Slackness in transmission

[gouldsborough7]

Hi Guys
In the past, I have inserted a couple of threads looking for ideas on improving the running of my Hunter's engine (2 litre Scorpio 8-valve electronic). The main problem is a certain amount of jerking caused by a flat-spot at around 1700rpm. Otherwise it performs as well as can be expected for a 15 year old car, with a 15,000 mile engine from new.

It occurred to me that some of the problem may be as a result of unnecessary slackness in the transmission, i.e. maybe 1) worn the propshaft U/J, 2) the differential, 3) duff axle mountings on the chassis. Items 1 and 2 will cost big-bucks to put right, so going for the cheap and easy option first: Can I replace any rubber mountings with e.g. Super Flex polyurethane types? Any other ideas would be welcome.

Cheers
Mike

[djj_engineer]

Re: Slackness in transmission

You may find that your engine mounts are also a bit soft.
There seem to be a number of different axle mounts but they only stop the diff moving around the driveshafts. The diff is also mounted fairly substantially at the front. It may be that you have the same sort of coupling at the front of the driveshaft as Doug Billings's Cabrio. which has a rubber coupling. This had seen better days and he managed to get a replacement. The rear U/J is fairly cheap it is getting the propshaft off that may be an issue. Sometimes there is not much room and either the engine/gearbox has to be moved or perhaps a better option is removing the diff.

[gouldsborough7]

Re: Slackness in transmission

Many thanks djj_engineer
Your ideas have given me something to work on.
Cheers
Mike

[chris_cussen]

Re: Slackness in transmission

Mike,
With your engine it is usual to have a MT75 gearbox fitted, and when I built mine Marlin recommended getting rid of the nasty rubber coupling at the tail of the gearbox and using a solid flange that is fitted to Transit vans. The propshaft then has a UJ at each end and is much more rigid. You could always check the nasty rubber coupling for wear.
If your Hunter does have the nasty rubber coupling and you go down the replacement route then the Transit flange costs about £60, and you will need to have the propshaft modified or a new one made (about £150, though that's a wild assed guess).

[cameronfurnival]

Re: Slackness in transmission

£150 is spot on Keith, I had mine made to measure and the flange supplied all in for just a tad under that.The bigger companies know exactly what bits you need and will supply it all off the shelf ready to fit (mine has a sliding spline)

[chris_cussen]

Re: Slackness in transmission

Keith?!

[gouldsborough7]

Re: Slackness in transmission

Thanks Chris
Your details are very interesting. With a gradual worsening of the jolting problem, although there must be a fault in the car's electronics, a dodgy transmission coupling would certainly make things a lot worse.

At this moment I have no idea whether my car has a rubber coupling at the gearbox end of the propshaft. I'll have to get it up on ramps and have a good look. As the car was built by Marlin, I would hope they option to fit the rigid version per Ford Transit. I could probably put the problems in the hands of my enthusiastic village garage, who are willing to tackle virtually anything. However, it looks to be a fairly big job if the prop has to come out, or worse still the gearbox.

Anyway, one thing at a time! I'll check out the coupling and feedback the info to this thread.

Cheers
Mike

[chris_cussen]

Re: Slackness in transmission

I think the job can be done in situ if you can detach the propshaft from the rubber coupling and remove the rear gearbox support. It is possible to then drop the front of the prop and detach it from the diff and slide it forward.
After that the centre nut holding the coupling in place needs to be undone. Its a big one, and deeply recessed with 12 points on it so it needs the right kind of socket to fit. Its also necessary to jam the rubber coupling to stop the output shaft rotating. I must admit I took the gearbox to a engine/gearbox re-manufacturer as I didn't have a suitable socket.
Reassembly is the reverse of dismantling as Haynes would put it.
Chris

[gouldsborough7]

Re: Slackness in transmission

Chris
I jacked up one side of the car (2 trolley jacks & 2 axle stands for safety) and squinted underneath. I was only able to see the front of the propshaft, which has a U/J and no sign of anything rubber. So presumably, Marlin did the conversion during their factory assembly. It all looked to be in good order.

Without getting the rear of the car up on my ramps (rubbish weather conditions not being very encouraging at present) I was not able to inspect the rear end of the prop. However, from your information, the likely problem would have centered around the nasty rubber coupling (if my car had one). So that area can be ticked off.

While one rear wheel was off the ground, with 1st gear selected I rotated the wheel forwards and backwards to its full extent. The total 'slackness' measured at the outside circumference of the tyre was 30mm. In my opinion, that is probably OK, bearing in mind that this movement is accommodating a combination of wear in all of the joints as well as the diff.

