LFA

1987 S+ with Automatic transmission, 50K miles

We are currently testing the 87 S4 and the 91 GT recently restored from empty shell

I need your expert advice on the following. tHanks for all your help.

1- ( 87 Auto)
The cars shifts up and down very smoothly after start/ cold. It again shifts up and down quite smoothly. When stuck in stop and go traffic and engine gets hot the upshift and especaşlly downshift ( from 2 to 1 for example) gets fought. You hear a metal banging sound under the car. What would be causing this?

2-The oil pressure is between 2 and 3 at idle and reaches 5 when you hit the accelerator. Again when stuck in stop and go traffic the oil pressure goes down to 2 at idle and reaches 4-4.5 max but not 5 when you cruise. ( currently using Mobil1 full synthetic 5W-50). Is this normal.

3- The alternator charges and the meter shows 13V on cold start and falls to 12 when again stuck in stop-go traffic.

Thanks for all your help

Best,

Evren

Mrmerlin

1. it could be the damper in the TT moving,
is the TT stock?
did you pin the damper?

Vibration could be worn trans mounts ,
and if you used the Volvo mounts for the engine then the fingers may need adjusting.

2. the oil viscosity is not the suggested oil.
You should be using 15W 50 or 20W 50
gauge readings are normal,

NOTE not going to 5 bar is indicative of a different make of oil sender being used ,
some types will not stay at 5 bar but go to just under it.
Swapping in the more expensive oil sender may restore this performance

ROG100

1) Refer to Mr. Merlin
2) Oil is not correct - you need at least 15W 50 or better still 20W 50. Here in Texas where it gets as hot as your home we use 20W 50.
3) Sounds normal. The gauge can be inaccurate - check at the jump post. As long as it is 12v or higher under load it should be OK.

SeanR

The banging of the trans when hot could be due to a compromised vacuum system under the air filter assembly. I'd ensure all of those connections are new, tight and working as they should be.

LFA

Thanks Mr. Merlin, Roger and SeanR for all your comments,

1- The TT is stock and we did not ''pin the damper''. I will look into that. As SeanR suggested I will also check the vacuum. The check-valve next to the brake master cylinder was making noise, we replaced it with a used but Ok one. I must also mention that the we replaced the part (vacuum activator?) on the automatic transmission ( the part which the vacuum hose enters the automatic transmission, like a small pump)Could malfunction of this part also cause the banging sound. It seems working when cold though.

One other problem I am trying to solve is; sometimes when you push the accelerator the auto transmission starts shifting from the existing gear to up but it takes some time, it does not happen quickly and the rev increases during this time. What might cause the auto transmission to have this extended /long shifting pattern

There is a metal banging sound when engine very hot during downshifting, this is instantaneous, one hit at during downshift.
I have the new Volvo mounts, (the engine sits a little high, that is normal I suppose) but you can move the engine side by side with your hand very easily. Is this normal with volvo mounts, they seem very soft. There is only 100 miles on the new engine, do they get tighter or settle in time?

2- I will replace the oil with 15-20/W50 and look into the oil sender. Could the 5W50 oil at hoot engine conditions causing lower oil pressure readings.

mike77

I don't think your oil pressure readings are low. Once the engine is fully warmed up 2 bar is fine at idle, my S4 is the same. Initially when you start the car up cold you'll notice higher pressure at idle and then as the oil comes up to operating temp the pressure drops.

dr bob

Replace the oil with the correct viscosity (15W-50 or 20W-50 per your owner's manual).

Why did you replace the transmission modulator? And how was it adjusted after replacement? The vacuum modulator adjusts the firmness of up-shifting. Control pressures are adjusted based on manifold pressure so that low-load shifts aren't harsh, yet higher-load shifts don't have a lot of slip.

First thing on my list would be a full trans fluid replacement with filter. Look carefully at the old fluid for signs of metal dust in the bottom of the transmission oil pan. Anything more than a very small amount of gray dust is cause for worry. Fluid should be light to medium red, with no burned smell. Drain the torque converter as part of the process. Replace with new good fluid of course. Filling is a multi-step process as you pump fluid to the reservoir, and start the engine briefly to pump fluid up through the converter and cooler plumbing to get the last fluid in. Verify the level is good with engine running warm/hot in neutral/park, after cycling the transmission through all the gears a few times. A small underfill will often cause odd shifting, so get it right before jumping into other things.

There are numerous tyhreads on B2 brake band piston replacement. Since you say it shifts OK under certain conditions, this probably isn't a concern for you. Still, it's worth a little searching/reading to get up to speed on the common issues.

Last but not least, we are often tempted to twiddle with this or make an adjustment to that when trying to 'fix' transmission symptoms. While it's once in a while possible to stumble on an adjustment that masks a symptom, it's just as likely to cause another problem in the process. Adjusting the vacuum modulator is a prime example. The Most Common Modulator Failure Mode is a cooked, split, or disconnected vacuum line from the intake. This cauises hard shifts and eventually damage, ultimately wearing and breaking brake bands with the constant harsh shifting. A good transmission shop that knows Mercedes will have the correct gauges to help you diagnose internal problems. It's money very well spent, giving you a real idea of what's been wearing and failing in the gearbox. Plus on the rack, some of your driveline noises/clunks/bangs are easy to hear and identify at least as far as location.