Replacing the DKW fuel pump membrane - Update

DKW's are quite light-on for maintenance; there's no engine tuning, no changing of oil, but there are several jobs that do need to be regularly attended to. One of those things is replacing the fuel pump membrane.

DKW introduced a fuel pump with their first postwar passenger car, the F89P, in 1950. Prewar cars and the Schnellaster van had their petrol tanks mounted over the engine so simply used gravity feed, like in a motorcycle. The petrol pump selected by DKW used vacuum pressure from the crankcase to pull petrol from the petrol tank in the boot. It was a very simple and economical solution, but also a weak point as the membrane in the pump wears out or stiffens over time, reducing the pump's effectiveness. A perforated or leaking membrane can actually lead to catastrophic engine failure by letting petrol leak into the crankcase, flushing the grease from the bearings.

My DKW F94 began to exhibit hard starting about three months ago. The car simply wouldn't start without a dose of starting fluid if it hadn't been driven in the past fortnight; then in the past week; then it wouldn't start without it at all. I had fiddled around with the carburetor as that is often a leading cause of hard starting, but it did not help. This weekend I decide it was time to look at the fuel pump.

It's a very simple process to remove the false radiator grill - undo the two clips holding the grill in place and it lifts straight out. This provides easy access to the ignition timing and the fuel pump.

Next the fuel filter is removed, then the pipe to the carburetor. Two 17mm bolts hold the pump to the engine. Undo the bolts carefully so as not to damage the gasket.

Eight 6mm bolts hold the two pieces of the fuel pump together. After removing the bolts you can carefully separate the two sides of the fuel pump. There is a spring underneath the membrane and you do not want that flying across the garage as you need to put the spring back in correctly. If you place it on the wrong side or upside down, it will not work.

The membrane on my pump seemed okay. It flexed well and the spring was tight, but I replaced it anyway. You must take care when reassembling the membrane with the spring. You do not want to the spring to penetrate the membrane and of course the spring wants to fly. Aligning the membrane with the bolt holes also takes care. Re-installation is simple enough, reversing the process.

Although the old membrane seemed okay, a quick test run showed that that was, in fact, the problem. After only a few seconds of cranking the engine spluttered and caught and then was away. I was very happy! How long do the membranes last? In my experience they only last (reliably) for about three or four years before they begin to deteriorate. Fortunately, it's an easy repair, even for an amateur like me!

This was the type of membrane I used. It has a larger metal backing plate. There are different sized membranes between the different engines - 900cc, 1000cc and 780cc - so you need to check you're ordering the right one.

Update 4 November 2024 - Oh dear!!

Well, it seems I was wrong, wrong, wrong about the fuel pump membrane. After running well for several weeks, I took the car to a show - she drove magnificently, no problems at all - and then died on the drive home. I could not get the car to run at all more than about a minute before fuel starvation kicked in. As I have to drive over a long bridge to get home, I chose to have the car towed. Thank you RAC Roadside Assist!! https://www.productreview.com.au/reviews/99d09025-ed41-59bf-840f-7ea571f1b02d

At home I pulled the fuel pump apart again. I swapped out the membranes three times and each time the fuel flow was nil or a trickle. A trickle was the best I could do so I settled for that. At least I could get the started and moved in the garage where it wasn't blocking the Karmann Ghia. What was wrong?

When I consulted this diagram on DKW Hesse website I suddenly noticed that the fuel pump shows TWO springs, one on each side of the membrane. Two? My fuel pump has only ever had one. Clearly at some point in the past one of the springs was lost and never replaced. For whatever reason, the fuel pump continued to work but only just enough. Possibly the issue with hard starting was always the sole surviving spring stiffening up. I've been pointlessly changing the membranes which possibly freed up the spring a little, giving the impression of fixing the problem.

My friend Brendan O'Dell in New Zealand is sending me some new springs - THANKS BRENDAN. Brendan supplies Brazilian made parts to owners in New Zealand and further afield. I'll pop his website up shortly.

Arrived 21 November 2024. Third time is a charm!

And the problem is quite obvious when the pump was removed. The spring as it was in my pump was wrong to start with - the outer (small) spring was the mounted on the inside. It's quite obvious where they should go.

