Transmission problem

[Marcusd]

Hi, I bought a 2000 E38 740i last week and have just taken it on a long run whilst towing a caravan. After about 40 miles the transmission wouldn't go higher than 3rd gear. Even in manual mode it refuses to go higher than 3rd. When accelerating from low sppeds it gets stuck in 2nd gear until I give the accelerator a big press then let off to get it to go into 3rd.

If you stop the car and leave it for a few minutes the problem goes away for the first few miles thyen comes back again.

When slowing down to a junction, the car goes down a gear a bit too early so the revs go up as you are slowing down. When driving through heavy rain the problem went away for a bit so I thought the transmission may be overheating.

We made it to our destination by driving at 55mph, 3,000rpm in third and I'm now here, 300 miles from home with only a few tools and no ramps etc.
Help! Is there anything I can check whilst I'm here? If this is a new transmission that's needed, I've bought a bad car.

I'm going to try driving it without towing today and see if the issue is just with the extra weight.

I am new to E38's and automatic transmissions after 10 years of driving manual E34 5 Series cars.

[shogun]

what you can do whilst you are on the trip: check the trans fluid level.
European Transmissions has a good write up how to test fluid level with or without trans dipstick
BMWtech.htm
also check if the fluid changed color or smells burnt.

To check which transmission type you have, check here under RealOEM.com Online BMW Parts Catalog

In the U.K. you have some good companies which repair automatic transmissions at reasonable prices.

[Marcusd]

Thanks Shogun. As I'm 300 miles from home with only minimal tools, I weighed up the cost of buying more ramps and tools compared to a basic level check at a dealer.

I've found a dealer about 15 miles away, which isn't bad as it's quite remote where I am at the moment. I explained the problem to their senior tech and they have agreed that if I can leave them the car all day on Monday, they'll find the time to get it up on the ramp and check the fluid level and oil condition.

Basically, it's overheating for some reason or another. When cold, it behaves fine apart from a being a little jerky when the car comes to a halt. I noticed that when driving through heavy rain and standing water, the fault went away for a bit as the water cooled the transmission.

After 10 + years of owning a couple of E34's I've been looking for a later E38 for a while now. This one had all the spec I wanted with the sport wheels, sport seats, sound system etc plus it has LPG (half the price of petrol here) and the removable towing hitch. I only paid £1650 for it so expected it to need a bit of work to bring it up to scratch.

At the worst it may need a reconditioned transmission, which will probably cost as much as the car did. As everything else seems to work fine, I think it's worth doing though.

[Marcusd]

Well, so far so good. This could be usefull info for anyone who has a similar overheating problem.

The dealer spent a couple of hours with the car and found that the transmission DME had corroded pins which were causing the issue. It wasn't sealed or mounted properly letting water get in. They have cleaned all the coroded pins and refitted it properly and so far the fault appears to have gone.

I got the impression from what was said, that the corroded pins were stopping the DME from getting the signal from the temperature sensor on the harness at the bottom of the transmission. The sensor should have been telling the DME that the transmission oil was up to temperature so it could close the bypass valve and let all the oil go through the trans cooler. Without this signal, it left the bypass valve open.

Sounds plausable, It's been fine on the 12 mile journey home so will give it a longer run tomorrow. It would be great if this is all it was as a transmission rebuild would have cost a lot more than the £200 the dealer have charged me for fix this.

I can now enjoy the rest of my holiday, UK rainy weather and all, without having to worry about being towed 300 miles home with a caravan!

[Marcusd]

Oh well, spoke too soon. The fault reappeared yesterday after about 50 miles and the main dealer apparently now, don't have the time to look at it. I'll just have to get towed 300 miles home with the caravan.

I have trawled the Internet on various forums and found a post with an identical problem and the fix.

