Toyota Wheel Studs - Replacing the standard 78/79 series studs with custom made, high tensile units

Saturday, Jan 01, 2011 at 01:00

Mick O

I suffered a couple of setbacks on the 2010 desert trip that left me asking some serious questions about the quality of the products I was using. On one occasion I had a wheel almost separate. Thankfully we identified the issue during a lunch break as the wheel had begun to chew through the wheel studs. It appeared in this first incident that the wheel had become loose through improper seating. I attributed this to the poor shaping of the stud holes in the wheel. They had almost vertical edges rather than a nice tapered cone meaning that the small 14mm wheel nuts may not have seated properly. Another consideration was the nuts themselves. Here I think the chamfer or cone end did not have enough width and depth to it. Both of these factors could have contributed to the failure but the end result was a chewed out and US rim, and damaged nuts and tyres.




The second failure involved a complete set of wheel nuts sheering and a rear wheel departing the vehicle for the bush. Thankfully I’d almost come to a complete halt at the time. Examination of the stud ends indicated that all had sheered right at the end of the knurl just before the thread of the stud. Thankfully I was carrying a full set of replacement studs so we were able to get going with a minimum of fuss.





These two incidents, together with a bit of research on the subject when I got home, made me question the quality of the standard wheel studs and nuts fitted to the Toyota vehicles. On examination, the standard stud has very little “shoulder” area once passed the knurl. In fact the nut actually indented or was concave for a few mm between the knurl and the commencement of the thread. This means that when the disc rotor was fitted, there was a gap of greater than 2 mm on each side of the stud. Now I’m pretty sure that in these days of generic parts most Toyota compliant disc products would have the generic 150 mm pattern with identical sized stud holes so there would be no need for this type of a sloppiness. In fact there was easily enough room to fit a 16 mm stud with space to spare. This meant that the axle ends would have had to have been drilled though to accomodate a larger stud.




On the way back from our Anne Beadell sojourn of April this year, I took the opportunity to stop in at Galpro engineering in Adelaide and have a chat with Barry about my concerns. The concave portion provided an obvious sheer point as it reduced the overall diameter of the stud by at least 2 mm meaning that the stud thickness was down to less than 12 mm once the vernier was placed over the gap. I was indeed shocked to find this and coupled with any opportunity for disk rotor to move under sudden impact (that you often get in four wheel driving), a guillotine effect could contribute to damage or weakening of the studs.



I scoured the Toyota website and even rang Toyota direct to try and ascertain the tensile strength of the steel studs they use to no avail. While Toyota recommend torque pressure of 90-110 foot pounds when tightening the wheel nuts, this didn’t seem overly oppressive. I was able to find many stories of wheel studs sheering due to over tightening so that led me to believe that the studs have a lower tensile strength than optimal. Certainly those crazy drift racers and drag specialists in their "doof doof" Celicas and Supras swap out their wheel studs for high tensile steel units.










Anyway, to cut a long story short, with Barry at hand, we made some design changes to the standard nut and I had Barry whip me up a full set of replacement studs with a few spares. The key difference (apart from the fact that they are machined from a slug of high tensile Swedish steel) is that the shoulder continues past the knurling to the outside edge of the disc rotor. This means the gap is reduced to less than a mm overall. The threads commences from the end of the shoulder meaning no reduction in stud thickness as is apparent in the Toyota units. Barry also made a set of wheel nuts to match. These nuts are a domed unit allowing for the uptake or full distance of the stud thread. They are a 23 millimetre width with a good sized end chamfer. The difference in look, feel and weight is considerable.



THE PROCESS FOR REMOVING AND REPLACING

For those who have never replaced wheel studs, the process for the rear wheels on the Toyota was quite simple. Loosen wheel nuts, jack and secure the vehicle. It’s a good idea to have all the wheels chocked so the vehicle can be placed in neutral. The handbrake also needs to be off to allow for removal of the disk rotor as the handbrake disc pads use the inside of the rotor as the disc drum.


Once the wheel is off, remove the brake calliper. This involves the removal of 2 x 17mm bolts that are situated on the end flange/plate of the diff housing. Once the brake callipers are removed, carefully place an object like a 10mm socket into the calliper between the pads. This will prevent the pads from springing out should the brakes of the vehicle be inadvertently applied while they are off.

Now remove the disc rotor. Ensure the handbrake is off. There is usually a separate screw hole on either side of the rotor. By screwing a bolt into these, they will push the disc rotor outwards from the axle. There should also be an inspection port with a rubber grommet in it. With this hole at exactly the 6 oclock position, you should be able to adjust the handbrake adjustment wheel. This little slotted wheel allows you to adjust the handbrake pads outwards or inwards. If the pads are still holding the rotor even with the handbrake off, you can remove the grommet and turn the wheel using a flat bladed screwdriver. It’s fiddly and you have to go by feel but it will assist.









Once the disc rotor is off, you will have clear access to the wheel studs. Toyota studs are pressed in these days and not screwed so carefully press them out with a hammer or use a centre punch if needed. You must be careful not to strike the hub housing. Once out, make sure you clear the holes of any muck or adhesive that may have been used. Also ensure that the back of the axle is clean around the holes so the studs will pull in evenly.

There are two ways to get studs in, either press them in from behind usually with a hammer, or by drawing them in from the front using a bolt. Each have their pros and cons. By removing the handbrake pads, you can actually get enough room to swing a hammer in one location. With the axles still in, it’s a pain so I prefer to draw them through using the flat side of a wheel nut. I use this to get it started using the standard tyre cross brace. This also allows you some leeway to move the studs to ensure they are pulling in evenly once the knurl starts. This is where it stiffens up and the going gets tougher. I use the flat side of the nut up to the point where the knurl starts drawing through the hole. Once started I back off the nuts and place a washer against the flat inside edge of the axle.




Make sure you apply even force across the wheel brace so that the stud is drawn in evenly. Because of the extended shoulder on the new stud, I then had two steel washers with a larger diameter hole which were centred over the stud to allow the shoulder to be drawn the whole way through. While I had to call on the muscles of the Crown Prince about half way through stud 4, a great result is achievable this way without the need to remove hand brake pads or the axle itself.

I hope to have the tensile strength figures for the wheel studs from Barry in due course and will add to this blog once they are to hand.

As to cost, both wheel and nut were less than two dollars more than replacing them through Toyota (The high tensile Galpro studs are actually cheaper than what I was quoted from Toyota for standard studs).

I’m very happy with the end result and hope that some of the pictures will amply illustrate the difference. Any questions, please don’t hesitate to contact me or Barry at Galpro who has the template for these now.

Cheers, Mick


Galpro Engineering - Adelaide

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