Like this - the spiral spring belongs on the engine side of the pump. The small spring fits on the outer side. The upper ends of both springs fit neatly into metal centre of the membrane. Another 30-40 minute job and it's done. The pump still only generates a weak flow, but its more consistent and is enough to get the engine running. I'll have to check in week or two whether I still have hard starting issues. In the meantime, a big thank you to Brendan O'Dell for his help. You're a champ!

1938 DKW SB350 Restoration Update November 2024

After whinging to my club mates about some of the issues I was having with the bike, Wayne from Classic Gasoline (who worked on my Tatra and DKW at various times) said bring it around and we'll have a look at it. Wayne has Vape ignition on several of his bikes and he felt he would be able to quickly nut out the issue.

It's much easier to solve these problems quickly when you have adult supervision. Kim and Gavin get stuck into it.

After some fiddling around with the Vape, a good, strong spark was achieved. This highlighted there were problems with the carburetor.

The carburetor was removed and cleaned with an ultrasonic cleaner - note the underlying bronze content of the Amal carb is exposed. The needle jet was misplaced and needed to be refitted. This was undoubtedly caused when I was trying to refit the choke slide. The choke itself was revealed to be a problem as the cable works in the reverse direction you would expect. What looks like 'choke off' is actually 'choke on.' This would explain some of the hard starting and choking out issues. Additionally we noted that the choke always wants to go 'on', springing back into the 'on' position by itself. There is a spring issue there to resolve.

With the carb largely sorted out (the choke spring still to be fixed), the engine would fire up easily and run but after a few minutes the carb would silt up with rust and dirt from the tank. Kim took the tank back to his workshop to have it cleaned up.

Electrical engineer Gavin set to work on the bikes confusing electrics. The bike is currently set up with the electrics running off the Vape magneto (no battery), but we've decided to fit a battery and kill-switch and wire in the horn and brake light. We are using the new wiring harness from https://www.motorradmeistermilz.de/
Once those jobs are done, the bike should be able to run. Everything else is mainly cosmetic - is fitting the chain guard and the speedometer cables. This where it pays to be in a club where you have access to people with actual, practical skills. It would have taken me ages of hit-and-miss, trial-and-error, repairs, with no guarantee that I'd be on the right path. Wayne, Kim and Gavin each have their specific skills and experience and were able to quickly identify the issue and the best path forward. Thank you guys!

Step One of the restoration effort: https://dkwautounionproject.blogspot.com/2024/08/1938-dkw-sb350-restoration-progress.html
Acquisition: https://dkwautounionproject.blogspot.com/2024/07/1938-dkw-sb350.html

1938 DKW SB350 Restoration update August 2024

Having seen videos of the motorbike being started and ridden I was confident that I would quickly be able to finish up the last few jobs to get the bike back on the road. I never intended a full restoration but would leave the bike 'as is' with it grubby and worn patina. However, after getting her home and trying to get her started, I ran into problems.

Firstly, the bike did not start easily. It took a lot of fiddling around before it finally kicked over and ran for about 8 minutes. It then began to backfire through the carburetor and the ignition was snuffed out. After changing the spark plugs, the bike would start up promptly but was constantly backfiring now. Then old petrol tap began leaking like a sieve and the carburetor began flooding. I had already ordered a replacement petrol tap and carburetor when I bought the bike so I put those jobs aside while I waited for the parts to arrive. Other items I ordered - mainly for general hygiene - were a taillight, a replacement  speedometer in kilometres (as opposed to miles) and all control cables. These arrived this week.

I decided to stick with the old Amal carburetor and used the new carburetor for parts. The replacement was actually a copy of an East German generic carburetor that fitted almost all old DKW and MZ motorcycles. The problem with the Amal carb proved to be a missing needle clip, so that was an easy fix.

This stopped the carburetor flooding and along with a little tightening here and there the steady drip from the carb stopped.

The next job was the replacement of the broken speedometer. After a bit of fumbling around I managed to remove the speedo housing, but then I found the original speedometer was very firmly attached to the housing and I could see no way to remove it. Discussions with the prewar DKW motorcycle owners club on Facebook (there are several groups) suggest this would need a lot of soaking in WD40 and then gingerly attempting to unscrew the speedo from the housing. I guess they made things to last in the old days and did not conceive the need to replace the speedo. I made several attempts to remove the speedo but I was unsuccessful. More advice required!

One long bolt secures the speedometer housing to the top of the forks.

I can see no way to unscrew the speedometer as there is nothing to get a purchase on.

