Front to rear brake pipes

Following an MOT request to renew my front to rear brake pipes on my P38 I decided to let the garage do it as it is a tricky task having read a lengthy previous thread on it. I now have the car back complete with a new MOT however I am not convinced it has been done properly. The car seems to snake under braking like the back brakes are playing catch up with the fronts. My question is, what if they have been put on the wrong way round? In other words is the P38 a diagonal split system in which case it would be left and right split if they are the wrong way round? This would not be a good set up especially once the winter sets in as it could play havoc with the ABS etc.

Any quick way of checking without stripping out the wheel arch liners again?

:welcome2:

As far as I know no vehicle would be split Left/Right - that would be ruddy dangerous if a circuit wer to fail.

The P38 has a dual circuit system with Primary feeding Front and Rear and Secondary feeding fronts only.

The most come reasons for snaking under braking are:

Wrong tire pressures (don't go by the book figure you'll need to experiment with what works right on your car!)
Duff Ball Joints.
Play in the steering box.
18" Alloys (For some reason even though they were standard - the P38 wanders with them - check tire pressures more crucial on the 18's)
Incorrect brake bleeding (there maybe an airlock in one caliper causing uneven braking)
Duff Steering damper
Overtightened Steering Box adjustment

Get onto a quiet straight road - accelerate up to 30, and make sure no one is around and brake with firm pressure (not hard just firm) and see if the car wanders over to one side.....repeat a few times and see if it does it consistantly and always to one side....

Most common is tire pressures

The system is split front and rear. Maybe it has not been bled properly. The correct method of bleeding is not standard and must be followed to the letter for proper operation.

I've had the car three years so am quite well used to it's handling. It does have 18s on it and it's only since coming from the garage that the snake has appeared. It's momentary, just a quick twitch then it settles. All the points mentioned in the first reply were covered in the MOT which I watched being carried out although brake bleeding sounds like it needs redone to begin with. Agreed split left and right would be horrendous, stupid and potentially disastrous. Thanks so far in any case.

Blenheim Rover said:

I've had the car three years so am quite well used to it's handling. It does have 18s on it and it's only since coming from the garage that the snake has appeared. It's momentary, just a quick twitch then it settles. All the points mentioned in the first reply were covered in the MOT which I watched being carried out although brake bleeding sounds like it needs redone to begin with. Agreed split left and right would be horrendous, stupid and potentially disastrous. Thanks so far in any case.

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Some vehicles are split diagonally right and left i think.

Siezed caliper pins or pistons?

aerofabrique said:

Siezed caliper pins or pistons?

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Maybe, but it's just got a ticket and had the brakes worked on, hard to believe they did not pick that up.

aerofabrique said:

Siezed caliper pins or pistons?

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It doesn't have pins just carrier sliders

Ask to have the system bled again including booster screws in master cylinder maybe you should take a copy of rave so that they know the correct procedure.
Very unlikely the pipe is the wrong way around . It not hard to do

I put new discs and pads on it all round before the MOT so everything is sliding fine in the caliper department. I still kind of suspect the pipe routing as I have now been told by the garage that both were taken off together rather than do one at a time. looks like a physical check against a known original one is on the cards. Won't be the first time I've had to re-do work I've already paid for.

You could just do a physical check by applying the brakes and checking all four calipers are gripping by turning each wheel independently

Oh, they are as when I stop after a short drive they are all warm and discs are shiny. The problem is if the front to rear left pipe has been connected to where the right one is and vice versa then the back end is all over the place. Both front to rear pipes run side by side until they get to the back axle.

Blenheim Rover said:

Oh, they are as when I stop after a short drive they are all warm and discs are shiny. The problem is if the front to rear left pipe has been connected to where the right one is and vice versa then the back end is all over the place. Both front to rear pipes run side by side until they get to the back axle.

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Why would that be? Both brakes receive the same pressure at the same time no matter which side they are connected to. If a front pipe was connected to one of the rear brakes you would notice a problem because of the brake balance valve. The rears are fed a slightly different pressure than the fronts.

Tbh iv never heard of snakeing due to brakes iv felt pulling to one side due to one of the front calipers defective due to leaking or stiff piston or stiff sliders and being that the rear brakes only contribute to 25% of overal braking efficiency I would of doubt you would notice.snakeing I would be looking in to the steering side of things and bushes alike

Steering and bushing all ok. The problem has only manifested since the front to rear pipes were changed. It's just a momentary blip then it all straightens out. No binding or sticky calipers either. Ideally if someone could tell me which pipe from the master cylinder goes to which rear pipe that would solve my concern. As it is if mine have been connected the wrong way round it will remain generally fine until I try braking on ice and snow as the ABS would surely be confused by trying to unlock a wheel that isn't locked, would it?

Blenheim Rover said:

Steering and bushing all ok. The problem has only manifested since the front to rear pipes were changed. It's just a momentary blip then it all straightens out. No binding or sticky calipers either. Ideally if someone could tell me which pipe from the master cylinder goes to which rear pipe that would solve my concern. As it is if mine have been connected the wrong way round it will remain generally fine until I try braking on ice and snow as the ABS would surely be confused by trying to unlock a wheel that isn't locked, would it?

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I can find no definitive diagram of pipe positions on booster. You will have to look at a known good vehicle. There are views in RAVE under brake repair. You may be able to extrapolate it from that by comparing runs to yours but they are far from clear.

How's about jacking up the back end, slackening a bleed nipple on a front caliper applying the brake and seeing which rear doesn't turn? That would confirm a cross split or whether they have inadvertently made it a side to side split - hopefully not!

i'd go and get them to re-bleed the system.

actually, maybe ask them how they did it and then refer to RAVE print out procedure if different.

thta would at least be a quick and no cost process of elimination.

Blenheim Rover said:

How's about jacking up the back end, slackening a bleed nipple on a front caliper applying the brake and seeing which rear doesn't turn? That would confirm a cross split or whether they have inadvertently made it a side to side split - hopefully not!

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To be honest don't know why you are buggering about with it. If it's not right take it back. It should not have passed ticket skipping about on braking.

Well RAVE didn't work. Downloaded but won't open. Been into main dealer to ask their opinion and was advised that it is a front and rear split, hydraulic with mechanical back up so that doesn't really help. What I really need to do is find out which outlet on the master goes to which side of the rear. The garage who did the job tell me they didn't necessarily mark which one went where and pulled both off at once. How stupid is that when there are two pipes that run together? (The bill only came in the other day too - which remains unpaid.) Looking at the master cylinder under the bonnet each pipe is marked with a label but just a number rather than FL, RL and so on. I know there is a second slave cylinder type thing out of site and that is what the replacement pipes to rear were run from. Any ideas?