Violent Twitch on braking - MK1 MX5

[snowen250]

Hello,

Now I think I know what the problem is, but i'd like to ensure I have all the bases covered before I chuck the thing at a garage.

I have a '94 Mk1 MX5 (actually a Eunos but...) It recently came back from the garage from having some general work done, this included a new right rear calliper (drivers side.)

Since it returned it has been pulling to the right on braking (not every time...but often) and if you dare to apply the brakes while also turning a corner it tries to swap ends on you! It steps to the right, violently, then back to the left.

The front right disc is also disproportionately warm compared to the others.

Now I presume the front right calliper is sticking, or maybe coming on too hard (oo-er) and is thus causing the car to shimmy and pull, I am also finding that both fronts lock up very very easily now. But the garage said they checked that calliper and found no issue.

So is there anything else it can be? The brakes work fine in general use, it pulls a bit but nothing awful. But as soon as you increase speed it becomes more pronounced, and as I do track days in it at Brands there is no way I could currently drive it round a whole lap.

Any other suggestions what the issue may be? Bias? Dodgy disc? Brake Lines?

Thanks!

[james_gt3rs]

What else did they do? Worn bushes can cause effects like that.

[snowen250]

They also did:

Gearbox and Diff oil.
Full alignment and tracking done.
Various gaskets and seals replaced in engine, it was leaking some oil.


I may ask them to replace the bushes as well then, doesn't sound an expensive job (I have no room at home to work on the car myself sadly)

Thanks

[JM]

snowen250 said:

They also did:

Gearbox and Diff oil.
Full alignment and tracking done.
Various gaskets and seals replaced in engine, it was leaking some oil.


I may ask them to replace the bushes as well then, doesn't sound an expensive job (I have no room at home to work on the car myself sadly)

Thanks

Surely they would have spotted worn bushes when they were doing the alignment and tracking.

[snowen250]

JM said:

snowen250 said:

They also did:

Gearbox and Diff oil.
Full alignment and tracking done.
Various gaskets and seals replaced in engine, it was leaking some oil.


I may ask them to replace the bushes as well then, doesn't sound an expensive job (I have no room at home to work on the car myself sadly)

Thanks

Surely they would have spotted worn bushes when they were doing the alignment and tracking.

Yes, I would expect so. I asked them to check these so I can only presume. They are a good garage who have carried out a lot of work for me in the past and I've never had any issues. But bushes do wear out, so il ask how worn they are and if it is a job that will need doing in the near future il get them to do it now to cross it off the list.

I can drive round most issues. but not scary brakes....

Thanks for your responses.

[james_gt3rs]

JM said:

Surely they would have spotted worn bushes when they were doing the alignment and tracking.

Quite hard to tell just be looking at them, don't need much play to cause an effect. If they just did the tracking they might not have checked anything else.

[TooMany2cvs]

Sounds like it'd fail the MOT on brake balance, if nothing else. Perhaps take it to a test centre, and ask them to put it on the brake rollers to see which corner is having the problem?

FR being warm certainly suggests that one's binding and snatching. But the only work they did on the brake was one rear? Presumably a fluid change, too?

[Mr Teddy Bear]

I'm not a MX5 expert, but that needs looking at immediately, I don't think that I'd drive the vehicle like that in case the problem is going to escalate.

If the car doesn't have ABS it will have a pressure limiting valve to both rear braking circuits, these can fail, usually a capped off orifice in the valve body that weeps brake fluid when it's defunct.

Apart from that it requires a complete suspension, steering and brake checkover, that's going to take at least an hour to do properly and time/ramps cost money!

I had my CLK Sport, Four Wheel Aligned twice and neither well respected establishment spotted the shot front wishbone ball joint.

[finishing touch]

How can you do "Full alignment AND tracking" ?


Surely it's the same thing.

[anonymous-user]

snowen250 said:

Any other suggestions

1. Stick it through an MOT test. They'll tell you if there are brake balance problems. If none, you know the problem lies elsewhere.
2. Find a competent garage.