I suspected that backfiring through the carburetor could be a symptom of the ignition being too far advanced. This was not a problem prior to my taking possession as the bike was starting and riding easily. All I could think is that the VAPE ignition has shifted during transport. It took some time to get the generator side engine cover off as it was firmly stuck. Looking at the Vape and the marks made on the housing, I thought the ignition timing may have moved about 3mm from where it should have been. Unfortunately, I didn't have a puller to remove the hub and make the adjustment.

While I was thwarted with the Vape, I attempted to replace the worn out choke cable. That proved to be more challenging than expected. The replacement cables were not the same size as the originals and their fittings did not necessarily fit (why? This seems so common - why don't they make replacements the same as the originals?). A lot of frustration and much swearing was involved in refitting the cable, but the result was less than perfect. The tension was all wrong and the choke automatically reverted to on.

All these frustrations were expressed to various Facebook groups and to members of my motoring club. One of the guys in the club took pity on me and invited me to bring the bike over to his place as he was sure he had a suitable puller.

Vendors I have used so far include:
1. https://www.motorradmeistermilz.de/
2. https://www.Zeitmaschinen-shop.de

Update 11 November 2024 - Adult supervision at last!!
The bike goes to my friends at Classic Gasoline for some fiddle farting.
https://dkwautounionproject.blogspot.com/2024/11/1938-dkw-sb350-restoration-update.html
Acquisition: https://dkwautounionproject.blogspot.com/2024/07/1938-dkw-sb350.html

1938 Wanderer W25K Project

Wanderer Werke AG was founded in Chemnitz by Johann Baptist Winklhofer and Richard Adolf Jaenicke in 1896. They originally manufactured typewriters, industrial tools and bicycles and in 1902 progressed to motorcycles. In 1912 they developed the car that would set them on the path as a fully fledged automobile company, the W1 "Puppchen." The Puppchen was a small, budget car seating two passengers in tandem. It was originally powered by a four-cylinder, four-stroke engine of approximately 1100cc, but rapidly evolved over the next decade, becoming larger and more powerful.

By the late 1920s, the Puppchen and its successors were quite out of date and the company sought outside help to design a new range of vehicles. In 1929, Ferdinand Porsche had been made redundant from Steyr in Austria and decided to strike out on his own as an independent design consultant. Wanderer engaged Porsche to design them a new engine. This would be the Porsche Design Bureau's first contract and it would ultimately make his career. Porsche designed a four cylinder and a six cylinder engine for Wanderer that would become the bedrock of all Wanderer vehicles for the next ten years. These engines were so reliable that they would even find their way in the trucks and tractors Wanderer built for the German war effort and copies would find their way into IFA's military vehicles in East Germany into the 1960s. https://dkwautounionproject.blogspot.com/2024/07/1956-ifa-p2m-gelandewagen.html

The first Porsche-engined Wanderer was the W21, which went on sale in 1930. Sales of Wanderer's mid-ranged cars continued strongly even through the years of the Great Depression, however, the auto industry in the state of Saxony was in a parlous state, largely due to the enormous debts owed by luxury car markers Audi and Horch, to the State Bank of Saxony. Should either of those companies fail, the State Bank's own survival was at risk. The board of the State Bank approached Jorge Rasmussen of JS Rasmussen and Co to bail out the faltering Audi. JS Rasmussen owned a diverse industrial empire, the jewel of which was the budget auto and motorcycle manufacturer, DKW. With complex debt restructuring, Rasmussen was able to fund the purchase the struggling Audi. Despite Rasmussen's efforts to revitalize the brand, the company proved unsalvageable. In 1931 production of Audi cars was halted and their factory in Zwickau given over to production of DKW budget cars.

Despite challenging economic times, DKW's new budget car, the Frontreib F1 (above), proved to be a hit and the company began to claw its way back into the black. Horch however remained a problem. The State Bank's directors approached Rasmussen again to buy out Horch, but after examining Horch's books, he declined. The purchase of Audi had been an enormous burden on the Rasmussen group and the company had no capital reserve to take on the enormous debts of Horch. Nevertheless, a plan was developed to form an automobile conglomerate comprising DKW, Audi and Horch, separate from the Rasmussen industrial empire (which included such diverse businesses as coal mining, steel smelting, wood-working, a leather tannery, aircraft, refrigerators, motorcycle accessories and specialist industrial parts). The capital for this merger would come from Wanderer, which were forced into the merger by the State Bank. The price Wanderer extracted from the State Bank was a dominant position on the board of the new Auto-Union, something that Jorge Rasmussen was not made aware of. As part of the deal, Wanderer was forced to sell off its motorcycle arm, which was purchased by Czech industrialist, Frantisek Janecek, cousin of Wanderer's founder, Richard Jaenicke. Frantisek Janecek's company would be named Jawa, a contraction of the first letters of his surname and the first letters of Wanderer. https://dkwautounionproject.blogspot.com/2021/02/jawa-700.html

