Buying tips, W126 420SEC

[PJayUK]

I am going to look at another SEC this weekend this is the first one I have seen that has the 4.2L V8 M116 engine in it. The car itself sounds like it could be a good one; it’s registered in 1989 on a G plate in metallic blue with ivory leather. It’s from a dealer in Surrey taken as a part ex and apparently is in very good overall condition with history and a large amount of bills etc.

Before I go and look at the car tomorrow there are a couple of things that I am unsure of and wanted to get some advice and views on.

Firstly I don’t know much about this engine what are the main things to look out for are there any common faults etc that I need to be aware of?

When I called the dealer he said that the car has a problem with the ABS that has not been fully diagnosed. Apparently the ABS light is on permanently but the car’s braking capabilities are fine. Sounds to me like it could simply be a faulty wheel sensor but again I am not that familiar with the ABS system on these beasts so would appreciate any advice.

The car is reasonably priced and has an MOT until July 2010, If I manage to buy the car I’ll get it serviced and the ABS issue fixed but I need to keep the initial purchase price and repairs within my budget, so I want to avoid buying the car if its got serious issues. Its going to be my “fun” car so I am expecting to have to spend some money on it but I do want it to be drivable and in good overall condition.

So any tips etc would be greatly appreciated!

 

[Tiff]

Never had an SEC, but always fancied one! I remember reading a buying guide on them a while back and the most important thing in their view was to open the boot,stick your head in and look up! Seemingly the rear scuttle/boot surround panel rots badly on them. Otherwise usual solid old Mercedes engineering. check all buttons/switches/ decent test drive and if all seems good,then they are bulletproof. ABS faults can show up in 2 ways. If the light goes out after starting,but comes on when you pull away, its likely to be a sensor. if it doesn't go out at all, its an electrical problem, possibly the Over voltage protection relay, which is fused. Can blow if the car is jump started carelessly etc.

 

[Will]

Good advice above. I'd go as far as to say that mechanical/electrical issues would probably be the easiest/cheapest to fix - rust/rot/bodywork can spell the end for these cars unless you're good at welding or it's a special car where the sums of money involved maybe not significant.

If there's little or no rust and the rest of the car (bodywork/interior etc) is fine, then it could be a goer

ABS light is unlikely to be particularly expensive to fix - as said, likely OVP fault or sensor etc.

I understand that the front/rear screens can be expensive too (?), associated with the rear parcel shelf rust issues that Tiff mentions.

Best of luck,

Will

 

[219]

I had a problem recently with the ABS on my 500SEL - unfortunately just before MOT time so it had to be fixed pronto ! Attempting to clean around the sensors with compressed air made no difference , nor did swapping over the identical control module from another of my cars .

In the end I put the car into a local indy as I did not want to start throwing expensive parts at it until the fault went away . In my case it turned out to be BOTH front wheel sensors that were faulty . On my car the light would be off when the engine was started , but would come on after a short distance was travelled - indicating that the ABS system had 'dropped out' , whereupon normal non-ABS braking was still available - the system would reset again after the engine was stopped and restarted . The drop out was caused by the failure of the signal from one or more sensor .

The wiring to the front sensors can be prone to breaking down as it flexes due to suspension movement ; but the rear sensor being fixed to the differential tends not to suffer from this problem .

In the end , it cost me something like £350 for the repair ( the sensors alone are a little over £100 each ! ) so I considered that entirely reasonable since the guy spent a couple of hours on 'manual' diagnosis looking at waveforms with his oscilloscope ( the car is too old to connect to STAR ) then some time fitting the parts once they arrived .

If the ABS light on this car is permanently on and does not reset when the engine is stopped then restarted then it may be something other than sensors . The same control box is used in W124 and other models which can be found in scrapyards . The OVP used in W126's is an older type and less likely to be found in breakers - but sometimes they just need opened up and resoldered .

 

[tromppost]

Check it has air con as it was an extra on the 420. When checking for rust and water leaks in the boot put your finger right up through the gaps just under where the rear window sits, you can get a fair idea if its been leaking in the past. They also smoke a lot when you pull away.
I had a 420 SEC (87) many years ago, you may find it a little slow.

