Technical issues solved
Michael Cleverley of Cleverley Repaired Cars, expert on all things MX-5, answers your questions
Fixing leaky roofs, noisy clutches, stiff gearchanges, and investigating a nasty coolant problem
QMy mk2 has just had its clutch replaced and now there’s a buzzing, rattling sound on the overrun. Any idea why, as it didn’t do it before?
AIt’s a problem we see quite a lot. The sound seems to come from the bellhousing and can be loud. Some say that the gearbox has been bolted into the PPF (power plant frame) at a different angle when the clutch is changed. The PPF bolts to the back of the gearbox and has elongated holes giving quite a lot of adjustment, allowing the rear of the box to be raised and lowered.
Adjusting this can reduce the noise a little but I can’t really see why it has any effect at all. The real problem seems to be the fit of the clutch friction plate’s splined centre on the gearbox input shaft. Many aftermarket friction plates are a sloppier fit than the original, allowing the splines to chatter and resonate on the input shaft. This is amplified through the bellhousing. The cure is a good fitting clutch friction plate such as those made by Exedy (fitted from new by Mazda). While you are in there, grease the clutch fork pivot as this commonly squeaks!
THE DREADED DROOP…
QMy mk2 sometimes suffers with an uneven tickover and stalling at junctions. I have cleaned the intake but the problem is still there. Any suggestions for a cure?
AThe dreaded idle droop seems to be a bit of an issue on some MX-5S, particularly mk2s and mk3s – unfortunately there is no blue pill to overcome this malady!
You have to go back to basics and ensure the throttle butterfly is correctly set (base idle), crank or cam angle sensors are in good condition and adjusted correctly, and clean the idle control valve, etc. However, on the last car we looked at with this fault, the problem was caused by a loose crankshaft pulley causing wear in the crankshaft nose and keyway; the cam and ignition timing was shifting by more than 10 degrees at idle, causing stalling and the tickover to be quite unpredictable. The engine was the improved long nose design, so I presume the crankshaft bolt was torqued incorrectly after a cam belt change. Unfortunately the repair in this case was either a new crankshaft and pulleys, or the chosen option of a good secondhand engine. Hopefully you car’s fault will be less dramatic.
PS: mk3s can suffer with uneven idle after a battery disconnect as the ECU has to re-learn the idle valve
operation. It should sort itself out after a few miles’ driving.
HOT AND BOTHERED
QMy mk1 is overheating when I drive quickly. It’s OK in normal conditions but gets really hot when pushed harder. Have you any idea why?
AThe cooling system and engine on the mk1 is very robust and reliable. However, the cars are quite old now and problems can occur because of incorrect maintenance or poor repair. We had one in this week with a good demonstration of this: it was behaving like yours.
In the engine bay there was rust staining at the rear of the head and one of the heater hoses had been replaced. The coolant in the radiator and header tank was brick red in colour. This usually suggests either a blown head gasket (combustion gases make the coolant acidic and corrosion takes place causing the colour), or overzealous use of some kind of Radweld-type product. The head gaskets on these cars are very tough and will usually only fail because of extreme overheating caused by coolant loss or similar.
In the case of this car, I suspect lots of radiator sealant had been added to the coolant in an attempt to cure a water leak (that heater hose maybe). This had partially blocked the radiator (with the car up to temperature, carefully check the core for cold areas). Also, the thermostat was blocked. We removed the radiator and thermostat, flushed the engine and heater matrix with a hose, cleaned and tested the thermostat and fitted a new rad. Fresh antifreeze mix and the car seems fine now. Left much longer and the head gasket would surely have blown.
WET, WET, WET…
QAfter a downpour last night my car is wet in the footwells. Why?
With most MX-5S there are a few things to check. But first it must be noted that these roofs are really well designed, but even the best will let a bit of water in during extreme circumstances, for example, pressure washers or hard driving rain hitting the side windows.
The rear section of the roof is designed to let water drain into a plastic gutter below the rear deck. This gutter leads the water to a drain either side of the car just behind where the hood frame bolts to the Bposts. These block with leaves and soil. We clear these with a slim plastic rod during a routine service. You can rod them from above or underneath (just inboard of the rear lower sills).
The hood can also leak from the corners of the front rail near the latches. The answer here is to prise the plastic locks from the latch adjusting rods and, using a 10mm spanner, shorten the threaded rod. This increases the clamping force of the front hood rail to the windscreen frame seal.
Finally, the rubbers that seal onto the side windows can be pulled off and the stainless retaining strips mounting screws loosened; next push the strips towards the window, tighten the screws and fit the rubbers. With the hood set correctly, leaks should be reduced.
QThe gearchange on my mk1 Eunos is quite stiff – can this be improved?
It’s important to remember that Mazda designed these cars with a short throw, precise gearchange, much like sports cars of old. As a result they feel firmer than the foot-long lever in your average Eurobox.
But there are a few things to check. Starting at the top, the gearlever gaiter can shrink and be too tight, thus restricting the stick’s movement. Next, take the gaiter off and remove the gearstick (three bolts), watching you don’t drip gear oil on your seats! There should be a small quantity of gear oil around the bottom of the lever where the gear selector rods slide. If dry, pour on some gear oil.
With the gearlever out, check the white nylon ball-socket on the base of the lever. If this is worn or broken the gearchange will be sloppy: just snap a new one into position to really sharpen up the selection.
Finally, it’s important to know that both the clutch master and slave cylinders are in good condition. Look up in the footwell where the pedal connects to the master cylinder; it should be dry. Replace it if in doubt. Also peel back the rubber boot on the slave cylinder and replace if it’s leaking. Now fill the master cylinder and bleed a little fluid from the slave cylinder to ensure it’s free of air. With these issues addressed, your car will have a very sweet shift again.
A possible source of buzzing after a clutch change is a sloppy fit of an aftermarket friction plate on the splined centre of the gearbox input shaft: as it moves slightly it creates an annoying resonance and chatter
The brown staining and goo are signs that someone has over-used a radiator sealant instead of hunting down the source of a coolant leak. Here, the whole coolant system was flushed and the radiator replaced before refilling with fresh antifreeze
This 10mm nut on your hood’s latches can be tightened to increase the force with which they clamp to the windscreen’s header rail
Grease (above) and a new nylon ball-socket, improve the shift