[snowen250]

Thanks for the replies. The garage is also an MOT centre, so will ask them to do the check as suggested.


Finishing Touch - yeah it probably is the same thing, that's me being dense, not them!


Car doesn't have ABS, so will add that to the list to be checked, it certainly feels unbalanced and as I said, having the front wheels at an angle when pressure is applied certainly exacerbates the issue.


No worries on it having a complete check over, I've said i'm willing to throw ££ at it til it is sorted. It is otherwise a very quick little MX5!


Thanks again for the help, on a recent track day I did manage to boil the fluid. It has since been changed (obviously) but would this affect the master cylinder, and then cause issues like this?

I am pretty certain it is a binding calliper, just want to cover all the bases.

[Vaud]

Put it through a council MOT centre. You garage has a bit of a conflict of interest...

[Krikkit]

Probably a stick caliper - well known for it, mine had 4x refurbished ones in pairs as 3 ended up going sticky. One was so bad (out of the blue one day) that it cooked the discs/pads while going down a dual carriageway.

[IanCress]

As above, the caliper is sticking. As you build up speed, the disc and pads are getting so hot that you're essentially sufferring from brake fade on one side. When you stand on the brakes, the performance differential between the hot and cold discs is causing the car to dive to the side of the cold disc.

[luckystrike]

Krikkit said:

Probably a stick caliper - well known for it, mine had 4x refurbished ones in pairs as 3 ended up going sticky. One was so bad (out of the blue one day) that it cooked the discs/pads while going down a dual carriageway.

I can only echo this - on both of mine I had calipers that needed replacing, and with the second one the front right calliper bound so suddenly and badly over the course of one day that I was able to completely stop at junctions and roundabouts without using the middle pedal. Calipers just seem to be one of those things that mx5s go through.

[SonicShadow]

snowen250 said:

I have a '94 Mk1 MX5 (actually a Eunos but...) It recently came back from the garage from having some general work done, this included a new right rear calliper (drivers side.)

Since it returned it has been pulling to the right on braking (not every time...but often) and if you dare to apply the brakes while also turning a corner it tries to swap ends on you! It steps to the right, violently, then back to the left.

This is almost certainly why, and this is why you should always replace calipers in axle pairs. You've most likely got a very mediocre caliper on the rear left. This means the braking force on the rear right is significantly higher, leading to wayward behaviour under braking. The fact it's pulling to the side with the more effective caliper almost confirms this.

[snowen250]

SonicShadow said:

snowen250 said:

I have a '94 Mk1 MX5 (actually a Eunos but...) It recently came back from the garage from having some general work done, this included a new right rear calliper (drivers side.)

Since it returned it has been pulling to the right on braking (not every time...but often) and if you dare to apply the brakes while also turning a corner it tries to swap ends on you! It steps to the right, violently, then back to the left.

This is almost certainly why, and this is why you should always replace calipers in axle pairs. You've most likely got a very mediocre caliper on the rear left. This means the braking force on the rear right is significantly higher, leading to wayward behaviour under braking. The fact it's pulling to the side with the more effective caliper almost confirms this.

Thanks everyone, I shall get them to replace all the callipers that aren't new (ish) Worth doing the discs and pads at the same time? As with anything MX5 related, they aren't exactly expensive....

[Hungrymc]

The warm front right disc certainly points to sticking calliper. Something not right there.

In the past, I've had a (fairly badly) damaged bush on the inner end of a track control arm that caused horrible things while braking, it was allowing the front right wheel to move quite a bit as the brakes were applied and then go back into something like the right place when they were let off... You might have more than one thing going on and your bushes are the next place I'd be checking after that suspect calliper.

[TooMany2cvs]

snowen250 said:

I shall get them to replace all the callipers that aren't new (ish) Worth doing the discs and pads at the same time?

No-brainer.

[Slipperywang]

Along with everyone else suggestions make sure you have 4 of the same tyre at roughly the same tread depth. My mx5 used to violently swing to the right when accelerating then swing back left on lift of 4 new tyres 100% fixed the problem!