Vibration got worse after changing transmission mount 300D and overheating

[Nicolasmabru]

I have a 1983 240d, I had a motor swap done with a 1982 300D that was purchased solely for that purpose. I used a shop that wasn't particularly familiar with these cars. Engine runs good, tranny shift great but I had to do some adjustments after I got the car back to get it running right. Anyways, I've had a vibration in the 30-40 mph range that I've just been ignoring but now after changing the transmission mount (used one that I had bought for the 240d and noticed that it was a bit smaller but figured that it was better than the shot transmission mount that was on) the vibration has gotten worse, it has also started shaking on acceleration from dead stop. Another problem - I can drive this car upto 65-70 mph with ac on with no overheating problems at all, stays at 85-90 degrees but if I try going 75-90, it overheats quick. If I slow down again, temp drops back down within a few minutes (I never let the car go over 100 degrees) I have also seen after my morning commute (about 20 min of highway driving) if I drive with the ac it, it will not overheat while I'm moving but if I catch a red light and sit for a few minutes, temp will climb to 95 from 85. Fan couch is new, couldn't find any problems with radiator and aux fan works. This car is still running with the 240d diff and currently has no antifreeze, only water. System was burped and holding pressure. Any tips?

[Nicolasmabru]

Vibration doesn't change when in neutral. If I rev, I get the same vibration

[cho]

Originally Posted by Nicolasmabru

Any tips?

yes...don't use "look alike' parts and don't use only water


.

[Stretch]

Firstly using only water in a cooling system will cause you loads of problems - these will be corrosion related problems. Only use water as an emergency get you home solution and when you are at home drain the entire system and refill with coolant.

To identify if you now have a coolant blockage an IR heat gun can be useful but even an old fashioned thermocouple and a DVM can help.

Did the "shop" who did the conversion send you on your way with water in the coolant system? If so that kind of indicates to me the standard of the conversion...


######


Vibration problems.

Get someone who knows what they are doing to check to see if the engine mounts have been fitted properly. The transmission mount should be adjusted after the propshaft has been installed...

...the propshaft commonly has marks on it that should be aligned to avoid vibration related problems (parts made from about 1981(?) have marks)...

...if the propshaft does not lie straight from the front of the car to the rear then vibration could occur as this system has only one universal joint (I can post a link to a thread about this if you like - or you can just take it from me!). To fix this you need to make sure that the engine mounts (again) and the subframe mounts are in good condition...

...I'm not too surprised that the engine overheats at high engine speeds as you have a differential designed for a much slower car. You must be the fastest W123 at the traffic lights but your ear drums must hurt at max chat.

[charmalu]

What transmission X mount are you using? the metal one. Is it the narrow 240D mount with only one bolt on each end? If so, how did they adapt it?
with this conversion, you should use a 240D automatic X mount, it is wider and uses 4 bolts, since the engine will move the mounting back.

What about the Fly-Wheel? did they match balance it? or just stick it on?.

Use the Differential from your donor car and it`s speedometer, they are geared together. if your donor is a 82 - 84, it will have a 3:07 Diff. If 85, will be a 2:88.
Your 240D has a 3:69 Diff.

Charlie

[Stretch]

Originally Posted by charmalu

...
What about the Fly-Wheel? did they match balance it? or just stick it on?.

...

Good point about the flywheel if it was also an auto to manual conversion - I got the impression it has an automatic transmission...

...re-reading it I'm not sure why...

So OP what have you got?

[Nicolasmabru]

The shop who did the conversion put green coolant, I just replaced radiator about 50 miles ago which is why there is just water now, I have blue mb coolant that should be in tomorrow, car is automatic and I'd switch the diff but I already got rid of the doner car. The think that I don't understand is let's say the driveshaft isn't aligned properly, I would have a shake when car is in drive and it would go away in neutral, correct? I will be doing a lot more work on this car once I have another car that I can drive when I'm working on this. I just don't get why the temp increase is so drastic. I don't have RPM readout at this time but will have to do that. I did see that if I stay within 5-7 lbs of boost (55-65 mph) car is fine. If I peak at 12lbs (80-95 mph) car will be at 95 degrees in less than a minute

[Nicolasmabru]

This is a ghetto rigged gauge that I installed to see boost levels one night

[Nicolasmabru]

And not sure if this is relevant but I have an exhaust leak on the bottom portion of the downpipe
And my ball joints on the lower control arm are also shot

[Nicolasmabru]

Mount looks like this but has a bracket that is held in place with an Allen screw through the middle 'hole' on the mount

[Nicolasmabru]

I'll post a picture of it when I get back home/ under the car

[laubscherc]

Originally Posted by Nicolasmabru

I'll post a picture of it when I get back home/ under the car

With such a diff ratio, you will suffer from some torque movement around the intermediate shaft bearing rubber. Check it out for softness or wear.