New I P CAUSING VACUUM / SHIFTING PROBLEMS - PeachParts Mercedes-Benz Forum

Lee C · #1 07-20-2008, 02:58 PM

Just had a rebuilt IP installed on the 87 300 TD and now my formerly smooth shifting trans is slamming into gear. I suspect that it must be a vacuum problem but I can't find a vacuum diagram. I have a new mity vac but where to start?

Jeremy5848 · #2 07-20-2008, 03:00 PM

A vacuum diagram for your car was posted here earlier this morning. Scan down the threads and you will find it.

Bio300TDTdriver · #3 07-20-2008, 03:14 PM

I would start by looking for a disconnected vacuum line. It's pretty easy to accidentally pull one loose when working on the engine.

Brian Carlton · #4 07-20-2008, 04:12 PM

Quote:

Originally Posted by Lee C

Just had a rebuilt IP installed on the 87 300 TD and now my formerly smooth shifting trans is slamming into gear. I suspect that it must be a vacuum problem but I can't find a vacuum diagram. I have a new mity vac but where to start?

The problem is most likely due to the VCV which is mounted to the side of the IP and has three vacuum lines that go to it. Two are on top..........one is the vacuum supply and the second is the output to the amplifier (blue flying saucer) on the fenderwell. If either of these lines were not connected to the new IP, the vacuum to the transmission will be zero and the shifts will be very harsh.

Lee C · #5 07-20-2008, 04:35 PM

I don't see anything loose or not connected. Where should I test first?

Brian Carlton · #6 07-20-2008, 04:47 PM

Quote:

Originally Posted by Lee C

I don't see anything loose or not connected. Where should I test first?

Find the VCV.

Test the inlet line and confirm that you have 20" vacuum at idle.

Test the output line and confirm that you have 10-12" at idle. If you have zero.........you found the problem. The VCV on the replaced IP is NG.

Lee C · #7 07-20-2008, 05:00 PM

7 on one side 0 on the other. Is it usual to replace the old VCV on a $1000 rebuilt IP

Brian Carlton · #8 07-20-2008, 05:07 PM

Quote:

Originally Posted by Lee C

7 on one side 0 on the other. Is it usual to replace the old VCV on a $1000 rebuilt IP

You must determine why you only have 7" on the supply line.

On the 603, the engine must be running for this test. Make sure you T into the supply line and read the vacuum.

Follow the supply line back to the source...........see where it goes. My guess is that it's not leading straight back to the vacuum pump or the test procedure is faulty.

Lee C · #9 07-21-2008, 12:39 PM

Checked the brake booster and I have 22'' there. Then upon closer examination I found a very short hose under the blue flying saucer that isn't attached to anything! It is the one that is off to one side. There is also a Y connector a few inches away with only two hoses attached. Intuition tells me to hook them up but the lines aren't long enough.and I'm wondering if there is some gadget that is suppose to go in between them.

Brian Carlton · #10 07-21-2008, 12:51 PM

Quote:

Originally Posted by Lee C

Checked the brake booster and I have 22'' there. Then upon closer examination I found a very short hose under the blue flying saucer that isn't attached to anything! It is the one that is off to one side. There is also a Y connector a few inches away with only two hoses attached. Intuition tells me to hook them up but the lines aren't long enough.and I'm wondering if there is some gadget that is suppose to go in between them.

The connection off-center on the bottom is the VCV port. The reason that it shifts too firmly is that the transmission has no vacuum because this hose is not connected. The hose goes to a T that is right at the switchover valve. One end of the T goes to the VCV..........one end goes to the amplifier..........and the bull goes to the switchover valve.