The new Auto-Union AG economized production by assigning company a specific market segment and removing duplication. DKW served the budget car and motorcycle segment, Wanderer served the middle-class market and Horch serviced the luxury market. The bringing together of the four companies design studio allowed standardization of parts and cross pollination of technical features. For instance, Wanderer cars quickly adopted the DKW 'floating' rear axle, which did much to improve their handling, while the association with Horch saw an uplift in quality fittings.

In 1936 Wanderer introduced a new sportscar - the W25K - to capitalize on the growing affluence of the German middle-class (Horch and DKW also introduced similar roadsters at the same time). The W25K was powered by a six-cylinder 2-litre engine with a compressor in a handsome two-seater roadster body by Baur. Sales were slow however. 149 were built in 1936, 72 in 1937, and 37 in 1938, when the model was withdrawn. Very few examples survive and they are highly desirable today.

The Australian Wanderer W25K

The chances that such a rare vehicle would end up in Australia was always pretty slim, but then stranger things have happened. Consider the 1944 DKW F9 pre-production car owned by Auto-Union technical director, William Werner, that ended up in Australia. After passing through several hands in the 1980s it ended up in the possession of Peter Thorogood, then president of the DKW Club of Victoria. After Peter sold the DKW F9 and it made its way back to Audi Tradition. See the story here: https://dkwautounionproject.blogspot.com/2021/08/the-werner-dkw-f9.html

After that adventure, Peter managed to acquire a 1938 Wanderer W25K. Peter recollects:

"The car came to Australia in the 1950’s with a migrating Dutch family. [Vehicles were limited and expensive in Australia after the Second World War so immigrants could import one personal vehicle without paying any import duties]. It then went to a Geelong family (I believe the father ran a car repair workshop). Along the way the original engine failed and was replaced with a Vauxhall engine. It then languished in a field under a pine tree for many years before it was eventually saved by DKW club member Bill Sheehan, about 35 years ago. Bill never did anything with it however, and it further deteriorated so a couple of years ago I persuaded him to part with it. The story was the original engine had been buried along with much other mechanical stuff in the garden of the Geelong property, but the family would not let Bill go and dig it up. When I bought the car I went around to the family to see if I could convince them to let me dig in their garden. When I got there the house had been demolished and the land leveled by the Ministry of housing. I paid a large bond and hired an excavator and dug a meter of soil from the whole site and found one saucepan and one boot! I was forced to search in Germany for an engine. Unfortunately, while I managed to find a correct 6 cylinder 2 litre Wanderer engine, it is not the supercharged variety, but beggars cannot be choosers."

The project itself lingered a with Peter as he had to source so many rare parts from Germany before he was in a position to start work. Fortunately, Wanderer specialists in the Auto Union Veteranen Club in Germany were able to assist.

The first step was to fit the chassis with the correct Wanderer engine. From this point however, things began to go wrong. The restoration shop Peter contracted sat on the project, promising to do work that was never done but charging quite liberally. After years of back and forth, Peter managed to get the car back in his garage. Much of the work that was done proved to be of poor quality and would need to be undone.

It took Peter several more years to find a restorer willing to take on the project. No restoration shop likes to pick up another shop's project as there are always doubts over the quality of earlier work. As mentioned, much of what had been done earlier needed to be undone and put right.

Motor Works Garage of Chewton, Victoria. Motor Works specialize in traditional coach-building for prewar cars with steel and aluminum bodywork, as well as mechanical repairs. Now things began to make progress.

The panelwork begins to come together.

Much of the cars bonnet and front end needed to be re-manufactured from scratch.

Back end. Trim is test fitted.

Finishing up the front end and lining up the bonnet.

And a view from the back end.

The car has really taken shape now. Wire wheels have now been refurbished.

