DIY power steering write up ?

[LindsayPorter]

That's a really impressive piece of work, Chris! You're putting a huge amount of time into making this work and, on top of that, it's all a very good 'read', too. Thank you.
I can see the logic in using the whole MGF/TF upper column assembly but I'm planning on doing it rather differently, if it's possible and practicable.
I want to try cutting the motor/drive assembly out of an F/TF column and letting it into the 'B's upper column. Since your work indicates that there is room for the complete F/TF kit, there should be room for the motor etc welded into an MGB column.
If this works, the original, overall appearance and the switchgear will remain the same and it's 'just' (hah!) a matter of siting the ECU (it's not huge) and finding an engine-speed and a road speed pulse to keep the electric PAS system happy. (Your advice will be invaluable here, Chris.)
I don't fancy experimenting with the original upper column on my '73 UK car (when I get it) so, I'm in the market for a suitable upper MGB column, complete, so I can cut-and-shut-and-play without affecting original parts. Anyone got one for sale?

[LindsayPorter]

I've got a couple of questions for Chris, please, regarding Part 1 of his brilliant write-up of his MGB ex-MGF power steering conversion. And incidentally, I'm now less certain that my idea of just using the EPAS mechanism rather than the whole top-end of the MGF column is such a good idea but I'll post my thought later, for what they are worth. But Chris:
1. You make the vital point that the EPAS needs to 'see' an engine speed pulse and that it's possible to 'fool' the system by using a pulse generator (£5-£8 off ebay) but bearing in mind that, as you say, you would lose the over/long-revving fail-safe cut-out. (Not that important on a B-Series engine???). These cheapo generators often have a variable rate (so 50Hz can easily be achieved - though how reliably it is maintained is probably another matter...) but they also have a variable 'duty cycle' - the ratio of the On to Off duration in the square wave cycle. Do you happen to know what the correct duty cycle would be?
2. Where is all this data to be found?
3. If you wanted to use the MGB engine's actual RPM signal, that could be tricky (I think) on all later MGBs where the tacho. pulse is taken from the coil. I believe that this coil signal is made usable by a module in the tachometer but would not be useful for the EPAS. But a. am I wrong? - which would make using the MGB's engine speed signal easy to use and . is there another engine speed source available? There's not one, AFAIK, on the 3-terminal alternator - but again, it would be nice to be wrong!
Sorry Chris, that was three questions: a couple + 1. Can't wait for your next installment...

[Not_Anumber]

Thanks Lindsay.

It would be interesting to see the EPAS motor joined into a B column so that you could keep the original steering wheel and stalks. In my case I decided this was beyond my engineering skills when i realised the turn sensor would also need to be transplanted.

To make mine less obvious eventually I will replace the MGF's slightly lumpy wheel with an after market steering wheel such as a Mountney or Momo using a steering boss to suit a non airbag Rover 25 which im told will fit the F /TF column. The most obvious give away then will be the squarer shape of the cowling and the slightly different stalks.

If you are fitting this to an early B with the non collapsible column and the smaller single speed wiper motor you should be able to orient it with the EPAS motor facing the outside of the car which is easier to do. For cars with the later column that have a large triangulated support bracket behind the dash or those with the heftier 2 speed wiper motor it will need to be fitted with the EPAS motor on the centre console side.

On your questions:

1. From memory, the ECU likes a duty cycle of between 40% and 60% for the square wave 50Hz 'engine run' signal. I tried it with 2 variable cheap Ebay signal generators, only one of which had a digital display. If you use a variable signal generator though you cant go wrong using those figures as a base.

2. Thats a very good question! There was some oft repeated misinformation across several forums that the MGF ECU needs a 1kHz input for the engine speed signal. I tried this multiple times and it doesnt work, it it much too high. 50Hz is provably what it needs. The GPS road speed unit I subsequently bought usefully also included a 50Hz output for the simulated engine speed signal, which works perfectly. [Sadly I dont have anything more sophisticated than a frequency range on a multimeter so cant verify that unit's duty cycle but would assume its something around ~ 50% ]

3. Ive not explored using the MGB's actual RPM signal from the coil. I read that would need to be reduced to 5 volts to avoid damage to the EPAS ECU and I couldnt then find an informed consensus whether the signal should be divided to provide the required input frequency. I decided to stick with simulated engine speed at that point given the only tangible advantage I could see of using true engine speed would be to cut the power to the EPAS in the event the ignition was left on without the engine running which could flatten the battery. Thats not a problem in my instance as I will be running the MGB fuel pump through an interactive fuel pump relay, sourced from a 1980's fuel injected Ford, that shuts off after a number of seconds if it fails to receive an active run signal from the ignition coil, a useful safety feature. I can power the green wire for the EPAS ECU from that to get the power steering shutting off at the same time.

[LindsayPorter]

Once again, some cracking info there, Chris - thank you.

You wrote: "The GPS road speed unit I subsequently bought usefully also included a 50Hz output for the simulated engine speed signal, which works perfectly." That is excellent news - one less gizmo to buy and fit. Is it this one? And if not, wot?
https://www.bridgwater-electronics.co.u ... rface-p139
If it is, I'll send for one.

You say it would be challenging to transplant the MGF/TF's EPAS turn sensor. I think I must be missing something. I thought it was simply a built-in part of the EPAS unit so that, if you cut the column above and below the EPAS unit and let the whole thing into your MGB (or MGA) column, the speed sensor would just work as it normally does. I'm quite good at missing the bleedin' obvious so please tell me what it is I've missed this time. :0 The image here is, I think, from a post by a wonderful, German MGF guru called Dieter. Also, I've got a part-dismantled 'F EPAS in my shed. I will dig it out this coming weekend and post any information or pictures that may be useful.

