90 Poor Brakes Even after Upgrades

I have trawled the forums and tried pretty much all suggestions others have received but no improvment.
Its an old 90 with a transplant 300tdi auto and the brakes are not good ! There appears to be a lot of pedal travel and it needs a lot of pressure to get them to work - when they do eventually cut in they are excellent but its a bit scary at times waiting for them to work !
I have discs on the rear and ive fitted 110 vented discs and new calipers to the front. Ive changed brake fluid and even tried back purging the system so there is no air in it. Ive tested the servo and vacuum pump and both seem good. Ive fitted ss hoses and checked all pipes etc.
The master cylinder and servo are still the original 90 versions from when it was rear drum and single front disc so is it a case of the MC needs upgrading as well ?

Yes your master cylinder is not correct for the enlarged calipers, I had this exact problem and swapped out MC and half solved the issue (see below for other half).
IIRC the 110 calipers had larger pistons in them compared to the older 90 pistons so had a corresponding MC that shunted more fluid. LR did eventually rationalise this, but if you fit later bits to an older vehicle you can run into this issue.

Also I had a weird issue with mine where the rubber boot on the caliper was rectracting the piston - like a spring effect - away from the pads. So every time I braked the first amount of pedal travel was taking up piston ‘slack’ before I got piston to pad contact.

I resolved that by taking the pads out of the piston and sliding a piece of wood thinner than the pad (to prevent the piston popping out) into the place where the pad went, then pressing the pedal until it was hard (engine off). Then I removed the wood and fitted the pads again, pushing the caliper back in only just enough to get the pads in.

Doing both these things made a huge difference.

Do the pad thing first and see if stuff improves, if not then probably MC but make absolutely sure you have checked other things first like Master cylinder adjustment (this can make a huge adjustment - adjust it as per the workshop manual), brake flexi pipes bulging and air in the system. Reverse bleed or manual bleed with pressure works well if you have issue with air that’s stuck.

Stupid question but the bleed nipples are at the top on the calipers right? Not mounted wrongly?

Check all these things first before splitting the hydraulic system again if I was you. It might be something simple.

Thanks Flat for speedy reply.
Yes calipers are mounted right - made that mistake before !!!
Pads seem to be sitting snug so thinking the MC is the issue - im guessing the 110 MC will fit direct onto existing servo and I dont need to change that as well ?
cheers.

I changed my servo as it was the original one and when I took the MC off it was not far off developing pin holes and failing, they aren’t particularly expensive so whilst I was there I just changed it for a new one. New mc would have fitted on the old servo though i think - I cant remember reading whether they were different or not so maybe read up on it or @jamesmartin might be able to say re: servo differences.

Read up on MC set up with the push rod etc

dj_uk said:

I have trawled the forums and tried pretty much all suggestions others have received but no improvment.
Its an old 90 with a transplant 300tdi auto and the brakes are not good ! There appears to be a lot of pedal travel and it needs a lot of pressure to get them to work - when they do eventually cut in they are excellent but its a bit scary at times waiting for them to work !
I have discs on the rear and ive fitted 110 vented discs and new calipers to the front. Ive changed brake fluid and even tried back purging the system so there is no air in it. Ive tested the servo and vacuum pump and both seem good. Ive fitted ss hoses and checked all pipes etc.
The master cylinder and servo are still the original 90 versions from when it was rear drum and single front disc so is it a case of the MC needs upgrading as well ?

Click to expand...

it would sound like servo push rod needs lengthening, you pull m/c aside carefully so you dont kink the pipes, get someone to hold pedal fully down hold rod and adjust the screw on the end, if you go too far there will be no pedal travel and brakes will apply themselves

For all they cost I'd replace the servo anyway. I found it improved my braking force even though the original one seemed to be working. You're going to have to remove the old one to replace the MC.