them.

The other point is that if those are original, they're bound to be tired even with "low" mileage.  I'm somewhat of an advocate to "not fix something that isn't broken" but 50+ year old rubber is probably a good candidate for replacement.  If now is a convenient time for you, I would consider it.  If it is not and you don't observe anything that leads you to believe they are an issue right now, you can wait until there is a better time.

I replaced mine when I dropped the front suspension, making the job much more accessible.

Harry

[VikDasor]

After reading this post and as I have just changed the front engine mounts, transmission mount and all shocks all around few weeks ago, the subframe mounts are also on my to do list.

With the car raised today took some pictures of my subframe mounts and I am assuming they are totally gone.

[stickandrudderman]

Yes, those are a perfect illustration of failed subframe mounts.
As I always say, It's best to change all of the rubber components at once so as to get the maximum benefit. Otherwise you're combining new rubber with old and getting much reduced ride quality.