 

[Mudster]

The 420 was the lowest volume SEC by a long margin, mainly becasue anyone buying one of these generally wasn't short of a few bob and didn't bother with the entry level model.

The 420 as adequate, the 500 is a little faster with no noticeable increase in running costs the 560 is noticeably faster again, fuel consumption difference is so negligeable it's not worth considering.

However, the 560SEC has ASR and Self levelling suspension which add to the possible issues the car may have.

This often makes the 500SEC the car of choice.

I owned a 1990 560SEC, you have to want to own one of these cars, they need a little looking after as they were at the time the most expensive model Mercedes sold.

Personally I'd give the 420 a miss, it's underpowered. Look for a good 500 or if you want a keeper maybe a 560.

These cars all rot under the rear window, it's a design problem, water collects in the corners of the screen at the seal, the pillarless design allows enough bodyflex to momentarily break the seal and allow water through - over time this rots the parcel shelf area.

Signs are a milky like bloom of the rear screen, this is a sign of delamination.

Front and rear wings rot (particualrly fronts) - not enormously expensive to replace at £200 a side new main dealer - bolt and paint.

Rear arches also rot - repair arches are available - not as plug and play as front wings.

Doors drop on the hinges - new hinges can often correct.

Butler seat belt presenters are generally temperamental.

If it has a sunroof, make sure it works, you wouldn't believe how many parts these sunroofs are made up of, it's like some sort of Chinese torture puzzle.

Hydraulic valve guides wear at around 100K plus, a smoky engine is often no more than a tops end valve rebuild - not as expensive as it sounds and the enginw will go for another 100K once done.

Having owned one of these cars, if buying again I would place a premium on aesthetic condition and lack of rot over mechanicals. Compared to modern models these are comparitively simple cars to repair mechanically - it's the bodywork and trim that really gets pricey.

 

[PJayUK]

Well it was a nice car, and despite the excellent advice from Mudster (which is greatly appreciated!!) about the 420 being underpowered I am seriously thinking about buying it. Overall external condition is very good there is some slight rust on the nearside front wheel arch but I could not find any under the parcel shelf area in the boot. I was thorough I took my new 1 million candle power torch with me and had a really good look. I could not find any more rust on the car although the underside of the car was really really dirty which I thought was slightly strange. Almost like the car had been driven off-road.

Anyway the bad points...

Aircon doesnt blow cold
ABS light permanently on from start
Front brake discs are worn
Slight gearbox whine in first gear

Other than for a car that was made in 1989 it was really nice, and DAMN IT!! I liked it so much that I left a deposit on it and plan to take the Mrs to have a look in the morning...It drove really well in fact it felt very similar to my W210 but with much more of a sense of occasion

If I buy it I'll need to have a serious chat with Olly at PCS to get the car sorted!

 

[BlackC55]

Sounds good!

Any pics?

 

[PJayUK]

Olly I'll get some pics tomorrow when I go back to have a look....

Pretty close to buying this one whats your view on the brake issue though? I was also wondering how much new discs and pads on the front would set me back? If I buy it I am going to stick it in the garage for now though as my EClass is still my priority as its my daily driver so I want to finish the jobs on that (trans fluid, plugs etc). Once thats fully sorted I'll start work on getting the SEC straightened out. As its a hobby car there's no urgency...

We'll have a chat on Thursday....

Still slightly in 2 minds though as its only the second one I have seen and there doesnt seem to be a shortage of them

 

[BlackC55]

The ABSfault could be a number of things. Remember it won't pass an MOT with that light on.

Bargain the price down 'cos of it. Worst case senario is the ABS control unit. Best case is the ovp relay.

Discs and pads???? Not too sure on the cost sitting here.

 

[Tiff]

Front Brake discs are about 30 quid each from Euro,pads are around 20.

Front ABS sensor £114 (bosch)


OVP relay or ABS unit can come from a breakers, most Mercs of this age have the same parts. I've used Mercman in the past for bits and have had no probs.In the great scheme of things this was a 40K+ car, and being able to put new brakes all round for less than a night out is a big bonus! try some modern car part prices!!!

Here is an ABS fault finding guide, its for the 190, but its a Bosch ABS11 system just the same..
http://www.mercedes190oc.com/uploads/articles/absmb190e.pdf

 

[PJayUK]

Ok, well that doesnt sound too bad.