[Not_Anumber]

The GPS unit I bought to generate the road speed signal came from a company called Lite Steer. I found it on Ebay rather than their own website which is focused more on complete steering systems rather than controllers.
Its case and connectors look extremely similar to examples on the Bridgwater Electronics site, so they might well be the source manufacturer. The Lite Steer version came in at £ 75 and just appealed as it was pre calibrated and also incorporates a 2nd, fixed, output for the engine run signal (50Hz) which allowed me to do away with the need to campaign a separate signal generator.

It would be challenging to transplant the section with the motor and sensor into the middle of an existing MGB column; it may be potentially possible to do this on an earlier MGB rigid column albeit it with additional machining but I noted that Phil H, not one to avoid an engineering challenge, on his early 70's B gave up on that idea https://www.mgexp.com/forum/mgb-and-gt- ... b.4178408/

For my own situation though with on a later B this would have been a non starter as it would have been impractical to join the EPAS unit into the middle of the later collapsible column with it's honey comb structure as well as the more limited clearance available given the bulky additional bracketry that supports it. As mentioned, I'l post full details once I have finished the new mountings

[LindsayPorter]

Well this is all very interesting and is certainly expanding my understanding of how ignorant I am!

Chris, you're obviously spot-on about the need to use an MGF upper column on an MGB and especially those with the collapsible columns and the decreasing amounts of free space beneath the dash on later models. Makes perfect sense. And I agree that the replacement of an F/TF steering wheel with (say) a woodrim or leather aftermarket wheel (14" for appearance's sake?) will go a long way towards making it blend in with the traditional MGB interior. It'll be great to see your results.

On the subject of the pulse module: I've been in touch with Bridgewater Electronics. Very helpful people! They need to know if the output signals for the MGF EPAS need to be "pull-up or pull-down". Apparently this means does it start off with a max - top of square wave - or min=0 - bottom of square wave, signal.

The simple answer could come from you, please, Chris. If the Lite-Steer module as-is really works with the MGF EPAS, Bridgewater will produce a 2-output module to precisely match Lite-Steer's, suitable for MGA/MGB owners.

The implication of all your fabulous writing is that the Lite-Steer module HAS been tried and DOES work with the MGF EPAS - but could you confirm this, please?

As I was typing this, another random thought popped up. MGF/TF steering around the year 2000 changed to an adjustable column. I know from experience that there are some electronic differences between the EPAS systems and that the ECUs are non-interchangeable. I don't suppose you, Chris, or anyone else, has tried the Lite-Steer module with the adjustable MGTF system?

PS As a 75 year old, it's not like the old days where you offered something up and, if it fitted, you bolted it on. But it's certainly more challenging and extremely interesting! At least people like you make it possible for an old duffer like me Chris; thank you!

[Not_Anumber]

Thanks Lindsay
I dont have an oscilloscope sadly to check whether the Lite Steer GPS device's square wave output for the road speed is pull-up or pull-down. It may be worth advising Lite Steer you have a specific requirement, are aware they supply a device for the MGF but need them to confirm the output. I have built the unit into a cut out in my dash top but if it helps you and Bridgewater are serious I could remove it and post it to them to clone.

Actually driving the car could be months away as I am (slowly) doing a bare metal respray at the same time and is consequently part stripped. However as soon as I have the support bracket fabricated I will at least be able to confirm the EPAS provides full power assistance to the wheels when the car is stationary.

The TFs did indeed have an adjustable column. Someone I know on the T Bar (MGF /TF forum) has fitted one in place of the non adjustable column on his earlier MGF. It was straightforward other than fettling the mounting holes. To ensure compatibility he changed to a matching EPAS ECU at the same time & has had no problems. I would always recommend buying the EPAS ECU to match the column. Though the pin outs and the wiring loom are just the same there is some difference in the sensors and some say the motor so best bought as a pair from the same vehicle. Darren from Mgfntfbitz has proved an invaluable source for this especially as i bought a spare MGF column to practice on. I havent tried the Lite Steer GPS with a later MG TF setup . I will try that but that it wont be for a while.

[LindsayPorter]

Thanks Chris, Yes I have fitted an adjustable column to my 'F - and that's how I know the earlier ECU is different :0 Different part number, too. I just think it might be useful for others if we can let them know for certain if the pulse module connections are the same for both EPAS types and I guess that will have to wait until you are able to find out.

Crikey, I don't have an oscilloscope either - never used one; only seen them in use. Bridgewater are absolutely serious so your kind suggestion might be just the job. I told them I would message them before tomorrow (Wednesday) so here's what I'll do: give them a few suggestions. 1. Let us know how (or if) we can test either an MGF EPAS or your Lite Steer unit for pull-up or pull-down. 2. Send you or me a 'test' unit with pull-up (the most common, I believe) and one of us can test it. 3. You send them your Lite Steer and/or I will send them an EPAS unit with your connection instructions.

My MGB purchase fell through so I'll be concentrating on the MGA pas system first - but will stick with MGB suggestions for the good people on this Forum.

I'm just off to the workshop now to do some more on my 1973 Citroen Ami 8's biscuit-tin bodywork so you have my full understanding regarding your MGB bare-metal job. Bet it'll be great!

[Not_Anumber]

If you can PM me your email address Lindsay I can send photos of how the EPAS column is shortened and an example of how to make up the intermediate shaft and bearing.