So, I think I am back to the electronics dept. To reiterate my previous thread on this, for some peculiar reason this flat-spot only occurs around 1700rpm in all gears, most noticably in the higher gears. Coasting along around these revs, with hardly any pressure on the accelerator, and then pressing the pedal to increase speed will guarantee every time a jolt in the transmission. Yet, if I accelerate from rest through all gears up to say 60mph, there is no jolting at all, and all works very smoothly.

So when the effects of Christmas are over, looks like I have to bite the bullet and visit a specialist with a rolling road or fancy analysis equipment.

Thanks for your advice.
Mike

[b_caswell]

Re: Slackness in transmission

Could be as simple as reducing the spring return on the throttle pedal so you get more progressive action. Next suspect would be as Derek says "the engine mounts"

[danny_nelson]

Re: Slackness in transmission

Hi Mike, I have read all the above , and while it is all correct and relevant I thought you might like to hear the following. I have experienced a flat spot( hesitation) on several Cabrio/Hunter cars fitted with the 8valve twin cam engine as was used in the Sierra GLS. This was at around 1500rpm. Now this can attribute to a (slap) in transmission and if not corrected will almost certainly cause some wear in one or more of the mounts, ujs, joints etc. The play in your system could well be within tolerances and if the flat spot problem is corrected then no noise will be heard in the transmission and no work required in that department. Worth mention here as well YKC had this problem with Zetec powered cars when a certain after market inlet was used. You should decide if you feel capable of tracking down this problem yourself or send the car to someone with a good reputation in the buisness.

[dogoncrazy]

Re: Slackness in transmission

Mike
I have just changed the Throttle position switch on my BMW powered cabrio for a 'good' used one and it's totally transformed the way it drives. Don't know if you have such an item fitted but well worth checking/replacing if you have.

[gouldsborough7]

Re: Slackness in transmission

I pursued the 'electronics' problem and took my car to a car analysis/tune-up garage. This firm cater for a multitude of cars and systems, and as well as dealing with the 'go-faster' brigade wanting their ECU's re-mapped and extra BHP squeezed out of their engines, they were willing to look at my problem.

Their 'expert' spent a great deal of time and effort on searching for a fault that would account for the jerking at 1700rpm problem. In the end, after spending some 2.5 hours in the garage, I was wondering what the eventual bill would be! He charged me only £48.72 with the conclusion that Lambda Sensor was duff. I didn't know exactly what this was, but was told that it was screwed into the exhaust and fed back heat data to the ECU, which in turn regulated the amount of fuel going into the engine. As a consequence, the gas emission out of the exhaust would have failed the next MOT by a big margin!

Needless to say, a Lambda had to be ordered and was fitted the following week at a modest cost of £122.18. This meant another 1.5 hours in the garage, but the end-product improved the emissions to a 'pass' level and the transmission jerking has been reduced to some extent. I was a bit disappointed that the latter was not entirely cured, but what with the slackness in the transmission, non-Ford stainless steel exhaust plus 15 years of life, I can't really complain. Even though the car was built by Marlin with a new engine & gearbox (I have invoices), I have no idea of the history of the rear axle/differential. Perhaps a recon of the diff might help to solve the problem, but a great expense I guess.

Incidentally, the ECU under the dashboard is of a design that a modern analysis garage cannot handle, as there is no jack-socket into which their clever machinery can plug into. Apparently even if it had a suitable socket, anything before the year 2000 would be too old for the modern programming. As a matter of interest, has anyone had to get their ECU repaired or replaced?

Cheers
Mike

[gouldsborough7]

Re: Slackness in transmission

As far as I can tell, the throttle linkage is just a conventional cable, not an electronic version as in my modern Skoda Rapid. I did fiddle about with the engine-end of the linkage, and couldn't find any slackness or wear. I had in mind the old carburettor days, when a worn throttle spindle would produce similar engine/transmission jerks. The puzzle goes on>>>>

Cheers
Mike

[dogoncrazy]

Re: Slackness in transmission

Mike
Throttle on bmw is cable also. The throttle position switch is in my case located by 2 screws under the throttle body and is 'driven ' by the throttle shaft. A signal is sent by the switch to the ecu to tell it the throttle position and to control the Idle control valve. It would seem in my case that the switch itself was faulty and of course the ecu then receiving incorrect signal. The switch can be tested with a simple multimeter and adjusted to a degree by rotating the switch body on elongated fixing points so it also possible for it to be out of range. If you do have one fitted it can be the source of your problem. I HAD SIMILAIR. GOOD LUCK