Once everything was fitted in place, it was pulled apart for painting. Here is the frame.

The completed project at the workshop. The car looks absolutely stunning.

And it finally returns home to Peter's garage. Behind the Wanderer is his 1938 DKW SB200. A fine pair.

And so, after a very long and torturous restoration, the project was completed and the car could finally be enjoyed.....but, it would not be. Towards the end of the restoration, with completion in sight, Peter was knocked down by a chronic disease. This sadly put an end to his ability to drive. His son took him on drives in the car (below), but it wasn't the same. Having seen the project through to its successful conclusion, with great regret, Peter was forced to put the car up for sale.

Rarity and quality of restoration are critical contributors to the overall value of a vehicle, but ultimately the decider is interest. If there is no interest, then its hard to achieve a reasonable price. Wanderer is virtually unknown in Australia so there was virtually no market for such an outstanding and unique vehicle in this country, which meant that the car eventually had to be sold overseas. In Germany, these cars are extremely prized so it's no surprise the now calls Germany home. But it is only thanks to Peter Thorogood that the car was saved and restored in the first place. Congratulations on a job well done Peter.

Peter's contribution to the saving of William Werner's 1944 DKW F9 is documented here:
https://dkwautounionproject.blogspot.com/2021/08/the-werner-dkw-f9.html

Development of the German motor vehicle industry 1929 - 1939 using the example of Auto Union AG Chemnitz

From the Faculty of Engineering Economics of Transport and Communications at the Friedrich List University of Transport in Dresden

“Development trends in the German motor vehicle industry 1929 - 1939 shown using the example of Auto Union AG Chemnitz”

Dissertation for the degree of Doctor of Economics submitted by Peter Kirchberg from Dresden in May 1964

Examiner: Prof. Dr.rer cec.habil E Rebbein

The aim of this work is to demonstrate the connection between fascism and motorization in Germany up to the beginning of the Second World War. From this point of view, the development trends of the German motor vehicle industry were examined within the framework of the state monopoly system of the economy in general and in the areas of production, sales and technical development in particular using the example of Auto Union AG. An analysis of the situation of the motor vehicle industry since around 1929 was chosen as the starting point for these presentations. The author studied sources in the archives
Saxon State Archive Leipzig
Saxon State Main Archive Dresden
German Central Archive Potsdam
Works Archive VEB Sachsenring "Zwickau"
Archive of the German Central Bank District Dresden Archive of the Central Development and Design Office of the VVB Automobilrau Karl Marx-Stadt

The work is based essentially on the Auto Union holdings in the Leipzig State Archives. This is, however, incomplete and may amount to less than half of the original holdings. The Dresden holdings (Central Bank and State Building Archives) have also been diminished by the effects of the war and post-war.

On the one hand, these gaps in the sources set certain limits to the work, but these were also limited by the possible scope. Therefore, some problem areas (e.g. motorsport, exports, the relationship between Auto Union and other companies in the motor vehicle industry) could be used. Others (e.g. technical development) are presented in more detail but more briefly than the author would have liked. An explanation of further development under the conditions of the war economy had to be dispensed with, as this would have exceeded the scope of the work. The fact that there are hardly any published studies on the development of the motor vehicle industry up to 1939 made things even more difficult. The general context, which could otherwise have been assumed to be known, therefore had to be presented more often.

I would like to thank Prof. Dr.habil. E.Rehbein for her helpful support of the work. I also gratefully accepted the numerous tips from Dr. Müller. The author owes thanks to Mr. General Director Lang of VVB Automobilbau; Mr. Herrmann, Director of the Advertising Department of VVB; Mr. Dr. Schußler, Head of the TKV Department at VEB Sachsenring, Zwickau; Mr. Albert Locke, Zwickau; Mr. Ing. Friedrich, VEB Motorradwerk Zschopau; Mr. Gaudlitz, commercial director of the Barkaswerke, Karl Marx Stadt for kindly providing eyewitnesses to the history of the Auto Union, numerous Saxon tips and the communication of technical details not on record. For kind support in technical and organizational matters, I would like to thank my colleagues from the Leipzig State Archives, the Saxon State Main Archives in Dresden, the archives of the German Central Bank in Dresden, and especially the documentalist from the Institute for the History of Technology at the TU Dresden, Herrn Schmadicke.

Dresden in May 1964

[This will eventually be translated into English when I get time.]

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