760GLE 1988 Seat Motor and Brake Booster

DeRail · Post by **DeRail** » 11 Sep 2009, 22:21

Hey everyone,

I've done a search here and over on brickboard and havent been able to run across any solutions a couple issues on my 760. Note that these have existed since I've owned the car, they're not affecting driveability but I'd like to just get a sense of what I'm looking at work and costwise if I wanted to take care of them.

First, on my electric drivers seat, the controls operate everything and things move when the respective switch is pressed. The only thing that is weird is when trying to move the back of the seat fore and aft. The left side moves back or forward while the right side is locked and the seat begins to bend. I'm wondering if this is something simple like a cracked solder joint in the control panel or if the motor on that side is hosed?

Second, my brake booster is leaking. I don't know if it is the little check valve or if it's leaking somewhere else. When I initially got the car, the mechanic who worked on it was able to route it to an unused vac port on the engine. Brakes work fine, but when I start the car after it has been sitting for a bit (maybe 1/2 hour or so) it seems like once the vacuum builds back up (albeit within seconds) the brake pedal pushes up, and you hear a quick "bwoooow" sound. Just curious if this is something stupid simple or, something more serious...

As always, your help is much appreciated!!
Darrell

Post by **billofdurham** » 19 Sep 2009, 12:32

Swedishbricks has quite a lot on the power seats and their problems, including one on the seat back jamming by Don Willson. power seat back tilt jammed. It may be an easy fix or........

The brake booster, or servo as we call it over here, often leaks at the valve. This is a simple repair. However, when the mechanic rerouted the pipe to another port did that stop the leak or does it still leak and now you also have the strange noise?

Bill.

DeRail · Post by **DeRail** » 20 Sep 2009, 08:20

Bill, thanks for the link about the seat, didn't think to check swedishbricks I will check it out and see if it is just the flexible shaft causing the problem (here's hoping it's not the motor).

The mechanic told me that it would still leak, but by routing the booster to an alternative port, the vacuum would build up near instantly, alas this is true however I still get the weird sound and the brake pedal jumps when the servo kicks in. I mentioned the check valve as a possibility when he worked on it a couple years back but it seemed as though he just disregarded it. Since then, I've begun doing my own work.

Thanks,
Darrell

Post by **billofdurham** » 20 Sep 2009, 11:36

Darrell, I would be looking at replacing the valve. It isn't too expensive from our sponsors, depending on the booster fitted, ATE or Bosch. Also it's not a hard job and could solve your problem.

Bill.

DeRail · Post by **DeRail** » 26 Sep 2009, 11:54

Cheers bill!

Even if it doesn't fix the problem completely, it's something that won't go on me for a while. I did notice that when it was cold out yesterday, braking was harder so I'm wondering if the plastic on it is just gone and the cold didn't help it.. either way I'm going to investigate the seat motor and see if I need anything else before I order to save from shipping.

My servo is considerably shallower and has a larger radius than the one here: http://www.fcpgroton.com/product-exec/p ... gory_id/57 But it looks as though it takes the same valve as the Bosch. Any particular place to look for the model?

On the seat, I'll see if I can't get some pictures and do a writeup.

Thanks
Darrell

DeRail · Post by **DeRail** » 02 Nov 2009, 18:45

Bill, picked up a replacement valve from the boneyard (I know, it's a risk) but I did notice that when I'm stopped and have my foot on the brake, the tachometer isn't as erratic as it was (which wasn't enough for me to even think about it) but the fact remains that it seemed to make a difference.

However, the growl from the servo still exists, and the pedal falls slightly when I hear it.

If it truly is the servo, I can pick up a replacement at the boneyard for ~$30 but it's fatter than the one on my car. My car's servo looks like a big disc. Are these interchangeable? Do the brakes have to be bled after replacing the servo?

Also, pulled up the leather on the seat and found that the drive cable isn't engaging at the motor, not the gearbox end like I had initially thought it would be. I want to try the "coat hanger trick" mentioned in another thread, I just don't know exactly where to place it, or if it will work in my case. Worse comes to worst, how much of a chore is it to replace the drive cable?

Thanks
Darrell

Post by **billofdurham** » 03 Nov 2009, 12:40

Did you use a new seal when you replaced the valve? It is essential and it is recommended that the seal be smeared with grease to aid insertion and to help it seal.

The '88 760 was fitted with either servo unit (oops, brake booster) the slim line version has a single 10" cylinder inside while the chunky version has 2 x 8" cylinders inside. The chunky version, according to my research, is a more efficient unit. Both are made by DBA, Disc Brakes Australia, and will fit.

When replacing a servo unit you only need to unbolt the master cylinder and move it aside so you don't need to bleed the brakes.

I have never done a repair on a power seat as Volvo thought we in the UK could move the seat using human power. I only had power seats on my old 960 and as my son and I were the only two drivers, and always have the seat in the same position, we set them once and never moved them.

More research needed.

Bill.