Rear Motor Mount Solenoid

[johnl]

Manual cars have a hydraulically filled rear mount.

I've Held my CB7s rear mount in my hands, and I saw no evidence of it being other than rubber and steel...

[NAiL05]

My 92 had some liquid coming out the bottom end of the mount when I pulled it out. then the whole center fell apart.

[James Matteu]

Must be a solenoid that operates a valve that allows / dissallows vaccum to the mount...? Is the idea to cause the mount to momentarily become even softer as the trans transitions from P or N to R or D (or between D and R etc)? ...

Correct, the solenoid allows / disallows vaccum to the mount's actuator diaphram. The idea is to isolate Chamber A from Chamber B when RPMs are above 3000. Keep in mind that Chamber B is the larger chamber at the bottom and the valve is normally closed; the diaphram is sprung to assist in valve closure. Vaccum is applied in low RPMs (below 3000) which opens the valve and allows fluid to be shared by the two chambers (isobaric). As I mentioned before, all this is controlled by the TCM and has nothing to do with transitions from Park to Nuetral, Reverse, Drive, etc.; only RPMs.

[Reignstarz]

Correct, the solenoid allows / disallows vaccum to the mount's actuator diaphram. The idea is to isolate Chamber A from Chamber B when RPMs are above 3000. Keep in mind that Chamber B is the larger chamber at the bottom and the valve is normally closed; the diaphram is sprung to assist in valve closure. Vaccum is applied in low RPMs (below 3000) which opens the valve and allows fluid to be shared by the two chambers (isobaric). As I mentioned before, all this is controlled by the TCM and has nothing to do with transitions from Park to Nuetral, Reverse, Drive, etc.; only RPMs.

Thanks for the advice.

The only problem is I have changed the rear mount and the solenoid that hooks up to it. My front mount and side mounts are changed too

But when I change into reverse you can hear a metal touching metal kinda noise.

The engine gives a nice jump too when it's warmed up and changing from reverse to drive. or vice.

Also when I come to a stop I do hear a popping noise or a CLICK kinda noise from the front end. I heard that might be the solenoid not working either.

[James Matteu]

...I have changed the rear mount and the solenoid that hooks up to it...

Please re-read my previous post. There is more to that system than the mount and the solenoid. You need to verify there is vaccum coming from the intake manifold; vaccum leaks are not unheard of. You need to verify the connection between the solenoid and the TCM is a good one.

I replaced the rear mount as well. As I always do, I tested the new unit before installation; buying a defective unit is not unheard of. I found my brand new (and expensive IMHO) came with a poorly manufactured actuator diaphram, it leaked. I could not return it for exchange since it was the only one at the store, all other stores had none in stock, and I needed it immediatly. I swapped the diaphram from the old mount to the new. I re-tested the unit and then installed it.

Please note in my previous post that I said if you come up with nothing, you should re-test everything. Same goes with new parts. Just because it is new doesn't mean it is above scrutiny. Check those new parts, check those wires, check that vaccum.

Keep a cool head and be objective, let us know what happens.

[johnl]

But when I change into reverse you can hear a metal touching metal kinda noise.

It may not be related to the mount etc. It could merely be clearances in the drive train (lash between gears and / or splines, or maybe wear in CV joints) being taken up as the load transitions from positive to negative (i.e. as drive force direction changes from forward to reverse). This can make metallic noises since metal will be impacting metal inside the box or inside the CVs.

The engine gives a nice jump too when it's warmed up and changing from reverse to drive. or vice.

High idle speed?? This might also tend to increase the likelihood and volume of any drive train metallic impact noises...

[johnl]

Yeh, its a vacuum actuated solenoid I believe

Sorry to be picky, but there is no such thing as a "vacuum actuated solenoid". A solenoid operates electro-magnetically, if not then it's not a solenoid. What we have here is (appears to be...) a solenoid that actuates a valve that opens and closes a vacuum line.

[Reignstarz]

Please re-read my previous post. There is more to that system than the mount and the solenoid. You need to verify there is vaccum coming from the intake manifold; vaccum leaks are not unheard of. You need to verify the connection between the solenoid and the TCM is a good one.

I replaced the rear mount as well. As I always do, I tested the new unit before installation; buying a defective unit is not unheard of. I found my brand new (and expensive IMHO) came with a poorly manufactured actuator diaphram, it leaked. I could not return it for exchange since it was the only one at the store, all other stores had none in stock, and I needed it immediatly. I swapped the diaphram from the old mount to the new. I re-tested the unit and then installed it.

Please note in my previous post that I said if you come up with nothing, you should re-test everything. Same goes with new parts. Just because it is new doesn't mean it is above scrutiny. Check those new parts, check those wires, check that vaccum.

Keep a cool head and be objective, let us know what happens.

Yeah there is a vacuum coming from the intake manifold. I took the hose off and the idle went up. Then I put my finger over the little spot where the hose would go and my finger got sucked to it and the idle leveled out.

I checked if there was power going to the connector that goes to the solenoid and there was. There wasn't a ground so I rewired the ground and checked once again for power and a ground and everything was okay. But it did not fix my problem.

should there be a vacuum going TO THE REAR MOTOR MOUNT as well?

Maybe ill make a video to show you what it's doing but basically the engine moves backwards then forwards. As if the front motor mount is non existent.

[James Matteu]

should there be a vacuum going TO THE REAR MOTOR MOUNT as well?

Yes, at idle you should have vaccum. According to Helm, if not, then the solenoid is bad, but what I would do is double check the TCM.

Connect a multimeter to the solenoid connection (ground wire to multimeter (+) and multimeter (-) to chassis), and check for ground at idle; i.e. set it to Ohms Resistance. Manipulate the throttle to raise the RPMs and see if the meter goes from 0 Ohms (at idle) to infinite Ohms (above idle).

Your solenoid could be bad like the Helms indicates. But I think you could have a bad connection between the solenoid and the TCM, or the TCM could be failing to properly ground the solenoid, or the TCM could be missing RPM data (does your TCM shift hard, do you have a flashing D4 light?), or etc.

Run your test and let us know what happens.