My e-type series 1 4.2 starts braking when getting hot in traffic. This gets worse with frequent starting and stopping. It feels like the braking is quickly increasing with the temperature, which ends up in stand still and overheating. I have changed the fan setting to permanent, but this does not help. Any tips on this?
Many thanks in advance.
I am not 100% sure if youâre reporting that the engine gets too hot, or the brakes begin to lock up and then make the car cease forward motion?
The fans have nothing to do with the brakes.
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Thanks for your reply Wiggles.
The brakes start locking when the engine gets too hot, typically in traffic with frequent start - stops. This gets worse and worse in a matter of minutes until the car cannot go forward anymore. The brakes locking seems to be a direct result of the engine heating.
Oliver - is there any chance that you have brake lines very close to the exhaust manifolds - this may cause heating of the brake fluid which may be causing the brake fluid to increase pressure against the brakes - just a suggestion - Tex.
First of all, welcome to the forum! You will find lots of helpful folks here, and rest assured that there is no problem that has not been discussed here before⌠The brakes locking up when the engine bay is hot is a common symptom on these cars and has been discussed in numerous threads here. You will not fix the problem by cooling the engine - the problem resides in the braking system. There are several possible causes of this symptom, so I suggest that you start by using the search facility (magnifying glass in the top RH corner of your screen) to check out previous threads in the archives. With that background, you should be able to be more specific in your description/diagnosis. Some questions that spring to mind are:
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Are all wheels affected?
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Has any work been done on the brakes recently?
Common causes of this problem are:
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Delaminating brake hoses - will only affect individual wheels
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Mal-adjusted pedal stop - no free play
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Sticking Master Cylinder Reaction Valve piston
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Master Cylinder piston rod sticking in plastic bearing
Unfortunately, the last two of these can happen with new reproduction Master Cylinders, so a recent history of what has been done to the car will be helpful.
-David
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Hello David, and thanks for your reply. I will look into the points you have mentionned. This is what I can say so far:
- Are all wheels affected? It feels like the front discs
- Has any work been done on the brakes recently? Not recently, but this has been going on for a long time now, since I took the car over. It is only getting worse. The car was fully restored 15 years ago.
I will check for more details.
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Thanks for your reply Tex, and for your suggestion.
I will check this out as well.
Oliver
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Everything that David said is spot on: the very first thing you need to check in to see if you have free play (head space) at the brake master cylinder. If not, thatâs likely the sole reason for this problem. If you do, then it gets a bit more complicated after that.
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I will check this out indeed.
Thank you
With the front discs itâs easy to determine which are binding just by feeling the temperature of the wheel spinner/knock off. They will get hot on a binding wheel. Itâs not so easy on the rears, as the disks are inboard so the heat doesnât transfer to the hubs so much. If both front wheels are binding, I would doubt that the problem is delaminating hoses, as two hoses would have to be affected at the same time - possible, but less likely. The rear wheels share a single flex hose.
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Clear, thanks for the tip David
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Oliver, welcome to JL! What year is your 4.2? The early 4.2 had one brake heat shield, the one located high on the frame that holds the clutch and brake fluid reservoirs. But not too long into production, around March â65 if I recall, Jaguar added a second shield mounted lower between the exhaust down pipes and the brake master and booster components.
My car is an early 4.2 without the lower shield, and I was having some issues with brake fade and neither I nor a well-known restoration shop could figure out why, as all the components checked out fine. Finally we decided to go ahead and add that shield and I havenât had any issues in the years since.
Clearly, Jaguar found an issue with heat and the brake cylinders or they would not have added this. My mechanic hypothesized that if everything in the braking system is absolutely perfect, it probably didnât show any heat issues, but with production tolerance variances, some might show heat sensitivity problems and some might not, which is why Jaguar went ahead and added the shield early in the production run. With Lyons running the fiscally tight ship he was known for, they clearly would not have added that shield unless it was considered necessary.
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Thanks for this Jeffrey. My 4.2 is from early 1967, and will have to check on the shields. This means a lot indeed!
I have an very large lower heat shieldâŚtwice the area of the factory shieldâŚthat I fabricated to protect the a/c hoses. I still have had problems with the brakes. This is problem is often attributed to heat, but Iâm not convinced. So some suggestions from hard experience:
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Make sure your brake pedal is returning to normal height. If not, replace or rebuild the master cylinder, and take the opportunity to remove the brake box and replace the return spring.
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Inspect the secondary piston in the master. This is an easy process, which doesnât require much diassembly or bleeding. Simply remove the reaction valve from the front of the master by undoing the six screws. Then take a drill or icepick and insert it into the hole in the middle of the shield (youâll see what I mean.) Hold it in place firmly and have someone step on the brake. You should find that your pick is pushed forward, and you canât resist the force. When they release the brake, you should be able to push it back with minimal effort. If you find the secondary is sticky, remove the metal shield. Hold a plastic bag over the front of the master, and have someone push the brakes. It should pop out into the bag. Clean it, check the seals, apply a light coat of silicone grease and reinstall. You should be able to get away without bleeding.
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Check the reaction valve. Since you have it out, inspect for dirt, cracks, damage, broken spring. Then reinstall. Plumb a fitting into the vacuum line which leads between the reaction valve and the rear of the booster. See diagram, and you can order fitting 44555K189 from McMaster:
With the fitting in place, plumb in a long hose and a vacuum gauge and run it into the cabin. When the problem occurs, observe the vacuum pressure. If itâs close to atmospheric, thereâs a vacuum leak either in the reaction valve, hose or the booster. You can replace the reaction valve and vacuum hoses, but it would be more likely that a rebuild or replacement of the booster/slave is going to be required.
- if all else fails, youâre stuck with throwing parts at it, starting with rebuilding the booster/slave.
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Rig up an auxiliary spring (archives) on the pedal to make sure it is coming âupâ sufficiently. this takes 2 minutes (might use a bungee cord) to check if the pedal is part of the problem. Best of luck.
Thanks for your input and experience Michael
If it were my car, the first thing I would do is replace both front disc brake hydraulic hoses to see if problem goes away. Collapsed inner part of hydraulic hose can give this exact symptom which gets worse with heat.
If that did not solve it I would replace the little o-ring in the master cylinder as arrowed in the photo.
If the o-ring swells a bit, the reaction valve can stick. Heat can swell it or poor quality rubber can mean it swells over time. The symptom of this starts with you pressing the brake and when you release it, it does not release until after a delay. When it really sticks, the brakes donât want to release when you take your foot off the pedal. See photo below with blue arrow. If you do replace the o-ring, clean and mildly surface the bore it runs in with very fine emory paper and flush reside out well
I have had both problems before
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I forgot that there is also a little rubber cup that is also on the reaction piston along with the o-ring
Many repo pads need to be trimmed on the sides or they bind in the calliper, donât think itâs been mentioned , any table top disc sander will work
I have the exact same issue on a v12. Should we look the same troubleshooting steps?