Mrs is not too keen, she wants to change the ML for an X5 at the moment so we'll pour another glass of wine and talk about it!

I must admit I do want to update her car soon, but seeing as I have now sold my XJR and my Pajero I think I need another hobby car....

 

[Tiff]

X5?? Yikes.

 

[PJayUK]

Yep, remember though its the Mrs!

(hate to say it we drove one and it was errr nice actually!)

 

[dinoy]

be very careful with the 380 and the 420 sec engines make sure of its history it is single chain as apposed to 500 and 560 which is double chained it it snaps yr camshat and cylinders will be gone and usually it is on the passenger side bank where it happens check rocker cover if u see it cracked and repaired walk away as this means chain has gone and before and cracked the rocker cover this same problem transfered itself from w107, 130k miles is when the chain should be changed.

other things is carpets behind the front seats push yr finger str8 through if u see water it means sunroof is leaking, front carpets and under carpets if wet means leaking from the front windscreen.

contrary to popular belief series 1 1981-1985 mechnically is better model as less electronics in them, series II have lots of ecu issues and expensive to fix when u r in a hurry, series I wood trim known to come off due to the glue used and this needs removing and reguling an expensive process if u want a mint show car.

i owned 10 in my time and they are lovely cars and have gr8 response and require little to look after them and there various variations with wide bodied gull wing and convertible (my personal favourite) in RHD i know of only three so far white one ordered new by james hunt, a blue one by mohammed al maktoum it sitting somewhere awaiting restoration and the asking price upwards of 20k, and finally recent maroon one which was on ebay bought by a polish guy condition unknown for 2.7k, still not willing to say if the engine is running or the top moves i presume he knows he bought a treasure or a lemon i offered him for it fully restored and working with current mot n tax a tax exempt 350 slc no 4xxx from original production with 80k miles insured for 12k agreed value as i have been told only handful survive from the early production

 

[kusanku]

The SECs also have a habit of leaking, and replacement rubber seals for the windows are not cheap. Also, they are quite prone to a problem with the heater, which I think is the duovalve. Will the car be garaged? Not a good idea to leave these cars standing outside. I had a 500SEC for a couple of years, and absolutely loved it. Nothing major went wrong with it, but even little things worked out quite pricey. Also, it did not like standard unleaded, and even most of the premium unleaded petrols. About the only thing it accepted was the high RON Shell petrol, otherwise it developed a misfire.

 

[dinoy]

The SECs also have a habit of leaking, and replacement rubber seals for the windows are not cheap. Also, they are quite prone to a problem with the heater, which I think is the duovalve. Will the car be garaged? Not a good idea to leave these cars standing outside. I had a 500SEC for a couple of years, and absolutely loved it. Nothing major went wrong with it, but even little things worked out quite pricey. Also, it did not like standard unleaded, and even most of the premium unleaded petrols. About the only thing it accepted was the high RON Shell petrol, otherwise it developed a misfire.

for proper running with unleaded u need the distrubter turned 15 degrees although u r right there is a little misfire and in series I the the fuel distributor goes, as for parts europarts sell parts for w126 cheap and ebay and people who brake w126 is another, generally i found parts for it in maintenance were really cheaper when sourced carefully

 

[grober]

try this guide Buyer's Guide

 

[NewMB]

My father have had a few...... one of them was a 420SEC and one 560SEC. Both rusted like crazy (despite sitting in a heated garage) under both front doors and on edge of boot lip.

Having driven both, I would not agree with another posted that the 420 is slow! A 4.2 litre V8 and 224bhp will not be slow. Loads of torque. However, it can not touch the power of the 560.

Fuel....well, a V8 will never be cheap and his current V12 is actually more fuel efficient (although some 10 yrs younger).

 

[grober]

My father have had a few...... one of them was a 420SEC and one 560SEC. Both rusted like crazy (despite sitting in a heated garage) under both front doors and on edge of boot lip.
.

Goes to the old maxim that a garaged car rusts quicker than one that lives in the open. Rusting is a thermodynamic process which slows down the colder it gets.Cars in the open also dry out underneath due to better air circulation. The down side is UV damage to paintwork and trim and chemical "debris" deposition ranging from bird sh** to volcanic ash!