Major Tranmission Issues (ZF 5HP24) - Bimmerforums - The Ultimate BMW Forum

These symptoms are exactly what I'm getting and the transmission is the same as in my car. Someone early on in the post who seemed to know his stuff suggested the transmission oil temp sensor would be at fault. It is part of the wiring harness that plugs into the bottom of thye transmission and the part number is listed.

Towards the end of the post, the original poster has posted back saying that it was indeed the tempo sensor and has posted pics of it being replaced. Hopefully this will do it. Apparently the sensor controls a bypass valve which stops the oil being forced through the trans cooler until it is up to temperature. If this sensor is at fault or the vavle is at fault the valve stays open so the cooling of the transission is effected.

I was kind of hoping the Bentley manual would list the pins and resistance tolerance of this so I could just test it before buying a new harness but nothing seems to be listed for this.

When it stops raining here, I'm going to have another look at the transmission DME and check how well the main dealer cleaned the corroded pins. It could be that the temp sensor has too high a resistance and the corroded pins are increasing this resistance.

So the plan when back home is to get the correct Esso LT oil and an OEM filter, a sump gasket and harness and give a transmission an oil change and new sensor.

Will post back the results.

Fingers crossed!

[Grantus]

I was about to post saying that my car has had similar problems, although less severe than yours.

I was advised to replace the voltage regulator on top of the trans heat exchanger.

I havent got around to doing it yet as I havent been using the car much.

Here is the post: Transmission Question for rf900rkw - Bimmerforums - The Ultimate BMW Forum

That forum has more E38 traffic than here.

[Marcusd]

I was about to post saying that my car has had similar problems, although less severe than yours.

I was advised to replace the voltage regulator on top of the trans heat exchanger.

I havent got around to doing it yet as I havent been using the car much.

Here is the post: Transmission Question for rf900rkw - Bimmerforums - The Ultimate BMW Forum

That forum has more E38 traffic than here.

Great, thanks. the link in that post is very useful and sounds just like the problem I'm getting. The transmission is definitley overheating as the fault dissappeared for a while when driving through heavy rain and standing water.

I have ordered the wiring harness, transmission oil LT71141 and filter so will do this anyway now. But I will definitely have a look at the heat exchanger.

I will have diagnostic cables and software by next week so can also plug in a laptop to monitor the transmission temperature whilst driving it.

Thanks for the info

[Marcusd]

I've had time to have a good look at the car now and have drawn up a list of things which need doing to get the car back to how it should. Until I do all this I won't be able to trust it

It needs the valve/rocker cover gaskets replacing, the drive belts are cracked and the radiator is leaking where the plastic meets the ally on the side.

I am going to change the voltage regualtor on the trans heat exchanger and have ordered the trans filter/oil and gasket plus the transmission wiring harness. Hopefully this will solve the trans overheat problem.

The sway bar drop link has completely sheared at one end so is not connected to the sway bar! eek!.

I bought this car blind because it was cheap at £1650 for a 2000 740i with LPG conversion. I knew I would have to do a few jobs to bring it up to scratch so am not too surprised to find it's been neglected on the maintenance front other than oil/filters. All the parts have been ordered and will be with me tommorrow, by my reckoning, I have spent about £450 on the parts I need to get this car back to how it should be.

Once I've done this work, the car should be OK.

[Grantus]

Where is the best price/place to buy parts from? specifically the trans voltage regulator.

I find that if I privately import parts I can save almost half of what they cost here in NZ.

[shogun]

I bought in the past from Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips
they ship also by cheaper USPS parcel service, others often insist on expensive FedEx or DHL. USPS takes a bit longer, but you can save a lot.
Also BMA ships overseas http://www.bmaparts.com/
or Pelican Parts - Porsche Parts & BMW Parts - Automotive Parts and Accessories - Porsche & BMW
or RockAuto Auto Parts
sometimes I also buy on Ebay USA, some sellers have reasonable shipping cost or combine orders too.


cheap is also
Discount Auto Parts Online -- ************** - Domestic & Import Auto Parts Warehouse but there you need someone in USA to buy for you and then ship to NZ